A longitudinal study of weight and fatness in sows from selection to parity five, using random regression

This study examined the changes in BW, fatness, and genetic parameters for these traits over a sow's productive life, using random regression. Data for BW (kg) and fat depth at the P2 site (mm) were recorded repeatedly on 3,324 sows from selection to culling. There were up to 19 recording events, defined as: 20, 21, 26, and 29 wk of age, followed by records at mating, d 110 of gestation (d110), and weaning, for parities 1 through 5. In this population, sows continued growing through parity 5 but achieved 90% of this BW by 22 mo, which is the average age at remating after parity 3. In contrast, sows increased fat levels until just before parity 1 farrowing, when a plateau in permanent reserves was essentially established. Heritability estimates were 0.31 ± 0.08 and 0.36 ± 0.08 for BW and fatness, on average, from the random regression analyses. However, the greatest heritabilities were estimated from data recorded before the first farrowing and diminished with increasing age as residual variation increased. Trajectories of heritability estimates for both BW and fat from random regression show that genetic variation is available for selection to alter sow development patterns. However, due to relatively low genetic correlations between early and later BW, repeated BW measurements would be required to effectively alter mature sow BW, in particular. The solutions for development patterns were obtained for individual sows from the random regression model and were used to extrapolate the expected individual sow BW at 30 mo. Genetic solutions, including the intercept and slope for BW and fatness, were used to rank sows into quartiles. Results suggested that genetically heavier/fatter sows are more likely to successfully enter and stay in the breeding herd, thus demonstrating increased lifetime performance. However, there is also evidence to suggest that sows with high growth potential expressed later in life were disadvantaged with respect to their longevity and productivity. Therefore, a breeding goal combining efficient lean growth in finishers with limits to mature sow size could be beneficial to sow herd performance.