Sexually active bucks are able to stimulate three successive groups of females per day with a 4-hour period of contact

Abstract

Bucks rendered sexually active by a photoperiod treatment of long days can induce fertile ovulation in a group of goats with only 4 h of contact daily with a male:female ratio of 1:10. Here we tested whether such bucks could induce fertile ovulations when stimulating successively three different groups of anovulatory goats when interacting 4 h per day during 15 consecutive days. Control males (n = 3) were introduced in the control group (n = 25) of does at 8:00 h and were removed at 12:00 h. Experimental males (n = 3) were in contact with the experimental groups of does: from 8:00 h to 12:00 h with a first group (n = 27), from 12:00 h to 16:00 h with a second group (n = 26) and with a third one (n = 27) from 16:00 h to 20:00 h. Bucks were then placed until next day in another pen. Both in the control and the experimental groups, more than 85% of females ovulated, and the proportions did not differ between the control and experimental groups (P ≥ 0.67) or between the three experimental groups (P ≥ 0.67). Moreover, the ovulation rate did not differ significantly between the control and the experimental females nor between the three experimental groups. Bucks were able to fertilize more than 72% of does independently of the number of females they were exposed to (P ≥ 0.17). Finally, more than 58% of females kidded and fertility did not differ between the control and experimental groups (P = 1) nor among experimental groups (P ≥ 0.77). We conclude that sexually active bucks are able to induce fertile ovulation in three successive groups of anovulatory goats even when the period of contact between sexes is reduced to 4 h per day.

Introduction

In breeds of sheep and goats that show a period of seasonal anestrous, the introduction of a male into a group of anovulatory females can stimulate their sexual activity within 72 h. This phenomenon, known as the “male effect”, has been extensively studied in ewes [1], [2], [3] and goats [4], [5], [6]. Factors such as the duration of contact between sexes, the intensity of the males' sexual behavior and the male:female ratio may influence the response of females exposed to males [6].

In ewes, it has been shown that the presence of the male 24 h per day during 15 days is required to obtain a maximum ovulatory response [7]. However, recent studies indicate that the decrease of the duration of contact between sexes from 24 to 16, 12, 8 or 4 h per day still enables to induce a high ovulatory response and fertility in Mexican goats [8], [9]. A likely explanation for the difference between the studies in ewes [7] and goats [8], [9] is that long-days-treated – and therefore sexually active – bucks were used in these two latter studies, whereas in the first one, they used rams that had not been treated with light and which were therefore probably either in sexual rest or with a low sexual behavior. Indeed, it was found in both goats and ewes, that a high sexual activity of males is a key component to obtain a high ovulatory response of females to the male effect [10], [11].

A recent study in goats indicates that the females' estrous response is not affected by decreasing male:female ratio but that some specific variables are [12]. Indeed, Carrillo et al. [12] found that a decrease in the male:female ratio from 4:39 to 2:39 or 1:39 had no effect on the occurrence of estrous behavior but lengthened mean interval between introduction of males and onset of estrous behavior. In our breeding conditions, several experiments have shown that a male:female ratio from 1:8 to 1:13 [10], [13], [14], [15] ensures proper fertilization of females and, more recently, it was demonstrated that such a ratio is sufficient to induce high ovulatory and reproductive responses in females even when daily contact between the buck and the females is reduced to 4 h [9]. However, whether sexually active bucks are able to induce ovulation, sexual activity and adequate fertilization to three groups of anestrous goats stimulated successively when the daily period of contact is 4 h remains to be investigated. Considering that a male:female ratio of 1:10 enable high ovulatory and reproductive responses, it could be expected that sexually active bucks will be able to stimulate three groups of females when the ratio is in this range and the daily period of contact is 4 h. To test this possibility, we exposed daily sexually active bucks either to a single or to three different groups of females during 4 h, at a ratio of 1:9 and for a period of 15 consecutive days.