Pilot study on the reproductive performance of Brazilian Nellore, Gir and Caracu cows

Post-partum ovarian activity in three different Brazilian beef breeds (Nellore, Gir and Caracu) was studied to evaluate the influence of nutrition and reproductive history on the time from calving to first ovulation. Multiparous Nellore (n=12), Gir (n=11) and Caracu (n=10) cows were fed improved pasture and supplemented with minerals. Milk samples for progesterone (P4) analysis were collected twice-weekly from the second week post-partum until the end of the breeding period (June). Faecal parasites, blood constituents and pasture nutrients were monitored monthly between January and June. Dry matter digestibility of the pasture declined from 81.7% in the wet season (October) to 58.4% at the beginning of the dry season (May). Phosphorus concentrations in the pasture were higher in February and March and the protein content lower in April. The faecal parasite egg counts were very low but showed a slight increase towards the end of the rainy season in April. Haemoglobin, packed cell volume (PCV) and total plasma protein were normal but inorganic phosphorus and plasma glucose levels were low throughout. The mean for days to first ovulation, proportion of cows cycling 60 days post-partum and days open for Nellore were 44.9 days, 90% and 110.9 days respectively, for Gir 52.3 days, 72.7% and 232.6 days, and for Caracu 79.5 days, 60.0% and 281.5 days. The Nellore cows performed considerably better than the other breeds in the first year of this continuing study. Analysis of variance indicated differences between breeds with respect to body weight of cows, calf body weight at weaning, average days open, plasma glucose, PCV and haemoglobin. Correlation analyses indicated that PCV and haemoglobin levels were interrelated with days to first ovulation and days open (P<0.05). (author). 20 refs, 1 fig., 2 tabs