Effect Of Dietary Energy Levels On Reproductive Performance And Blood Biochemical Profile Of Transition Beef Cattle

The objective of present study was to investigate the effect of dietary energy levels on productive performance and blood biochemical profile of transition beef cattle and calf growth.It provides data support and experimental evidence for scientific feeding and management of beef cattle in transition period in actual production.The main contents are as follow:21 healthy late pregnant(-45d)Chinese Simmental crossed cattle(Simmental bull × Yunnan yellow cattle cow)heifers with similar body weight which is 335.7±21.60 kg were selected and divided into 3 treatments randomly,that were high energy diet(HE)with 1.06×NRC energy requirement,medium energy diet(ME)with 1×NRC energy requirement and low energy diet(LE)with 0.94×NRC energy requirement.And experiment will run for 60 d as all transition period of heifers.Results showed that:(1)LE diet increased the DMI of transition beef cattle when compared with ME and HE(P<0.05).And the MEI per kg MBW increased with the increasing diet energy.Body weight loss of HE cattle was 15.6kg and 16.6kg less than ME and LE.And HE diet increased Birth weight of calves and calving weight of heifers(P<0.05).(2)The colostrum protein,fat,Ig and milk protein of HE was higher that LE and ME(P<0.05).Milk protein and lactose of LE was lower than HE(P<0.05).(3)LE diet reduced the NDF,ADF,Ca and Ca apparent digestibility in comparison with HE(P<0.05).(4)The serum NEFA and BHBA in HE was less than that in LE and ME after calving(P<0.05).And in postpartum,the serum PEPCK levels in HE was significantly lower than that in LE(P<0.05).The serum FAS levels of heifers in HE was higher than LE and ME in transition period(P<0.05).(5)In close-up period,the serum INS levels in LE increased compared with ME and HE;The serum LEP levels in HE was significantly lower than that in LE(P<0.05).(6)The serum E2,LH and FSH levels of heifers in LE decreased compared with HE(P<0.05).We found that the interval between childbirth and first estrus of heifers in HE was 4.9 and 14 d earlier than that in ME and LE(P<0.05).(7)The serum TNF-? and IL-1? increased and serum IL-4 and IL-10 decreased with the dietary energy levels(P<0.05).(8)In transition period,the serum Cor,HSP-70 and LPS levels in HE was less than that in ME and LE significantly(P<0.05).After calving the antioxidant ability of heifers in LE was higher than HE,and MDA contents was lower than that in HE(P<0.05).In conclusion,HE diet significantly help heifers get a higher nutrient apparent digestibility and energy intake before calving,improved better colostrum and milk for calves.And reduced the weight loss in transition period and increased birth weight of calves.In the same time,HE diet reduced content of serum NEFA,BHBA and improved the serum INS and FAS levels and reduced the serum LEP and PEPCK levels of heifers.And that means HE diet can significantly reduce gluconeogenesis and lipolysis and relieve negative energy balance of heifers.Compared with LE and ME,HE diet can significantly improve the serum E2,LH and FSH levels of heifers after calving.Shorten the interval between childbirth and first estrus.HE diet decreased antioxidant capacity of heifers.