Effect of within-year variation on growth performance and subsequent reproductive performance in gilts

Abstract

Uniform performance is required for optimal production. This study aimed to examine within-year variation observed on gilts for production traits and their subsequent breeding performance. Data consisted of 5060 gilts from 3 breeds (Large White, Landrace and Duroc) and 3 herds in Australia over 15 years. Production traits were average daily again (ADG μ = 662g/d) and backfat (BF μ = 10.9mm) recorded at a live weight (WT) of 100kg. Reproduction traits were total born (TB μ = 10.6), the number born alive (NBA μ = 9.76), the number of stillbirths (SB μ = 0.83) and farrowing age (FA μ = 384) recorded in the first parity. General linear models were utilized to examine variation associated with month (12 levels, calendar month) at recording. Significant effects for all traits were herd, year, month, breed and the interaction between month and breed, which were fully cross-classified in these data. Farrowing age was fitted as a linear covariate for TB, NBA and SB, and TB was a linear covariate for SB. The production traits were also corrected for dam parity and birth litter size. Models for reproduction traits also included the animal's performance traits fitted within month. Least squares means (LSM) and associated P-values by breed, month and the month*breed interaction were assessed to examine differences in the within-year variation for traits and any possible breed (genetic) differences. The ranges in LSM for the effects of month were ADG = 50g/d, BF = 1.1mm, TB = 0.67, NBA = 0.72, SB = 0.23 and FA = 15.7d (min and max for all traits P < 0.05 difference). Growth rate was higher and BF was lower in cooler months. The differences between winter and summer were larger in magnitude for Duroc in comparison to the other 2 breeds. For reproduction traits, less TB were produced in cooler months (mated during the summer) and SB was higher for summer farrowings. Further analyses showed that if variation is generated in growth performance before breeding, then there is a differential effect on variation in the reproductive traits. Linear regressions of FA on ADG nested within month of farrowing resulted in ADG solutions of -0.35d/g in winter and -0.12d/g in summer. Quantifying the different sources of within-year variation and their interactions is of economic importance and could suggest paths for intervention strategies to increase uniformity in performance.