Abstract

The effect of strain of Holstein-Friesian and level of feed allowance on milk composition, individual milk proteins, and minerals was examined in a seasonal calving pastoral dairying system. The trial included two high genetic merit strains of either North American (OS90) or NZ (NZ90) genetics, and one strain representing NZ 1970’s genetics (NZ70). Each strain was farmed under systems designed to provide total feed allowances of 4.5 to 7.0 t DM/cow/year. Milk composition was affected by strain of cow and by feed allowance. Strain of cow influenced crude protein (P<0.05), true protein (P<0.01) and casein (P<0.01) concentrations, with the NZ90 and OS90 strains having higher concentrations than the NZ70 strain. Increased feed allowance resulted in increased crude protein (P<0.05), true protein (P<0.05) and casein (P<0.05) concentrations. Strain, but not increased feed allowance affected the protein:fat ratio, with the OS90 strain having a higher ratio (P<0.05) than the NZ strains. Strain altered concentrations of á-casein (P<0.05), with NZ90 having the highest concentrations and NZ70 the lowest concentrations. No consistent effect of strain or feed allowance was determined on whey proteins except for â-lactoglobulin (P<0.027), where the OS90 strain had higher concentrations than the NZ strains. No consistent effect of strain or increasing feed allowance was seen on milk mineral concentrations. These results demonstrate that different selection and breeding policies have influenced major milk components which may influence milk processing and product characteristics.

S-A, Turner, KA MacDonald, PJ Back, and NA Thomson

Proceedings of the New Zealand Society of Animal Production, Volume 66, Napier, 397-402, 2006