Phenotypic correlations between reproductive characteristics related to litter and reproductive cycle length in sows

The study estimated phenotypic correlations between reproductive traits in sows classified as maternal (Polish Large White, Polish Landrace, and Yorkshire) and paternal (Duroc, Berkshire, and Hampshire) components, kept on farms located in Poland and in the United States. Altogether, it used data on 736 litters from 196 sows to analyse traits related to litter and reproductive cycle length. The former included litter size, the numbers and the percentages of piglets born alive, stillborn, and weaned; the latter included gestation length, lactation length, and the lengths of weaning-to-conception, farrowing-to-conception, and farrowing intervals. The strongest positive correlations between the litter-related traits were those between litter size and the number of piglets born alive (0.90), the number and the percentage of piglets born alive (0.88), the numbers of piglets born alive and weaned (0.78), and litter size and the number of weaned piglets (0.68); the strongest negative correlations were between the percentage of piglets born alive and the percentage (-0.95) and the number (-0.82) of stillborn piglets. Among the traits related to reproductive cycle length, the strongest positive correlations were those between the length of weaning-to-conception interval and the lengths of farrowing-to-conception (0.96) and farrowing (0.97) intervals, and between the length of farrowing-to-conception interval and farrowing interval (0.98). Gestation length and lactation length were weakly negatively correlated (-0.25). Correlation coefficients between the traits related to litter size from one side and reproductive cycle length from the other were low and mostly statistically non-significant, suggesting that using phenotypic correlations can help improve economically important reproductive traits, but only within the two above-mentioned groups of traits.