Pasture availability and composition in relation to diet selection and diet quality by grazing sheep : a thesis presented in partial fulfilment of the requirements for the degree of Master of Agricultural Science at Massey University
Some factors influencing grazing behaviour, diet
selection and diet quality by sheep were investigated.
The influences of pasture availability, accessibility,
composition and digestibility on diet selection by grazing
sheep at two stocking rates (24 and 36 sheep per hectare)
over three-day grazing periods during two seasons (summer
and autumn) were examined. The stocking rates were
replicated twice and measurements were recorded at six
intervals, each a three-day grazing period., over the
summer and autumn seasons. Dietary samples were obtained
by the use of oesophageal fistulated sheep, and comparisons
between extrusa samples and cut pasture were made. Pasture
type contrasted between seasons with extremes of availability,
structure, accessibility and quality. These evolving
pasture types and their changing properties are discussed.
Sheep grazing pasture have the ability to be selective,
the extent of diet selection being dependent on pasture
properties of availability, composition and quality.
Diet preference is for the green leaf component of the
pasture with avoidance of mature stem and dead matter.
However in situations of low pasture availability and
poor accessibility of the preferred green leaf component,
increasing amounts of dead herbage were ingested, as was
evidenced in comparisons between periods and during three-day
Digestibility values of the sheeps' diets are higher
than corresponding values from available pasture the
magnitude of the difference being dependent on pasture
composition, availability and accessibility, ie. the
opportunity afforded for diet selection.Descriptions of experimental site, climatic
conditions and animal management are recorded. The
results are discussed in relation to other research
findings, and their practical implications.