Effects Of Negative Energy Balance On Reproductive Performance And Follicular Development During Early Lactation In Dairy Cows

Negative energy balance(NEB)is a physiological imbalance that the postpartum cow’s energy intake can not meet the demands of lactation.It has a serious harm to the reproductive health and reproductive performance in dairy cows and has caused great economic losses to intensive cattle farms.At present,there are few systematic studies on the relationship between NEB and reproductive performance,ovarian diseases and follicular development of cows in early lactation.Therefore,this study explored the influence of NEB in early lactation on reproduction of cows through B-ultrasound,blood clinicopathology,biostatistics to provide theoretical basis for improving the reproductive efficiency and fertility of cows in the future.Test Ⅰ: Effect of NEB on reproductive performance during early lactation in dairy cows.In this experiment,118 Holstein dairy cows with a frontal milk output of 9 tons or more were selected as test animals in a large intensive cattle farm in Heilongjiang Province.Based on the plasma levels of BHBA,NEFA,and GLU and clinical manifestations at 14 to 21 days postpartum,61 cows were assigned into a positive energy balance(PEB)group(BHBA < 1.2mmol/L,GLU > 2.8 mmol/L)and 57 cows were assigned into a NEB group(BHBA > 1.2mmol/L,GLU < 2.8 mmol/L).Cross-sectional study,independent sample T test,Pearson correlation analysis and prospective cohort study were used to analyzed the data from tested cows.The results showed that the BCS,body condition loss,milk urea nitrogen,plasma BHBA and NEFA levels,first estrus days,number of insemination,mating and conception days,and calving interval in NEB group were significantly higher than those in PEB group at 14 to 21 days postpartum(P < 0.05);the average daily milk production,milk protein and plasma GLU levels,number of estrous,estrus rate,and conception rate were significantly lower than those in the PEB group(P < 0.05).Among them,the loss of body condition was positively related to first estrus days,number of insemination,and mating and conception days(P <0.05),significantly negatively related to number of estrus,estrus rate,and conception rate(P <0.05),milk yield per day was significantly negatively related to number of insemination,and mating and conception days(P < 0.05).In addition,there was a strong positive correlation between NEB and anestrus inearly lactation(c2M-H= 12.63,P = 0.0004),and risk of anestrus in cows with NEB at 14 to 21 days postpartum was 3.67 times that of cows with PEB,indicating that NEB is an important risk factor of the increase in postpartum anestrus rate of dairy cows.Test Ⅱ: Effect of NEB on ovarian diseases during early lactation in dairy cows.In this experiment,22 healthy control cows were selected from PEB group of Test I,6 cows with follicular cysts,6 cows with luteal cysts,and 4 cows with inactive ovaries were selected from NEB group of Test I.Kruskal-Wallis,Spearman correlation analysis,Binary logistic regression and ROC analysis were used to analyzed the data from tested cows.The results showed that compared with healthy cows,plasma levels of NEFA and E2 in cows with follicular cysts were significantly increased(P < 0.05),and plasma levels of ALT,P4 and IGF-1 were significantly decreased(P < 0.05);plasma levels of NEFA and P4 in cows with luteal cysts were significantly increased(P < 0.05),and plasma levels of Ca,P and Mg were significantly decreased(P < 0.05);plasma levels of NEFA in cows with inactive ovaries were significantly increased(P < 0.05),and plasma levels of ALT,Ca,P,E2,P4 and IGF-1 were significantly decreased(P < 0.05).In addition,at 14 to 21 days postpartum,plasma levels of NEFA were positively correlated with cow ovarian disease(P <0.05),plasma levels of ALT,Ca,P and IGF-1 were negatively correlated with cow ovarian disease(P < 0.05).It was determined that the early warning value of dairy cows with ovarian disease is plasma NEFA > 0.50 mmol/L(sensitivity and specificity are81.3% and 90.9%,respectively)and plasma Ca < 2.02 mmol/L(Sensitivity and specificity were56.3% and 90.9%,respectively)at 14 to 21 days postpartum.Test Ⅲ: Effect of NEB on follicular development during early lactation in dairy cows.In this experiment,15 cows each were selected from PEB group and NEB group from Test I.Independent sample T test and repeated measurements were used to analyzed the data from tested cows.The results showed that compared with PEB group,plasma levels of BHBA,NEFA,TG,BUN,GH,IL-6 and FGF21 in NEB group were significantly increased(P < 0.05);plasma levels of GLU,TC,INS,IGF-1,IGFBP3,LP,BDNF,and ANGPTL8 and the follicle growth rate at 50 to 55 days postpartum were significantly reduced(P < 0.05),and plasma levels of E2 and P4 were lower;while plasma macro mineral concentration was not significantly changed(P > 0.05).And these changes will continue until 50 to 55 days postpartum,which hinders the normal growth and development of follicles.Conclusion: This study found that NEB during early lactation can reduce the cow reproductive performance,confirmed that NEB is a significant risk factor of of the higher anestrous rate of dairy cows postpartum,determined the risk early warning indicators and early warning value of ovarian diseases during early lactation in dairy cows,clarified that NEB during early lactation may suppress normal growth and development of follicles postpartum 50 to 55 d,which is related to the abnormality of energy metabolism,hormones and tissue cytokines caused by NEB.