New Zealand Journal of Agricultural Research abstracts

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Reaction norms used to quantify the responses of New Zealand dairy cattle of mixed breeds to nutritional environment

J. R. Bryant^1*
N. López-Villalobos¹
J. E. Pryce²
C. W. Holmes¹
D. L. Johnson²

¹Institute of Veterinary, Animal and Biomedical Sciences
Massey University
Private Bag 11222
Palmerston North 4442, New Zealand

²Livestock Improvement Corporation
Private Bag 3016
Waikato Mail Centre
Hamilton 3240, New Zealand

^*Present address: AgResearch Limited, Grasslands Research Centre, Tennent Drive, Private Bag 11008, Palmerston North 4442, New Zealand. jeremy.bryant@agresearch.co.nz

Abstract  A reaction norm, where phenotype or genotype is expressed as a function of environment, can be used to measure environmental sensitivity. This study investigates the environmental sensitivity of dairy cattle genotypes (or breeds), in relation to the range of herd milksolid yields (a proxy for feeding level) in New Zealand. Genetic variation in environmental sensitivity was observed with overseas Holstein Friesian genotypes, originating largely from North America, exhibiting higher environmental sensitivity levels and environmental optimums than New Zealand Friesian and Jersey genotypes in a range of feeding level environments. Overseas Holstein Friesian genotypes were more likely to be considered specialists (i.e., perform to high levels in superior feeding level environments), whereas New Zealand Friesian and Jersey genotypes were largely generalists (i.e., tolerant to changes in environment), or specialists in a grassland-type environment. This confirmed the theory that generalist genotypes evolve in heterogeneous environments, whereas specialist genotypes evolve in homogeneous environments. However, variations in environmental sensitivity within genotypes did exist. Generalist genotypes appear to be indirectly selected in New Zealand as environmental sensitivity levels are decreasing. Potential ways in which environmental sensitivity information can be used in dairy cattle systems and evaluation are suggested.

Keywords  dairy cattle; reaction norm; environmental sensitivity; pasture-based

New Zealand Journal of Agricultural Research, 2006, Vol. 49: 371–381
0028–8233/06/4904–0371  © The Royal Society of New Zealand 2006

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