This study was conducted to determine the effect of genotype on milk composition, milk value and economic farm surplus (EFS). The trial included two high breeding worth ($BW) strains of either North American (OS90) or New Zealand (NZ) (NZ90) genetics, and one low $BW strain of NZ genetics (NZ70). Each strain was farmed under systems designed to provide total feed allowances of 4.5 to 7.0 t DM/cow/year. For two years (2001/2002 & 2002/2003) monthly average milk yield and composition were determined for each of the 11 herds. A simulation model was used to calculate milk value using three product mixes. Using either the simulated values or actual values (paid by Fonterra 2002/2003) for milk and its components, milk value ($/litre and $/kg milksolids (MS)) and an EFS for each herd was determined. The OS90 strain produced milk with lower concentrations of fat and protein and higher protein:fat ratio than NZ70 or NZ90 strains. The effect of strain on milk price was unaffected by product mix. Milk value differed between strains irrespective of method of determination. Milk value expressed as $/kg MS was lowest for the NZ70 and highest (P < 0.001) for the OS90 strain. When expressed as $/litre milk value was highest (P < 0.001) for the NZ90 strain. Milk value expressed as $/kg MS was positively associated with protein:fat ratio whereas milk value expressed as $/litre was positively associated with MS concentration. Average EFS was greater for the NZ90 than the NZ70 strain and was least for the OS90 strain. The factors associated with EFS were MS production; milk value and milk composition had minimal impact. New Zealand’s dairy cattle breeding programme has produced a strain of Holstein- Friesian with increased milk fat and protein concentration, an increased protein:fat ratio, and an associated increased milk value and increased EFS. In comparison, the OS90 strain which the current $BW index ranks as high as the NZ90, produced milk with higher value ($/kg MS) but resulted in lower EFS. Key words: milk price; milk value; milk composition; economic farm surplus.

NA, Thomson, S-A Turner, CB Glassey, and N Lopez-Villalobos

Proceedings of the New Zealand Society of Animal Production, Volume 65, Christchurch, 276-282, 2005
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