Effects of Weaning Age on Growth and Blood Parameters of Replacing Holstein Calves Fed on a Restricted Step Up and Down Milk Feeding Program

The objective of this study was to investigate the effects of different early weaning programs on growth performance and blood parameters of dairy calves. To meet this objective, thirty Holstein calves with initial body weight of 36 ± 5 kg were randomly assigned at birth to one of the three weaning programs. Experi-mental groups were: 1) starter diet and whole milk from birth to 6 weeks and weaning at 42 d old (6WW)), 2) starter diet and whole milk from birth to 9 weeks and weaning at 63 d old (9WW) and 3) starter diet and whole milk from birth to 12 weeks and weaning at 84 d old (12WW). Starter diet and water were available ad libitum throughout the experiment. Daily starter intake and growth performance of calves were measured until d 90 of life for all groups. Body weight (BW) and starter intake in all measured periods (on d 28, 56 and 84) did not differ between experimental groups. Calves weaned at 42 d (6WW) had higher average daily gain (ADG) in second month than 9WWand 12WWgroups (P<0.05). Calves reared in 6WW group had significantly greater total ADG values than calves weaned on 63 and 84 d (P<0.05). Total feed conver-sation ratio affected by experimental treatments and was lowest in 6WWcalves (P<0.05). Body length, heart girth and withers height of calves did not differ among treatments at 28, 56 and 84. Plasma cholesterol con-centration of calves weaned in 6WWgroup was lower (P<0.05) than calves weaned in 9WW and 12WW. Under the conditions of this study, the results suggest that calves weaned at 42 d were more efficient at utilizing dry matter intake for body weight (BW) gain and growth.