Analysis of sources of variation and relationships among sow productivity traits

Richard L Cutshaw, Purdue University

Abstract

The swine industry has witnessed major changes in the past three decades in terms of selection tools and implementation of effective selection. As the pork industry continues to consolidate, it is increasingly important to be able to accurately predict and direct future performance toward increased overall profitability. Overall, sow productivity greatly affects a pork producer's ability to be profitable in the industry and have sufficient knowledge of production levels to improve the likelihood of remaining profitable into the future. The relationships among sow productivity traits including total number born, litter birth weight, number weaned, preweaning survival, mean piglet birth weight, and litter weaning weight in purebred and crossbred litters and their relationships with growth performance and composition were evaluated. The initial study found that relationships among many commonly measured sow productivity traits have changed dramatically since the 1980's and selection for certain traits have been more effective than others. The second study found that variation in birth and weaning weights in swine had a large positive effect on the days to market but litter effect on loin muscle area or backfat depth. Sow productivity traits such as litter, birth, and weaning weights have increased drastically in the past whereas threshold traits like survival percentage have not greatly changed in the same time period. Many of the relationships observed in sow productivity were examined by their relationship between number of pigs the sow is allowed to nurse as well as the parity of the dam. These data suggest that genetic superiority for milk production potential may be expressed when the sows are subjected to litter sizes that are larger than average. As number of pigs born alive increases, the percentage of piglets that are light weight increases, competition for food resources increases, and the likelihood of a pig being weaned decreases. Maximum litter weight and number weaned were observed when sows were allowed to nurse 12 to 14 piglets. Above these levels of number of pigs nursed there was no increase in number of piglets weaned or litter weaning weight. Number weaned increased as number after transfer (NAT) increased in a linear fashion up to NAT equal to 10. After 10, there was a curvilinear relationship between number weaned and NAT until number weaned reached a maximum value at NAT equal to 12 to 13. In current studies, increasing litter size did not significantly increase the amount of variation in the piglet birth weights; nor did increasing the number of piglets allowed to nurse increase the variation in piglet weaning weights. It is important to understand these relationships for adjustment of raw data to allow more accurate genetic evaluation. Overall, for most sow productivity traits, parity 2 sows had litters with the greatest birth and weaning weights. For other traits there were no differences from parity 2 sow litters to parity 3 through 5 sow litters. Both birth and weaning weight were found to be related to days to 250 pounds, backfat depth, and loin muscle area. Overall, birth and weaning weight had greater effect and accounted for more of the residual variation of days to 250 pounds (20.5 %) than backfat depth (2.4%) or loin muscle area (0.6%). Pigs with lighter than average birth and weaning weights required more days to achieve 250 pounds bodyweight. Pigs with the lightest birth weight had smaller loin muscle areas and slightly greater backfat depth than pigs with average and above average birth weights. Parity 1 dams required approximately 3 more days to achieve 250 pounds. When adjusted for linear-quadratic effects of both birth and weaning weight, the difference in days to 250 pounds was not significant. This suggests in these high health purebred herds, the increased days to 250 pounds of the parity 1 dams was accounted for by their decreased birth and weaning weights. Selection for increased birth weight and increased preweaning survival has become more important than selection for increased litter size. Future selection must also consider the magnitude of variation for birth and weaning weight, along the percentage of lightweight piglets born as these traits are more closely related to piglet survival and post weaning performance.

Degree

M.S.

Advisors

Schinckel, Purdue University.

Subject Area

Animal sciences

COinS