Abstract
Responses in ewe and lamb performance to mid pregnancy
supplementation and to the method of providing the supplement were
examined when Scottish Blackface ewes grazed heather dominant hills
in winter.
In these experiments, ewes grazed areas with 20% Agrostis/
Festuca and 80% heather at a stocking rate of 2 ewes /ha during mid
pregnancy, and were adequately fed in late pregnancy. Treatments
were compared where ewes were unsupplemented in mid pregnancy or where a barley based supplement supplying 1.6 - 1.8 MJ ME and 3 - 6 g N /d,mainly as urea, was offered. Mid pregnancy supplementation
reduced ewe liveweight and condition score losses, and there was a linear relationship between these two factors and lamb birthweight,
which was increased with mid pregnancy supplementation by 10% over
three experiments.
When areas with 20 - 40% Agrostis /Festuca vegetation were
grazed at stocking rates of 1.2 - 2.1 ewes /ha to create a fourfold
difference in herbage allowance of Agrostis /Festuca, there was no effect on ewe liveweight change during mid pregnancy, and a response
in lamb birthweight was obtained only in 2- year -old ewes. These
findings were supported by the small differences found in the
concentrations of plasma urea and ruminal ammonia, and in the in
vitro digestibility of oesophageal extrusa samples collected from
sheep grazing areas of Agrostis /Festuca during the mid pregnancy
period. In a further experiment, diet selection differences
attributable to herbage mass at the start of the winter were not
manifest where Agrostis /Festuca swards had a herbage mass of less
than 3,000 kg DM /ha (with approximately 10% green material) and
where ewes were grazed at 2 /ha. It was inferred that the benefits
of mid pregnancy supplementation could apply to a wide range of
heather dominant hills.
No gross differences in ewe and lamb performance were found
with the use of hand fed pellets, compared with self help feedblocks
in mid pregnancy. Voluntary intake of feedblock was related to the
composition of the supplement, but was not affected by the siting of
feedblocks either on heather or on Agrostis /Festuca areas, by
xi
hardness or by the use of containers. Considerable variation in
daily group intakes of feedblock occurred when voluntary intakes
of feedblock were high, and the frequency of replenishment was
restricted, but the variation was also high when feedblocks were
offered ad libitum. Variability between ewes in feedblock intake
was high. There was a significant rank correlation in feedblock
intakes by ewes in a group, which suggested that, with an understanding of the factors affecting intake, this variability could
be reduced.
Social dominance explained 25% of the variation in supplement intake when feedblock was offered ad libitum. Two -year -old
ewes were of lower social rank, had lower supplement intakes, and
were the most numerous non -feeders. A simple device to identify
non-feeders was successfully tested. It was considered that the
high coefficients of variation between days and between animals
in intake of feedblock might lead to inefficient use of the
nutrients supplied.
