DIFFERENCES IN GONADOTROPIN-SECRETION POST PARTUM BETWEEN ZEBU AND EUROPEAN BREED CATTLE

Patterns of LH and FSH secretion were determined for Brahman (GB, Bos indicus), Hereford Shorthorn (HS, Bos taurus) and Brahman-Hereford Shorthorn cross (BX) primiparous and multiparous cows at different times post partum. From around day 30 post partum a higher proportion of HS compared with GB cows showed pulsatile LH secretion and at around days 40 and 50 mean LH concentrations were higher in HS than in GB cows. These differences were particularly noticeable between multiparous HS and GB cows. BX cows were intermediate with regard to numbers showing pulsatile LH and mean LH concentrations. For all genotypes plasma FSH concentrations were highest around day 18 post partum; there were no consistent genotype effects on FSH. During a mating period from days 50 to 120 post partum, a higher proportion of HS cows became pregnant compared with GB and BX cows. The differences in LH between HS and GB cows could reflect genotype differences in LH-secreting capacity of cows in a comparable reproductive state or, alternatively, the differences could have been temporally related to the onset of cyclic ovarian activity. © 1990.