Sexual behaviour and gonadal activity during the year in the tropical Creole meat goat. I. Female oestrous behaviour and ovarian activity

Abstract

An experiment was carried out over two consecutive years on 30 adult creole goats to determine if ovarian activity and oestrous behaviour varied seasonally and if feeding plane affected these responses. The animals, maintained on a pangola (Digitaria decumbens) pasture with a stocking rate of 1.060 kg liveweight/ha, were divided into two groups: C (control) and S (supplemented). Every month pasture quality was assessed and the animals were weighed. Goats of group S received a daily supplement of 0.3 kg of a commercial concentrate. Oestrous behaviour was monitored daily using a marking harness on a vasectomized buck in each group; ovarian activity was observed by monthly laparoscopy. Wide variations in pasture quality were observed from one month to another; dry matter and crude fiber generally were elevated (40 and 32 %) and crude protein content was low 6.6 %). In spite of poor quality pasture, goats of both groups showed a liveweight gain (C; + 30%; S: + 41%) throughout the experiment. During all of the experiment, more than 87 % of the females ovulated monthly, and this percentage did not vary with the month; the percentage of females showing oestrous behaviour (on average 82 %) varied significantly with the month and was lower than ovarian activity, indicating existence of silent ovulations. Supplementation had no effect on monthly ovarian activity or oestrous behaviour. Ovulation rate averaged 2.27 and varied significantly with the month. However, in spite of significant month effect, it was difficult to distinguish a clear seasonal effect except in May during which ovulation rate and oestrous behaviour were slightly depressed. The length of the oestrous cycles fell into two frequency categories: 5-8 days and 21 days; 45 % of the short cycles (< 17 days) lasted from 5 to 8 days. Frequency of short cycles did not vary with the month. Supplementation significantly reduced short-cycle frequency (C: 38 %; S; 27 %). There were significant rank correlations between some reproductive responses and environmental factors. The most important were between the monthly percentage of goats in oestrus and minimal temperature and maximal hygrometry (-0.66 and -0.61 respectively). It was concluded that creole meat goats maintained in good condition did not show marked seasonal variations in ovulatory activity or oestrous behaviour. Season had only a subtle effect on some reproductive characteristics. Immediate thermal environment of goats seemed able to modify the expression of oestrus probably by modifying thermal comfort.