Effects of Diets with Different Energy Levels on Growth Performance and Serum Indices in Chinese Holstein Heifers Aged 7 to 10 Months

The objective of this study was to investigate the effects of diets with different energy levels on growth performance and serum indices in Chinese Holstein heifers aged 7 to 10 months.Twenty four heifers aged(200±3) days were randomly divided into 3 dietary treatments with 8 replicates and 1 heifer per replicate,and heifers were fed diets with net energy for lactation(NEL) of 5.40(group A),5.90(group B) and 6.40(group C)MJ / kg,respectively.The pre-experiment lasted for 10 days,and the experiment lasted for 90 days.At 210,240,270 and 300 days of age,growth performance indices including body weight,withers height,body length,heart girth,abdominal girth,hip width,nipple length and body condition scoring were determined before morning feeding,and blood samples were collected for the analysis of serum indices including triglyceride,urea nitrogen,estrogen,estradiol,leptin,growth hormone and insulin-like growth factor 1.The results showed as follows: 1) at 210 to 300 days of age,the average daily gain of heifers in groups A,B and C was 0.69,0.81,0.96 kg / d,respectively,and group C was significantly higher than group A(P0.05).2) At 240 days of age,the length of left posterior nipple of heifers in group A was significantly higher than that in group C(P0.05),while at 240 and 270 days of age,the length of right posterior nipple of heifers in both groups A and B was significantly higher than that in group C(P 0.05).3) At 240 days of age,the content of serum triglyceride of heifers in groups A and B was significantly lower than that in group C(P 0.05).4) At 300 days of age,the content of serum estradiol of heifers in group C was significantly higher than that in groups A(P0.05) and C(P0.01).In conclusion,the body figure and development of mammary gland of heifers can be maintained when dietary NELis 5.90MJ/kg under the conditions in the present study.