Effect of Sex Ratio in the Litter in Which Polish Large White and Polish Landrace Sows were Born on the Number of Piglets Born and Reared

The aim of the study was to determine the effect of sex ratio in the litter in which Polish Large White (PLW) and Polish Landrace (PL) sows were born on the number of piglets born and reared to 21 days of age. Results obtained in nucleus herds from one breeding region were analysed. A total of 518 multiparous sows (179 PLW and 339 PL) were evaluated based on data from their litters (790 PLW and 1540 PL litters). The proportion of females in the litter in which the sow was born served as a basis for dividing the females into groups: group 1 <40%, group 2 - 40-50%, group 3 - 50-60%, group 4 - 60-70%, group 5 >70%. Significant differences in the average number of piglets born were found between the groups for PLW sows; compared to sows from groups 1, 2 and 3, females from group 5 gave birth to 8.0% (P≤0.05), 9.4% (P≤0.01) and 6.6% more piglets (P≤0.01), respectively, and compared to sows from group 2, those from group 4 gave birth to 5.1% more piglets (P≤0.05). The average number of piglets born and reared to 21 days by PL sows did not differ significantly between groups. The greater the proportion of females in the litter in which the PLW sow was born, the greater the preweaning mortality of piglets: 0.79, 0.87, 0.99, 1.02 and 1.24 piglets in groups 1 to 5, respectively. Preweaning mortality of PL piglets (0.93, 0.89, 0.81, 0.76 and 0.65 in groups 1 to 5, respectively) decreased with increasing proportion of females in the litter of origin and was lower than that of PLW piglets. It seems appropriate to account for the sex ratio of the litter in which the gilts were born when selecting them as mothers of the next generation as part of herd replacement; this parameter may improve fertility and production efficiency.