Abstract
Two hundred and eighteen cross-bred pigs (Duroc × Hampshire × Landrace × Yorkshire) were assigned to a 3 × 2 factorial experiment; the factors being composition of the group and density. The composition of the group factor consisted of pigs not reaggregated (NR), re-aggregated below the median body weight (RBMW), and re-aggregated above the median body weight (RAMW) at the time of transfer to the finishing pens. The density factor consisted of groups of 6 or 12 pigs/pen. Two trials with 2 replications of each trial were conducted. Twenty-six gilts from Trial I were used to determine their age and ovulation rate at the pubertal oestrus. During the nursery phase, composition of the group had no effect ( P>0.05) on average daily feed intake (ADFI) or feed efficiency (F/G). Pigs in the NR and RAMW groups had a similar ( P>0.05) average daily gain (ADG), whereas, those pigs in the RBMW group gained ( P<0.05) at a slower rate. Pigs housed in groups of 6 had a higher ( P<0.05) ADFI, had similar ( P>0.05) ADG and poorer ( P<0.05) F/G than those housed in groups of 12. During the finishing phase, composition of the group had no effect ( P>0.05) on ADFI, ADG or F/G. Pigs housed in groups of 6 had a greater ( P<0.05) ADFI and ADG, but similar ( P<0.05) F/G compared to those housed in groups of 12. Correlation coefficients between the various behaviours and the performance variables suggested that the more active pens of pigs gained less per day and were less efficient. Gilts housed in the NR groups of 6 were younger ( P<0.05) at puberty than gilts in the other groups of 6 or 12. Also, gilts housed in the RBMW groups of 6 were younger ( P<0.05) at puberty than those housed in the RAMW groups of 6, whereas those housed in the RBMW groups of 12 were older ( P<0.05) at puberty than those housed in the RAMW groups of 12. Ovulation rate was not affected ( P>0.05) by composition of the group, density or their interaction. In summary, composition and density of the group affected the performance of pigs and was correlated to some of the behavioural measurements. The most noticeable effect was that these same factors caused a delay in the onset of puberty in gilts.
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