Performance, rectal temperature and respiratory ratio of dairy heifers from three genetic groups fed diets with different levels of fiber

This work aimed to evaluate the performance, rectal temperature and respiratory ratio of dairy heifers, from three genetic groups Holstein x Zebu (7/8HZ, 15/16HZ, Graded Holstein-GH),confined and fed total mixed diet with different levels of neutral detergent fiber (30 and 60%), using chopped elephantgrass (Pennisetum purpureum, Schum., cv. Mineiro) as forage. Intake, weight gain and physiological responses of these animals were determined under different environmental conditions. The experiment was conducted according to a 3 x 2 factorial arrangement (genetic group x fiber level), in a completely randomized design, with three replicates. The values related to physiological responses were analyzed according to split plot design in the time. Average intakes of DM, NDF and ADF of 10.13, 2.69, and 1.45 kg/day and 2.70, 0.71 and 0.38% LW, respectively, were observed for the diet with low fiber content versus 10.68, 6.17, and 2.92 kg/day and 2.90,1.67, and 0.79% BW for the diet with high fiber content and weight gains of 1.28 and 0.92 kg/day, respectively were obtained. The DM intake in % BW for GH animals was higher (2.94 % BW) than for animals 7/8HZ (2,65% LW). When elephantgrass was used as forage only, heifers fed diets with 60% of NDF ingested greater amount of DM, NDF and ADF and gained less weight per day in relation to those fed diets with 30% of NDF. GH heifers ingested more DM (% LW) than 7/8 HZ heifers, for both diets with 30 and 60% NDF. In thermal environment conditions observed during the experimental period, heifers 7/8HZ, 15/16HZ and GH keep the rectal temperature inside the physiological limits considered normal.