Studies on cyclic ovarian activity in pre-puberal heifers and post-partum cows of the Gobra Zebu breed in Senegal

The objective of this study was to determine the age at the onset of puberty in heifers, and the resumption of ovarian activity post-partum in cows of the Gobra Zebu breed. The study was conducted at the Centre de Recherches Zootechniques (CRZ) in Dahra. The CRZ is located in the sylvo-pastoral zone of Senegal. The female offspring were kept with their mothers until weaning at an age of 7 months. After this age they were grazed on natural pasture with ad-lithium watering. The heifers and cows were monitored for 14 and 4 months respectively. This monitoring included the detection oestrous behaviour, weighing, and RIA of progesterone in blood plasma. The heifers showed an average daily weight gain of 418 and 235 g/d prior to and after weaning respectively. An an age of 14 months, 17 of the 21 heifers had shown signs of oestrus behaviour at least once. The average age at first plasma progesterone rise was 413 ± 64 days(X-bar ± sem) with and average body weight of 176 ± 22.2 kg. This age is correlated with the body weight at weaning. In cows the resumption of ovarian activity post-partum proceeded progressively. Based on heat observations, 4 and 6 out of 13 cows resumed ovarian activity 50 and 60 days post-partum respectively. Based on plasma progesterone levels, resumption of ovarian activity occurred between 36 and 48 days post-partum in 7 out of the 13 animals. Other data collected showed that Gobar Zebu cattle have a late age at first calving (51 months) and long calving intervals (430 to 530 days). This study shows that the Zebu Gobra can commence cyclic ovarian activity at an early age, and that the duration of post-partum acyclicity can be short. This allows the development of strategies to improve the productivity of Zebu Gobra cattle. (author). 41 refs, 3 figs, 1 tab