Abstract:
Proc. Aust. Soc. Anim. Prod. Vol. 19 GROWTH AND PARASITIC WORM BURDEN OF PRIME LAMBS RUN ON CONSERVATION REGROWTH A. S. BEATTIEA, D. L. HOPKINSAB, N. J. MURRAYA and K. L. PIRLOT A ATasmanian Dept of Primary Industry, P.O. Box 180, Kings Meadows, Tas. 7249. BPresent address: NSW Agriculture, P.O. Box 242, Cowra, N.S.W. 2794. Spring pasture conservation is mostly used to overcome pasture deficits. The economic value of fodder conservation is often calculated from the extra animal production or survival achieved through utilizing the conserved feed. Forage conservation can also result in benefits such as improvement in summer pasture quality (Kaiser and Curl1 1987) and pastures with low nematode parasite contamination (Morley and Donald 1980) but these are rarely considered in any economic analysis. This paper presents data comparing the growth rate and parasitic worm burden of lambs run during the summer on conservation regrowth or pasture previously grazed through the spring. Ninety-two Poll Dorset x Border Liecester x Merino short scrotum male lambs were divided into 2 groups at weaning (7 January 1991), drenched (Ivomec) and then each group grazed on 2 ha of pasture. Short scrotum lambs have had their testes pushed into the abdominal cavity and retained there or externally against the body wall using an elastrator ring. The pasture for 1 group was regrowth from a hay cut (2300 kg DM/ha, 32.5% green leaf) while that for the second group was pasture grazed during the spring (2200 kg DM/ha, 19% green leaf). Both groups were fed silage (60.8% organic dry matter digestibility) ad tibitum from 22 January. Faecal egg counts (eggs/g of Strongytoid spp. and Nematodirus spp.) were estimated by pooling 2 g faecal samples from 10 lambs selected at random. The lambs on grazed pasture were drenched again with Ripercol on 6 March. Mean growth rate differences were analysed with a students t-test. Lamb growth rates and faecal egg counts are shown in Table 1. Table 1. Growth rate (g/day) and parasitic worm burden (eggs/g faeces) of lambs grazing pastures previously cut for hay (regrowth) or grazed during the spring Grazing the conservation regrowth produced an extra 114 kg of lamb/ha. This may have been due to better pasture quality, less parasite contamination or a combination of both. The growth rate of both groups of lambs reduced through the summer probably due to the reduction in available quality pasture. The lower growth rate of lambs, on previously grazed pasture, during January was probably due to initially poorer pasture quality. The increase in weight of these lambs after drenching indicates the lower production at the end of summer was exacerbated by internal parasites. The silage was not of sufficient quality to give high growth rates. Although not a replicated experiment in terms of paddocks, the conservation treatment demonstrated improved pasture quality and supported the accepted view of providing a relatively ` ' pasture in terms of internal parasite contamination. Benefits of these types safe should be included in cost/ benefits of forage conservation. KAISER, A. G. and CURLL, M. L. (1987). In ` Temperate Pastures: their Production, Use and Management.' (Eds J. L. Wheeler, C. J. Pearson, and G. E. Robards.) pp. 397411. (Australian Wool CorporationKSIRO.) MORLEY, F. H. W. and DONALD, A. D. (1980). Vet. Parasit. 6: 105-34. 393