Lay Summary Finishing pig growth potential varies across different genotypes; however, limited research is available on performance of nursery pigs sired from boars selected for different finishing growth patterns. With selection of terminal sires focused on improved lean gain in late finishing, anecdotal or field observations suggest that starting weanling pigs on feed has become more challenging. Hence, our hypothesis that improving post-weaning feed intake by creep feeding may be of greater importance today than in the past due to sire line selection criteria. Therefore, our objective was to determine the possible interaction of Duroc sires selected for early vs. late maturing growth rates and creep feeding on the growth performance of pigs from birth to market. Early maturing pigs had increased feed intake from days 2 to 14 post-weaning compared to late maturing pigs. Likewise, a lower percentage of early maturing pigs lost weight from weaning to 3 d post-weaning. Early maturing pigs had improved average daily gain (ADG) and average daily feed intake until approximately 100 kg, at which point late maturing pigs began to exhibit greater ADG. Overall, offering creep feed to late maturing pigs resulted in improved growth performance compared to no creep feed, whereas creep feed did not impact early maturing pigs. A total of 21 litters (11 early and 10 late maturing Duroc x DNA 241) resulting in 241 pigs were used in 170 d trial to determine the effect of sire lines selected for either early or late maturing growth rates and creep feeding on the cortisol concentration, intestinal permeability, and growth performance of nursery and finishing pigs. Treatments were arranged in a 2 x 2 factorial with main effect of Duroc sire line (early or late maturing) and creep feeding (with or without). Creep feed was provided for 14 d prior to weaning. After weaning (approximately 21 d of age; initially 6.4 kg), no interactions were observed for blood cortisol. However, blood cortisol levels were increased (P = 0.011) in late maturing pigs compared to early maturing pigs. A lower percentage (P < 0.001) of early maturing pigs lost weight 3 d post-weaning compared to late maturing pigs. Likewise, early maturing pigs had improved (P < 0.001) average daily gain (ADG) and average daily feed intake (ADFI) during the first 3 d in the nursery and also had increased ADFI (P < 0.001) from days 2 to 14 in the nursery. Creep feeding had no effect on initial nursery performance. On day 7, after a 2-h fast, a subsample of pigs was administered an oral gavage of lactulose and mannitol dissolved in distilled water. No differences by sire line, creep feeding, or their interactions were observed in lactulose:mannitol ratio. For overall nursery growth performance, an interaction was observed for ADG (P = 0.007) and ADFI (P < 0.001), with creep feed providing a benefit in late maturing pigs, but not in early maturing pigs. Early maturing pigs had poorer gain-to-feed ratio (G:F) (P < 0.001) than late maturing pigs. For overall finishing performance, an interaction was observed for ADG (P = 0.037) and ADFI (P = 0.007), with creep feed providing a benefit in late maturing pigs, but not in early maturing pigs. This resulted in an interaction for final body weight (P = 0.005), with late maturing pigs that did not receive creep feed having decreased market weights (P <= 0.003) compared to the other treatments. In summary, early maturing pigs had decreased cortisol concentration at weaning and improved ADG and ADFI until approximately 100 kg, at which point late maturing pigs began to exhibit greater ADG. Late maturing pigs had improved G:F from 46 d of age until market. Interestingly, creep feeding late maturing pigs resulted in increased day 170 weight compared with providing no creep feed, whereas creep feed did not impact early maturing pigs (sire line x creep feed interaction, P < 0.005). Early maturing pigs exhibited improved average daily gain (ADG) until approximately 100 kg, at which point late maturing pigs had improved ADG. Improved growth was observed in late maturing pigs when provided creep feed but did not impact early maturing pigs.
