Abstract:
Proc. Aust. Soc. Anim. Prod. Vol. I9 MINERAL SUPPLEMENTATION OF YOUNG SHEEP ON THE SOUTH COAST OF WESTERN AUSTRALIA P. T. DOYLEA, R. A. LOVEB and T. W. PLAISTED A *W.A. Dept of Agriculture, Sheep and Wool Branch, Albany Regional Office, Albany, W.A. 6330. BW.A. Dept of Agriculture, Epidemiology Branch, Albany Regional Office, Albany, W.A. 6330. SUMMARY Mineral supplementation experiments were conducted at 5 sites across the south coast of W.A. in summer/autumn over 2 years. Merino weaners grazing dry pasture were fed lupins (L) to maintain liveweight. Supplementation was either L, L coated with gypsum (LS), or L with access to a loose mineral lick (LM). Marker bar results indicated most (80 - 100%) sheep were licking the minerals, and estimates of average daily intake were generally between 10 and 20 g/head. There were no liveweight responses to gypsum or the mineral lick in comparison with sheep given only L at any site in either year. Keywords: minerals, young sheep, sulfur, dietary nitrogen. INTRODUCTION Liveweight and wool growth rate increases have been reported in young sheep grazing annual pastures in response to supplementation in summer-autumn with a mineral lick, Sirornin (a multi element mix containing essential minerals, White et al. 1991) or inclusion of sulfur (S), as gypsum, in a lick (Peter et al. 1987). However, such responses may not occur when green pasture is available (Doyle et al. 1992), and intake of loose salt-based licks may vary considerably between sheep (Wheeler et aZ. 1980). Concentrations of S and phosphorus in dry pasture on the south coast of W.A. may decline to levels which impair feed utilization (Doyle et a2. 1990). However, sheep may select higher quality components within the pasture and young animals are usually given grain supplements during the summer-autumn. The experiments reported examined production responses to mineral supplements across the south coast of W.A. This preliminary report presents results of mineral lick acceptance and intake and liveweight responses. MATERIALS AND METHODS Experiments were conducted over 2 years at 5 farms (Bremer Bay, Fl and F2; Wellstead, F3; Mettler' Lake, F4; Denbarker, F5), with average annual rainfall varying from 480 to 670 mm. The s botanical composition and amount of annual pasture accumulated at the end of the growing season varied markedly between sites and between years; percentage clover ranged from 10 to 75%. At each site, Merino wether weaners were supplemented with lupins (L) alone, lupins coated with gypsum (LS), and lupins with access to Siromin (LM). Treatments were replicated 3 times at each site. Gypsum (15-20 g/kg lupins) was bound to lupins with methyl cellulose by mixing in a rotating drum. Lupins were fed once weekly in trails, commencing at 75 g/head.day in 1989-90 and 30 g/head.day in 1990-91, when pastures dried off. In 1989-90, feeding commenced between 4 and 7 December at Fl to F4 and on 19 December at F5. At each site, lupin feeding levels to all plots were increased through the sunnner/auturnn to amounts which were estimated to be necessary for maintenance of liveweight of weaner sheep on treatment L (i.e. amounts of lupins fed to LS and LM were equal to that given to L). Supplementary feeding finished in May or June and the peak amount of lupins fed at all sites was 150 g/head.day. In 1990-91, feeding began between the 22 and 30 November at Fl to F4,and on 4 January at F5. Supplements were again given until May or June, the peak amount of lupins fed being 125 g/head.day at Fl to F4 and 300 g/head.day at F5. In 1989-90, the lupins contained 41.4 to 45.6 g/kg DM nitrogen (N) and 2.0 to 2.2 g/kg DM S. Coating with gypsum reduced the N to S ratio to less than 10: 1. The N and S concentrations in lupins were determined using procedures listed by Doyle et aZ. (1990). Analyses for 1990-91 are not yet available. The gypsum was adhered to lupins to ensure sheep consumed the grain and S simultaneously. Siromin was offered as a fine ground material (about 140 g/head/week) in troughs once weekly. Lick remaining at the end of each week was collected and weighed. Estimates of the number of sheep consuming lick in each plot were obtained on 1 occasion in 1989-90 and 3 in 1990-9 1 using ink on marker bars over 2 to 3 days (McDonald et aZ. 1990). Average intake of lick was calculated assuming all sheep on a plot consumed equal amounts, with no account taken of sheep which may not have ingested minerals. 371 Proc. Aust. Sot. Anim. Prod. Vol. 19 Sheep were provided by the farmers. At Fl and F2, equal numbers of sheep from each farm grazed each plot. This also occurred at F3 and F4 in 1989-90, but not in 1990-9 1. At F5, only sheep from that farm were used. Plots at Fl to F4 were 2 ha, and stocking rates were 8 weaners/ha in year 1, but were increased to 10 weaners/ha in year 2 at Fl and F4. At F5, plots were 1.2 ha and the stocking rate was 16.7 weaners/ha. The weaners were given Permaco (cobalt) and Permasel (selenium) pellets in spring and were drenched with Ivomec and Seponver in November and Ivomec in late January. Sheep were stratified on the basis of liveweight for allocation to treatments and plots. Liveweights were recorded at all sites every 3 weeks. Within sites and years, comparisons between treatments were made by analysis of variance using plot mean values. RESULTS The average percentage of sheep across 3 plots that were identified by marker bars at the troughs containing the lick on the different occasions ranged between 88 and 100 (Table 1). Estimated lick intake averaged between 15 and 20 g/head.day at all sites in both years (Fig. 1). While intakes varied over time at each site, most of the amount offered was usually eaten. Table 1. Average percentage of sheep marked at troughs containing Siromin at 5 different locations Values in parentheses are ranges There were no significant effects of mineral supplementation on liveweight at any site in either year (Table 2). Liveweights were generally maintained over the period animals grazed dry feed; the 1 exception being F5 in 1990-91. Sheep were heavier at the end of supplementation, except at F5 in year 2, as they were fed through the break of season. Table 2. Liveweights (including wool, kg) of weaner sheep given lupins (L), L coated with gypsum (LS) and L with access to a mineral lick (LM) at the commencement (C) and end (E) of supplementary feeding in summer-autumn at 5 sites DISCUSSION Rumen micro-organisms may require a dietary N to S ratio of about 10: 1 for efficient activity and production of protein (Moir 1970). In 1989-90, the ratio in lupins was between 19 and 22: 1, which is consistent with previous reports (White et aZ. 1981). The protein in lupins and lupin meal is largely degraded in the rumen (Hume 1974; Lindsay et aZ. 1982) and improved uptake of N released during ruminal digestion might occur if additional S was supplied. However, no liveweight responses occurred to coating lupins with gypsum. 372 Fig. 1. Estimated intake (g/weaner&y) of mineral lick at 5 sites, Fl (a), F2 (+), F3 (*), F4 (A), F5 (a), in (a) 1989-90 and (b) 1990-91. The lack of response in liveweight to S may have been due to a narrower N to S ratio in the total diet (Doyle et al. 1992) than that in lupins. During 1989-90, considerable quantities of green feed (>200 kg DM/ha) were available at all sites from early February (P- T. Doyle et al. unpubl. data). A green pick became available in March 1991, but the amount on offer during autumn was less than in the first year. Young green pasture contains 35 to 41 g/kg DM N and 2.7 to 2.8 g/kg DM S. The N to S ratio in dry annual pastures may be 11: 1 (Doyle et al. 1992). Also lupins were only a small component of the 373 Proc. Aust. Sot. Anim. Prod. Vol. 19 diet until late autumn. Taken collectively, it is feasible that the ratio of N to S in the total diet may have been close to 10: 1. It is also possible that the optimum N to S ratio for rumen micro-organisms might vary from 10: 1. For example, Bird (1973) reported the ratio of N to S in rumen bacteria was 20.2 to 21.8: 1. While this question cannot be answered from measurements made in the experiments reported here, it would seem more appropriate to evaluate requirements for S by micro-organisms in relation to digestible energy supply as is the case with N. There were no liveweight responses to a complete mineral mix, despite high apparent acceptance rates in our weaners that were treated with selenium and cobalt, and fed lupin supplements to maintain weight. These liveweight results contrast with those of White et al. (1991), who found liveweight responses in sheep which were gaining weight and which were treated at weaning with vitamin B12, but not selenium (C. L. White, pers. comm.). Wool growth rate results are not yet available from our experiments and cannot be ruled out, but such responses were not evident in the work of Doyle et al. (1992). Obviously, requirements for minerals are lower in sheep at maintenance than in growing animals, and it is currently recommended that weaners are fed for maintenance through the summer/autumn. Liveweight responses to sulfur and/or mineral licks cannot be expected to occur consistently under these conditions. 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