Effects on milk fat composition and cow performance of feeding concentrates containing full fat rapeseed and maize distillers grains on grass-silage based diets

Abstract

Two experiments were carried out to determine the effect on milk fat composition and cow performance of including ground full fat rapeseed (FFR) and maize distillers grains (MDG) in the concentrate supplement. Unwilted grass-silage was the basal forage in both experiments. In Expt. 1, 8 kg/day of concentrate containing 0 (control), 80 (low), 140 (medium) or 200 g/kg (high) FFR was fed to four groups of 16 cows each for 7 weeks. Milk yield, milk constituent yield and milk composition which was compared using 13 cows per treatment were not significantly affected by FFR inclusion. The milk fat (using all 64 animals) from cows on the high FFR concentrate contained significantly lower proportions of C6:0, CS:O, C14:0, C14:l (P <0.05) compared to those produced by cows on the other three concentrates. It also contained lower proportions of ClO:O and C12:O (P<O.OS) compared to that from cows on the control or medium FFR concentrate. Cows on the high and medium FFR concentrate had significantly lower proportions of C 16:0 (P < 0.01) and significantly higher proportions of C 18: 1 (P < 0.05) in their milk fat compared to the other two treatments. Solid fat content in the milk fat at 10°C was also significantly lower on the former two treatments (P < 0.05). In the second experiment 6 kg/day of concentrate containing 0 (control), 700 (MDG 1) and 920 g/kg (MDGZ) MDG was fed to three groups of 12 cows each for 6 weeks. Silage intake, milk yield or the concentration or yield of milk fat and lactose were not significantly different between treatments. Milk protein concentration and yield were depressed (P < 0.05) by the inclusion of both levels of MDG. Including both levels of MDG significantly reduced the proportions of ClO:O, C12:0, C14:0, C14:1, C16:0, C16:l and Cl&3 (P<O.O5) and significantly increased the proportions of C4:0, C18:0, C 18: 1 and Cl&2 (P < 0.05). The changed fatty acid composition resulted in a softer fat as indicated by the solid fat content at 10°C which was 480,355 and 314 g/kg on the control, MDGl and MDG2 concentrates, 8 days after feeding commenced. The results of these experiments show that, on a grass-silage based diet, the fatty acid profile of milk fat can be significantly altered, resulting in a softer fat, by feeding 1.12 or 1.60 kg of FFR or 4.20 or 5.52 kg of MDG in the concentrate supplement daily. FFR may be the supplement of choice because the levels of MDG required to give similar changes in milk fat composition and softness had negative effects on milk protein concentration.