Effects of nutritional supplementation and exposure to bulls on resumption of post-partum ovarian activity in Bunaji (Bos indicus) cattle.

A total of 51 pluriparous post-partum Bunaji (Zebu) cows belonging to agropastoralists were involved in a 2 x 2 factorial experiment for a period of 180 days. The cows were assigned randomly at calving to four treatments: (1) grazing only (no supplementation) and exposure to bull (NSBE); (2) grazing only (no supplementation) and no exposure to bull (NSNE); (3) grazing plus feed supplementation (each cow received 600g of 20.8% crude protein of whole cottonseed supplement per day) and exposure to bull (FSBE); (4) grazing plus feed supplementation and no exposure to bull (FSNE). Cows with an increase in milk progesterone (P(4)) concentration of > or =1 ng/mL from the weekly milk samples were used to analyse the number of days from calving to the time of resumption of ovarian activity. The mean interval from parturition to cyclic ovarian activity for FSBE cows was 95 days, compared to 119 days for the FSNE cows. Intervals to onset of post-partum ovarian activity were 24, 33 and 39 days which were significantly earlier in the FSBE cows, than the FSNE, NSBE and NSNE cows, respectively. Intervals to cyclic activity were 9 and 15 days earlier in FSNE cows than in NSBE and NSNE cows. By 150 days post-partum, 100% and 92% of the cows in the supplemented groups (FSBE and FSNE), had resumed cyclic ovarian activity compared with 75% and 69% for the unsupplemented cows (NSBE and NSNE). It is concluded that nutritional supplementation and exposure to bulls synergistically shortened the length of post-partum anoestrus in zebu cattle. The economic benefits of using exposure to bulls and cottonseed supplementation in this study to enhance early resumption of post-partum ovarian activity of cattle may serve as a management tool in tropical areas where livestock production has some constraints.

Fertility in zebu cattle (Bos indicus) after prostaglandin administration and artificial insemination.

A total of 137 cycling zebu cows, each receiving a single dose of prostaglandin PGF(2alpha)were used in an oestrus synchronization programme on three different farms. Of the cows on the three farms, 60.6 and 90.5% showed overt oestrus and luteolysis, respectively. Pregnancy rate to fixed time inseminations following single injection of PGF(2alpha)was 61.4% for farm 1, significantly higher than the values of 45.7 and 46.9% for farms 2 and 3, respectively. The pregnancy rates to second service of rebred cows were 53.3, 50.0 and 50.0% for the three farms, respectively, with no significant differences between each. Fertility classification of the cows based on progesterone (P(4)) concentration showed that 6.6% of cows on the three farms were incorrectly diagnosed as having corpora lutea; 2.9% of them had incomplete luteolysis and 5.1% may have lost their embryos between days 21 and 45 post-insemination. The pregnancy rate was 10% higher in the rainy season than in the dry season. Cows with body condition scores of 3 and 4 had a higher overall pregnancy rates than those with a body condition score of 2. The findings of this study further confirm the luteolytic efficacy of prostaglandin in inducing oestrus in zebu cattle and indicate that the nutritional status of the cows must be satisfactory before embarking on oestrus synchronization programmes.