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 71.75.7
84.04.0 68.75.8
67.25.7 0.18
0.05 0.40
0.06
a b
ab a
DR 26.95.6
15.13.9 29.95.7
29.25.6 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 P s 0.005 .
Ž .
Eating rate was decreased P s 0.02 by Q, but not by PEG. When fed Q, heifers Ž
. exhibited eating rate lower by 25, 23 and 19, compared with C P s 0.008 , PEG
Ž .
Ž .
P s 0.01 and Q-PEG P s 0.06 , respectively. The duration of eating bouts and, in Ž
. particular, of the first eating bout Fig. 6, P s 0.01 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, .
P s 0.04 . 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 P s 0.08, 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, P s 0.03 . Heifers drunk less water when fed the Q diet than the PEG diet
Ž .
P s 0.007 , other treatments being intermediate. A strong heifer effect was found on Ž
. water intake
P s 0.006 . 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 .
food intake, as found before in various ruminant animals Silanikove, 1989 .
5. Conclusions
