Short-term changes in eating patterns explain the effects of condensed tannins on feed intake in heifers

Ingestion of condensed tannins decreases feed intake in ruminants. Polyethy lene glycol (PEG) forms high-affinity complexes with tannins. In two experi ments carried out on Holstein heifers, quebracho (Q) from the Aspidosperma quebracho served as source of condensed tannins. The aims of the study were (i) to quantify the effect of Q on feed intake and eating behaviour in cat tle fed complete mixed diets (CMDs); (ii) to clarify if changes induced in ingestive behaviour and feed intake by Q in cattle can be reversed by feedi ng PEG; and (iii) to clarify if the decrease in feed intake is associated w ith short-term (astringency, post-ingestive malaise) or longer-term effects . In experiment 1, 500 g/day of Q was found to be the minimal dose that dec reased feed intake in heifers. A ratio of PEG:Q equal to 1:12.5 did not ful ly restore feed intake. In experiment 2, four heifers received a random seq uence of four rations in a Latin-square design with feeding cycles of ca. 7 days: CMD containing no supplements (C), or supplemented with 625 g/day of Q without PEG (Q), with 625 g/day of Q and 250 g/day of PEG (Q-PEG), or wi th 250 g/day of PEG without Q (PEG). Individual rations were continuously w eighed in the trough and the behaviour of heifers was observed for 180 min after distribution of CMD. Overall. feeding Q was associated with lowered f eed 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 effec ts of Q on feed intake were attenuated by feeding PEG. Heifers adapted effe ctively to condensed tannins by increasing the number of eating bouts and t he portion of diet consumed subsequent to 180 min after distribution, so th at no differences in feed intake were noted on the last day of each feeding cycle. Data are interpreted to show that: (i) negative effects of Q on fee d intake derive from astringency of CT and short-term post-ingestive malais e; (ii) the increased number of eating bouts and their wider partition thro ughout the day are means to preserve the ruminal environment in Q-fed heife rs; (iii) PEG has the potential to neutralize negative effects of condensed tannins in cattle. (C) 2000 Etevier Science B.V. All rights reserved.