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In southern Australia, winter-born calves may not be at marketable weights until 18 months of age and can thus compete with their dams and the next crop of calves for the pasture resource. We investigated supplementary feeding options to improve calf liveweight gains and overcome this problem. Weaned beef calves confined to feedlots for 70 days were fed different ratios (1 : 1 up to 1 : 4) of sunflower meal to oat grain (Experiment 1) or barley grain (Experiment 2) at levels of 3–6 kg air-dry/day, plus either oaten hay (Expt. 1) or pasture hay (Expt. 2) fed ad libitum. Liveweight gains at 3 kg supplement/day were ~1.2 kg/day at all ratios and were slightly higher at the higher feeding levels. The intake of hay varied inversely with the amount of supplement fed and substitution rates were 0.49 with oaten hay and 0.47 with pasture hay. Total DM intakes did not decline in Experiment 1 as supplement intake increased and increased in Experiment 2 with increasing supplement intake. A separate group of calves that had been grazing mature pasture while their cohorts were in the feedlot showed good compensatory growth when transferred to good pasture, whereas calves coming out of the feedlot onto the same pasture initially lost weight before regaining weight. This suggests that such feedlot-reared calves should be sold direct from the feedlot. In a third experiment, over 2 years, weaned calves grazed mature summer pasture for 81 days and were fed 0, 1, 2, 3 or 5 kg/day of a 1 : 2 ratio of sunflower meal : hammer-milled oat grain. Weight gains were less than in Experiments 1 and 2 and responses of gain to supplement intake were curvilinear. Gains did not exceed 0.75 kg/day and peaked at supplement intakes of 4.3 and 2.8 kg DM/day in years 1 and 2, respectively. Liveweight gains/kg supplement consumed were similar to those in previous studies. A preliminary assessment of supplement costs and the economic value of liveweight gain showed a curvilinear response to supplement intake and suggested that the greatest economic return resulted from an intake of 1.9–2.4 kg/day of the supplement, lower than the supplement intakes for maximum liveweight gain.

The term dual-purpose canola describes the use of a canola crop for forage before seed production. It could potentially provide a profitable and flexible break-crop option for mixed farms, but there have been no studies to test the concept in Australia. We investigated the feasibility of using canola in this way in field experiments near Canberra, Australia, from 2004 to 2006, using European winter and mid–late maturing Australian spring canola varieties. Winter varieties sown from early March to mid-April produced 2.5–5.0 t/ha of biomass providing 0.3–3.5 t/ha of high-quality forage grazed by sheep in winter. The spring varieties produced similar amounts of vegetative biomass from April sowing but were unsuited to the earlier March sowing as they flowered in early winter and did not recover from grazing. The canola forage was readily eaten by sheep; alkane-based estimates of diet composition indicated that >85% of the organic matter intake consisted of canola. Canola forage was also highly digestible (86–88%) and Merino hoggets grew at 210 g/day from a dry matter intake of 1530 g DM/day. The canola generally recovered well when grazed in winter before bud elongation. Delays in flowering associated with heavy grazing ranged from 0 to 4 days when grazed before buds were visible, to 28 days if the crop had commenced flowering. Significant delays in flowering (>14 days) associated with winter grazing did not reduce seed yield or oil content when favourable spring conditions allowed compensatory growth. Yield loss was observed when winter and spring conditions were unfavourable for compensatory growth, or if grazing continued too late into spring (late September) irrespective of seasonal conditions. The yield loss was more than offset by the value of the grazed forage and the mean gross margin for dual-purpose canola over the four experiments was $240 to $500 higher than for grain-only canola depending on the value assumed for the forage. The study indicates there is considerable scope to capture value from grazing early-sown canola crops during winter without significant, uneconomic trade-offs with seed yield. Further investigations in other medium to high rainfall environments in southern Australia are warranted.

We evaluated the integration of a spring forage brassica crop (Brassica campestris cv. Hunter) into a cereal–pasture rotation, as a means of assessing the effects of this practice on the subsequent establishment and grain yield of wheat and oat crops. A brassica crop was grown for lamb production on 0.2 ha plots prepared for dual-purpose cereals, in spring 2003 near Canberra, ACT, Australia. Mackellar winter wheat and Blackbutt oats were sown in the following autumn on the previously sown brassica plots and on plots left fallow over the spring–summer period. A factorial experiment was used to determine the effects of (i) cultivar, (ii) brassica v. fallow, and (iii) grazing on cereal establishment and grain yield. Lamb liveweight gains on brassica over 33 days were rapid (294 g/day) and provided 2141 grazing days/ha and 637 kg lamb weight gain/ha. Average grain yield of Mackellar on plots following brassica (2.8 t/ha) was reduced by 29% compared with plots following fallow. Average grain yield on grazed plots (2.6 t/ha) was reduced by 38% compared with ungrazed plots. In both Mackellar and Blackbutt, reduced numbers of kernels per spike and reduced kernel weight accounted for the reduction in grain yield under grazing. Two other experiments were conducted at a separate site to obtain data on the nutritive value of the cereal forages and to record phenological development of the two cereals and compare grain yield responses to cutting before and after stem elongation stages. In vitro and in vivo measurements of digestibility in the vegetative phase were similar in the two cereals (91–94%). Grain yield was significantly reduced following cutting at the post stem elongation stage in Mackellar and Blackbutt and, in Mackellar, was attributable to reduced kernel number per spike and kernel weight. The overall economic return, combining actual returns from lamb production on the forage brassica, and estimated returns from grazing and grain production, after variable costs of each phase were accounted for, were $1117/ha for Mackellar wheat and $1081/ha for Blackbutt oats. These returns were $583/ha and $910/ha more than the estimated return from the fallow, ungrazed treatments for wheat and oats, respectively.

The feeding of known amounts of supplements to grazing animals can be accomplished relatively easily. If the supplement and the other diet components have distinctive profiles of cuticular wax n-alkanes, then the supplement intake and the alkane profiles of the supplement, other dietary components and faeces can be used to estimate the proportions and hence intakes of several forages by the grazing animal. However, this method requires knowledge of recoveries of n-alkanes in faeces. Twenty four wethers were fed one of four diets comprising equal combinations of 1, 2, 3 or 4 forages. Forages used were subterranean clover, phalaris, annual ryegrass and wheat straw. Forages were chopped using a chaff cutter and fed with solvent-extracted cottonseed meal (CSM) labelled with beeswax and synthetic C28 alkane to provide a characteristic alkane profile. Faecal grab samples were taken from sheep from 14 to 23 days after administration of an intra-ruminal controlled-release device (CRD) containing 1 g of each of C32 and C36 alkane. Total faeces were collected from half the sheep on each treatment in order to measure alkane recoveries in individual sheep. Faecal concentrations of the n-alkanes C25 to C31 and C33 were corrected for recovery using the individual sheep value, the treatment mean or the grand mean for all four treatments. Dietary compositions were then estimated from corrected faecal concentrations of n-alkanes using a least-squares procedure and, together with the known supplement intakes, were used to estimate the intakes of all other diet components. Estimates from this ‘labelled supplement’ method were compared with the amounts fed or those estimated using the alkanes derived from the CRD. The labelled supplement method accurately and precisely estimated dietary component proportions and intake for all treatments when measured recoveries for individual sheep were used. Precision declined when recovery was based on estimated recoveries for treatment means or the grand mean. Estimates of intake based on dietary C33 and the measured release rates of C32 or C36 alkanes from the CRD did not differ from measured intakes. Estimates based on the C32 : C31 alkane pair over-estimated intake. Estimates of whole-diet digestibility based on the various ways of estimating intake were all very close to the digestibilities calculated from directly-measured intakes and faecal outputs. It is concluded that the feeding of a known amount of supplement can be successfully used to estimate dietary proportions and hence intakes of diet components, in mixed diets with up to five ingredients, but this approach requires estimates of faecal alkane recovery.

Two experiments were conducted to evaluate factors influencing the release rate of octacosane (C28) and dotriacontane (C32) synthetic alkanes from controlled-release devices (CRD) inserted into the rumen of sheep, and the resultant accuracy of alkane-based estimates of herbage intake. In the first experiment, estimates of the rate of release of alkanes from CRD suspended in the rumen of 7 rumen-fistulated ewes were obtained by directly measuring the rate of CRD plunger travel. In the second experiment, CRD were administered orally to 24 castrate male sheep to evaluate the effects of level of feeding (1200 v. 600 g DM/day), frequency of feeding (continuous v. once-daily), and number of CRD inserted (1 v. 2) on temporal trends in faecal alkane concentrations and ratios and on the accuracy of estimation of intake. In both experiments, animals were also dosed orally, once daily with paper pellets containing 56 mg hexatriacontane (C36). In Expt 1, linear alkane release from the CRD commenced after a lag period of 2-3 days, at mean rates of 40.1 mg/day (C28) and 41.7 mg/day (C32), close to the desired rates of 40 mg/day. There was no evidence of curvilinearity, and differences in release rate between sheep were small (CV 4.1%). Alkanes attributable to the CRD appeared in faeces after 2-3 days and reached plateau concentrations by 6-7 days. Data are presented to indicate that the release rate was not affected by the removal of CRD from the rumen for measurement, and that the release rates in fistulated (Expt 1) and intact sheep (Expt 2) were similar. In Expt 2, there was no effect of level of feeding on CRD release rates and faecal alkane concentrations were consistent with the differences in faecal output caused by feeding level. As a result, the accuracy with which known intakes were estimated was unaffected by level of feeding. Similarly, there were no effects of feeding frequency on the accuracy of estimated intake, implying that in this study, feeding frequency had no effect on CRD release rates. The administration of 2 CRD to half the animals in this experiment increased faecal concentrations of C28 and C32 and the synthetic : herbage alkane ratios associated with these alkanes [e.g. faecal C32 : tritriacontane (C33)] but these changes were not significantly different from those expected from the release rates estimated in Expt 1. As a result, the accuracy with which known intakes were estimated was not influenced by the number of CRD administered. In both experiments, once-daily dosing with C36 alkane resulted in a more rapid rise in faecal C36 concentrations and faecal C36 : pentatriacontane (C35) ratios to maximal levels (3-4 days), compared with alkanes derived from the CRD (6-7 days), but thereafter, faecal C36 concentrations were much more variable, especially in the fistulated sheep. As a result, intake estimates based on the C36 : C35 alkane pair significantly over-estimated known intakes by 13% (Expt 1) and 8% (Expt 2). Data are presented to indicate that C36 alkane functioned satisfactorily as a faecal output marker and, with C32 : C33 estimates of intake, provided accurate estimates of herbage digestibility. The results indicate that intra-ruminal controlled-release devices provide a satisfactory means of delivering an accurate, daily dose of alkanes for the estimation of herbage intake, faecal output, and digestibility in sheep.

A short-term shading treatment was used to create a Phalaris aquatica L. pasture with alternating strips of ‘low’ [62 mg/g dry matter (DM)] and ‘high’ (126 mg/g DM) water-soluble carbohydrate (WSC) concentration. Analyses showed that starch and all components of the WSC were reduced in concentration by shading. The shaded and unshaded pasture strips did not differ significantly in in vitro DM digestibility (84% DM), nitrogen (3.1% DM), or neutral detergent fibre concentration (42.4% DM). Synthetic alkanes were applied to the pasture strips as markers to measure the selection of the shaded and unshaded pasture by sheep. When 12–13-month-old Merino wethers were given simultaneous access to both pasture treatments, they selected 2.6-fold more unshaded (high WSC) pasture than shaded pasture. The results indicate the involvement of herbage total WSC and its components in the process of diet selection by sheep, and suggest that in future studies, more attention should be paid to reporting data for total WSC concentration.

The concentrations of water-soluble carbohydrate (WSC) and its components, starch, total nitrogen, and dry matter of phalaris (Phalaris aquatica L. cv. Australian) pasture were varied by shading for periods ranging from 38.5 to 46.5 h. In unshaded pasture, WSC concentrations were lowest at sunrise [103 mg/g dry matter (DM)] and increased until early afternoon (to 160 mg/g DM). Sucrose and starch increased in concentration during daylight, whilst the concentrations of glucose, fructose, fructan, and a component of WSC considered to be mainly the carbohydrate moiety of glycoside(s) were relatively constant. The concentrations of starch, and all components of WSC except sucrose, were reduced by shading, but increased to the concentrations observed in the unshaded pasture within 2–4 h after removal of the cover. The fructans present in phalaris were determined to be oligosaccharides of degree of polymerisation (DP) 3 and DP 4 and high molecular mass fructans with DP >10. Nitrogen concentration of shaded pasture was initially higher (4.7% DM) than in unshaded pasture (3.9% DM), but decreased after removal of the shade cover. Dry matter content was reduced in shaded pasture, partly due to increased retention of water on the exterior of plants. The experiment was a precursor for a grazing trial in which the WSC content of pasture was to be altered by shading. It indicated that shading would potentially alter WSC and N concentrations, and DM content, but would have only a relatively small impact on the digestibility of the pasture.

The n-alkane and chromium/in vitro procedures for estimating herbage intake were compared in grazing ewes during late pregnancy, early lactation, and mid-lactation. To ensure differences in herbage intake, the ewes were grazed in 4 plots of phalaris-dominant pasture at 2 levels of stocking: 17.1 ewes/ha and 30.8 ewes/ha. To investigate whether either procedure for estimating herbage intake was influenced by supplement consumption, half of the ewes at each stocking level received 500 g/day air-dry of a pelletted supplement (1 : 1 milled oat grain : sunflower meal). Supplement intakes were estimated using tritiated gypsum as a marker. During intake measurement periods, ewes were dosed twice daily with both alkane capsules and capsules containing chromium sesquioxide. For the last 6 days of the 12-day dosing period, rectal faecal samples were taken twice daily, immediately before the dosing. Over these same periods, wether sheep fitted with faecal collection harnesses were similarly dosed and sampled, and their total faecal output collected to establish the faecal recovery of chromium and the alkanes. Herbage intakes were estimated using the C27/C28, C29/C28, C31/C32, and C33/C32 alkane pairs. Estimates of intake based on the shorter alkane pairs were lower than those estimated with the C33/C32 alkane pair, by amounts which differed between the periods. Evidence is presented that estimates based on the last pair of alkanes (C33/C32) are the most accurate and are also more accurate than those based on the chromium/in vitro procedure. The relationship between these 2 methods for estimating intake was different in mid-pregnancy compared with either stage of lactation. The consumption of supplement did not interfere with any of the methods for estimating herbage intake. Estimates of faecal output based on the use of chromium, C28 alkane, or C32 as an external marker were statistically identical, indicating that the difference between the 2 methods for estimating herbage intake was not related to a failure to accommodate the incomplete recovery of any of the markers used or to the failure of rectal grab samples to be representative of total faeces. Our results indicate that herbage collected by oesophageally fistulated (OF) sheep was representative of that grazed by the ewes and could thus be used to provide the herbage alkane data needed to estimate herbage intake by the alkane method. However, the in vitro digestibility values obtained from the OF samples did not represent the digestibilities actually occurring in vivo. This was the main cause of the observed difference between the 2 methods for estimating intake. Possible reasons for the differences between the in vitro and in vivo estimates of digestibility are discussed.

Annual grass pasture (mainly annual ryegrass) was treated at seed head emergence (12 October 1990) with the herbicide glyphosate to delay loss of digestibility during late spring and summer. The lowest rate of glyphosate application needed to retain a high digestibility in the dry matter (DM) of the senescent grass sward was 180 g a.i./ha. The in vitro DM digestibility of control (unsprayed) pasture declined rapidly from relatively high levels near anthesis (28 October) (77n86%, leaves and seed head; 66%, stems) until about 38 days after anthesis (51n71%, leaves and seed head; 24%, stem). Thereafter, the digestibility of the plant parts did not change appre- ciably over at least 4 months. Treatment with glyphosate significantly slowed the loss in digestibility of stem, leaf sheaths, and seed head but did not affect the decline in digestibility of leaf blades. For example, the digestibility of stem in the sprayed pasture was 26 percentage units higher than that in the control pasture 38 days after anthesis. If the time at which digestibility of stems reached 50% is taken as an indication, the effective delay in loss of digestibility was of the order of 5 weeks. However, improved digestibility in the treated pasture was achieved at the expense of pasture yield, with the peak yield of control pasture being 4 t DM/ha (45%) higher than that of the treated pasture. Improved digestibility in treated grass pasture was mainly associated with delayed loss of water-soluble carbohydrates (WSC), except in the seed head. Improved cell wall (neutral detergent fibre) digestibility also con- tributed to varying degrees and was the main factor contributing to improved digestibility in the seed head. The major WSC present in the treated pasture was fructan. The crude protein concentrations of all plant parts of the senescent pasture, except the leaf blades, were also increased by treatment with glyphosate. Additional keywords: annual ryegrass, digestibility, fodder, fructans, herbicide, Lolium rigidum, senescent pasture, soluble carbohydrates.

The treatment of annual ryegrass–silver grass pasture with the herbicide glyphosate at seed head emergence delayed the loss of soluble carbohydrates and improved herbage digestibility. The present study investigated whether this improvement in nutritive value had any influence on the diet preference, intake, and performance of housed sheep. Since the effects of glyphosate on digestibility were most marked in stem tissue, preference was examined not only in relation to sprayed v. unsprayed herbage, but also in terms of preference for individual plant parts. In the preference testing, sheep showed a marked preference for sprayed rather than unsprayed herbage. They also consumed more of it, such that their digestible dry matter intake from sprayed herbage was nearly twice that from unsprayed herbage. When sheep were offered different plant fractions from the control herbage, they selected against stem material and preferred leaf or seed head. By contrast, when offered fractions from the sprayed material, they preferred stem to leaf, but showed no strong preference for stem over seed head. Preference was related more to the soluble carbohydrate content of a plant part than its digestibility, and only when soluble carbohydrate contents were similar was there preference for the more digestible material. The consumption of sprayed herbage, compared with control herbage, led to higher concentrations of rumen volatile fatty acids in the period 4 h after feeding. Moreover, the feeding of these herbages over a 6-week period resulted in significant reductions in pre-feeding plasma urea and β-hydroxybutyrate concentrations. When control herbage was fed with supplements of fructose, urea, or fructose+urea, in an attempt to mimic the possible differences in nutritive value between control and sprayed herbage, the responses in rumen and blood metabolites were less marked than when sprayed herbage was fed. As a consequence of the higher nutritive value of the sprayed herbage and the higher intakes by the animals fed this material, sheep fed sprayed herbage were able to maintain weight over the feeding period, whereas those offered the control herbage lost weight at 130–150 g/day

Previous papers in this series have demonstrated that, when annual pastures were sprayed at seed head emergence with low rates of the herbicide glyphosate, the nutritive value of the sprayed herbage was improved. Housed sheep preferred sprayed herbage to unsprayed herbage and, within sprayed herbage, appeared to have a preference for stem material. The housed sheep ate more of the sprayed material and their weight gains were improved. If such responses occurred in grazing animals, they could result in substantial improvements in animal liveweights or wool production. The present paper describes the alkane-based procedures used to investigate diet selection and herbage intake in grazing animals, with the emphasis placed on methodological and statistical issues. The alkane concentrations in the plant fractions (leaf, leaf sheath, stem, seed head) of sprayed and unsprayed herbage are reported. Similarly, the alkane concentrations in extrusa samples collected by oesophageally fistulated sheep given access to the grazed areas, and in the faeces of sheep grazing the areas, are reported. Patterns of alkane concentrations in extrusa and faeces were similar and indicated that, in the short term, oesophageally fistulated animals consumed a diet of similar composition to that selected by the animals resident on the plots. Using these data for alkane concentrations, multivariate statistical analyses are presented which provide an objective basis for selecting the alkanes to be used in the estimation of diet selection. The results of the first of 4 grazing periods are presented, as an example of the application of the alkane-based procedures for estimating herbage intake and, in particular, diet composition. Use of these techniques indicated that, when given access to sprayed senescent pasture, sheep consumed more digestible dry matter and selected more of it from the stem fraction than was the case with unsprayed herbage. These results are similar to those found with housed animals and demonstrate that patterns of herbage and faecal alkane concentrations can be used to estimate diet composition of grazing animals in terms of the plant parts on offer

We report the effects of spray-topping annual grass pasture with glyphosate (180 g a.i./ha as Roundup CT, at the seed head emergence stage) on the nutritive value of herbage and on subsequent performance of grazing sheep. Eight 1-ha plots, consisting of 4 sprayed and 4 unsprayed (control) plots, were set-stocked with Merino wethers (18 months old, 12 sheep/ha) from 8 days after anthesis in the control plots (late spring) until 165 days after anthesis (mid-autumn). In 4 periods (15–20, 36–41, 71–76, and 99–104 days after anthesis; Periods 1–4, respectively) sheep were dosed with synthetic alkanes and herbage and faecal samples were taken, in order to estimate diet composition (in terms of plant parts), faecal output, herbage intake, and the digestibility of the whole diet. As described in our earlier papers, spray-topping reduced the yield of pasture dry matter, but also slowed the loss of water-soluble carbohydrate (WSC) and digestibility during pasture senescence. The present paper shows that as a result, sheep grazing sprayed herbage in Periods 1 and 2 consumed significantly more organic matter (OM) and digestible OM (DOM) than sheep grazing the control pasture. Their diet contained a higher proportion of stem with a higher WSC concentration than that of the sheep grazing the control plots. The proportions of different plant parts (leaf blade+sheath, stem, seed head) in the diet of both the plot sheep and oesophageally fistulated (OF) sheep, which grazed treatments for short periods, differed significantly between treatments in all periods. However, the compositions of the diets selected by plot and OF sheep were similar. These results confirmed diet preferences measured using housed sheep and demonstrate the usefulness of alkane-based procedures for quantifying diet composition and intake in grazing animals. As a result of their higher intake of DOM, sheep grazing sprayed herbage had a significantly higher liveweight gain over the first 2 periods (40 g/day). In Period 3, sheep grazing sprayed herbage consumed more OM than sheep grazing control herbage. However, DOM intakes from sprayed or control plots were not significantly different in either Period 3 or Period 4, and were lower than in Periods 1 and 2. Sheep grazing both treatments lost liveweight at a similar rate over this time. Wool growth in sheep grazing sprayed herbage was improved by 10% during the experimental period; wool strength was also improved significantly. The implications for the management of sheep grazing spray-topped pastures over summer are discussed.

Plants of the pasture species Phalaris aquatica cv. Sirosa, Lolium perenne cv. Victorian, Trifolium repens cv. Irrigation White, T. subterraneum ssp. subterraneum cv. Mt Barker, T. subterraneum ssp. yanninicum cv. Trikkala, and Medicago sativa cv. Siriver were grown under controlled glasshouse conditions. At weekly intervals, 6 plants of each species were harvested and dissected into their component plant parts. The concentrations of n-alkanes in plant parts from all species were then estimated using gas chromatography. Results confirmed earlier studies that alkanes with odd-numbered carbon chains were predominant in cuticular wax, especially C27, C29, C31, and C33 alkanes. For the individual alkanes (225433, differences between species accounted for 85% of the total variance in alkane concentration. Calculation of similarity coefficients indicated that the greatest similarities in the pattern of alkane concentrations occurred either between plant parts within a species or between the same plant part in closely related species. Multivariate statistical analysis using canonical variates analyses indicated that despite these similarities, it would still be possible to distinguish both plant species and plant parts in mixtures of these components. In particular, an examination of hypothetical perennial ryegrass-white clover or phalaris-subterranean clover pastures demonstrated that all fractions of all species would be likely to be distinguishable. The results are discussed in relation to the use of herbage and faecal alkane concentrations in least-squares estimates of the composition of the diet of the grazing animal.

The existing mathematical methods for estimating botanical composition of an animal's diet from the concentrations of plant alkanes in herbage and faecal samples all have significant limitations. These include the need for an arbitrary selection of a subset of alkanes for use in the calculations, the loss of information, or the generation of negative estimates for diet components when more than two species are present. We present a new algorithm for solving the diet composition problem, which overcomes these difficulties and is rapid to compute. This algorithm (known as non-negative least squares-NNLS) is shown to perform as well as previous methods on a set of herbage mixtures of known composition. Issues relating to the estimation of the errors of diet composition estimates are discussed.

Over 3 years, we examined the possible benefits of moving the joining date from mid March to early February for the productivity of a prime lamb system based on Border Leicester x Merino ewes on the southern tablelands of New South Wales. The proportion of ewes with >1 lamb (fertility) was affected more by year and by age of ewe than by joining date. The mean proportion of fertile ewes with >1 lamb (fecundity) was reduced from 0.28 to 0.15 at the earlier date, while immunisation against androstenedione increased fecundity at both mating times to 0.42 but significantly reduced fertility in the earlier group. Over the 3 years, the earlier joining produced 12 fewer lambs per 100 ewes mated and immunisation increased lamb number by 17, but flushing (for 3 weeks with sunflower meal) had no significant effect. Immunisation did not have a consistently greater effect at the earlier joining. Groups of these ewes, balanced for fetus number, grazed at 6.5, 10, or 13 per ha on pastures based on phalaris and subterranean clover. Ewe liveweight after lambing, lamb birth weight, and perinatal mortality were not affected by joining date, but mean daily weight gain by later born lambs over the first 90 days of life was 44 g greater than for earlier born lambs. However, earlier joining enabled 17 more lambs per 100 ewes to reach a marketable weight of 31 kg within the pasture season. Twins grew more slowly and relatively few reached sale weight. With a mean 1.4 lambs per ewe, the optimum stocking rate on these pastures appeared to be 6.5-10 ewes/ha. Superphosphate application to half of the experimental area, after 17 years without treatment, increased pasture weight, lamb growth rate, and numbers sold. The increase was such that a treated pasture could have carried an extra 3 ewes/ha without depression in individual productivity, relative to an untreated pasture. Supplementation of ewes in late pregnancy and early lactation benefited only twin lambs at the higher stocking rates. The results suggest that a prime lamb system in this environment is more likely to succeed with the earlier joining date. The lower lambing percentage, resulting from a decrease in fecundity, is likely to be of benefit, rather than detriment, to the efficiency of a system in which single- and twin-bearing ewes and their lambs are given equivalent treatment.

In 2 experiments, Merino sheep aged about 18 months grazed cereal stubbles for 12 weeks and were either: (i) given no supplement; (ii) given free access to blocks containing 30% urea; or received daily about 300 g DM sheep-1 of (iii) rapeseed meal (RSM); (iv) formaldehyde-treated RSM (FRSM); (v) sunflower meal (SFM); or (vi) formaldehyde-treated SFM (FSFM). In experiment 1, wethers grazed a barley stubble at stocking rates (SR) of 18 and 36 sheep ha-1, and in experiment 2, mixed flocks of wethers and ewes grazed wheat stubble at 10 and 20 sheep ha-1. Mean daily intakes of urea were about 8.5 and 11.5 g sheep-1 for experiments 1 and 2 respectively. Both forms of SFM were readily eaten throughout, but in both experiments, intakes of RSM and FRSM were low and were characterised by high variability from day to day, and among individual sheep within groups. In both experiments, all sheep gained some weight during the first 2-3 weeks; thereafter control and urea fed sheep lost weight at mean rates varying from about 96 to 180 g day-1 depending on SR. Feeding SFM or FSFM reduced this loss to about 20 g day-1 at SR of 10-20 ha-1, and to 60 g day-1 at a SR of 36 ha-1, while losses were intermediate in sheep fed RSM or FRSM. In experiment 1, daily wool growth rates varied from about 5.5 g clean dry wool (CDW) sheep-1 for control and urea-fed sheep to about 11 g CDW sheep-1 for sheep fed SFM and FSFM; respective daily rates in experiment 2 were 3.6 and 8.2 g CDW sheep-1. Wool growth of sheep fed RSM and FRSM was intermediate in both experiments. When ewes were mated on high-quality feed after grazing stubbles, conception was delayed for about 14 days in a high proportion (about 40%) of those ewes that had lost considerable weight during stubble grazing. This effect was overcome by feeding daily 300 g DM sheep-1 of SFM for 7 days prior to and during mating. Delayed conception extended the lambing period. although final numbers of lambs born were not different among groups.

Weaned crossbred lambs grazing mature pasture in summer at stocking rates of 14, 28 or 42 lambs/ha were supplemented for 60 days with 0, 400, 600 or 800 g/day of either sunflower meal or a 1:1 mixture of sunflower meal and oats. Mean daily gains in fasted weight without and with supplement were - 51 and 62 g, respectively, with no significant difference between the three feeding levels. Greasy wool production increased from 4.7 g/day without supplement to 9.9 g/day at the 600 or 800 g level but the composition of the supplement had no effect. Stocking rate had no effect on animal performance. It was estimated that pasture intake increased slightly with the first 400 g of supplement but fell sharply as the level increased further, with a substitution rate of 1.3. In two experiments, yarded lambs were offered oaten or lucerne hay ad libitum and mixtures of sunflower meal and oats at levels from 400 g/day to ad libitum. Mean daily gain in fasted weight increased from about 140 to about 190 g/day over this range of supplementation and greasy wool production from about 9 to about 10 g/day. In one experiment weight gain and wool production were significantly lower with a 1:6 mixture of sunflower meal and oats than with a 1:2 mixture and the same trend was shown in the other experiment. Measurements of intake showed that the substitution rate for both types of hay was only about 0.5. Comparisons of the animals' estimated requirements and intake in all three experiments indicated that the relatively poor performance of grazing animals was due to the very high substitution rate for grazed pasture at levels of supplement intake above 400 g/day.