Sex ratio of offspring in pigs: farm variability and relationship with litter size and piglet birth weight

The purpose of this article was to analyse data available on pig sex ratio at birth to provide information on its variability and the possible factors of influence. Factors that can influence the proportion of female or male offsprings are of interest in livestock production for practical reasons. Previous works show that exhaustive and conclusive information is not available in pigs. Nowadays, data collected by computerised pig management systems, or experimental projects aimed to test other hypotheses, enables the study of sex ratio variation. As an example, a small data set from a previous project aimed to evaluate the effect of birth weight on survivability was used in this study. The sex ratio variability among farms and its relationship with litter size and birth weight were analysed and discussed. Although not free of sampling error, neither of selective reporting, results showed that variability can exist among commercial farms, and that sex ratio was not clearly affected by litter size but varied among classes of piglets with different birth weight. Additional key words: gender distribution, sex proportion, swine.