Postpartum follicular development in Brahman cows under two stocking rates.

The aim was to study postpartum follicular population dynamics in Brahman cows in the Mexican humid tropics and under different stocking rates. Lactating adult cows (n = 104) grazed native grammas (Paspalum spp., Axonopus spp.) under two stocking rates: 2.8 (high) or 1.7 (low) cows/ha. Follicle numbers and their size (millimetres) were measured by ovarian ultrasound scanning. Animals detected in oestrus and inseminated were taken out of the study. Both stocking rates produced similar (P < 0.05) body condition scores (BCS) and follicular dynamics. The percent of follicles, averaged over stocking rates, of <4 mm diminished and those of 5-8 mm increased with time, whilst those of >9 mm remained constant; respective values for the previously mentioned sizes were 60 days postpartum (n = 101), 49%, 56% and 5%; 120 days (n = 70), 28%, 66% and 6%; and 180 days (n = 15), 9%, 79% and 12%. There was a positive correlation between BCS and follicle number for size <4 mm (r = 0.73, P < 0.01), whilst for size 5-8 mm, this was negative (r = -0.51, P < 0.05), for follicles >9 mm, no difference was found (r = -0.08, P > 0.05). It was concluded that stocking rate did not affect follicular population dynamics of Brahman cows, but BCS dictated the number and categories of follicles present regardless of the stocking rate utilised.