Abstract
Daily feed intake data of 1 279 French Landrace (FL, 1 039 boars and 240 castrates) and 2 417 Large White (LW, 2 032 boars and 385 castrates) growing pigs were recorded with electronic feed dispensers in three French central testing stations from 1992–1994. Male (35 to 95 kg live body weight) or castrated (100 kg live body weight) group housed, ad libitum fed pigs were performance tested. A quadratic polynomial in days on test with fixed regressions for sex and batch, random regressions for additive genetic, pen, litter and individual permanent environmental effects was used, with two different models for the residual variance: constant in model 1 and modelled with a quadratic polynomial depending on the day on test dm as follows in model 2: . Variance components were estimated from weekly means of daily feed intake by means of a Bayesian analysis using Gibbs sampling. Posterior means of (co)variances were calculated using 800 000 samples from four chains (200 000 each). Heritability estimates of regression coefficients were 0.30 (FL model 1), 0.21 (FL model 2), 0.14 (LW1) and 0.14 (LW2) for the intercept, 0.04 (FL1), 0.04 (FL2), 0.11 (LW1) and 0.06 (LW2) for the linear, 0.03 (FL1), 0.04 (FL2) 0.11 (LW1) and 0.06 (LW2) for the quadratic term. Heritability estimates for weekly means of daily feed intake were the lowest in week 4 (FL1: 0.11, FL2: 0.11) and week 1 (LW1: 0.09, LW2: 0.10), and the highest in week 11 (FL1: 0.25, FL2: 0.24) and week 8 (LW1: 0.19, LW2: 0.18), respectively. Genetic eigenfunctions revealed that altering the shape of the feed intake curve by selection is difficult.
Highlights
Today, selection of pigs for growth performance considers average daily feed intake and average daily live weight gain over the whole growing period and/or the ratio of the two, i.e. feed conversion
For French Landrace the change in partition ofvariances occurred after 150 000 rounds, as shown in Figure 1 for the covariance between linear and quadratic regression coefficients
We believe that the Gibbs sampler reached this different configuration ofvariance distribution among additive genetic and permanent environmental effects for regression coefficients in the affected chains just by chance
Summary
Selection of pigs for growth performance considers average daily feed intake and average daily live weight gain over the whole growing period and/or the ratio of the two, i.e. feed conversion. Selection for increased leanness and improved feed conversion has led to a decrease in the feed intake capacity (FIC) [27]. Early fattening period where FIC of pigs is determined by mechanical constraints and FIC is less than the optimum level of feed intake (FI(opt)), where lean deposition rate is at its maximum and fat deposition rate at its minimum for the given lean deposition rate [4], 2. Intermediate fattening period where FIC is still determined by mechanical constraints but FIC > FI(opt), 3. Late fattening period where FIC is determined by metabolic constraints with FIC > FI(opt) De Vries and Kanis [5] have suggested dividing the growing period into three phases: 1. early fattening period where FIC of pigs is determined by mechanical constraints and FIC is less than the optimum level of feed intake (FI(opt)), where lean deposition rate is at its maximum and fat deposition rate at its minimum for the given lean deposition rate [4], 2. intermediate fattening period where FIC is still determined by mechanical constraints but FIC > FI(opt), 3. late fattening period where FIC is determined by metabolic constraints with FIC > FI(opt)
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