A study was designed to examine the effects of neonatal environments and puberty induction strategies for replacement gilts on their longevity and reproductive performance over six parities.

The study was conducted within an 80,000-sow commercial production pyramid with an in-house gilt multiplication program.

A total of 3,180 gilts were randomly allocated to a factorial arrangement of treatments involving season of birth (spring or fall); neonatal litter size (less than 7 littermates or more than 10 littermates); and puberty stimulation (boar exposure at 140 days of age; boar exposure at 140 days of age + P.G.600 (Intervet/Schering Plough Animal Health); or boar exposure at 170 days of age).

Replacement gilts remained on-site until they were between 190 and 210 days of age, when they were moved to commercial farms. The commercial farms were positive for porcine reproductive and respiratory syndrome (PRRS), but considered to be PRRS stable. On average, gilts were bred at 232 days of age, which did not differ among treatments.

Season of birth did not significantly influence sow longevity or reproductive performance. Similarly, the productivity of gilts exposed to boars at 140 days of age and treated with P.G.600 was the same as their counterparts receiving only boar exposure during the same time period. Consequently, the only two factors that significantly affected sow longevity and reproductive performance were age at which puberty induction was initiated (140 or 170 days of age) and the size of the litter in which gilts were raised (less than 7 piglets or more than 10 piglets).

At the end of six parities, regardless of age of puberty induction, significantly more of the females raised in small litters (35%) were still in production compared with those raised in large litters (17%). Similarly, regardless of the size of the litter in which they nursed, significantly more sows exposed to boars at 140 days of age (33%) remained in the herd compared with their counterparts given boar exposure at 170 days of age (16%).

The positive effects of being raised in a small litter and receiving boar exposure at a young age on longevity were additive. As a result, at the end of six parities, 45% of sows raised in litters of 7 or fewer piglets and given boar exposure at 140 days of age were scheduled to be rebred after Parity 6 compared with only 10% of females raised in litters of 10 or more piglets and given boar exposure at 170 days of age.

A similar response was present for farrowing rate.
Being raised in a small litter or receiving boar exposure at 140 days of age resulted in a 5% increase in farrowing rate in each of six parities. Consequently, sows from small litters and exposed to boars at 140 days of age had a mean farrowing rate of 90.8%, while sows from large litters and exposed to boars at 170 days of age had a mean farrowing rate of 79.8%.

In contrast, only the neonatal environment significantly influenced number of pigs born alive. Sows reared with seven or fewer littermates farrowed an average of 11 piglets/litter over six parities compared with 10.5 piglets/litter for sows raised in litters of 10 or more pigs.

Collectively, based on the differences in longevity, farrowing rates and numbers of pigs born alive observed in this study, the total number of pigs produced through six parities per gilt bred in each management system was determined and these estimates are as follows:

  • Large neonatal litter + Boar exposure at 170 days – 21.9 pigs;
  • Large neonatal litter + Boar exposure at 140 days – 29.7 pigs;
  • Small neonatal litter + Boar exposure at 170 days – 29.8 pigs; and
  • Small neonatal litter + Boar exposure at 140 days – 43.2 pigs.

Given the management structure of many operations in the swine industry, providing good, consistent boar exposure to gilts at 140 days of age might be technically challenging and present biosecurity problems. Thus, it may not be practical for many operations to implement this strategy. In contrast, because males born as littermates to maternal line replacement gilts have less economic value as market animals, strategic crossfostering for sows nursing potential replacement gilts is a technique that should be easy to implement and could improve sow longevity and reproductive performance.

Researcher: W.L. Flowers, North Carolina State University; e-mail Flowers at: William_Flowers@ncsu.edu.