RESUMEN
The severe loss of body condition score (BCS) during the early lactation period has been associated with infertility in cows. However, the mechanisms are not fully understood. The aim of this study was to examine the effect of BCS loss on liver health, and ovarian functions in cows during early lactation. Retrospectively multiparous cows from two farms were categorized based on units of BCS (1-5 scale) loss as Moderate (MOD, <0.75 units; n = 11) or Severe (SEV, ≥0.75 units; n = 9) loss groups. From Weeks -3 to 7, relative to calving, MOD and SEV cows lost on average 0.4 and 1.0-unit BCS, respectively. All data except hepatic transcriptomes were analyzed with PROC MIXED procedure of SAS. The plasma concentration of non-esterified fatty acids at Week 0 and 1, ß-hydroxy butyrate at Week 1, and γ-glutamyl transferase at Weeks 1 and 7 relative to calving were higher in SEV cows. Hepatic transcriptome analysis showed that 1 186 genes were differentially expressed in SEV (n = 3) compared to MOD (n = 3) cows at Week 7 after calving. Pathway analysis revealed that significant DEGs in SEV cows enriched in lipid metabolisms including, lipid metabolic process, ether lipid metabolism, fatty acid beta-oxidation, fatty acid biosynthetic process, fatty acid metabolic process, fat digestion and absorption, linoleic acid metabolism, alpha-linolenic acid metabolism. The impaired liver function in SEV cows was associated with 1.5-fold reduction of hepatic IGF1 gene expression and lower serum IGF1 concentrations. At the ovarian level, SEV cows had lower IGF1 concentration in the follicular fluid of the dominant follicle of the synchronized follicular wave compared to that of MOD cows at 7 weeks after calving. Further, the follicular fluid concentration of estradiol-17ß was lower in SEV cows along with lower transcript abundance of genes from granulosa cells associated with dominant follicle competence, including CYP19A1, NR5A2, IGF1, and LHCGR. These data show that SEV loss of BCS during early lactation leading up to the planned start of breeding is associated with liver dysfunction, including lower IGF1 secretion, and impaired function of the dominant follicle in the ovary.
