Ovarian and pituitary function during the post-partum interval in Brahman and Brahman crossbred cows

Abstract

Studies were designed to determine: 1) the effect of post-partum nutritional restriction on serum luteinizing hormone (LH) concentrations and blood metabolites; 2) changes in ovarian cell type numbers, follicular populations, dissected diameters and surface diameters and follicular fluid (FF) steroid concentrations, and 3) steroidogenic capabilities of granulosa (GC) and thecal cells (TC) from follicles collected on Days 20, 30 and first oestrus post-partum from suckled beef cows following in vitro culture with LH, follicle-stimulating hormone (FSH) and forskolin (FSK) in vitro. A nutritional treatment x day post-partum interaction affected bioactive LH (BLH) concentrations and relative biological activity, as measured by B:l ratios. Likewise, serum cholesterol concentrations were higher on Days 7, 21 and 35 post-partum in cows fed to maintain body condition (MBC) compared to cows fed to lose body condition (LBC) post-calving. In summary, MBC cows had an enhanced metabolic state and pituitary function that resulted in shorter intervals to first oestrus (PPI) and greater conception rates compared with longer PPI, higher non-esterified fatty acids and lower blood urea nitrogen of LBC cows losing body energy reserves post-partum. Ovarian GC and TC numbers and viability were lower in follicles collected between Days 20 and 30 post-partum compared to follicles collected at first behavioral oestrus post-partum (FOP). Follicular fluid pregnenolone (PE), progesterone (P) and oestradiol (E) concentrations (ng/follicle) were lower in follicles collected on Day 20 post-partum, whereas testosterone (T) concentrations were higher in those same follicles. Greater T:P, T:PE and P:PE ratios were found in FF of follicles collected at Day 20 post-partum compared with lower ratios found in FF of follicles collected at FOP. Cows ovariectomized at FOP had corpora lutea that were accompanied by sub-luteal phase serum P concentrations. Follicular surface diameter measurements underestimated dissected diameters at ail times. Granulosa and TC from follicles collected at Day 20 have lower basal concentrations of PE, P and E compared with follicles collected at FOP...