8 Effect of group size during the nursery period on wean-to-finish growth performance in a PRRS positive population of pigs

Abstract

It is common commercial practice in wean-to-finish facilities to pin pigs in large groups during the nursery phase. The effect of overstocking on wean-to-finish performance has been studied; however, there is limited information on the effect of group size during the nursery period on overall growth performance, particularly in PRRS positive populations. This study was carried out using a RCBD (blocking factor date of start of test) to evaluate the effect of 3 nursery group size treatments (61, 79, and 96 pigs/pen) on wean-to-finish growth performance (from 6.0 ± 0.10 to 122.2 ±0.8kg BW) in a PRRS positive population. During the 7-wk nursery period, when the group-size treatments were applied, pigs were housed in mixed-sex pens; floor space for all treatments was 2.4ft2/pig. After the nursery period, pigs on all treatments were housed in groups of 34 at a floor space of 6.5ft2/pig. A total of 3,672 pigs in 12 replicates were used. Pen of pigs was the experimental unit; data were analyzed using PROC MIXED of SAS (SAS Inst. Inc., Cary, NC) with the model including fixed effect of group size treatment and random effects of block and replicate. During the period from weaning to wk 7 post-weaning, when the group size treatments were applied, growth rate and live weight was lower (P < 0.05) for the largest group size (96 pigs) than for the 2 smaller group sizes (61 and 79 pigs). However, subsequently from wk 7 to end of test and for the overall wean-to-finish growth performance was similar (P > 0.05) for the 3 group size treatments. This study showed that group size (at the same floor space) had an effect on growth performance in the nursery period but had no effect on overall wean-to-finish growth performance in PRRS positive pigs.