New Zealand Journal of Agricultural Research abstracts
Reaction norms used to quantify the responses of New
Zealand dairy cattle of mixed breeds
to
nutritional environment
J. R. Bryant1*
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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