Stress: should animals be fed to their potential requirements?

Abstract

The experiment was a 4 x 3 factorial design with the respective factors being four lysine treatments (13.5, 11.5, 9.5 and 7.5 g lysine/kg feed) and three group sizes (one, seven and 13 pigs/pen or 2.0, 1.0 and 0.5 m 2 /pig, respectively). Two hundred and sixty four female Large White x Landrace pigs were grown from 20 to 60 kg live weight in two different houses (group vs individual). There were three replications per group treatment and six replicates per single-penned treatment. Three pigs per treatment were slaughtered at 60 kg for analysis of carcass composition. A summit-dilutio n technique was used to produce the four dietary treatments. The summit diet contained 14.0 MJ DE/kg feed, and 13.0 g lysine/kg (110% of requirements) with the remaining essential amino acids at 130% of requirement, thereby ensuring that this was the limiting amino acid in the feed. A non-protein dilution diet containing the same concentrations of energy and all nutrients, other than the amino acids, was used to dilute the food of the three other feeds in the dilution series. Feeds were blended in the following proportions (summit:dilution): 100:0, 85:15, 70:30, 55:45, to obtain the four dietary treatments. A single self-feeding feed bin was placed in each pen. Residual maximum likelihood (REML) analysis in Genstat 5 Release 4.1 (1997) was used to test for significant interactions between the main effects in a linear model with both fixed (stocking density and lysine content) and random (house) effects. Linear regression analyses were conducted on all data to compare the growth responses to dietary lysine and number of pigs per pen. Starting weight was a significant covariate and therefore all analyses were adjusted accordingly.