Positive correlation between the body weight of anestrous goats and their response to the male effect with sexually active bucks

In the present study, we analyzed the results of two years of response to the male effect in seasonally anestrous goats to investigate whether the activation of female reproductive activity by the male effect is related to the body weight of the females. Seventy-nine adult female Mexican mixed breed goats were used. The anestrous females were exposed during 15 days to sexually active males, and were classified into three categories according to their mean body weight $\pm $SD (42 $\pm $ 9 kg) (Light: $\le $ 33 kg, $n$ = 19; Medium: 34–50 kg, $n = 46$; Heavy: $\ge $ 51 kg, $n$ = 14). More than 98% of the goats from the Medium and Heavy groups showed at least one estrus behavior within the first 15 days following the introduction of the bucks, versus only 63% of the females from the Light group ($P < 0.01$). The interval between the introduction of the males and the onset of estrus behavior was longer in the females of the Light and Medium groups (4.2 $\pm $ 0.8 and 3.3 $\pm $ 0.3 days) than in the females of the Heavy group (2.0 $\pm $ 0.2 days; $P < 0.03$). Also, body weight was negatively correlated with latency to first estrus (Spearman $r = -0.57$; $P < 0.001$). These results are in agreement with the hypothesis that the ability of anestrous goats to respond to the male effect is positively influenced by their body weight