Short- and medium-term changes in performance and metabolism of dairy calves offered different amounts of milk replacers

The objective of the present study was to evaluate short- and medium-term growth performance and glucose metabolism of dairy calves fed 2, 3 or 4 L of milk replacer (MR) twice a day. One hundred and twenty female Holstein calves were randomly assigned to 3 groups: 2 L of MR twice daily (4 L), 3 L of MR twice daily (6 L), and 4 L of MR twice daily (8 L). The MR was mixed to have a 15.0% DM content. Daily MR and starter feed intake were recorded from days 2 to 70. Calves were weighed at days 0, 35, 63 and 300 and average daily gain (ADG) and gain to feed ratio (GtoF) was calculated. A glucose tolerance test (GTT) was performed at 42, 86, and 300 d of life. Overall, total DMI during the first month of life was greatest for 8 L calves (1010±22 vs 950±23 g/d), but 6 L and 8 L calves consumed less starter feed (205±21 g/d) than 4 L calves (400±22 g/d). Calves on 8 L had the greatest ADG at 35 d of life (752±29 g/d) followed by 6 L (564±29 g/d) and 4 L calves (484±29 g/d). In contrast, at 63 d of age, calves on 4 L had the greatest ADG (660±29 g/d) being 495±29 and 394±29 g/d for 6 L and 8 L calves, respectively. At 300 d of life, ADG did not differ among treatments. Allowance of MR did not affect GtoF. Age at first breeding was greater when calves received 4 L/d, but no differences were found on age at pregnancy and conception rate. The amount of MR offered had short- and medium-term effects on glucose metabolism. When calves were fed 8 L/d, serum insulin to glucose ratio increased independently of age and insulin sensitivity (IS) tended to decrease. However, differences in IS disappeared as calves became older. It is concluded that calves fed 8 L of MR daily had greater ADG during the pre-weaning period, but were unable to compensate the lack of MR during the weaning process resulting in a decreased ADG compared with calves fed 4 L daily. Also, offering 8 L/d of MR had transitory negative effects on glucose metabolism, but those disappeared with age.