165
Effects of reducing the dietary Omega-6 to Omega-3 fatty acid ratio in low protein quality nursery diets on growth performance and immune response in starter pigs
We hypothesised that reducing the dietary omega-6 (ω-6) to omega-3 (ω-3) fatty acid ratio (ω-6:ω-3) in low protein quality diets will improve growth performance and immune response of starter pigs. Thus, the objective of this study was to define optimum ω-6:ω-3 in low protein quality diets for growth performance and immune response in post weaning pigs. Newly-weaned pigs (age 21 d; BW 6.43±0.33 kg) were randomly assigned to 5 dietary treatments (6 pens/treatment; 8 pigs/pen; d 0 of study): positive control diet (High; animal protein), negative control diet (Low; soybean protein), 3 Low diets with 1.25% (Low1.25), 2.5% (Low2.5) and 5 % (Low5) fish oil to achieve 4:1, 2:1 and 1:1 ω-6:ω-3, respectively. Pigs were fed treatment diets in two phases for 7 and 14 d, respectively, followed by a common phase III diet for 21 d. On d 6 and 20, 12 pigs per treatment were sensitized with 0.5 mg ovalbumin (OVA), 0.5 mg killed C albicans, and 0.5 mg Quil A adjuvant in 1 ml saline. Blood samples were collected at d 20 and 34 for determination of anti-OVA IgG, and d 22 and 28 for haptoglobin (Hp) analysis. The dermal hypersensitivity response (DHR) was evaluated on d 40, using intradermal injection of OVA in thigh skin, and skin fold thickness (SFT) was measured at 6, 24 and 48h post- injection. During phase I, ADG, ADFI and G:F were greater (P<0.05) in pigs fed High diet, as compared to Low diet, and improved in pigs fed Low1.25 and Low2.5 . In contrast, further reducing the ω-6:ω-3 (Low5) lowered ADFI, ADG and G:F during phase I (Quadratic effect, P<0.05; ADG for respective treatments: 109, 61.4, 87.8, 97.1, 69.8 g/d, ±9.22). Diet did not affect growth performance after Phase I. At d 34, intake of fish oil linearly decreased (P<0.05) anti-OVA IgG response. At 6h, DHR to OVA was lower (P<0.0.5) in pigs fed Low2.5 as compared to all other treatments. The serum Hp were influenced (P<0.05) by diets on d22. The highest (P<0.05) serum Hp were in pigs fed Lowand linearly attenuated (P<0.05) in pigs fed fish oil diets. In conclusion, 2.5% fish oil (2:1, ω-6:ω-3) in low protein quality diets resulted in best growth performance and immune response. Thus, in this experiment, low protein quality diets with 2.5% fish oil could replace high quality protein diets in early weaned pigs.
Keywords: fish oil, protein quality, starter pigs