The Effect of Breeding Herd Parity Structure on Genetic Improvement of the Sow Herd

This study focuses on the value of the genetic lag associated with maintaining sows for additional parities in a commercial swine herd. Three traits were included in this study: number born alive (NBA), 21 day litter weight (W21), and days to market (D250). The economic values assigned to these traits were $22.00/pig,$0.70/lb., and $0.17/day, respectively. The genetic improvement per generation made for each trait was assumed to be 0.3 pigs, 3.0 lbs., and 3.0 days, respectively. It was estimated that the value of the genetic lag associated with retaining a sow to P3, P5, and P7 was$24.80, $46.89, and$73.97 in a herd whose seedstock supplier has a generation interval of 1.5 years. This minimal loss does not justify the costs of developing a gilt and decreased P1 production. Therefore, sows should remain in the breeding herd until culling for non-voluntary reasons or inferior production becomes necessary

The use of selection to improve sow longevity

The objective of this dissertation was to evaluate multiple approaches to incorporating sow longevity or lifetime sow productivity into a selection program. Sow longevity can be selected for using indicator traits, such as structural soundness and lameness. In the first study, objective measurements to detect sow lameness were examined. Lameness was chemically induced for a short time period in multiparous sows and their weight distribution and walking gait were objectively measured in the days following lameness induction. Using a classification tree analysis, it was determined that the mean weight being placed on each leg was the most predictive measurement when determining whether the leg was sound or lame after injection. The weight distribution measures had a greater predictive ability compared to the walking gait indicators. These measures could be used to select sows that are less likely to become lame and be removed from the breeding herd. While reducing the lameness instances in a herd would improve sow longevity, direct selection for longevity would be desirable. In the second study, genetic correlations between purebred and crossbred sow longevity were estimated. Most genetic improvement programs are based on an assumed relationship between purebred performance in a nucleus herd and their relatives\u27 crossbred performance in a commercial herd; however, this study found that there was little to no genetic correlation between purebred and crossbred sow longevity for this population. While longevity is heritable at both the nucleus and commercial levels, results from this study indicate that little improvement would be made in crossbred longevity if selection relies solely on purebred information. One way to select for sow longevity would be to estimate purebred genomic breeding values using records from a related crossbred population. A spreadsheet for estimating the total costs associated with incorporating genome-enabled selection into a swine breeding program was developed as the final part of this dissertation. This tool will aid producers in estimating the economic viability of incorporating genome-enabled selection into their specific breeding program. Based on the results from these projects, it is recommended that a commercial test herd be implemented as part of a selection program to improve longevity or sow productive lifetime. If a genetic company can succeed in improving sow longevity through an effective breeding program, production efficiency and profitability can be improved for commercial swine operations

Evaluation of litters per sow per year as a means to reduce non-productive sow days in commercial swine breeding herds and its association with other economically important traits

The purpose of this project was to determine the value of implementing litters per sow per year (LSY) into a selection program. Two studies were conducted to achieve this objective. The goal of one study was to determining the genetic and phenotypic relationships between LSY and other economically important reproductive and post-weaning traits from a commercial swine breeding company. Determining the genetic and phenotypic correlations among traits can help breeders evaluate the expected impacts their selection decisions have on other economically important production traits. These other economically important traits may or may not be included in the selection criteria. This is particularly important when considering reproductive and post-weaning traits because of the undesirable genetic relationships that typically exist between reproductive and post-weaning traits. The traits collected included number born alive (NBA), wean to estrus (W2E), adjusted back fat (BF), percent lean (PCL), and days to 100 kg (D100). Litters per sow per year (LSY) was calculated based on recorded information. Genetic parameter estimates were calculated using ASREML. The heritability estimates for NBA, LSY, W2E, BF, D100, and PCL were 0.15, 0.03, 0.03, 0.52, 0.33, and 0.36, respectively. The genetic correlation between LSY and W2E was large and favorable. The genetic correlations between LSY and the three post-weaning traits (BF, D100, and PCL) have large standard errors and are unclear in direction. Some economically important traits can be favorably changed indirectly with selection on LSY; however, a selection index will be needed to ensure that post-weaning growth traits are not adversely affected by selection for LSY in a maternal line breeding program. The goal of the second study was to determine the relationship between individual sire breeding values (BV) for LSY and progeny means for farrowing rate, removal parity, and lifetime born alive. Landrace, Large White, and F1 (YyL or LyY) crossbred females were included in the analyses. Estimated breeding values (EBV) for LSY were calculated using ASREML. The heritability estimate for LSY was 0.11. Sire progeny (daughter) farrowing rate means were calculated as total number of services of the sire\u27s daughters divided by the total litters farrowed from the sire\u27s daughters. Similar values were calculated for daughter average removal parity, and daughter average lifetime born alive. The Spearman rank correlation between the LSY EBV and the progeny farrowing rate of the sires was calculated using SAS software. When all sires with 10 or more daughters were included in the analysis, the Spearman rank correlations between the sire\u27s LSY EBV and daughter means for farrowing rate, removal parity, and lifetime born alive were 0.49, 0.23, and 0.25 (P\u3c0.01). The LSY EBV was favorably correlated with the daughter means for all three traits. This provides evidence that selecting sires with high LSY EBV to improve the LSY could also improve the herd farrowing rate, removal parity, and lifetime born alive. Sires ranked in the top 25% for LSY EBV had a 15.3% higher average farrowing rate compared to sires in the bottom 25%. Daughters from the top sire had a one parity greater average removal parity than daughters from the other sire group. This extra litter corresponded to an average of 8.9 more pigs produced in a sow\u27s lifetime. Based on the results of this project, LSY is heritable. There is a genetic component of LSY and there is sufficient biological variation of the trait for traditional selection methods to be efficient and effective. There are little to no antagonistic relationships between LSY and the other economically important traits considered in this study. A selection index must be employed to ensure that there is no adverse effect on other economically important traits when selecting for LSY. There is evidence to suggest that a desirable relationship exists between LSY and farrowing rate, removal parity, and lifetime born alive. Improving farrowing rate through improving LSY can reduce the number of costly non-productive sow days in the herd. Improving removal parity and lifetime born alive through increasing LSY could improve sow longevity

Evaluation of Knife Separable Lean Content of Cull Sows at Harvest and Development of a Prediction Equation for Pounds Lean

A study was conducted to measure the quantity of fat and muscle from 4 primal cuts of cull sows from the four USDA market grades based on weight, and to develop prediction equations for estimating cull sow knife separable lean content. Lean and fat weights by primal within and across the USDA cull sow weight classes. These prediction equations could assist processors in their decision to purchase cull sow weight classes that meet the processors needs for pork products with defined lean:fat content, such as brats and sausage. Hot carcass weight and 10th rib backfat resulted in a prediction equation that had an R-square greater than 0.90. This equation was developed across weight classes and was more predictive that any one single class equation

Digital Evaluation of Structural Phenotypes Common among Higher Parity Crossbred Sows

Two independent, commercial, crossbred sow populations were selected to compare feet and leg structure in order to identify commonalities among them that may contribute to their long herd life. Digital imagery was used to measure the angle of the knee, pasterns and hock joints as well as the overall rear stance in sows ranging from parity 5 to 14. Parity and population effects were evaluated for each angle analyzed. Significant population effects (P\u3c 0.05) were observed for the angle of the knee. Significant parity effects (P\u3c0.05) were observed for the angle of rear leg stance. Similar leg conformation values across populations and parities for the front and rear pasterns and the hock may suggest that these values are within an acceptable range to allow for long herd life