Group size and floor-space allowance can affect weanling-pig performance

Crossbred weanling piglets (n = 1,920; mean initial BW, 5.3 +/- .7 kg) were used in two 9-wk trials employing a randomized block design in a 2 x 2 fac torial arrangement of treatments to determine effects of group size (20 [Sm all= S] or 100 [Large = L] pigs/pen) and floor-space allowance (calculated requirement [CR] or calculated requirement less 50% of estimated "free spac e" [CR-50])on growth performance. Free space was estimated for each group s ize. From wk 1 through 4 after weaning, S and L groups at CR were allowed a floor space of .17 m(2)/pig, and at CR-50, S and L groups were allowed .15 m(2)/pig and.13 m(2)/pig, respectively. From wk 5 through 9 after weaning, all CR treatment pigs were provided a floor space of .38 m2/pig, and for t he CR-50 treatment, S and L pigs were allowed .32 m(2)/pig and .28 m(2)/pig , respectively. Piglets had free access to feed and water. Feeder-trough sp ace per pig was the same for both group sizes. Feed-intake data were collec ted for only wk 1 through 4. Group size by floor-space allowance interactio ns (P < .05) were found for gain/feed ratio (G/F) for wk 1 and wk 2 through 4, but not for wk 1 through 4. Piglets in L groups were lighter (P < .001) at the end of wk 1, 4, and 9 by 2, 4, and 5%, respectively, and had lower ADG (6%; P < .001) throughout the trial than S piglets. During wk 1 through 4, feed intake was lower (7%, P < .001) in L piglets than in S piglets, bu t G/F was similar (P > .05). Piglets in CR groups had greater ADG (5%; P < .01) throughout the trial, with a greater G/F (P < .05) for wk 1 through 4, and were heavier (P < .01) than those in CR-50 groups at the end of wk 4 ( 3%) and 9 (4%). Pigs in L groups had a greater within-pen coefficient of va riation in BW at the end of wk 9 than pigs in S groups. Large groups and re duced floor-space allowance reduced piglet growth performance in the nurser y.