EFFECTS ON COW PERFORMANCE AND MILK-FAT COMPOSITION OF FEEDING FULL-FAT SOYBEANS AND RAPESEEDS TO DAIRY-COWS AT PASTURE

Three experiments were undertaken where the effects of feeding full fat soyabeans (FFS) and full fat rapeseeds (FFR) on milk fat composition and cow performance were studied. In Expt. 1, four groups of 15 cows each, on pasture, were put on the following supplementation treatments, (1) none (control), (2) 1.6 kg/cow/day FFS (1.6 FFS), (3) 3.2 kg/cow/day FFS (3.2 FFS), and (4) 3.2 kg/cow/day soyabean meal (3.2 SBM), for 1 1 weeks. Milk yield, milk constituent yield or milk composition were not significantly different between treatments. The fatty acid composition and solid fat content of the milk fat were similar on the control and 3.2 SBM treatments. However, feeding both levels of FFS significantly decreased the proportions of C6:0 (P <0.01), C8:0, C10:0, C12:0, C14:0, C14:1 and C16:1 (P <0.001), significantly increased the proportions of C18:0, C18:1, C18:2 (P < 0.001) and C18:3 (P < 0.01) and significantly reduced the solid fat content at 0, 5 and 10 degrees C (P < 0.001) relative to the control. In Expt. 2, three groups of 15 cows each, on pasture, were put on the following supplementation treatments, (1) none (control), (2) 3 kg/cow/day of concentrate containing 275 g/kg FFR ( low FFR), and (3) 3 kg/cow/day of concentrate containing 550 g/kg FFR (high FFR) for 8 weeks. Both FFR supplements significantly increased milk yield (P >0.001), protein yield (P< 0.001) and lactose yield (P <0.001). Milk fat concentration was significantly reduced (P <0.001) by the supplements. Feeding both FFR supplements significantly reduced the proportions in milk fat of C4:0 (P<0.01), C14:1 (P <0.05), C6:0, C8:0, C10:0, C12:0, C14:0, C16:0 and C18:S (P <0.001), significantly increased the proportions of C18:1 (P <0.001) and significantly reduced the solid fat content at 0, 5 and 10 degrees C (P <0.01) relative to the control. In Expt. 3, two groups of 33 cows each were assigned to the following treatments; (1) no FFR supplement (control) and (2) 3 kg/cow/day of a supplement containing 550 g/kg FFR (FFR). Cows were on average 21 days calved (range 11-44) at the start of the experiment which was terminated at the end of lactation. FFR feeding significantly increased milk yield (P <0.01),lactose yield (P < 0.01) and significantly reduced milk fat concentration (P <0.001). Fertility performance of the cows or milk somatic cell count (SCC) levels were unaffected. The proportions of C16:0 and solid fat content at 10 degrees C were consistently lower and the proportion of C18:1 was consistently higher in the milk fat of the FFR treatment compared to the control. Feeding FFR or FFS to cows on pasture did not adversely affect the yield of fat, protein or lactose or cow fertility or udder health. It resulted in reduced proportions of short to medium chain-length fatty acids, increased proportions of C18 fatty acids particularly C18:1 and a softer milk fat with reduced solid fat content at low temperatures.