Relationship between fertility and postpartum changes in body condition and body weight in lactating dairy cows

Abstract Text: The relationship between energy status and fertility in dairy cattle was analysed retrospectively by: analysing the effect of early postpartum changes in body condition score (BCS; Expt 1) and post-partum changes in body weight (Expt 2) on fertility. To reduce the effect of cyclicity status, all cows were presynchronized with Ovsynch before to a second Ovsynch and timed AI (TAI after Double-Ovsynch; Expt 1; First GnRH at 53±3 DIM; TAI at 80±3 DIM) or synchronized superovulation (Expt 2). Data were analysed by logistic regression with GLIMMIX and ANOVA using the MIXED procedure of SAS. In Expt 1, lactating dairy cows on two commercial dairies (n=1,887) were divided by BCS change from calving until third week postpartum. Overall, P/AI at 70 d pregnancy diagnosis differed dramatically (P<0.001) by BCS change and were least for cows that lost BCS, intermediate for cows that maintained BCS, and greatest for cows that gained BCS (22.8% [180/789], 36.0% [243/675], and 78.3% [331/423], respectively). Effects of BCS change on fertility were similar for primiparous and multiparous cows, but differed by farm with BCS change dramatically affecting (P<0.001) P/AI on one farm however there was no effect (P=0.35) on the other farm. In Experiment 2, body weight of lactating dairy cows (n = 71) was measured weekly from first to ninth week postpartum. Cows were divided into quartiles by percentage of body weight change from calving until third week postpartum. (Q1=+2.39%; Q2=-0.07%; Q3=-3.50%; Q4 =-6.84%). Cows were superovulated (TAI=70±3 DIM) and there was no effect of quartile on number of ovulations (17.9), total embryos/oocytes collected per cow (8.5), or percentage of oocytes that were fertilized (77.5%). In contrast, the percentage of fertilized oocytes that were transferable embryos was greater (P=0.04) for cows in Q1, Q2 and Q3 than Q4 (83.8%, 75.2%, 82.6%, and 53.2%, respectively). In addition, percentage of degenerated embryos was less (P=0.02) for cows in Q1, Q2, and Q3 compared to Q4 (9.6%, 14.5%, 12.6%, and 35.2% respectively). In conclusion, change in BCS during the first three weeks postpartum had a profound effect on P/AI to first TAI. This effect could be partially explained by the reduction in embryo quality and increase in degenerate embryos 7 d after AI in cows that lost more body weight from first to third week postpartum. Supported by Hatch project WIS01171

Keywords:

BCS loss; Body weight loss; Embryo quality; Fertility