Short- and medium-term changes in performance and metabolism of dairy calves offered different amounts of milk replacer
The objective of the present study was to compare the intake, growth, and glucose metabolism of dairy calves fed 4, 6 or 8 L/d of milk replacer (MR). One hundred and twenty female calves were randomly assigned to one of the 3 groups (4L, 6L, and 8L) differing only in the quantity of MR offered. Daily MR and feed intakes were recorded. Calves were weighed at days 0, 35 and 63. Average daily gain (ADG) at day 35 (ADG35) and at day 63 (ADG63) as well as gain to feed (GtoF) were calculated. A glucose tolerance test (GTT), consisting of 180 mg of glucose per kg of BW infused into the jugular vein of 15 heifers per group, was performed at days 42 and 86 of life. Blood samples were collected at -5, 0, 4, 8, 12, 18, 25, 35, 35 and 60 min relative to glucose infusion and glucose and insulin levels were analyzed. Area under the curve (AUC), clearance rate (CR), insulin to glucose rate (ItoG) and insulin sensitivity were calculated. Data were analyzed using a mixed effects model with repeated measures. Total DMI was greatest (P < 0.05) for 8L calves (1,010 ± 22 vs 950 ± 23 g/d), but 6L and 8L calves consumed less starter feed (P < 0.05; 205 ± 21 g/d) than 4L calves (400 ± 22 g/d). Calves on 8L had the greatest (P < 0.01) ADG35 (757 ± 20.1 g/d) followed by 6L (566 ± 19.8 g/d) and 4L calves (476 ± 20.4 g/d); but ADG63 did not differ among treatments. Allowance of MR did not affect GtoF ratio. Glucose AUC or CR did not differ between treatments. However, calves on 8L produced more (P < 0.005) insulin (2,365 ± 211 µU/mL x 60min) than 6L (1,353 ± 219) or 4L (1,300 ± 219) calves. Calves on 8L, had an ItoG (177.5 ± 20.76 µU/mg) that was almost 2-fold greater (P < 0.05) than in 4L (93.1 ± 21.17) and 1.5-fold greater (P < 0.05) than in 6L (113.6 ± 21.17) calves. Insulin sensitivity tended (P = 0.07) to be less in 8L (3.38 ± 0.30 mL/min x µU/mL per kg of BW) than in 4L or 6L calves (3.43 ± 0.30). We concluded that offering 8 L/d of MR elicits a decrease in starter feed intake and tends to decrease insulin sensitivity of calves.
Keywords: calves, enhanced-feeding, metabolism