Effect of feeding level on the growth performance of growing-finishing pigs from two genetic lines

Abstract Text: The evaluation of genetic lines of pigs for growth performance is typically conducted under ad libitum feeding over the growing-finishing period.  There is limited data, however, on the impact of restricting the amount of feed given to growing-finishing pigs on growth performance of different genetic lines.  This study was carried out from 36.2 ± 0.47 kg to 129.4 ± 2.20 kg BW as a RCBD with a 2 × 2 factorial arrangement of treatments: 1) Sire line [Blue (Landrace ancestry, low feed intake) vs. White (Yorkshire ancestry, high feed intake)]; and 2) Feeding level (Ad libitum vs. Restricted).  Crossbred barrows from the two sire lines (n = 40; 20/line and feeding level) were individually housed and fed.  Pigs on the restricted level were fed at approximately 94% of the intake of pigs on the ad libitum level with feed being offered once/day.  Diets were formulated to meet the energy and amino acid requirements of the restricted fed pigs and to meet or exceed the requirements for other nutrients proposed by NRC (1998).  As expected, under ad libitum feeding, ADFI was lower (P = 0.03) for the Blue line compared to the White line (2.63 vs. 2.81 kg, respectively; SEM 0.079).  There was a sire line by feeding level interaction (P ≤ 0.05) for overall ADG.  Under ad libitum feeding, there was no difference (P > 0.05) between the lines (952 vs. 989 g for the Blue and White line, respectively; SEM 24.5), however, under restrict feeding, Blue line pigs grew faster (P ≤ 0.05) than the White line pigs (916 vs. 844 g, respectively; SEM 24.5).  Compared to the Blue line, the White line had lower G:F (0.362 vs. 0.341, respectively; SEM 0.0056; P = 0.01) and  Longissimus muscle area (47.2 vs. 44.6 cm², respectively; SEM 1.02; P = 0.05) and greater backfat depth at the 10^th rib (21.3 vs. 28.4 mm, respectively; SEM 1.12; P < 0.001).  Pigs on the Restricted compared to the Ad libitum treatment had similar G:F (0.345 vs. 0.357, respectively; SEM 0.0055, P > 0.05).  These results suggest that when evaluating genetic lines for differences in growth performance, the ranking of the lines can be influenced by the feeding level used to test the animals.

Keywords: feeding level, growth, pigs