Effect of milk replacer program on calf performance and digestion of nutrients in dairy calves to 4 months of age

Calves fed >0.7 kg of dry matter from milk replacer (MR) typically have greater growth preweaning but lower growth postweaning. This is partially explained by lower digestibility of starter due to less development of the rumen at and after weaning; however, it is unclear when digestibility matures postweaning to levels typical of mature ruminants. Thus, we fed Holstein calves (initially 2 to 3 d of age) 3 MR programs (MOD = 0.66 kg daily for 39 d, and then 0.33 kg daily for 3 d, n = 15 calves; HIMOD = 0.88 kg daily for 5 d, then 1.1 kg daily for 23 d, then 0.66 kg daily for 18 d, and then 0.33 kg daily for 3 d, n = 16 calves; HI = 0.88 kg daily for 5 d, then 1.1 kg daily for 37 d, and then 0.56 kg daily for 7 d, n = 15 calves). The MR consisted of 28% crude protein and 20% fat and was reconstituted to 14% solids and fed at 0630 and 1400 h daily. A 39% starch textured starter (19% crude protein) was fed free-choice for the first 56 d of a nursery trial with calves in individual pens. From 56 to 112 d, calves were grouped by MR program into pens of 3 to 4 calves and offered a starter with the same ingredient composition blended with 5% chopped grass hay for ad libitum consumption. Digestion was estimated at 11 and 16 wk. Measurements in the first and second 56 d were analyzed separately in a completely randomized design using repeated measurements when applicable. Preplanned contrasts of MOD versus HIMOD and MOD versus HI were used to separate means. Milk replacer dry matter intake was 26.6, 42.4, and 48.7 kg in calves fed MOD, HIMOD, and HI, respectively. Starter intake was less for calves fed HIMOD and HI versus MOD from 3 to 8 wk. Efficiency of metabolizable energy and protein used for body weight gain did not differ among programs. During the second 56 d, body weight gain and hip width changes were greater for calves fed MOD than HI. Total 112-d body weight gain and total hip width changes were 101.4, 101.3, and 101.7 kg, and 9.0, 9.1, and 8.7 cm for MOD, HIMOD, and HI, respectively. Digestibility of all nutrients except starch were greater at 16 versus 11 wk of age. Digestibility of dry matter, organic matter, neutral detergent fiber, and acid detergent fiber were less for HI versus MOD at 11 wk of age explaining much of the why postweaning body weight gain advantages were lost postweaning in calves fed the HI program. Feeding more than 0.66 kg of dry matter intake from a MR during the preweaning phase did not increase total body weight or hip width gain from 0 to 4 mo of age.