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Growth performance, carcass characteristics and serum cholesterol and progesterone concentrations of heifers fed different energy sources on pasture
Twenty-four Brangus heifers (average BW=317 kg and BCS= 5.4) on winter pasture (Lolium Multiflorum) were used in a completely randomized design to evaluate the effect of feeding different energy supplements on growth performance (BW, ADG, BCS), carcass ultrasound characteristics (rump fat thickness [RFT], subcutaneous fat thickness [SFT], LM area) and serum concentrations of cholesterol and progesterone. The treatments were: 1) Control (70 g trace-mineralized salt); 2) Corn (1.2 % of BW; 3.8 kg cracked corn, 46 g urea, 70 g trace-mineralized salt); 3) PPUFA (Polyunsaturated fatty acids protected from rumen degradation; 0.071% of BW; 150 g of PPUFA, 10 g urea and 70 g trace-mineralized salt); 4) Corn+PPUFA (1.2% of BW; 3.7 kg of cracked corn, 150 g of PPUFA, 52 g of urea, 70 g trace-mineralized salt). Heifers were supplemented two times a day in individual stalls (08:00 and 14:00) and were subjected to fixed time AI at the end of the supplementation period (d 40). Forage availability was greater (d 28, P = 0.007; d 40, P = 0.10) in Corn+PPUFA (d 28, 1845 kg/Ha and d 40, 2348 kg/ha) than the other treatments (average = d 28, 1253 kg/Ha and d 40, 1641 kg/Ha). Body weight and BCS were greater in supplemented animals than Control (373 vs 347 kg; 6.3 vs 2.7; d 40; P = 0,05) . Average daily gain was greater for supplemented animals than Control (Corn+PPUFA = 1.19 kg ≥ Corn = 1.10 kg ≥ PPUFA = 0.90 kg > Control = 0.73 kg; P=0.004). Rump fat thickness was greater for Corn+PPUFA (8.72 mm) than the other treatments (average = 5.04 mm; d 30; P = 0.03). Subcutaneous fat thickness was greater in Corn+PPUFA (6.76 mm) and Corn (5.21 mm) than the others treatments (average = 3.49 mm; d 28; P = 0.07). However there was no differences in serum cholesterol (Average = 201.9 mg/dl; d 40, P = 0.52), progesterone (Average = 3.23 ng/ml; d 47, P = 0.52) and pregnancy rates (58%; P = 0.52) between treatments. Supplementation to heifers on winter pasture with PPUFA and Corn could improve growth performance and carcass characteristics but may not affect serum cholesterol and progesterone concentrations.
Keywords:
Energy supplementation, protected polyunsaturated fatty acids, growth performance