The effects of group size and subtherapeutic antibiotic alternatives on growth performance and morbidity of nursery pigs: a model for feed additive evaluation

Olsen, Kristin M; Gabler, Nicholas K; Rademacher, Chris J; Schwartz, Kent J; Schweer, Wesley P; Gourley, Gene G; Patience, John F

Pigs were housed in groups of 31 (large groups; Fig. 1 ) or 11 pigs each (small groups; Fig. 2 ). In the small groups, a gate was installed to block off approximately two-thirds of the pen to reduce usable floor space; the two outer spaces of the feeders were blocked off to achieve approximately equal feeder space per pig. Not counting the space occupied by each feeder, large pens had 0.41 m 2 per pig, and small pens had 0.42 m 2 per pig. Sixty pens were utilized for a total of 15 replicates of each diet (eight large groups and seven small groups each), 32 replicates of large groups and 28 replicates of small groups. Pigs were assigned to blocks based on weaning date, sire line, and sex. Pigs held for 4 d or 2 d post-weaning were balanced within block to account for the potential influence of days post-weaning. Since four different sire lines were used, sire line was balanced within block. Mixedsex pens were used, and sex was balanced within block. A total of 8 blocks were used, and pens were assigned to experimental treatments so that each combination of diet and group size was represented in each block. However, since there were only 60 pens, one block had only four large groups and no small groups. 9 Diets with no value did not have high enough resistant starch content to be accurately measured by this assay.