Compensatory Responses to Dietary Protein, Length of Starter Period and Strain of Pig

Abstract

Forty-eight 3-week-old crossbred pigs were used to determine main and interaction effects of crude protein level (10 and 20%) in starter diets, genetic strain (lean and fat) and length of starter period (to 20 and 35 kg body weight) on performance, body chemical composition and muscle development. Protein restriction (10% protein) in the starter period had the following effects: 1) reduced rate and efficiency of weight gain in the starter period; rate of gain being reduced more in lean-strain than in fat-strain pigs, 2) improved feed efficiency in the grower period (to 57 kg), 3) decreased rate of gain of lean-strain pigs in the grower period but slightly increased rate of gain of fat-strain pigs, 4) reduced rate of gain for the entire period (5 to 100 kg); the reduction being much greater in lean-strain than in fat-strain pigs, 5) decreased the cross section area of the longissimus in lean-strain but not in fat-strain pigs, 6) decreased empty body weight gains of water and protein and increased gain of ether extract in the starter period, and 7) increased empty body weight gains of water and protein and decreased gain of ether extract in the grower-finisher period. Compared to the fat-strain pigs, lean-strain pigs: 1) grew slower in the starter, grower and the entire feeding periods, 2) utilized feed more efficiently in the grower period, 3) had less backfat thickness and larger longissimus cross section area, 4) gained more weight of water and less of fat in the empty body during the grower-finisher period, and 5) had heavier rectus femoris. The lean-strain rectus femoris contained more total RNA, DNA and protein and had smaller protein:DNA and RNA:DNA ratios. Length of starter period had no effects on subsequent performance, body composition and muscle development. The results of the experiment indicate that fat-strain and lean-strain pigs responded differently to a 10% protein starter diet. Fat-strain pigs made partial or complete compensation at 100 kg body weight for rate and efficiency of gain and for body composition. The lean-strain pigs, however, did not make compensatory weight gains after protein restriction and the cross section areas of their longissimus were decreased by protein restriction.