67 Targeting inflammatory tone with daily oral ω-3 polyunsaturated fatty acids improved growth and body composition in heat-stressed finishing lambs.

Abstract Growth and efficiency in finishing livestock are worsened by heat events. Heat stress increases inflammatory tone, which appears to be a key factor in poor growth and body composition. Thus, we hypothesized that targeting heightened inflammation during heat stress would improve growth performance. Our objective was to determine if supplementing an ω-3 polyunsaturated fatty acid Ca2+ salt (ω-3 PUFA) would improve growth and skeletal muscle mass of chronically heat-stressed finishing wether lambs. Wethers (40.1 ± 0.5 kg) were randomly assigned to 30 d of heat stress (39 ºC, THI = 85) or thermoneutral conditions (pair-fed controls; 19 ºC, THI = 64; n = 12). Wethers exposed to heat stress received a daily oral bolus of 0.42 g/kg of ω-3 PUFA Ca2+ salt (Virtus Nutrition; HS+ω3; n = 11) or placebo (HS; n = 12). Initial bodyweight did not differ among groups, but final body weight was less (P < 0.05) for HS (44.6 ± 0.4 kg) and HS+ω3 (44.9 ± 0.4 kg) wethers than for controls (46.1 ± 0.3 kg). However, average daily gain tended to be less (P = 0.08) for HS wethers (0.104 ± 0.017 kg) but not for HS+ω3 wethers (0.127 ± 0.014 kg) than for controls (0.153 ± 0.015 kg). Similarly, gain-to-feed ratios tended to be less (P = 0.07) for HS wethers (0.065 ± 0.014) but not for HS+ω3 wethers (0.081 ± 0.012) than for controls (0.097 ± 0.011). After 30 d of heat stress, ultrasound-estimated back fat thickness was less (P < 0.05) for HS wethers (3.42 ± 0.19 mm) than for controls (4.11 ± 0.28 mm) and was intermediate for HS+ω3 wethers (3.93 ± 0.37 mm). Ultrasound-estimated loin eye area was less (P < 0.05) for HS wethers (11.48 ± 0.22 cm2) but not HS+ω3 wethers (12.65 ± 0.21 cm2) than for controls (12.70 ± 0.27 cm2). Actual loin eye area measured at necropsy tended to be less (P = 0.07) for HS wethers (12.71 ± 0.56 cm2) but not HS+ω3 wethers (13.48 ± 0.59 cm2) than controls (14.73 ± 0.88 cm2). Longissimus dorsi, gastrocnemius, and biceps femoris weights were less (P < 0.05) for HS but not HS+ω3 wethers than for controls, but semitendinosus and soleus weights did not differ. Protein content of the longissimus dorsi tended to be less (P = 0.09) for HS wethers (20.6 ± 0.2%) but not HS+ω3 wethers (21.2 ± 0.2%) than for controls (21.2 ± 0.2%), but intramuscular fat content (4.5 ± 0.5%) and fat-to-protein ratios (0.22 ± 0.03) did not differ among groups. These findings demonstrate that mitigating heightened inflammatory tone via daily oral ω-3 PUFA supplementation can improve growth, efficiency, and body composition of heat-stressed finishing livestock.