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A study of the acceptability of Holcus spp. to Perendale sheep : a thesis presented in partial fulfilment of the requirements for the degree of Master of Agricultural Science in Plant Science at Massey University
Various characters are reputed to reduce the acceptability of
Yorkshire fog grass (Holcus lanatus) to sheep. The relative importance
of these characters in determining the acceptability of Yorkshire fog to
sheep was investigated in summer, autumn, and early-winter of 1978, using
standardised regression, and based upon a phenotypically diverse
collection of spaced plants from fifty-three seed populations. A clump
defoliation score was used to assess sheep preference.
Cluster analysis of ratios of the standardised partial regression
coefficients from individual genotype populations generally confirmed the
results obtained from the standardised partial regression coefficient
ratios of pooled genotype populations.
Sheep rejected plants exhibiting a high proportion of inflorescences,
dead leaf and sheath material and crown rust infection. The presence of
inflorescences and crown rust were respectively 1.5 and 0.86 times as
important as clump greenness over all genotype populations, in the
summer period. Leaf pubescence was only 0.13 times as important as
clump greenness and was therefore considered relatively unimportant
in determining sheep preference. Leaf tensile strength, leaf width,
clump height and diameter, clump erectness, leaf flavanol level and
soluble sugar level, were also considered unimportant in this study, and
ranged from 0.57 to 0.019 times as important as clump greenness in determining
sheep preference. However only 20-25% of the variation in
sheep preference was explained by the characters examined in the three seasons
of this study. The unexplained variation may have been due to a high level
of amongst sheep preference variance or to unassessed plant characters.
The phenotypic variation of each character was partitioned using a
split-plot-in-time model. Broad-sense heritability estimates for all
characters examined were low and ranged from 34% to 0.4%. It was
suggested from these results that the acceptability of Yorkshire fog grass
to sheep, by reduction of inflorescences and crown rust infection,
and by removal of excessive dead leaf and sheath material, was largely
under the control of grazing management (i.e. an aspect of the
environment). However, some progress might be achieved by selection
and breeding for genotypes with reduced levels of inflorescences (h2= 34%)
and crown rust infection (h2= 29%).