The aim of this study was to estimate breed and heterosis effects for milk protein composition found within the two main breeds farmed in New Zealand, Holstein-Friesian (HF) and Jersey (J). Groups of 20 F, 20 J and 20 HFxJ crossbred cows (3 years and older) calved at pasture between July and September 2003 and were monitored throughout the 2003/04 season. Breed and heterosis effects were estimated for daily yields of milk, crude protein, true protein and casein and concentrations of crude protein, true protein, casein, α-casein, β-casein, κ-casein, α-lactalbumin and β-lactoglobulin, bovine serum albumin (BSA) and immunoglobulin G (IgG). Breed effects were significant (P<0.05) for all traits except for β-lactoglobulin, BSA and IgG. Compared to J cows, HF cows had significantly (P<0.05) higher daily yields of milk (+5.32 kg), crude protein (+0.13 kg), true protein (+0.11 kg) and casein (+0.10 kg) but significantly (P<0.05) lower concentrations of crude protein (-0.50 g/kg), true protein (-0.51 g/kg), casein (-0.45 g/kg), α-casein (-3.77 g/kg), β-casein (-2.08 g/kg), κ-casein (-1.74 g/kg) and α-lactalbumin (-0.14 g/kg). Estimates of heterosis effects for concentration of milk proteins were negative but only significant for κ-casein (-0.60 g/kg). These results show that that the individual protein fractions of milk are affected by breed but crossbreeding has no beneficial effect on milk protein composition.
Proceedings of the New Zealand Society of Animal Production, Volume 67, Wanaka, 399-402, 2007
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