Impact of early postweaning growth rate as affected by diet complexity and space allocation on subsequent growth performance of pigs in a wean-to-finish production system

The objective was to evaluate the effect of restricted early postweaning growth rate due to diet complexity, pen space, or both on subsequent growth to market in a wean-to-finish system. Pigs (n = 1,728) were used in a randomized block design with a 2 x 2 factorial arrangement of treatments: 1) diet complexity (Complex vs Simple) and 2) space allocation (Unrestricted vs Restricted). Treatments were imposed for the first 8 wk after weaning (period 1) and growth was measured from weaning (5.0 ± 0.01 kg body weight; 15 d of age) to the end of wk 23 postweaning. The Simple diet was based on corn-soybean meal with minimal inclusion of milk products, processed cereals, and animal protein-based ingredients compared to the Complex diet. Floor and feeder-trough spaces were 0.63 m² and 4 cm and 0.21 m² and 2 cm per pig for Unrestricted and Restricted space treatments, respectively. From the end of wk 8 to end of wk 23 (period 2), pigs on all treatments had the same floor and feeder spaces and were fed common diets. There was no interaction (P > 0.05) between diet and space treatments. In period 1, Simple diets resulted in similar average daily feed intake (ADFI; 639 vs 650 ± 5.4 g; P > 0.05), but lower average daily gain (ADG; 408 vs 424 ± 3.8 g; P < 0.01) and gain:feed ratio (0.64 vs 0.65 ± 0.002; P < 0.001), and lighter body weight (2.8%; P < 0.01) compared to the Complex diets. In period 2, growth was not affected (P > 0.05) by previous diet complexity, and pig body weight was similar (114.4 vs 114.4 ± 0.37 kg; P > 0.05) at the end of wk 23. In period 1, pigs with Restricted space had lower ADG (398 vs 434 ± 3.8 g; P < 0.001), ADFI (621 vs 668 ± 5.4 g; P < 0.001), and gain:feed ratio (0.64 vs 0.65 ± 0.002; P < 0.01), and were lighter at the end of wk 8 (6.5%; P < 0.001) than those with Unrestricted space. However, in period 2, pigs with Restricted space had higher (P < 0.01) ADG (3%), ADFI (2%), and gain:feed ratio (3%) than those with Unrestricted space, and body weight was similar (114.5 vs 114.3 ± 0.37 kg; P > 0.05) at end of wk 23. Carcass backfat and loin-eye depth at market body weight were influenced by neither diet nor space treatment. Using a simple diet program and restricted space allowance immediately postweaning resulted in a lower early growth rate, but had no impact on pig body weight or carcass measures at market.