Effect of natural progesterone with and without estradiol benzoate on the onset signs of oestrus, ovulation and pregnancy in Bos indicus cattle raised under mexican tropical conditions

Abstract

The effect of a intravaginal device containing 1.9 g of progesterone and one capsule of 10 mg of estradiol benzoate (EB) (CIDR-B) was evaluated in Bos indicus cattle. Upon withdrawal, calculations regarding estrous rate, ovulation and pregnancy were considered. 122 Bos índicus cows (experiment 1) and 30 heifers (experiment 2) were used and randomly divided in three groups: Group ST: 20 cows and 10 heifers without treatment, group CIDR-B-E: 51 cows and 10 heifers with the device withdrawal at 10 or 13 days respectively (CIDRB+ E:). Finally, 51 cows and 10 heifers with the device withdrawal at 10 or 13 days respectively plus an injection 24 hours late of 1 or 2 mg of EB for cows and heifers respectively.

The animals were observed for oestrus detection during 96 hours continuously after CIDR-B removal. Afterwards, starting at day 17 the animals were observed twice daily for one hour each period until 90 days. The cows that showed oestrus between 0 to 47 days were artificially inseminated and open cows in oestrus between 48 to 90 days post CIDR-B withdrawal were placed with a bull. Blood samples were collected for progesterone evaluation to confirm ovulation and ovarian activity. Pregnancy diagnosis was carried out via rectal palpation and ultrasonography. Discrete variables were analysed using the exact Fisher test. Continuous variables were analysed by Student t test, and reproductive parameters in the cows were related to oestrus, ovulation and pregnancy through a CATMOD SAS general lineal model.

In both experiments the group CIDR-B+E showed a high rate of oestrus 92.2 and 90.0% for cows and heifers respectively and was different (p < 0.05) to CIDR-B-E (60.8 and 50.0%) and ST (35.0 and 0.0%). In relation to ovulation, no significant difference was found between groups (p > 0.05). However, CIDR-B-E showed better rates 51.6 and 60.0% than ST group 28.6 and 30.0% and CIDR-B+E group 36.2 and 30.0%. Global pregnancy during 90 days was 25.4% in experiment 1 and 56.7 in experiment 2 (p < 0.05). However, pregnancies obtained during the 0-5 days of CIDR-B withdrawal and the next four oestrus cycles were not significantly different in the three groups (p > 0.05). Nonetheless, 83.8% and 82.3% of the pregnancies concur in the first five days after withdrawal and the next two cycles.

Therefore it can be concluded that the oestradiol injection induced the presence of high number of animals in oestrus, but the ovulation rate and pregnancy rate was not improved. However, others factors influenced the results such as nutrition and suckling.