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.

PJ, Back, and N Lopez-Villalobos

Proceedings of the New Zealand Society of Animal Production, Volume 67, Wanaka, 399-402, 2007
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