Offspring sex ratio in domestic goat (Capra hircus)

Abstract

The Capra genus is sexually dimorphic, males are substantially bigger than females, they fight for mating privileges and sometimes even form harems. Thus Capra genus meets the assumptions of the Trivers-Willard hypothesis. However, in case of the domestic goat Capra hircus their reproduction is man-managed. We assessed whether maternal hornedness, maternal and paternal breed and age, maternal birth year, litter size, previous year offspring sex, and litter birth year influenced offspring sex ratio in the domestic goat. We examined 268 litters born in the years 1997-2002 at the Experimental Farm in ZÅotniki. The statistic methods used were logistic regression and Spearman rank correlation. The offspring sex ratio in the herd differed significantly from unity: 55.8% kids were females, p < 0.01. The factors that significantly influenced offspring sex ratio were maternal hornedness and maternal birth year. Horned dams (occupying high positions in the social hierarchy) produced fewer daughters (52.2% of offspring) than hornless nannies (62.2%). The fact that dams born later produce more daughters can be connected with their origin from different farms and worse environmental conditions in ZÅotniki in the consecutive years (because of the Experimental Farm financial problems). Moreover, Spearman rank correlation between sex ratio in the first and in the second litter was marginally significant and negative (R = -0.25, p = 0.061).