Genetic Optimization of Sow Productivity

M. T. See and S. H. Oh

Introduction

Optimal sow productivity occurs with maximum number of pigs per litter, litters per year and lactation yield while also optimizing pig birth weight, sow longevity and lifetime productivity. Most genetic evaluation systems focus on only some of these traits for selection. For example, the Swine Testing and Genetic Evaluation System (STAGES) has traditionally addressed genetic evaluation of number of pigs born alive, 21-day litter weights and number of pigs weaned. However, litter birth weight and the interval from weaning to mating are additional traits that deserve consideration to fully optimize sow productivity.

Materials and Methods

This project utilized 11,578 records of pigs born alive, litter birth weight, 21-day litter weights, number of pigs weaned, and weaning to mating interval from Duroc, Yorkshire, Hampshire and Landrace sows from 10, National Swine Registry member farms (Table 1). The analysis model for litter birth weight included the genetic effect of the sow and the fixed effects of contemporary group, herd, parity of sow and number of pigs born alive. The analysis model for weaning to mating interval include the genetic effect of the sow, a covariate for 21-day litter weight adjusted for age at weighing, and the fixed effects of contemporary group, herd, and parity of sow.

Results and Discussion

Heritability estimates pooled across breeds were 0.32 and 0.20 for litter birth weight and weaning to mating interval, respectively. The range in EPDs for the 451 Yorkshire sires represented with daughter records was 4.92 pounds of litter birth weight and 2.15 days in weaning to mating interval indicating dramatic genetic differences for these traits amongst animals. Assuming the cost of a non-productive sow day is $1.65/day the additional value due to genetic differences between daughters of the highest ranking and lowest ranking Yorkshire boars for weaning to mating interval would be $3.55/litter.

A comprehensive sow productivity index has also been developed that includes number of pigs born alive, litter birth weight, number of pigs weaned, litter weight at 21-days, and weaning to mating interval.

Conclusion

Utilization of these five traits in genetic selection allows for the selection of optimal sow productivity that more closely resembles the accepted industry measure of pig per sow per year. This genetic evaluation system does not account for the longevity or lifetime production of the sow because of the selection and culling practices followed in nucleus herds. More comprehensive genetic evaluation and selection for sow productivity should allow pork producers to enhance overall productivity and profitability.

Table 1. Summary statistics for weaning to mating interval and litter birth weight.

	WTE			LBW
Breed	Mean	SD	Records	Mean	SD	Records	Animals	Herds	Sires*
Yorkshire	5.70	1.9	5,212	33.8	10.0	5,212	10,198	9	451
Landrace	6.00	3.0	2,092	35.5	10.6	2,092	3,414	5	206
Duroc	6.58	3.5	3,835	32.0	8.84	3,836	6,681	4	327
Hampshire	5.58	1.8	439	28.2	8.43	439	1,981	2	65

* Sires that have produced daughters with WTE or LBW records.

Table 2. Summary of genetic parameters for weaning to mating interval and litter birth weight.

Breed	σ²_{G WTE}	σ_G	σ²_{G LBW}	h² _WTE	r_g	h² _LBW	σ²_{R WTE}	σ_R	σ²_{R LBW}
Yorkshire	0.83189	-0.04641	10.51279	0.24	-0.02	0.39	2.64298	0.23145	16.66305
Landrace	2.08501	0.55721	10.83811	0.24	0.12	0.35	6.62949	0.08669	19.78142
Duroc	0.95159	-0.02532	4.61249	0.13	-0.01	0.21	6.49182	-0.0425	16.94919
Hampshire	0.17702	-0.08759	5.92397	0.06	-0.09	0.26	2.75383	-0.1465	17.22752
Pooled*	1.10844	0.00000	8.5425	0.20	0.00	0.32	4.71678	0.10995	17.3472

*Weighted average of Yorkshire, Landrace and Duroc.