Grazing management of native pastures in the New England region of New South Wales. I. Pasture and sheep production with special reference to systems of grazing and internal parasites

Abstract

In a 4-year grazing experiment with Merino sheep, on a native pasture dominated by Bothriochloa ambigua S.T. Blake, three rates of stocking and continuous v. rotational grazing were compared. The effects of these treatments on the forage available and the botanical composition of the pasture and on sheep liveweights, size of sheep, wool production, wool fibre diameter, and parasitic infestation, both with and without drenching with phenothiazine, mere studied. The effects of seasonal conditions on the above and on the chemical composition of the pasture were also recorded. No consistently significant differences between grazing treatments in their effects on the pasture or on sheep liveweights or parasitic infestation were recorded, although during the final 3 years the total forage available was less under heavy stocking. Seasonal variations in total forage mere not marked, but, production of green forage increased greatly in the spring and declined to a very low level during winter. Similarly, sheep liveweights increased during spring and summer and declined in the winter. These liveweight changes were significantly correlated with the amount of green forage available. Wool fibre diameter showed similar seasonal fluctuations but the maximum diameter was attained earlier than maximum liveweight. Coincident with a spring rise in the amount of green forage there was also an increase in the percentages of crude protein and phosphorus in the green components of the pasture. Liveweight gains of the drenched sheep were significantly greater from the beginning of each experimental year in the late spring (November) to late winter (August) in all stocking treatments. In the spring, when the quality of the pasture improved and worm egg counts were low, drenching had no effect on liveweight gains in three out of four years. Drenching also significantly improved wool production and resulted in an increase in skeletal size of sheep in three out of four years. Drenching reduced egg counts of the parasites Oesophagostomum spp. and Haemonchus contortus (Rudolphi) Cobb but was less effective against Trichostrongylus-Ostertagia spp. For all grazing treatments there was no significant difference in the amount of wool produced per head, but over the 4-year period 56 per cent. more wool per acre was produced from the heavy than from the light rate of stocking.

Pasture herbage mass, quality and growth in response to three whole-farmlet management systems

“…With native pastures on the Northern Tablelands of NSW, Roe et al (1959) showed little effect of rotational grazing v. continuous grazing on animal production whereas increasing stocking rate had a large effect on production. In addition, they showed that the availability of high quality green forage was the key pasture factor linked to animal productivity.…”

Livestock weights in response to three whole-farmlet management systems

“…Liveweights generally increased in spring and summer and declined in winter and were closely related to the amount of green herbage available (Roe et al 1959). The crucial role of green pasture in winter in this region for supporting increased sheep liveweight and wool production was also identified by Willoughby (1959), suggesting that, in order to be valid, experimental studies of grazed pastures needed to consider both the effects of animals on pastures and of pastures on animals and of the balance between supply and demand.…”

Grazing systems and worm control in sheep: a long-term case study involving three management systems with analysis of factors influencing faecal worm egg count

“…At 20 C and 65% RH, the half-life was estimated at 33 days. The longer survival period under temperate conditions, coupled with use of rotational grazing schemes that fail to adequately disrupt the nematode lifecycle has resulted in many studies failing to show major benefits of rotational grazing for worm control in sheep in temperate climates (Morgan 1933;Morgan and Oldham 1934;Roe et al 1959a;Gibson and Everett 1968). Other studies that did show beneficial effects used such long spelling periods that pasture and animal productivity were impaired (Robertson and Fraser 1933;Eysker et al 2005) as also occurred on farmlet C in this experiment.…”

“…This revealed considerable concern about control strategies for sheep intestinal worms and the potential for drench resistance as well as interest in alternative control strategies including that of intensive rotational grazing (IRG). Even though short-term rotational grazing, using weekly rotation across four paddocks, was found not to affect worm burdens (Roe et al 1959b), there has been anecdotal evidence of low drenching requirements on some properties practising more IRG or 'cell grazing' with shorter graze and longer rest periods. Producer members of the Cicerone Project were thus keen to compare grazing strategies that used short graze periods and long rest periods with more typical management strategies.…”

“…The latter two species are 'scour worms', which are associated with lower reproductive rates and a more chronic course of infection leading to reduced production as the major economic impact. Severe infections of any of these worm species can result in animal deaths and these occur most commonly under moist summer conditions (Gordon and Whitten 1941;Roe et al 1959b).…”