Breeder dam parity does not affect lifetime reproductive performance

Progeny born to primiparous sows contribute significant performance variation which impacts herd feed conversion efficiency. Compared to progeny from multiparous sows, the progeny of gilts are lighter at birth and weaning (Hendrix et al. 1978), have reduced lifetime growth rates (Rehfeldt and Kuhn 2006) and a greater susceptibility to disease (Miller et al. 2013). With gilts making up one quarter of the breeding herd (Koketsu 2007), selection of replacements from these gilt litters is likely, however little is known about the impact of dam parity on subsequent reproductive performance. The objective of this study was to compare the performance of breeders born to primiparous sows v. multiparous sows, with the null hypothesis that there is no difference in performance between breeders born from gilt or sow litters.

Performance records of 1034 breeders from first litter sows, and 4721 breeders from multiparous sows that farrowed at SunPork Farms, Tong Park Piggery, during 1 January 2006 to 31 December 2015, were included in this study. Data was mined from existing herd records (EliteHerd, Genetic Solutions Ltd, Palmerston North, NZ). Selection criteria of the 5755 breeders was broad, and was based on any gilt that entered the herd, successfully farrowed, and had a traceable pedigree. Analysis included; pedigree information, age at mating, reproductive performance from Parity 1 to 7, and removal information. Data was cleaned by tracking each sow within the herd recording software correcting obvious entry errors or discarding the sow if error was not obvious. Data was analysed using Genstat (Genstat 18.1, VSN International Ltd, Hemel Hempstead, UK). A general linear model ANOVA was used to analyse continuous variables (age at first mating, reproductive data, etc.) with dam parity (gilt v. sow) as the treatment factor. Chi-squared (χ²) analysis was used to assess discrete variables (reasons for removal).

Breeders from primiparous sows were 1 day older at first mating than those from multiparous sows (Table 1). In the first parity there was no significant difference in total born per litter or number weaned, however, there was an increase (P < 0.05) in the number of stillborn piglets per litter, and wean-to-oestrus interval was extended compared to breeders of multiparous sows. In the second parity, breeders from gilts had an increased total born. Dam parity had no effect on the age and parity at which breeders were removed from the herd, nor was there any impact on the reasons for removal (not shown). Effects on stillborns and wean-to-oestrus interval may be a reflection of lower muscle fibre numbers in gilt progeny, reducing body size, uterine size and contractile ability, and decreased body reserves. The absence of differences in stage and reason for removals is unexpected, given known health effects, but may reflect poorer gilt progeny not being considered for selection.

Table 1.  Age at first mating (Age 1^st Mate), reproductive performance, and parity (RemPar) and age (RemAge) at removal of breeders compared by dam parity, Gilt (Parity 1) or Sow (Parity 2+)

This study suggests producers do not need to be concerned with selecting breeders from gilt litters as no difference was found in performance between gilt and sow litters.