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www.elsevier.comrlocaterapplanim

Short-term changes in eating patterns explain the

effects of condensed tannins on feed intake in

heifers

q

S. Landau

a,)

_{, N. Silanikove}

b

_{, Z. Nitsan}

b

_{, D. Barkai}

c

_{, H. Baram}

a

_,

F.D. Provenza

d

_{, A. Perevolotsky}

a a

Department of Natural Resources, Institute of Field and Garden Crops, Agricultural Research Organization, The Volcani Center, P.O. Box 6, Bet Dagan 50250, Israel

b

Department of Cattle Physiology and Nutrition, Institute of Animal Science, Agricultural Research Organization, The Volcani Center, P.O. Box 6, Bet Dagan 50250, Israel

c

Department of Natural Resources, Institute of Field and Garden Crops, Agricultural Research Organization, The Volcani Center, Gilat Experiment Station, Mobile Post NegeÕ2, Gilat 85280, Israel

d

Range Science Department, Utah State UniÕersity, Logan, UT 84322-2810, USA

Accepted 9 March 2000

Abstract

Ž .

Ingestion of condensed tannins decreases feed intake in ruminants. Polyethylene glycol PEG forms high-affinity complexes with tannins. In two experiments carried out on Holstein heifers,

Ž .

quebracho Q from the Aspidosperma quebracho served as source of condensed tannins. The

Ž .

aims of the study were i to quantify the effect of Q on feed intake and eating behaviour in cattle

Ž . Ž .

fed complete mixed diets CMDs ; ii to clarify if changes induced in ingestive behaviour and

Ž .

feed intake by Q in cattle can be reversed by feeding PEG; and iii to clarify if the decrease in

Ž .

feed intake is associated with short-term astringency, post-ingestive malaise or longer-term effects. In experiment 1, 500 grday of Q was found to be the minimal dose that decreased feed intake in heifers. A ratio of PEG:Q equal to 1:12.5 did not fully restore feed intake. In experiment 2, four heifers received a random sequence of four rations in a Latin-square design with feeding

Ž .

cycles of ca. 7 days: CMD containing no supplements C , or supplemented with 625 grday of Q

Ž . Ž .

without PEG Q , with 625 grday of Q and 250 grday of PEG Q-PEG , or with 250 grday of

q

Contribution from the Agricultural Research Organization, Institute of Field and Garden Crops, Bet Dagan, Israel, No. 115r99. This research was supported by Research Grant No. US-2625-95 from BARD, The United States-Israel Binational Agricultural Research and Development Fund.

)_{Corresponding author. Tel.:q972-396-86482; fax:q972-396-69642.}

Ž .

E-mail address: vclandau@agri.gov.il S. Landau .

0168-1591r00r$ - see front matterq_{2000 Elsevier Science B.V. All rights reserved.}

Ž .

Ž .

PEG without Q PEG . Individual rations were continuously weighed in the trough and the behaviour of heifers was observed for 180 min after distribution of CMD. Overall, feeding Q was associated with lowered feed intake and shorter duration of eating bouts, mainly of the first eating bout, immediately after distribution of the diet. A larger portion of the diet was consumed subsequent to 180 min after distribution in Q-fed heifers. Eating rate and the water to food ratio were not affected by Q. The effects of Q on feed intake were attenuated by feeding PEG. Heifers adapted effectively to condensed tannins by increasing the number of eating bouts and the portion of diet consumed subsequent to 180 min after distribution, so that no differences in feed intake

Ž .

were noted on the last day of each feeding cycle. Data are interpreted to show that: i negative effects of Q on feed intake derive from astringency of CT and short-term post-ingestive malaise;

Ž .ii the increased number of eating bouts and their wider partition throughout the day are means to

Ž .

preserve the ruminal environment in Q-fed heifers; iii PEG has the potential to neutralize negative effects of condensed tannins in cattle.q_{2000 Elsevier Science B.V. All rights reserved.}

Keywords: Cattle; Tannins; Feeding and nutrition; Quebracho; Feeding behaviour

1. Introduction

Ž

Condensed tannins have deleterious effects on feed intake in cattle Smith et al.,

. Ž

1995 . Astringency exerts a short-term effect in the mouth Kumar and Vaithiyanathan,

.

1990 which can be felt immediately. In contrast, effects that are associated with

Ž

decreased ruminal digestibility Waghorn et al., 1994; Silanikove et al., 1997a; Salawu

. Ž .

et al., 1997 , probably mediated by antimicrobial effects Scalbert, 1991 , express themselves more than an hour after a meal rich in condensed tannins.

Ž . Ž

Spray-dried meal from the South American quebracho Q tree Aspidosperma

.

quebracho , has been used as source of condensed tannins in in vitro experiments

ŽMakkar et al., 1995; Salawu et al., 1997 . The effects of Q tannins on feed intake and.

ingestive behaviour of cattle have not been reported, to our knowledge.

Special adaptative mechanisms are found in animals for which tannin-rich plants are part of the diet. These mechanisms appear at the ruminal level and at the animal level. At the ruminal level, Streptococcus caprinus, a specific inhabitant of the caprine rumen,

Ž .

has the ability to degrade tannin–protein complexes Brooker et al., 1994 . The ruminal flora of goats adapted to browse oak foliage degrades more dry matter from oak foliage

Ž .

than flora from unadapted goats Bederski et al., 1992 . Strains of Streptococcus boÕis

that have tannin-complex degrading activity are found in the feces of browsing, but not

Ž .

grazing, animals Osawa and Sly, 1993 . Microorganisms isolated from the rumen of cattle naive to diets rich in condensed tannins did not have enzymes for degrading condensed tannins and their exposure to spray-dried tannins from Q for 8 days in a

Ž .

rumen simulator did not induce production of such enzymes Makkar et al., 1995 . At

Ž .

the animal level, the secretion of proline-rich saliva Hagerman and Robbins, 1993 is the most prominent of the adaptation to diets containing condensed tannins. However,

Ž .

cattle lack this adaptative feature Austin et al., 1989 .

Ž

Tannins have a higher affinity to form complexes with polyethylene glycol PEG,

.

molecular weight 4000 than with proteins. The PEG–tannin complex is irreversible over a wide range of pH, which markedly reduces the formation of protein–tannin

Ž .

complexes Jones and Mangan, 1977 . PEG has been used to neutralize the negative

Ž .

effects of condensed tannins on feed intake Silanikove et al., 1994 and digestibility

Ž_{Silanikove et al., 1996; Salawu et al., 1997 and attempts have been made to boost the}. Ž

ingestion of tannin-rich foliage by supplementing ranging cattle with PEG Smith et al.,

.

1995 .

Goats fed tannin-rich foliage exhibit a cyclic pattern of meals, which is different from goats fed a high-fiber tannin free diet. The characteristics of feeding activity recorded during 8 h were affected by PEG supplementation in goats fed a diet rich in condensed

Ž .

tannins Silanikove et al., 1997b .

The effect of condensed tannins on the eating activity of cattle, and interactions with PEG supplementation, have not been reported. In particular, although cattle seem to be deprived of adaptative features to tannins, they will ingest substantial amounts of tannin rich vegetation. The way they adapt to such diets has not been investigated.

Ž .

The aim of the present study was: i to quantify the effect of Q on feed intake and

Ž .

ingestive behaviour in cattle; ii to clarify if changes in ingestive behaviour and feed

Ž .

intake induced by Q in cattle can be reversed by feeding PEG; iii to clarify if the

Ž

decrease in feed intake associated with feeding Q is due to short-term oral or

.

post-ingestive effects or to digestive effects.

2. Materials and methods

Experiment 1 was aimed at establishing the dose of Q needed to negatively affect feed intake in Holstein heifers, and the dose of PEG needed to restore feed intake. The purpose of experiment 2 was to assess the effects of Q and to clarify how they interact with PEG on feed intake and feeding behaviour.

2.1. Sites, housing and animals

Experiment 1 was carried out at the Metabolic Cow Unit of the Agricultural Research Organization at Bet Dagan. Experiment 2 was carried out at the Agricultural Youth Village of Eshel Hanassi in the Northern Negev of Israel. In both locations, heifers were housed in individual pens in which daily food intake could be measured. In Eshel Hanassi, continuous weighing of the ration for each heifer was carried out, using an electronic balance that weighed in the range of 0 to 50 kg with an accuracy of"10 g

Ž_{Merav 2002, Shekel Balances, Bet Keshet, Israel . Water was available at all times and}.

water intake was measured using a ruler in calibrated plastic troughs. Four heifers were used in each of experiments 1 and 2. Initial body weights were 316.2"7.3 and

Ž .

358.0"13.0 kg average"s.e. in Bet Dagan and Eshel Hanassi, respectively. Overall body gain was 145"30 grday.

2.2. Diets

Ž . Ž

Complete mixed diets CMDs , formulated to fulfill standard requirements NRC,

. Ž .

9.9% pea hay, 10% wheat straw, 30.5% wheat silage and 35.3% commercial pelleted

Ž .

concentrate Matmor, Ashdod, Israel . Chemical composition was 56.3% DM and, on

DM basis, 13.4% crude protein, 9.83 MJrkg metabolizable energy, 45.6% neutral

detergent fiber. In both experiments, the ration was distributed once daily between 10:00 and 12:00. The diet was formulated to limit residues to 5% of offer. Food residues were gathered and weighed for each heifer individually before the daily ration was distributed.

Ž .

The quebracho meal used in both experiments Trask Chemical, GA contained 47%

Ž .

condensed tannins, as assayed according to Hagerman and Butler 1978 . 2.2.1. Experiment 1: effects of quebracho meal and PEG on food intake

During the first phase of this experiment, aimed at reaching approximate evaluation of the amount of Q that decreases feed intake in heifers, all four heifers were fed the same diet. From day 0 to day 26, amounts of Q were gradually included in the diet from 0 to 500 g in increments of 50 or 100 g. On day 27, the Q allowance was reversed to 500 g and increased again to 1000 g on days 38–39. The second phase of the experiment was implemented as a Latin square in which treatments were switched weekly. Heifers

Ž .

were allotted to one of the following treatments: CMD, without Q control, termed C ,

Ž .

supplemented with 1 kg of Q without PEG Q or supplemented with 1 kg of Q with

Ž . Ž . Ž .

PEG MW 4000 given at two levels: 40 grday Q-PEG40 or 80 grday Q-PEG 80 .

2.2.2. Experiment 2: effects of quebracho meal and PEG on food intake and feeding behaÕiour

The experiment was designed as a Latin square with Q and PEG given at two levels: 0 and 625 grday for Q, and 0 or 250 g for PEG. Diets were given sequentially to each heifer in four feeding cycles of 9, 6, 7 and 8 days. Heifers were allocated to cycles at random.

Ž .

During the control cycle termed C , heifers were fed a CMD with no Q and no PEG. During the PEG cycle, heifers were fed the control diet, supplemented with 250 g of PEG, but no Q. During the Q cycle, heifers were fed the control diet, supplemented with 625 g of Q, but no PEG. During the Q-PEG cycle, heifers were fed with the control diet supplemented with 625 g of Q and 250 g of PEG.

( )

2.3. ObserÕations on behaÕiour experiment 2

The behaviour of heifers was continuously observed for 180 min on each of 18 days, subsequent to distribution of the diet. This included the first day of each cycle, on which diets were novel to heifers, and the last day of each cycle, when heifers were presumed to have adapted to their diets. One observer was in charge of recording one or two heifers. An eating bout was defined as the period of time during which the only

Ž .

behaviour was keeping the head in the food trough foraging on CMD , including head raising interruptions -20 s in duration. Other behaviours were drinking, ruminating, standing idle, and lying. The time at which eating was discontinued or resumed was recorded, together with the weight of the food trough. The time at which drinking was discontinued or resumed was recorded, together with the level of water in the trough. The number and duration of eating and drinking bouts and the amount of food and water

ingested during each bout were calculated. On total, the behaviour analyses were based on 2756 observations.

2.4. Data analysis

Behaviour data, as expressed in percentages of time devoted to a single behaviour, were homogenized for variance, using arcsine transformation, before analyses of vari-ance were carried out. The effects of level of Q and PEG supplementation, of heifer and

Ž .

of feeding cycle, on feed intake experiments 1 and 2 , and on feeding behaviour

Žexperiment 2 were evaluated by bifactorial Latin square analyses SAS, 1985 . In. Ž .

addition, paired T-tests were used to verify if PEG supplementation neutralised the effects of Q on feed intake and behavioural characteristics.

3. Results

3.1. Effects of quebracho meal and PEG on food intake in heifers 3.1.1. Experiment 1

In the first phase of experiment 1, no changes in feed intake occurred when heifers were provided with Q at levels less than 500 grday, but higher levels of Q impaired

Ž .

intake Fig. 1 . A 33% decrease in feed intake from ca. 12 to 8 kg was noted when 1 kg of Q was included in the diet. Feed intake was restored to 12 kg when the daily supply of Q was reduced to 500 g. When the feed intake data were sorted into three classes

Ž .

according to levels of Q viz. 0, 0–500, )500, a significant Ps0.05 depression was

Ž .

noted for the )500 level Fig. 2 .

Ž . Ž . Ž

Fig. 1. The effect of quebracho supplementation - - - on the daily feed intake FI, — of Holstein heifers kg,

. Ž .

fresh fed CMD ad lib experiment 1 .

Ž . Ž .

Ž .

Fig. 2. The effect of quebracho supplementation, as classified in three levels, on the daily feed intake FI of

Ž .

Holstein heifers fed CMD ad lib experiment 1 .

Ž . Ž .

Titles: X-axis: level of quebracho grday . Y-axis: FI kg .

In the second phase of experiment 1, provision of 1 kg of Q lowered feed intake from

Ž . Ž . Ž .

11.8 control to 9.6 kg Q Fig. 3, Ps0.005 . None of the PEG levels completely

succeeded in restoring feed intake. When heifers were given Q-PEG40, they consumed 10.3 kg of CMD, which did not differ statistically from the Q diet. When given Q-PEG80, feed intake was increased to 10.6 kg which still tended to be lower than the

Ž .

control Fig. 3; Ps0.08 . Intense salivation was noted in heifers at all levels of Q ingestion.

3.1.2. Experiment 2

Pre-experimental feed intake during 1 week prior to experiment 2 was similar

Ž

between heifers, i.e., 12.1"0.15 kg. Overall, supplementation of Q decreased Table 1,

Ž .

Fig. 3. The effect of PEG level on the daily feed intake FI, kg of Holstein heifers fed CMD ad lib and

Ž .

supplemented with 1 kg of quebracho Q .

Ž . Ž .

Table 1

Ž . Ž . Ž . Ž

Average feed intake FI, kg , number of eating bouts NEB , time spent at eating ET, min , eating rate ER,

. Ž . Ž . Ž .

grmin , water intake WI, kg , watering rate WR, mlrmin , feed:water ratio FIrWI within 180 min after

Ž . Ž .

distribution of the ration, feed intake subsequent to 180 min observations FI)180 and daily FI kg in heifers

Ž .H fed a CMD without supplement C, control , or supplemented with 625 gŽ . rday of quebracho Q , with 250Ž .

Ž .

grday of PEG, or with 625 grday of quebracho and 250 grday of PEG Q-PEG .

Ž .

Diet C Q Q-PEG PEG Main effects Ps

Q PEG Q=PEG H

Within 180 min

) ) a b a a

FI 10.5"0.9 6.4"0.6 9.8"0.9 9.9"0.9 0.007 0.09 0.06 0.31

b b

) ) a b

NEB 15.0"1.9 24.3"1.8 13.3"1.9 12.6"1.7 0.007 0.01 0.02 0.26

) a b a a

ET 130"9 101"5 130"9 120"8 0.16 0.17 0.03 0.10

) a b a a

ER 84.4"6.3 63.3"4.0 78.4"6.3 81.8"6.0 0.02 0.23 0.20 0.81

ab b a ab

WI 19.4"2.6 15.8"1.6 23.3"2.3 21.1"2.4 0.16 0.03 0.80 0.01 WR 5.6"1.3 3.4"0.8 5.5"1.2 4.1"1.1 0.68 0.77 0.18 0.01 FIrWI 0.52"0.10 0.40"0.06 0.42"0.10 0.47"0.09 0.59 0.76 0.23 0.39

) a b ab ab

Daily FI 12.7"0.6 11.0"0.4 12.5"0.7 12.0"0.5 0.23 0.33 0.14 0.50

b a b b

FI)180 2.2"0.5 4.6"0.4 2.7"0.6 2.1"0.5 0.001 0.01 0.77 0.15 Within rows, means with a common superscript do not differ significantly.

)

P-0.05 ) )

P-0.01.

.

Ps0.007 feed intake during the 180 min subsequent to distribution of rations, while

Ž .

PEG tended to have a positive effect Ps0.09 . The Q=PEG interaction also tended

Ž .

to be significant Ps0.06, respectively . Average overall feed intake by heifers fed the Q diet, as measured within 180 min after CMD distribution, was 60% of that measured

Ž .

Fig. 4. Daily feed intake FI, kg in heifers during 180 min following feed distribution: heifers were fed CMD

Ž . Ž .

with no supplement C , or supplemented with 625 grday of quebracho Q , with 250 grday of PEG, or with

Ž .

625 grday of quebracho and 250 grday of PEG Q-PEG . Arrows indicate first days of the four cycles in the Latin square.

Ž .

Ž .

Fig. 5. The number of eating bouts for 180 min after food distribution NEB : heifers were fed CMD with no

Ž . Ž .

supplement C , or supplemented with 625 grday of quebracho Q , with 250 grday of PEG, or with 625

Ž .

grday of quebracho and 250 grday of PEG Q-PEG . Arrows indicate first days of the four cycles in the Latin square.

Titles: X-axis: days on experiment. Y-axis: no. of eating bouts.

Ž .

in the controls Table 1, Ps0.006 . Intense salivation was noted in Q, and to lesser extent, in Q-PEG-fed heifers. The feed intake of heifers fed PEG or Q-PEG did not

Ž .

differ from that of the controls. A larger portion of the diet 41% vs. less than 22% was consumed after the 180-min observation period by heifers when fed Q, compared with

Ž .

other diets Table 1, Ps0.05 . The overall daily feed intake was still lower in heifers

Ž

fed Q than in all the other groups. This reduction represented 10% compared with

. Ž .

P-PEG, Ps0.07 to 14% compared with C, Ps0.03 of the total daily intake.

Ž .

When analysed on a day-by-day basis Fig. 4 , it appears that Q-fed heifers ingested consistently less feed throughout the experiment than counterparts fed other diets. However, in each of the four feeding cycles, the difference in intake within 180 min

Fig. 6. The duration of eating bouts for 180 min following food distribution: heifers were fed CMD with no

Ž . Ž .

supplement C , or supplemented with 625 grday of quebracho Q , with 250 grday of PEG, or with 625

Ž .

grday of quebracho and 250 grday of PEG Q-PEG .

Ž .

Ž .

Fig. 7. Eating rate ER, grmin at eating bouts for 180 min following food distribution: heifers were fed CMD

Ž . Ž .

only C , or CMD supplemented with 625 grday of quebracho Q , with 250 grday of PEG, or with 625

Ž .

grday of quebracho and 250 grday of PEG Q-PEG .

Ž .

Titles: X-axis: no. of eating bout. Y-axis: ER grmin .

after distribution between the Q group and the controls was highest on the first day and lowest on the last day of the cycle. Similarly, differences in total daily intake between Q

Ž . Ž .

and C decreased from 4.2"0.05 kg Ps0.04 to 0.1"0.03 kg not significant from the first day to the last day of each cycle. This observation suggests that heifers adapted, at least partly, to diets containing Q. No differences in feed intake were found at any date between Q-PEG and C, indicating that the negative effect of Q on the intake of CMD was neutralised by PEG from the first day of each experimental period.

On average, the number of eating bouts for 180 min after distribution of the ration

Ž . Ž .

was increased by Q Table 1 and Fig. 5, Ps0.007 and decreased by PEG Ps0.01 ,

Ž .

with a significant Ps0.02 interaction between these effects. When supplemented with

Ž .

Q, without PEG, heifers exhibited a higher Ps0.0007 number of eating bouts during the 180 min observation period, compared with other dietary treatments, that did not

Ž . Ž .

Fig. 8. Feed intake FI per eating bout for 180 min after food distribution: heifers were fed CMD only C , or

Ž .

CMD supplemented with 625 grday of quebracho Q , with 250 grday of PEG, or with 625 grday of

Ž .

quebracho and 250 grday of PEG Q-PEG .

Ž .

Table 2

Ž . Ž .

Percentage of eating bouts that ended in standing ST or drinking DR during 180 min after distribution of diets.

C Q Q-PEG PEG Main effects

Q PEG Q=PEG H

b a ab b

ST 71.7"5.7 84.0"4.0 68.7"5.8 67.2"5.7 0.18 0.05 0.40 0.06

a b ab a

DR 26.9"5.6 15.1"3.9 29.9"5.7 29.2"5.6 0.26 0.08 0.33 0.06 Within rows, means with a common superscript do not differ significantly:‡P-0.10.

differ between them. In other words, PEG supplementation annihilated the effects of Q on the eating bout pattern after feed distribution.

No significant effect was found for Q and PEG on time spent at eating. However,

Ž .

heifers spent 22% less time eating when fed Q than when fed C or Q-PEG Ps0.005 .

Ž .

Eating rate was decreased Ps0.02 by Q, but not by PEG. When fed Q, heifers

Ž .

exhibited eating rate lower by 25%, 23% and 19%, compared with C Ps0.008 , PEG

ŽPs0.01 and Q-PEG P. Ž s0.06 , respectively. The duration of eating bouts and, in.

Ž .

particular, of the first eating bout Fig. 6, Ps0.01 was shorter in heifers when fed the

Ž

Q diet, compared with other diets. This, added to lower eating rate in heifers fed Q Fig.

. Ž .

7 , resulted in lower feed intake during the main eating bout Fig. 8 , which could not be bridged within 180 min.

While the number of eating bouts did not differ between the Q-fed and control heifers on the first day of each cycle on which diets were just switched, Q-fed heifers exhibited

Ž

more eating bouts, starting from the second or third day of each feeding cycle Fig. 5,

.

Ps0.04 .

Ž .

The percentage of eating bouts that ended in standing Table 2 was higher when

Ž

heifers were fed the Q diet than the C, PEG and Q-PEG diets 84% vs. approximately

.

70% . Respective differences were significant at Ps0.08, 003 and 0.02. In contrast,

Ž

less eating bouts ended in watering in Q-fed heifers higher 15% vs. approximately

.

30% .

The water intake during 180 min after distribution of the diet was increased by PEG

Ž_{Table 1, Ps0.03 . Heifers drunk less water when fed the Q diet than the PEG diet}. ŽPs0.007 , other treatments being intermediate. A strong heifer effect was found on.

Ž .

water intake Ps0.006 . The ratio of food to water intake did not differ between

Ž .

groups Table 1 .

4. Discussion

4.1. Does ‘‘noÕelty’’ explain depressed feed intake in heifers fed diets containing

quebracho?

Were diets containing Q considered a novel food by heifers? If positive, this would explain depressed feed intake in heifers fed Q, although diets were thoroughly mixed

and the selective ability of cattle is restricted. This is because novel foods are carefully

Ž .

sampled by animals, which results in depressed feed intake Provenza et al., 1992 .

Ž .

Eating behaviour was modified within minutes when Q 625 grday was withdrawn

from or included in the ration in experiment 2. Therefore, it is clear that heifers were capable of discerning the presence or absence of Q in the diet in this experiment. However, if Q-feeding was associated with more careful sampling of the diet, as a novel food, then this would apply to any diet containing Q, including Q-PEG. No differences

Ž . Ž .

in eating behaviour Fig. 5 or in daily intake Table 1 were found between C and Q-PEG in experiment 2, in spite of the great amount of Q that was distributed. It seems, therefore, that novelty cannot be claimed the cause of depressed intake in Q-fed heifers. 4.2. Astringency and post-ingestiÕe malaise, and not gut-fill effect, seem to be the

primary reason for depressed food intake in heifers fed quebracho

Effects of CT on food intake in this study can be classified as oral sensations exerted

Ž .

at very short time after ingestion a few minutes , post-ingestive malaise felt within less

Ž .

than 1 h Provenza et al., 1992 , longer-term effects due to digestion inhibition, or possible associations between them.

A prominent finding in experiment 2 was that the reduction in daily feed intake associated with the Q diet was closely linked with reduced food intake immediately after

Ž .

food distribution less than 20 min, Fig. 6 . An effect exerted in the mouth, such as

Ž

astringency was probably associated with the lower duration of the first eating bout Fig.

.

6 . In addition, the intense salivation noted in heifers fed the Q diet supports the notion that the interaction of tannins with salivary and mucous proteins in the mouth might be a factor for reduced palatability of tannin-rich diets. This hypothesis is in accord with the observation that much less salivation was noted in Q-PEG fed heifers than in Q-fed counterparts. The design of the present study does not allow dissociation of oral sensations from post-ingestive effects that are not exerted in the mouth. A research based on factorial comparisons of dietary effects in ruminally fed and orally fed animals is, therefore, needed.

The decrease in microbial activity subsequent to ingestion of tannins which results in decreased digestibility can occur only after dilution and mixing of ingested matter in the ruminal fluid. The post-ingestive toxic effects of tanniferous plants on animals are

Ž

caused by metabolites following biodegradation, as was established for oak tannins Shi,

.

1992 . It takes more than minutes for such processes to be completed. Condensed

Ž

tannins reduce food digestibility Waghorn et al., 1994; Silanikove et al., 1997a; Salawu

.

et al., 1997 . Therefore, one of the prevailing views is that reduction in the rate of

Ž .

evacuation of digesta from the rumen gut-fill effect is a factor that may explain the

Ž .

negative effects of tannins on feed intake in ruminants Kumar and Singh, 1984 . This is because the digesta content in the rumen is regulated at about a constant level, and thus, any increase in digestibility also increases the rate of evacuation allowing more food to be consumed. Because the negative effects of CT from Q can be reversed within minutes by PEG, it is clear that in Q-fed heifers, gut-fill effect can provide, if any, only partial explanation for the effects of CT on feed intake. In addition, Q-fed heifers ingested most of their diet more than 3 h after distribution, at a time when reduced digestibility should

Ž .

have impaired feed intake Table 1 . Our findings are compatible with the recent finding in goats that, contrary to expectation from the gut-fill effect theory, maximal feed intake in response to neutralization of tannins with PEG preceded maximal organic matter

Ž .

digestibility Silanikove et al., 1996 .

To summarise, we suggest that two mixed factors might be associated with the impaired intake in Q-fed heifers: the very short-term astringency effect of CT in this diet, felt in the mouth of heifers, and possibly, an immediate post-ingestive malaise. Digestive inhibition does not seem to have been the primary reason for depressed intake. 4.3. PEG doses required to neutralise the effects of quebracho meal on food intake and feeding behaÕiour

The supplementation of PEG to heifers did not affect food intake or feeding behaviour, when compared to control. This is not surprising because PEG is not

Ž

absorbed by animals and serves as inert marker in digestion experiments Bauman et al.,

.

1971 . In addition, PEG seemed to have no special taste per se, because switching from C to PEG or from PEG to C had no effect on food intake or feeding behaviour. However, the presence of PEG, which had no particular taste or smell, reversed behaviours associated with consumption of Q. This strengthens our assumption that the immediate chemical link between CT and PEG neutralized the effect of Q on feed intake

Ž .

in Q-fed heifers. However, the finding that PEG affects water intake Table 1 is worth further investigation. In particular, short-term beneficial effects of PEG on body gain in

Ž .

animals feeding on tannin-rich diets Silanikove et al., 1996 could be attributed, at least partially, to differences in gut contents subsequent to higher water ingestion.

Our results substantiate previous findings indicating that the level of food intake is inversely related to the level of condensed tannins in the food consumed by small

Ž . Ž .

ruminants Silanikove et al, 1994, 1997a and cattle Smith et al., 1995 . In experiment

Ž

1, Q did not affect intake in heifers until offered at amounts )500 grday Fig. 1 and

. Ž .

Fig. 2 , or ca. 5% CT on DM basis. This is in agreement with Waghorn 1990 and

Ž .

Kababya et al. 1998 who reported no ill effects of CT when present at concentration close to 4% in diets for ruminants. In contrast, when CT concentration amounted to 6.5% and more, feed intake was impaired in both experiments 1 and 2.

In the present study, feeding PEG increased the intake of the tannin-rich Q ration as

Ž .

found before in goats Silanikove et al., 1997a,b; Decandia et al., 1998 and in sheep

Ž_{Silanikove et al., 1994; Salawu et al., 1997 fed tannin-rich foliage. Providing heifers}.

with 80 grday of PEG did not completely neutralise the effects of 630 g CT on food intake in experiment 1, while 250 grday was fully successful in neutralizing 394 g CT in experiment 2. The efficiency threshold of PEG:CT ratio must therefore be found in the range 1:1.6 to 1:7.9, and more research on this dose–response issue is needed.

Ž .

Minimal PEG:CT ratios of 1:4.0 to 1:8.0 for goats Silanikove et al., 1997a , and 1:2.0

Ž .

for sheep Silanikove et al., 1994 allowed maximal feed intake when foliage from Mediterranean tanniferous species was given as sole diet. It is probable that the dose of PEG necessary to neutralize CT effects in cattle is closer to that required for sheep than for goats.

4.4. Adaptation of heifers to quebracho

Ž .

The heifers in the present study adapted to tannin-rich 6.5% CT diet and the difference in daily feed intake between them and the controls tended to decrease after being fed a few days with the Q diet. Consumption of the Q diet was associated with more time spent standing instead of eating, i.e., shorter eating bouts. Also, more time was devoted to eating subsequent to 180 min following distribution of the diet. This may be explained as a need to maintain functional ruminal environment because the reduction in ammonia and volatile fatty acid concentration that follows ingestion of

Ž

tannin-rich diets see review by Kumar and Singh, 1984; Silanikove et al., 1994, 1996,

.

1997a is expected to impair voluntary feed intake. In heterogeneous environment, ruminants and, in particular goats, will cope with such nutritional situation by ingesting

Ž

ruminally degradable sources of protein after a meal of tannin-rich foliage Meuret,

.

1997 , which results in steady and moderate concentration of dietary CT throughout the

Ž .

year Kababya et al., 1998 . Heifers in experiment 2 were given only one thoroughly mixed food. Thus, they could not diversify the diet, and the way chosen to minimize variations of ruminal environment was to partition meals into smaller eating bouts. Once it was established that this behaviour was safe, after a few days, the number of these small eating bouts was increased to compensate for their short duration, and the portion of time devoted to eating throughout the day was also increased. This is compatible with

Ž .

the finding of Aharoni et al. 1998 that tannins do not increase the nondegradable fraction of foods but decrease the degradation rate of ruminally degradable matter.

Ž

The negative effects of tannins on appetite can occur in the short term within 20 to

. Ž .

60 min and the long term days and weeks . Thus, the increase in food intake in Q-fed heifers may reflect a gradual increase of ammonia and volatile fatty acids concentra-tions, concomitant with the adaptation of the microbial system in the rumen to tannins. Rumen microorganisms, which are resistant to high levels of CT may constitute a unique

Ž

response in various ruminants to the nutritive depressing effects of tannins Osawa and

.

Sly, 1992 . In goats, microbial adaptation to tannins increases substantially the

effi-Ž .

ciency of degradation of tannin-rich foods in the rumen Bederski et al., 1992 . In some mammals such as rats or mice, secretion of proline-rich proteins with affinity for tannins appears to be of physiological significance in their adaptation to tannins

Ž_{Hagerman and Robbins., 1993 . The salivary proteins of cattle, though lacking proline-}.

Ž .

rich proteins Austin et al., 1989 , have a high affinity for tannins and these proteins

Ž

have a high tendency to form soluble tannin–protein complexes Silanikove,

unpub-.

lished . Thus, salivating in excess, a feature noted in our study in heifers naive to CT

Ž .

when first given Q, and also found in goats and cattle Silanikove, unpublished , may be another factor that contributed for the adaptation for ingestion tannin-rich food. The biological significance, both qualitatively and quantitatively, of saliva in cattle, as means to adapt to CT is worth investigation.

Ž .

Water drafts were not more numerous Table 2 and water intake was not higher in

Ž .

Q-fed heifers than in heifers in other groups Table 1 . In other words, heifers did not try to rinse out or dilute the soluble tannin–protein complexes. Because the food: water ratio did not differ between groups, it seems that the need for drinking was elicited by

Ž .

5. Conclusions

In Mediterranean countries, beef cattle grazing is used in combination with goat grazing to prevent encroachment in woodlands and shrublands. The foliage of shrubs

Ž .

and trees in these environments is high in CT Kababya et al., 1998 . In cattle, foliage from tanniferous species represents 23% and 53% of food ingested in the spring and the

Ž .

summer, respectively Rothman, 1999 . In goats, which are better adapted to the same environment, foliage from tanniferous species represents 45% and 75% of food ingested

Ž .

in the spring and the summer, respectively Kababya et al., 1998 . This comparison suggests that if the CT problem is overcome, foliage from tanniferous species may contribute more to cattle diets than it does today. Data from the present study show that PEG supplementation may alleviate or even totally neutralise the negative effets of CT

Ž .

on the intake of tannin-rich foods. Decandia et al. 1998 have shown that Sarda goats supplemented with PEG spend more time at foraging on, and ingest more Pistacia lentiscus, a shrub that contains 20% CT.

Therefore, it can be anticipated from our results that cattle behaviour in Mediter-ranean woodland can be modified by PEG supplementation to increase ingestion of tree and shrub foliage, which also may have important implications on the stocking rate of cattle in these environments.

References

Aharoni, Y., Gilboa, N., Silanikove, N., 1998. Models of suppressive effects of tannins. Analysis of the suppressive effects of tannins on ruminal degradation by compartmental models. Anim. Feed Sci. Technol. 71, 251–267.

Austin, P.J., Suchar, L.A., Robbins, C.T., Hagerman, A.E., 1989. Tannin-binding proteins in saliva of deer and their absence in saliva of sheep and cattle. J. Chem. Ecol. 15, 1335–1347.

Bauman, D.E., Davis, C.L., Frobish, R.A., Sachan, D.S., 1971. Evaluation of polyethylene glycol method in determining rumen fluid volume in dairy cows fed different diets. J. Dairy. Sci. 54, 928–930.

Bederski, H.J., Rice, R.W., Gomes, S.H., Ruyle, G., Cuneo, S.P., 1992. Adaptation of goat rumen microflora

Ž )

to tannin rich shrub live oak. Quercus turbinella . In: Proc. Western Section, American. Soc. Anim. Sci., July 8–10, 1992.

Brooker, J.D., O’Donovan, L.A., Skene, I., Clarke, K., Blackall, L., Muslera, P., 1994. Streptococcus caprinus sp. nov., a tannin-resistant ruminal bacterium from feral goats. Lett. Appl. Microbiol. 18, 313–318. Decandia, M., Molle, G., Sitzia, M., Cabiddu, A., Ruiu, P.A., Pampiro, F., Pintus, A., 1998. Effect of

polyethylene glycol on browsing behaviour and performance of late lactating goats. In: 8th meeting on

Ž .

Nutrition of Sheep and Goats, 3–5 Sep. 1998, Grignon France .

Hagerman, A.E., Butler, L.G., 1978. Protein precipitation method for the quantitative determination of tannins. J. Agric. Food Chem. 26, 809–812.

Hagerman, A.E., Robbins, C.T., 1993. Specificity of tannin-binding salivary proteins relative to diet selection by animals. Can. J. Zool. 71, 628–633.

Ž .

Jones, W.T., Mangan, J.L., 1977. Complexes of condensed tannins of sainfoin Onobrychis viciifolia Scop. with fraction-1 leaf protein and with submaxillary mucoporotein, and their reversal by polyethylene-glycol and pH. J. Sci. Food Agric. 28, 126–136.

Kababya, D., Perevolotsky, A., Bruckental, I., Landau, S., 1998. Selection of diets by dual-purpose Mamber goats in Mediterranean woodland. J. Agric. Sci. 131, 221–228.

Kumar, R., Singh, M., 1984. Tannins, their adverse role in ruminant nutrition. J. Agric. Food Chem. 32, 447–453.

Kumar, A., Vaithuyanathan, S., 1990. Occurrence, significance and effect on animal production of tannins in tree leaves. Anim. Feed Sci. Technol. 30, 21–38.

Makkar, H.P.S., Becker, K., Abel, H., Szegletti, C., 1995. Degradation of condensed tannins by rumen

Ž . Ž .

microbes exposed to quebracho tannins QT in rumen simulation technique RUSITEC and effects of QT on fermentative processes in the RUSITEC. J. Sci. Food Agric. 69, 495–500.

Meuret, M., 1997. How do I cope with that bush? Optimizing less palatable foods at pasture using the MENU

Ž .

model. In: Lindberg, J.E., Gonda, H.L., Ledin, I. Eds. , Recent Advances in Small Ruminant Nutrition. CIHEAMrFAO Pub, Zaragoza, Spain, pp. 53–57.

NRC, 1989. Nutrient Requirements of Dairy Cattle. 6th rev. edn. National Academy Press, Washington, DC. Osawa, R., Sly, L., 1992. Occurrence of tannin–protein complex degrading Streptococcus sp. in feces of

various animals. Syst. Appl. Microbiol. 15, 144–147.

Provenza, F.D., Pfister, J.A., Cheney, C.C., 1992. Mechanisms of learning in diet selection with reference to phytotoxicosis in ruminants. J. Range Manage. 45, 36–45.

Rothman, S., 1999. Determination of intake and diet composition for goats and cattle on natural shrublands in the Galilee, Israel. MSc thesis, The Hebrew University of Jerusalem.

Salawu, M.B., Acamovic, T., Stewart, C.S., Howell, F.D.D., 1997. Quebracho tannins with or without Browse

Ž .

Plus a commercial preparation of polyethylene glycol in sheep diets: effects on digestibility of nutrients in vivo and degradation of grass hay in sacco and in vitro. Anim. Feed Sci. Technol. 69, 67–78. SAS, 1985. SASrSTAT guide for personal computers, Version 6. SAS Institute, Cary, NC. Scalbert, A., 1991. Antimicrobial properties of tannins. Phytochemistry 30, 3875.

Shi, Z.C, 1992. Research on the pathogenesis of oak leaf poisoning in cattle. In: James, L.F., Keeler, R.F.,

Ž .

Bailey, E.M., Hegarty, M.P. Eds. , Proc. Third Int. Symp. on Poisonous plants. Iowa State University Press, Ames, IA, pp. 509–516.

Silanikove, N., 1989. Interrelationships between water, food and digestible energy intake in desert and temperate goats. Appetite 12, 163–170.

Silanikove, N., Nitsan, Z., Perevolotsky, A., 1994. Effect of a daily supplementation of polyethylene glycol on

Ž .

intake and digestion of tannin-containing leaves Ceratonia siliqua by sheep. J. Agric. Food Chem. 42, 2844–2847.

Silanikove, N., Gilboa, N., Nir, I., Perevolotsky, A., Nitsan, Z., 1996. Effect of a daily supplementation of

Ž

polyethylene glycol on intake and digestion of tannin-containing leaves Quercus calliprinos, Pistacia

.

lentiscus, Ceratonia siliqua by sheep. J. Agric. Food Chem. 44, 199–205.

Silanikove, N., Gilboa, N., Nitsan, Z., 1997a. Interactions among tannins, supplementation and polyethylene-glycol in goats given oak leaves: effects on digestion and food intake. Anim. Sci. 64, 479–483. Silanikove, N., Gilboa, N., Nitsan, Z., Perevolotsky, A., 1997b. Effect of foliage-tannins on feeding activity in

Ž .

goats. In: Lindberg, J.E., Gonda, H.L., Ledin, I. Eds. , Recent Advances in Small Ruminant Nutrition. CIHEAMrFAO Pub., Zaragoza, Spain, pp. 43–46.

Ž .

Smith, T., Ncube, S., Dube, J.S., 1995. Dry season supplementation with polyethylene glycol PEG or a

Ž .

digestive modifier Browse plus . J. Zimbabwe Soc. Anim. Prod. 7, 181–186.

Waghorn, G.C., 1990. Effects of condensed tannins on protein digestion and nutritive value of fresh herbage. Proc. Austr. Soc. Anim. Prod. 18, 412–415.

Waghorn, G.C., Shelton, I.D., Mc Nabb, W.C., 1994. Effects of condensed tannins in Lotus pedunculatus on its nutritive value for sheep: I. Non-nitrogenous aspects. J. Agric. Sci. 123, 99–107.

Table 2

Ž . Ž .

Percentage of eating bouts that ended in standing ST or drinking DR during 180 min after distribution of diets.

C Q Q-PEG PEG Main effects

Q PEG Q=PEG H

b a ab b

ST 71.7"5.7 84.0"4.0 68.7"5.8 67.2"5.7 0.18 0.05 0.40 0.06

a b ab a

DR 26.9"5.6 15.1"3.9 29.9"5.7 29.2"5.6 0.26 0.08 0.33 0.06

Within rows, means with a common superscript do not differ significantly:‡P-0.10.

differ between them. In other words, PEG supplementation annihilated the effects of Q on the eating bout pattern after feed distribution.

No significant effect was found for Q and PEG on time spent at eating. However,

Ž .

heifers spent 22% less time eating when fed Q than when fed C or Q-PEG Ps0.005 .

Ž .

Eating rate was decreased Ps0.02 by Q, but not by PEG. When fed Q, heifers

Ž .

exhibited eating rate lower by 25%, 23% and 19%, compared with C Ps0.008 , PEG

ŽPs0.01 and Q-PEG P. Ž s0.06 , respectively. The duration of eating bouts and, in.

Ž .

particular, of the first eating bout Fig. 6, Ps0.01 was shorter in heifers when fed the

Ž

Q diet, compared with other diets. This, added to lower eating rate in heifers fed Q Fig.

. Ž .

7 , resulted in lower feed intake during the main eating bout Fig. 8 , which could not be bridged within 180 min.

While the number of eating bouts did not differ between the Q-fed and control heifers on the first day of each cycle on which diets were just switched, Q-fed heifers exhibited

Ž

more eating bouts, starting from the second or third day of each feeding cycle Fig. 5,

.

Ps0.04 .

Ž .

The percentage of eating bouts that ended in standing Table 2 was higher when

Ž

heifers were fed the Q diet than the C, PEG and Q-PEG diets 84% vs. approximately

.

70% . Respective differences were significant at Ps0.08, 003 and 0.02. In contrast,

Ž

less eating bouts ended in watering in Q-fed heifers higher 15% vs. approximately

.

30% .

The water intake during 180 min after distribution of the diet was increased by PEG

Ž_{Table 1, Ps0.03 . Heifers drunk less water when fed the Q diet than the PEG diet}.

ŽPs0.007 , other treatments being intermediate. A strong heifer effect was found on.

Ž .

water intake Ps0.006 . The ratio of food to water intake did not differ between

Ž .

groups Table 1 .

4. Discussion

4.1. Does ‘‘noÕelty’’ explain depressed feed intake in heifers fed diets containing

quebracho?

Were diets containing Q considered a novel food by heifers? If positive, this would explain depressed feed intake in heifers fed Q, although diets were thoroughly mixed

and the selective ability of cattle is restricted. This is because novel foods are carefully

Ž .

sampled by animals, which results in depressed feed intake Provenza et al., 1992 .

Ž .

Eating behaviour was modified within minutes when Q 625 grday was withdrawn from or included in the ration in experiment 2. Therefore, it is clear that heifers were capable of discerning the presence or absence of Q in the diet in this experiment. However, if Q-feeding was associated with more careful sampling of the diet, as a novel food, then this would apply to any diet containing Q, including Q-PEG. No differences

Ž . Ž .

in eating behaviour Fig. 5 or in daily intake Table 1 were found between C and Q-PEG in experiment 2, in spite of the great amount of Q that was distributed. It seems, therefore, that novelty cannot be claimed the cause of depressed intake in Q-fed heifers.

4.2. Astringency and post-ingestiÕe malaise, and not gut-fill effect, seem to be the

primary reason for depressed food intake in heifers fed quebracho

Effects of CT on food intake in this study can be classified as oral sensations exerted

Ž .

at very short time after ingestion a few minutes , post-ingestive malaise felt within less

Ž .

than 1 h Provenza et al., 1992 , longer-term effects due to digestion inhibition, or possible associations between them.

A prominent finding in experiment 2 was that the reduction in daily feed intake associated with the Q diet was closely linked with reduced food intake immediately after

Ž .

food distribution less than 20 min, Fig. 6 . An effect exerted in the mouth, such as

Ž

astringency was probably associated with the lower duration of the first eating bout Fig.

.

6 . In addition, the intense salivation noted in heifers fed the Q diet supports the notion that the interaction of tannins with salivary and mucous proteins in the mouth might be a factor for reduced palatability of tannin-rich diets. This hypothesis is in accord with the observation that much less salivation was noted in Q-PEG fed heifers than in Q-fed counterparts. The design of the present study does not allow dissociation of oral sensations from post-ingestive effects that are not exerted in the mouth. A research based on factorial comparisons of dietary effects in ruminally fed and orally fed animals is, therefore, needed.

The decrease in microbial activity subsequent to ingestion of tannins which results in decreased digestibility can occur only after dilution and mixing of ingested matter in the ruminal fluid. The post-ingestive toxic effects of tanniferous plants on animals are

Ž

caused by metabolites following biodegradation, as was established for oak tannins Shi,

.

1992 . It takes more than minutes for such processes to be completed. Condensed

Ž

tannins reduce food digestibility Waghorn et al., 1994; Silanikove et al., 1997a; Salawu

.

et al., 1997 . Therefore, one of the prevailing views is that reduction in the rate of

Ž .

evacuation of digesta from the rumen gut-fill effect is a factor that may explain the

Ž .

negative effects of tannins on feed intake in ruminants Kumar and Singh, 1984 . This is because the digesta content in the rumen is regulated at about a constant level, and thus, any increase in digestibility also increases the rate of evacuation allowing more food to be consumed. Because the negative effects of CT from Q can be reversed within minutes by PEG, it is clear that in Q-fed heifers, gut-fill effect can provide, if any, only partial explanation for the effects of CT on feed intake. In addition, Q-fed heifers ingested most of their diet more than 3 h after distribution, at a time when reduced digestibility should

Ž .

have impaired feed intake Table 1 . Our findings are compatible with the recent finding in goats that, contrary to expectation from the gut-fill effect theory, maximal feed intake in response to neutralization of tannins with PEG preceded maximal organic matter

Ž .

digestibility Silanikove et al., 1996 .

To summarise, we suggest that two mixed factors might be associated with the impaired intake in Q-fed heifers: the very short-term astringency effect of CT in this diet, felt in the mouth of heifers, and possibly, an immediate post-ingestive malaise. Digestive inhibition does not seem to have been the primary reason for depressed intake.

4.3. PEG doses required to neutralise the effects of quebracho meal on food intake and feeding behaÕiour

The supplementation of PEG to heifers did not affect food intake or feeding behaviour, when compared to control. This is not surprising because PEG is not

Ž

absorbed by animals and serves as inert marker in digestion experiments Bauman et al.,

.

1971 . In addition, PEG seemed to have no special taste per se, because switching from C to PEG or from PEG to C had no effect on food intake or feeding behaviour. However, the presence of PEG, which had no particular taste or smell, reversed behaviours associated with consumption of Q. This strengthens our assumption that the immediate chemical link between CT and PEG neutralized the effect of Q on feed intake

Ž .

in Q-fed heifers. However, the finding that PEG affects water intake Table 1 is worth further investigation. In particular, short-term beneficial effects of PEG on body gain in

Ž .

animals feeding on tannin-rich diets Silanikove et al., 1996 could be attributed, at least partially, to differences in gut contents subsequent to higher water ingestion.

Our results substantiate previous findings indicating that the level of food intake is inversely related to the level of condensed tannins in the food consumed by small

Ž . Ž .

ruminants Silanikove et al, 1994, 1997a and cattle Smith et al., 1995 . In experiment

Ž

1, Q did not affect intake in heifers until offered at amounts )500 grday Fig. 1 and

. Ž .

Fig. 2 , or ca. 5% CT on DM basis. This is in agreement with Waghorn 1990 and

Ž .

Kababya et al. 1998 who reported no ill effects of CT when present at concentration close to 4% in diets for ruminants. In contrast, when CT concentration amounted to 6.5% and more, feed intake was impaired in both experiments 1 and 2.

In the present study, feeding PEG increased the intake of the tannin-rich Q ration as

Ž .

found before in goats Silanikove et al., 1997a,b; Decandia et al., 1998 and in sheep

Ž_{Silanikove et al., 1994; Salawu et al., 1997 fed tannin-rich foliage. Providing heifers}.

with 80 grday of PEG did not completely neutralise the effects of 630 g CT on food intake in experiment 1, while 250 grday was fully successful in neutralizing 394 g CT in experiment 2. The efficiency threshold of PEG:CT ratio must therefore be found in the range 1:1.6 to 1:7.9, and more research on this dose–response issue is needed.

Ž .

Minimal PEG:CT ratios of 1:4.0 to 1:8.0 for goats Silanikove et al., 1997a , and 1:2.0

Ž .

for sheep Silanikove et al., 1994 allowed maximal feed intake when foliage from Mediterranean tanniferous species was given as sole diet. It is probable that the dose of PEG necessary to neutralize CT effects in cattle is closer to that required for sheep than for goats.

4.4. Adaptation of heifers to quebracho

Ž .

The heifers in the present study adapted to tannin-rich 6.5% CT diet and the difference in daily feed intake between them and the controls tended to decrease after being fed a few days with the Q diet. Consumption of the Q diet was associated with more time spent standing instead of eating, i.e., shorter eating bouts. Also, more time was devoted to eating subsequent to 180 min following distribution of the diet. This may be explained as a need to maintain functional ruminal environment because the reduction in ammonia and volatile fatty acid concentration that follows ingestion of

Ž

tannin-rich diets see review by Kumar and Singh, 1984; Silanikove et al., 1994, 1996,

.

1997a is expected to impair voluntary feed intake. In heterogeneous environment, ruminants and, in particular goats, will cope with such nutritional situation by ingesting

Ž

ruminally degradable sources of protein after a meal of tannin-rich foliage Meuret,

.

1997 , which results in steady and moderate concentration of dietary CT throughout the

Ž .

year Kababya et al., 1998 . Heifers in experiment 2 were given only one thoroughly mixed food. Thus, they could not diversify the diet, and the way chosen to minimize variations of ruminal environment was to partition meals into smaller eating bouts. Once it was established that this behaviour was safe, after a few days, the number of these small eating bouts was increased to compensate for their short duration, and the portion of time devoted to eating throughout the day was also increased. This is compatible with

Ž .

the finding of Aharoni et al. 1998 that tannins do not increase the nondegradable fraction of foods but decrease the degradation rate of ruminally degradable matter.

Ž

The negative effects of tannins on appetite can occur in the short term within 20 to

. Ž .

60 min and the long term days and weeks . Thus, the increase in food intake in Q-fed heifers may reflect a gradual increase of ammonia and volatile fatty acids concentra-tions, concomitant with the adaptation of the microbial system in the rumen to tannins. Rumen microorganisms, which are resistant to high levels of CT may constitute a unique

Ž

response in various ruminants to the nutritive depressing effects of tannins Osawa and

.

Sly, 1992 . In goats, microbial adaptation to tannins increases substantially the

effi-Ž .

ciency of degradation of tannin-rich foods in the rumen Bederski et al., 1992 . In some mammals such as rats or mice, secretion of proline-rich proteins with affinity for tannins appears to be of physiological significance in their adaptation to tannins

Ž_{Hagerman and Robbins., 1993 . The salivary proteins of cattle, though lacking proline-}.

Ž .

rich proteins Austin et al., 1989 , have a high affinity for tannins and these proteins

Ž

have a high tendency to form soluble tannin–protein complexes Silanikove,

unpub-.

lished . Thus, salivating in excess, a feature noted in our study in heifers naive to CT

Ž .

when first given Q, and also found in goats and cattle Silanikove, unpublished , may be another factor that contributed for the adaptation for ingestion tannin-rich food. The biological significance, both qualitatively and quantitatively, of saliva in cattle, as means to adapt to CT is worth investigation.

Ž .

Water drafts were not more numerous Table 2 and water intake was not higher in

Ž .

Q-fed heifers than in heifers in other groups Table 1 . In other words, heifers did not try to rinse out or dilute the soluble tannin–protein complexes. Because the food: water ratio did not differ between groups, it seems that the need for drinking was elicited by

Ž .

5. Conclusions

In Mediterranean countries, beef cattle grazing is used in combination with goat grazing to prevent encroachment in woodlands and shrublands. The foliage of shrubs

Ž .

and trees in these environments is high in CT Kababya et al., 1998 . In cattle, foliage from tanniferous species represents 23% and 53% of food ingested in the spring and the

Ž .

summer, respectively Rothman, 1999 . In goats, which are better adapted to the same environment, foliage from tanniferous species represents 45% and 75% of food ingested

Ž .

in the spring and the summer, respectively Kababya et al., 1998 . This comparison suggests that if the CT problem is overcome, foliage from tanniferous species may contribute more to cattle diets than it does today. Data from the present study show that PEG supplementation may alleviate or even totally neutralise the negative effets of CT

Ž .

on the intake of tannin-rich foods. Decandia et al. 1998 have shown that Sarda goats supplemented with PEG spend more time at foraging on, and ingest more Pistacia

lentiscus, a shrub that contains 20% CT.

Therefore, it can be anticipated from our results that cattle behaviour in Mediter-ranean woodland can be modified by PEG supplementation to increase ingestion of tree and shrub foliage, which also may have important implications on the stocking rate of cattle in these environments.

References

Aharoni, Y., Gilboa, N., Silanikove, N., 1998. Models of suppressive effects of tannins. Analysis of the suppressive effects of tannins on ruminal degradation by compartmental models. Anim. Feed Sci. Technol. 71, 251–267.

Austin, P.J., Suchar, L.A., Robbins, C.T., Hagerman, A.E., 1989. Tannin-binding proteins in saliva of deer and their absence in saliva of sheep and cattle. J. Chem. Ecol. 15, 1335–1347.

Bauman, D.E., Davis, C.L., Frobish, R.A., Sachan, D.S., 1971. Evaluation of polyethylene glycol method in determining rumen fluid volume in dairy cows fed different diets. J. Dairy. Sci. 54, 928–930.

Bederski, H.J., Rice, R.W., Gomes, S.H., Ruyle, G., Cuneo, S.P., 1992. Adaptation of goat rumen microflora

Ž )

to tannin rich shrub live oak. Quercus turbinella . In: Proc. Western Section, American. Soc. Anim. Sci., July 8–10, 1992.

Brooker, J.D., O’Donovan, L.A., Skene, I., Clarke, K., Blackall, L., Muslera, P., 1994. Streptococcus caprinus sp. nov., a tannin-resistant ruminal bacterium from feral goats. Lett. Appl. Microbiol. 18, 313–318. Decandia, M., Molle, G., Sitzia, M., Cabiddu, A., Ruiu, P.A., Pampiro, F., Pintus, A., 1998. Effect of

polyethylene glycol on browsing behaviour and performance of late lactating goats. In: 8th meeting on

Ž .

Nutrition of Sheep and Goats, 3–5 Sep. 1998, Grignon France .

Hagerman, A.E., Butler, L.G., 1978. Protein precipitation method for the quantitative determination of tannins. J. Agric. Food Chem. 26, 809–812.

Hagerman, A.E., Robbins, C.T., 1993. Specificity of tannin-binding salivary proteins relative to diet selection by animals. Can. J. Zool. 71, 628–633.

Ž .

Jones, W.T., Mangan, J.L., 1977. Complexes of condensed tannins of sainfoin Onobrychis viciifolia Scop. with fraction-1 leaf protein and with submaxillary mucoporotein, and their reversal by polyethylene-glycol and pH. J. Sci. Food Agric. 28, 126–136.

Kababya, D., Perevolotsky, A., Bruckental, I., Landau, S., 1998. Selection of diets by dual-purpose Mamber goats in Mediterranean woodland. J. Agric. Sci. 131, 221–228.

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