Utilization of the buck effect to stimulate ovarian and oestrous cycles in anovulatory goats

Abstract

The introduction of bucks among anovulatory females, after a period of complete segregation (odor, sight, sound and touch), induces synchronous ovulations in the following days. The contact with males causes, in the doe, an immediate increase in the number and the amplitude of LH pulses, followed by an LH preovulatory surge leading to ovulation. The suppression of olfactory cue does not modify the immediate LH response but causes a two-fold decrease in the percentage of ovulating does. In intact females, the buck odor is sufficient to induce ovulation, however the percentage of responding does is lower than for does in direct contact with males, indicating a complementary action of several senses to induce the response of intact does. The first induced ovulations are silent (i.e. not associated with oestrous behaviour) in 40 % of the does and are followed by a short luteal phase of 5 days duration, in 75 % of the does. Later on, oestrous and ovarian cycles are restored. The quality of the stimulation by teaser bucks influences the response. Direct contact between sexes increases the percentage of ovulating females and an increase in the number of males leads to a rise of the induced ovulation rate. "Depth" of anoestrus, which varies with season, breed and physiological state of females, affects the capacity of does to respond ; when anoestrus is deep, the percentages of silent ovulations and of short ovarian cycles increase. When stimulation is sufficient and anoestrus not too deep, conception rate and litter size of females, which were anovulatory before introduction of males, are equivalent to those of previously cyclic females.