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
Ž .
Makkar 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
