The growth performance of the progeny of two swine sire lines reared under different floor space allowances D. N. Hamilton*, M. Ellis* 1 , B. F. Wolter*, A. P. Schinckel†, and E. R. Wilson‡ *Department of Animal Sciences, University of Illinois, Urbana 61801; †Department of Animal Sciences, Purdue University, West Lafayette, IN 47907; and ‡PIC USA, Franklin, KY 42134 ABSTRACT: A total of 736 pigs was used in a study with a 2 × 2 × 2 factorial arrangement to investigate the effects of and interactions between sire line (Line A vs. B), floor space (unrestricted vs. restricted), and gender (barrow vs. gilt) on growth performance, BW, and protein and estimated lipid accretion curves from 40 to 120 kg of BW. Pigs were by eight Line-A and nine Line-B sires mated with PIC C22 dams. Line A was of Pietrain ancestry and Line B was a synthetic line. The unrestricted floor space treatment consisted of small groups (four pigs) with 0.93 m 2 /pig of floor space for the entire grow-finish period. Pigs in the restricted floor space were in larger groups (12 pigs) with 0.37 and 0.56 m 2 /pig of floor space for the grower and finisher phases, respectively. Pigs were given ad libitum access to a three-phase dietary program, and one and three nipple waterers were available in the groups of 4 and 12 pigs, respectively. No sire line × floor space interactions were found for any of the traits measured. Line A pigs grew more slowly (50 g/d, P < 0.05), took longer (4.1 d, P < Key Words: Floor Space, Growth, Pigs, Sires 2003 American Society of Animal Science. All rights reserved. J. Anim. Sci. 2003. 81:1126–1135 Introduction Many studies have reported differences in growth and carcass characteristics between breeds and lines of pigs. Also, the environment in which the animal is reared, including factors such as group size and floor space allowance, influences feed intake and growth rate (Edmonds et al., 1998; Hyun et al., 1998). A number of studies have investigated the effects of various genetic lines reared at several test stations and reported the occurrence of genotype × environment interactions in swine populations (Merks, 1989; Bidanel and Ducos, 1996). However, there is limited information on the 1 Correspondence: 216 Animal Sciences Laboratory, 1207 W. Greg- ory Dr. (phone: 217-333-6455; fax: 217-333-7861; E-mail: m-ellis7@ uiuc.edu). Received June 4, 2002. Accepted January 20, 2003. 1126 0.05) to reach harvest weight (120.3 kg), and had simi- lar feed intakes, but a lower gain:feed ratio (2.8%, P < 0.05) than Line B pigs. Line A pigs had greater longissi- mus muscle depth (P < 0.05) and estimated protein accretion rate (P < 0.05) than Line B pigs, but Line A and Line B pigs had a similar estimated percentage of lipid-free soft tissue. Pigs reared in the restricted floor space grew more slowly (105 g/d, P < 0.05) and con- sumed less feed (280 g/d, P < 0.05) but had a similar (P > 0.05) gain:feed ratio to pigs reared in the un- restricted floor space. Pigs reared in the unrestricted floor space had greater (P < 0.05) predicted protein and lipid accretion rates throughout the growth period than pigs reared in the restricted floor space. Differences between genders for growth traits and carcass measure- ments were in agreement with previous research. The differences in growth performance, carcass measures, and compositional growth curves between these two sire lines were similar in the two floor spaces. impact of a controlled rearing environment on the rela- tive performance of contemporary genetic lines of dif- fering growth potential. If commercially important ge- notype × environment interactions do exist, then this would have major implications for swine producers when selecting genetic lines for their specific operation. The objective of this study was to investigate the inter- action between genetic growth potential and space al- lowance in growing-finishing pigs. Materials and Methods The protocol for this study was approved by the Uni- versity of Illinois Laboratory Animal Care Committee. Experimental Design and Treatments The treatments were arranged in a 2 × 2 × 2 factorial consisting of two sire lines, two floor spaces, and two genders. Sire lines were a Pietrain-based line (Line A)