Effects of Diets with Different Energy Levels on Growth and Development and Serum Indexes of Calves Aged from 3 to 6 Months

This experiment was conducted to investigate the effects of diets with different energy levels on growth and development and serum indexes of calves aged from 3 to 6 months.A total of 32 Chinese Holstein calves aged about 98 days were randomly divided into 4 groups(groups A,B,C and D).Each group was subjected to one of the following 4 diets with 6.24,7.04,7.53,and 7.85 MJ/kg net energy for lactation for82 days.Body growth and blood samples were determined at 98,120,150 and 180 days of age prior to morning feeding.The results showed as follows:1) during the experimental whole period(98 to 180 days of age),the average daily gains which were 0.64,0.75,0.78,and 0.84 kg/d,respectively,for the 4 groups,did not differ(P 0.05),but during 151 to 180 days of age,the calves of group D had greater average daily gain than those of group A(P 0.01).2) At 180 days of age,the body length of calves of group D was significantly higher than that of group A(P 0.05).The calves of group D had greater body condition score than those of group A(P0.01).3) The diets with 7.53 and 7.85 MJ/kg net energy for lactation improved the feed conversion ratio(P 0.05).Nipple length did not differ among groups(P 0.05).4) During the experimental whole period,calves fed high net energy for lactation diets(groups C and D) had higher serum cholesterol content than group A(P 0.05);serum low density lipoprotein content tended to increase with the increasing net energy for lactaion(P 0.10),whereas serum urea nitrogen content had the opposite tendency(P 0.10).5) Calves fed the diet with 7.04 MJ/kg net energy for lactation had the highest serum contents of estradiol and leptin,and those fed the diet with 7.85 MJ/kg net energy for lactation had the lowest serum contents of insulin and insulin-like growth factor-Ⅰ.The diet with 7.53 MJ/kg net energy for lactation can maintain the average daily gain of calves(0.78 kg/d) with no adverse effects on body dimensions and mammary development.