Efficiency of replacement gilt production is affected by litter birth weight phenotype

Abstract Text: The successful selection for increased litter size has resulted in an overall decrease in litter average birth weight (LBW). However, irrespective of litter size, a genotype x environment interaction has also been reported to result in a repeatable low LBW phenotype in a sub-population of mature sows.  In the preliminary phase of a National Pork Board-funded project to investigate links between LBW phenotype and sow lifetime productivity (SLP), conducted in collaboration with Holden Farms Inc., individual piglet weights were used to determine LBW in parity 2 - 4 PIC Line 3 sows in a commercial genetic nucleus population (n=1150). Excluding sows with a total born (TB) of < 7 and > 20, TB was negatively correlated (P < 0.0001) to LBW [(LBW) = -0.037 (TB) + 1.87, R² = 0.20], representing a 500 g difference between the smallest and largest litters.  In contrast, the variation in LBW among litters with the same TB was greater (mean = 950 g, range 600 - 1400 g). Sows with two consecutive parity records (n=183, to date) were classified as having a repeatable low (LLBW, n=24) or high (HLBW, n=28) LBW phenotype, if LBW fell 1 standard deviation below or above the population mean, respectively, and a repeatable medium (MLBW, n=131) phenotype for intermediate weight litters. Overall, there was a significant correlation between LBW measured at consecutive farrowings (r = 0.4; P < 0.0001). Furthermore, supporting previous results, no sows first giving birth to a LLBW litter produced a HLBW litter at the next farrowing.  An extreme LLBW phenoptype is, therefore, repeatable and predictable within sows.  Considering L3 sows bred to produce replacement L3 gilts in the nucleus population, preliminary analyses identify entire sets of littermate gilts that are already subjectively designated “non-select” at weaning or the pre-selection stage on the basis of being “small” or “thin”, suggesting that a LLBW phenotype has a major impact on the efficiency of replacement gilt production. Further evidence to substantiate the hypothesis that “a repeatable low LBW phenotype will negatively impact the production of selectable replacement gilts at nucleus and multiplication level” will continue to be a major component of this ongoing collaborative study.

Keywords: Gilt, birth weight, selection