Effects of dietary DL-2-hydroxy-4(methylthio)butanoic acid supplementation on growth performance, indices of ascites syndrome, and antioxidant capacity of broilers reared at low ambient temperature.

Abstract

This study examined the effects of dietary DL-2-hydroxy-4(methylthio)butanoic acid (DL-HMTBA) supplementation on growth performance, antioxidant capacity, and ascites syndrome (AS) in broilers reared at low ambient temperature (LAT) from 7 to 28days of age. Eight hundred 7-day-old broilers were randomly assigned to two ambient temperatures (LAT and normal ambient temperature [NAT]), four supplemental DL-HMTBA levels (0.17, 0.34, 0.51, and 0.68%) of the basal diet in a 2×4 factorial arrangement (ten replicate pens; ten birds/pen). LAT and NAT indicate temperatures of 12-14 and 24-26°C in two chambers, respectively, and broilers were reared at these temperatures from 7 to 28days of age. LAT significantly decreased body weight gain (P<0.001), serum glutathione (GSH) content (day 14, P=0.02; day 28, P=0.045), glutathione peroxidase (GSH-Px) activity, and total antioxidant capacity (T-AOC) at 21days (P=0.001, 0.015) and 28days (P=0.017, 0.010) and increased feed conversion ratio (FCR) (P<0.001), serum malondialdehyde (day 21, P=0.000) and protein carbonyl Level (day 14, P=0.003; day 21, P=0.035). As for incidence of AS, there were significant effects of LAT on red blood cell (RBC) count (P<0.05), hematocrit (HCT) (P<0.05), and the right to total ventricular weight ratio (RV/TV) at 21days (P=0.012) and 28days (P=0.046). Supplementation of DL-HMTBA markedly decreased RV/TV at day 28 (P=0.021), RBC (day 21, P=0.008), HCT (day 21, P<0.001), mean cell hemoglobin (day 14, P=0.035; day 21, P=0.003), and serum protein carbonyl level (day 21, P=0.009), while significantly increased serum GSH content (day 14, P=0.022; day 28, P=0.001), SOD and GSH-Px activities at 21days of age (P<0.001 and P=0.037). The optimal supplemental DL-HMTBA levels in basal diet of broilers aged from 7 to 28days under low or normal temperatures were similar, so the authors recommended supplemental of DL-HMTBA level was 0.46%.