Graduate Thesis Or Dissertation
 

Criteria for selection and management in the swine breeding herd

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  • Oregon State University swine herd records of four genetic groups were analyzed to determine: (1) the association of occurrence of a small litter (≤ 7) at birth with size of subsequent litters for gilts and sows, separately; (2) the effect of parity, genetic background and litter size on mean birth weight and mean number weaned; and (3) the effect of same-day weaning of dams to achieve contiguity of farrowing and increase neonatal pig survival by transferring pigs from excessively large litters to smaller ones. Analysis of differences for size of subsequent litters between first parity dams that had farrowed small (≤7) and non-small (> 7) litters showed differences (P < 0.023) between the means of 9.64 pigs born alive and 10.27 pigs born alive in the two groups respectively. Correlation and regression coefficients for litters subsequent to first parity non-small litters were 0.19 (P < 0.01) and 0.32 Mean number weaned in litters of 8, 9, 10, and 11 were 6.71, 7.25, 8.16 and 8.74 pigs respectively. These means were different (P < 0. 005). Differences in genetic background, parity and effects of interactions were nonsignificant within constant litter size at birth. Increases in mean number weaned with increasing litter size indicate that the number surviving is associated with number born and neonatal management. Neither genetic background nor parity appear to have effects on maternal performance in the population used when litter size at birth is held constant. Assembling sow records to simulate 5, 10, 15 or 20 sows weaned at the same time resulted in farrowings occurring contiguously enough to permit transfers of pigs from litters larger than 12. The total number of pigs at birth in excess of 12 per dam was 11, 1 and 0 respectively for dam groups of 5, 10 and 15. The mean range in time from first to final farrowing was 4.68, 6.45, 8.86 and 10.60 days for groups of 5, 10, 15 and 20 dams respectively. These data indicate that increasing the number of dams weaned on the same day results in increased opportunity to transfer pigs from excessively large litters to smaller ones. The increase in size of dam groups also increases the efficiency of utilization of labor and facilities at farrowing by increasing the average number of farrowings from one per day for groups of five dams to two per day for groups of 20 dams. (P < 0.002) respectively; correlation and regression coefficients for litters subsequent to first parity small litters were small and not significant. Mean litter size of all gilts was 9. 15 live pigs at birth, which is 0.49 of a pig less than the mean of litters subsequent to small litters. Thus, in this population, culling based on a small first parity litter would result in decreasing the mean number born alive in the next farrowing. Also, there would be added expense associated with raising the replacement to breeding age. Mean pig weight was significantly different (P < 0.005) between litters from gilts vs sows; birth weights were 2.72 and 2.91 lbs respectively. Differences (P < 0.01) in mean birth weights were found among litters of 8, 9, 10, and 11; the means were 2.87, 2. 93, 2.75, and 2.70 lbs respectively. No significant differences were found among genetic background groups or for effects of interaction. These results indicate that sows on the average farrow slightly heavier pigs than gilts in litters of the same size and, as litter size increases, the mean birth weight decreases but numbers weaned continue to increase with increasing numbers born alive. Lack of significant difference of birth weights among genetic groups indicates that other factors, such as number in litter and parity, rather than genetic influences are responsible for differences in average pig birth weight.
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