Effects of different stocking intensities in early life on the productivity of Merino ewes grazed as adults at two stocking rates. 1. Wool production and quality, lamb growth rate, and size and liveweight of ewes

Abstract

Ewe lambs born to Merino ewes grazed at 10 or 20 sheep/ha were weaned at three months (L-, H-) and randomized to low or high stocking rate treatments (-L, -H) until 15 months old. Ewes from each of the four groups (LL, LH, HL and HH) then grazed at 10 or 20 sheep/ha until nine years old. Liveweight in early adult life and some body dimensions were reduced by a low plane of nutrition during rearing. The differences in liveweight declined with time and were not significant after 2% years in ewes stocked as adults at 10/ha or after 5% years in ewes stocked at 20/ha. Wool production and growth rates of lambs were reduced when ewes were stocked at the high stocking rate, but were not affected by rearing treatment. Wool production per sheep was about 30% greater at the lower stocking rate but about 33% less when expressed on a unit area basis. Fibre diameter and fleece length were reduced by a high stocking rate in adult life but were not affected by rearing treatment. Yield was not affected by stocking rate at any time. A number of subjective assessments of wool quality were also recorded; quality declined at a high stocking rate but was not affected by rearing treatment. Trends in wool production and quality with age of ewe are reported.

On-farm factors affecting physical quality of Merino wool. 1. Nutrition, reproduction, health and management

“…Increasing stocking rate generally reduces FOO, wool growth and SL (White and McConchie, 1976;Brown, 1977;Langlands et al, 1984;Craig, 1992;Doyle et al, 1999) although in some studies measured SL was only reduced at the lowest FOO (Thompson et al, 1994). Doyle et al (1999) reported that strip grazing reduced SL compared with set stocking as both fleece growth and FD declined.…”

“…At any point in time however, liveweight reflects both the long term effects of growth towards mature size, and the effects of short term seasonal changes in nutrition, typified in much of the wool growing regions of Australia by liveweight loss during periods of low pasture digestibility and availability and liveweight gain with the return of pastures with high digestibility. Such changes in liveweight are documented in multi-year studies of grazing sheep (White and McConchie, 1976;Brown, 1977;Black and Reis, 1979;Langlands et al, 1984;Craig, 1992;McGregor, 2010). Thus it is not possible to separate the effects of nutrition on wool growth and quality from the effects of nutrition on the liveweight of sheep.…”

“…Such analyses did not determine if variations in liveweight were more important than age in determining FD as exemplified by the well documented effects of stocking rate on Merino wethers and ewes, where increases in liveweight with age may not occur at higher stocking rates and FD may not change (e.g. White and McConchie, 1976;Brown, 1977;Langlands et al, 1984;Craig, 1992). FD is known to change in response to changes in nutrient availability, as indicated by changes in liveweight (Allden, 1979).…”

“…Thus it has been known that increasing the stocking rate of sheep results in sheep of lower average liveweight, lower wool production and wool that is finer, shorter and less sound (i.e. the wool is tender and will break more easily under gentle hand stretching) (White and McConchie, 1976;Brown, 1977;Langlands et al, 1984).…”

Grazing management of oversown tussock country 3. Effects on liveweight and wool growth of Merino wethers

“…It is generally contended that as stocking rate is increased, Merino wool production per unit area will increase proportionately (Chisholm 1965;Blackburn et al 1973). Although Merino wool quality may be reduced somewhat at high stocking rates (Langlands et al 1984), it is clear that stock numbers will strongly influence the income from high country runs.…”