关键词: 犊牛, 表观消化率, 能量利用, 氮代谢

Abstract:

The current study was performed to investigate the effects of different energy levels on nutrients digestion and metabolism of weaned heifers.Thirty-two Holstein heifers aged 98 days were divided into 4 groups (A，B，C and D)，each with 8 heifers，and was fed with a diet which the net energy for lactation (NE_L) was 6.24，7.04，7.53 or 7.85 MJ•kg^-1 for 89 days，respectively.The weight，feed intake and glucose，urea nitrogen，and triglyceride content of serum were measured.Two digestion and metabolism trails were conducted at 151-157 and 181-187 day-old，respectively.Four heifers were randomly selected from each group，feces and urine were collected and the apparent digestibility，utilization rate of energy and nitrogen were measured.The results showed that：the average daily gain of heifers in 4 groups at aged 150-180 days were 0.77，0.91，0.86 and 1.11 kg•d^-1，respectively，the value of group D was significantly higher than that of group A (P<0.05).Body weight of heifers aged 180 days had an increasing trend with the amount of dietary NE_L increasing (P<0.10)；the apparent digestibility of gross energy increased before decreased (P<0.10).The NE_L level had significant effect on the apparent digestibility of dry matter，neutral detergent fiber and acid detergent fiber，digestible energy and metabolic energy (P<0.05)；When heifers aged 180 days，the ratio of retained nitrogen/nitrogen intake and retained nitrogen/nitrogen digestion increased first and decreased later with dietary NE_L increasing(P<0.10)，and the value of group C reached the peak.In conclusion，as for the overall nutrition balance of heifers and digestion and metabolism levels，the optimum dietary NE_L of heifers is 7.53 MJ•kg^-1.

Key words: heifer, apparent digestibility, energy utilization, nitrogen metabolism