37 Associations Among Individual Gilt Birth Weight with Subsequent Weights, Selection Rates, and Age to Reach 135 kg

Abstract Our objective was to investigate the associations among individual gilt birth weight (BiWt) of modern genotype gilts with their subsequent weights, age at puberty, and selection rates for the breeding herd. A total of 3,452 PIC gilts (Landrace x Large White) were included in the analysis. Gilts were individually weighed within 12h of birth, and associations with weights at weaning, the end of nursery, and at selection were determined through regression models. Gilts BiWt was also classified into four categories: Below1.04kg, 1.04-1.38kg, 1.38-1.72kg, Above1.72kg. Stimulus for puberty onset started when gilts were 146d old. Gilt age at the first detected heat was recorded. Selection rate was determined as: Selection Rate, % = number of gilts selected at 146d/number of gilts born alive; and Age to 135kg, d = Age at selection+Days to 135kg, where Days to 135kg = (135–Selection Weight,kg)/Average Daily Gain from Birth to Selection. Data were analyzed using generalized linear models with the lm and glm functions of R. Results suggested that weaning and end of nursery weights increased (linear, P≤0.05) as the gilt BiWt increased. For each additional 100g in gilt BiWt, weaning and end of nursery weights were increased by 131g and 379g, respectively. The weight at selection increased (quadratic, P≤0.05) as gilt BiWt increased. There was no evidence of gilt BiWt impact on age at first detected heat (P>0.10; 170.2, 167.7, 168.2, and 167.4d). Heavier gilts at birth reached 135kg at a reduced age (P≤0.05; 211.8, 201.4, 194.5, and 188.0d) and had greater selection rate (P≤0.05; 44.0, 58.1, 62.2, and 64.9%). In summary, this data indicated that gilts with phenotypically greater birth weight had better chances to be selected for the breeding herd and achieved the minimum weight target (135kg) for the first breeding at a younger age.