The effect of lysine restriction during grower period on productive performance, serum metabolites and fatness of heavy barrows and gilts

Abstract

A total of 200 Duroc cross (Landrace×Large White) pigs, 50% barrows and 50% gilts, of 26.3±0.55kg body weight (BW) were used to study the effect of Lysine (Lys) restriction in the grower period on subsequent performance, serum metabolites and fatness. Four diets with Lys contents of 11.0, 9.1, 7.8 and 5.2g/kg were offered to animals during the grower phase (45d) in a two (sex)×four (diet) randomized block factorial design with five pens (replicates) per treatment and five pigs each. At the end of the restricted period, one pig per pen (five pigs per treatment) was slaughtered and the rest were fed a common finishing diet with 9.1g/kg Lys until slaughter at 123kg±2.35kg BW. During the grower phase, Lys restriction reduced average daily gain (ADG) (P<0.001), average daily feed intake (ADFI) (P=0.008) and feed conversion ratio (FCR) (P=0.003). The responses were quadratic and similar for both sexes. At the end of this period, restricted pigs showed lower backfat thickness (P<0.001) because they were lighter (47 vs. 64±0.7kg BW) but had higher serum concentrations of triglycerides (linear; P=0.001) and cholesterol (quadratic; P=0.039). Also, serum albumin decreased quadratically (P=0.004) with Lys restriction while urea increased with the highest level of restriction. During the finisher phase, ADG increased linearly (P<0.001) in response to previous Lys restriction which was related with a trend to higher ADFI (P=0.0.97), resulting in a linear increase of FCR (P=0.002). However, the compensatory growth was incomplete and, during the overall period, there was a reduction of ADG (quadratic; P=0.041) and of FCR (linear; P=0.001) as dietary Lys content decreased, whereas fat depth at the gluteus medius (GM) muscle increased linearly (P=0.004). This entailed a delay to reach the slaughter BW of 1.8±0.43d per g Lys restriction/kg of diet which was related to worse FCR by 0.034±0.0095 and to an increase of fat thickness at GM muscle of 0.51±0.168mm. At the end of the trial, barrows grew faster, ate more feed and were fatter than gilts (P<0.001). These results confirm that the Lys restriction during the grower period promoted an incomplete compensatory growth and might be a useful strategy to increase the fatness albeit with a cost in terms of FCR in production systems of heavy barrows and gilts intended for dry-cured products.