EFFECT OF UNDERNUTRITION AND REFEEDING ON DIGESTION IN BOS-TAURUS ANDBOS-INDICUS IN A TROPICAL ENVIRONMENT

The effect of underfeeding and refeeding on digestion was studied in B os taurus and Bos indicus cows. Eight nonlactating cows, four B. tauru s and four B. indicus (live weight 156 kg and 207 kg respectively) wer e first given a forage-based diet at a level above energy maintenance requirements for 4 weeks (3.65 and 4.66 kg dry matter (DM) per day res pectively for B. taurus and B. indicus). They were then restricted at a low level of intake for 2 months (1.83 and 2.33 kg DM per day respec tively for B. taurus and B. indicsus) and finally refed at the first l evel for 2 months. Digestion measurements were made before the underfe eding period, at 3 and 8 weeks of underfeeding and at 3 and 8 weeks of refeeding. Organic matter apparent digestibility decreased with under feeding and increased with refeeding (0.637, 0.592, 0.652, 0.692 and 0 .669 in B. taurus and 0.674, 0.560, 0.580, 0.698 and 0.692 in B. indic us, respectively 1 week before, 3 and 8 weeks after underfeeding, and 3 and 8 weeks after refeeding). This lower apparent digestibility at l ow level of intake was not expected either by ruminal particle retenti on time, which increased when intake decreased, or by measurements of microbial activity: DM degradability measured in situ and ruminal part icle size did not vary with level of intake. An effect of the length o f underfeeding and refeeding was seen: the apparent digestibility tend ed to increase after several weeks of undernutrition and was higher af ter refeeding than before underfeeding. No difference was observed bet ween the two genotypes.