A study was made over 2 years of the nutritive value of the subterranean clover (Trifolium subterraneum L.) cultivars, Trikkala, Larisa and Goulburn, in grazing experiments with Border Leicester x Merino lambs. Liveweight gain was similar for all cultivars in the first year and in the second year was higher on Larisa (153 g/day) compared with Goulburn and Trikkala (131 and 103 g/day, respectively). Wool growth was not significantly different between cultivars. Both the digestibility and water-soluble carbohydrate content of the petiole and stem plant fraction were significantly (P<0.05) higher than those of the leaf fraction, even though the leaf had a lower level of cell wall organic matter. The ratio of lignin to cell wall organic matter was also higher in the leaf fraction. Samples obtained via oesophageal fistula showed that petioles comprised most of the dry matter in the diet and, thus, were the major contributor to energy supply. Differences were found in the degradability characteristics of the 3 cultivars which led to significant (P<0.05) differences in the concentration of rumen degradable dry matter and effective rumen degradable protein (ERDP). During the vegetative and early flowering stages, the concentration of ERDP exceeded the supply of fermentable metabolisable energy required for microbial protein synthesis. In mature clover, the concentration of ERDP was low and limiting microbial protein synthesis. The degradation characteristics of protein were highly correlated with liveweight gain (r2 = 0.90) and wool growth (r2 = 0.70). It is suggested that increasing the petiole : leaf ratio could increase the efficiency of utilisation of subterranean clover diets.

Lamb growth, carcass and pelt measurements are reported from 5775 lambs born to Border Leicester × Merino (BLM) and Hyfer (Dorset × Merino composite) ewes joined to Dorset, Suffolk and Hyfer rams in three lamb-production systems at Cowra and Wagga Wagga over 5 years. The production systems involved lambings at different seasons of the year and increasing levels of intensification from autumn annual joining, spring joining with a backup mating for non-pregnant ewes, to an accelerated 8-monthly lambing system. Lambs from BLM ewes were 0.7 kg heavier at birth and grew 3% faster and reached slaughter, at 18 kg carcass weight, 1–2 weeks earlier than did lambs from Hyfer ewes (P < 0.01). The advantage in growth rate of lambs from BLM compared with Hyfer ewes was greater for lambs born in November. These lambs had poorer growing conditions over the summer months, with 22% lower growth rate and taking 5 weeks longer to reach slaughter than did lambs born in March or August. There was no difference between Dorset and Suffolk sire breeds for any lamb growth traits, with lambs from Hyfer sires growing 7% slower. Ram and cryptorchid lambs reached slaughter 1 week earlier than did wethers, with ewes a further 9 days later (P < 0.01). Sex differences were maximised when lamb growth was greatest. There were no differences in carcass fat measurements between ram and cryptorchid lambs, although both were considerably leaner than wethers (2.2–3.0 mm fat at the GR site), which were 1.3–2.1 mm leaner than ewes at 18-kg carcass weight. The range in average growth rate of progeny of the BLM ewes from the 12 different source flocks at Cowra and Wagga Wagga was 10–14% of the mean which was twice the difference in average growth rate of progeny from the BLM and Hyfer dams. There was also significant variation among the BLM source flocks for carcass fat measurements. Lamb progeny from the different sire- and dam-breed combinations had varying levels of heterozygosity. There appears to be little loss of heterosis or hybrid vigour for lamb growth, although the sire breed × dam breed interaction was significant (P < 0.01) for age at slaughter at Wagga Wagga, in which the ranking of the lamb types was consistent with the levels of heterozygosity. The estimates of between-lambing repeatability for the ewes were highest for birthweight (0.35 Cowra and 0.27 Wagga Wagga) and declined at later ages (0.26–0.17), with lower estimates for carcass traits.

Mature crossbred wethers, grazed for 11 weeks on oat stubble at a stocking rate of 20 sheep ha-1, were unsupplemented or offered supplements of a urea-mineral block, a molasses lick or a urea-molasses lick. Following rain in the fourth week, half of the area was sprayed with desiccant herbicide to establish weed-free stubbles. The stubble initially yielded c. 2600 kg DM ha-1 of dead crop residues plus 900 kg DM ha-1 of fallen grain; after 11 weeks this had fallen to c. 1400 kg DM ha-1 of dead crop residues. Initially the sheep selected diets of 0.03-0.22 grain and 0.78-0.97 dead herbage and, during this time, urea-supplemented sheep selected diets lower in grain and nitrogen (N) content than those selected by unsupplemented sheep. On weedy stubbles, where green herbage yielded more than 100 kg DM ha-1, sheep selected a diet containing c. 0.78 green herbage (N content 2.6%), ate more digestible organic matter (DOM) and gained more weight than those on weed-free stubbles, where the diets consisted of 0.98 dead crop residues (N content 1.1 %). All sheep ate some of the urea-mineral blocks throughout, but 100% acceptance of the licks only occurred by the 6th week. Mean intakes reached desired levels (10 g urea and/or 50 g molasses sheep-1 day-1) thereafter, but individual intakes varied widely on all supplements, with the coefficient of variation generally > 50%. In most periods, supplementation had only small effects on the intake of DOM. During the first 4 weeks, sheep lost weight except those offered the urea-mineral blocks. Over the whole experiment, urea-supplemented sheep lost less weight than unsupplemented sheep, but this was mainly due to higher weight gains on the weedy plots. Mean concentrations of rumen volatile fatty acids (VFA) were < 80 mmol l-1 throughout, and fell to <40 mmol l-1 on the weed-free plots in the latter stages of the experiment. Mean rumen ammonia levels, which were < 100 mg N l-1 in unsupplemented sheep, were generally increased by urea supplements, and by grazing weedy stubbles. Responses to supplementation are discussed in terms of the quality of the available plant material, the diet selected, the levels of rumen metabolites and the intake of supplements.

Supplements of urea, molasses and minerals were offered for 15 weeks to mature crossbred wethers grazing wheat stubble at Condobolin in central New South Wales. The sheep were then grazed without supplements on a phalaris-subterranean clover pasture for a further five weeks. On the wheat stubble, dead crop residues amounted to more than 4000 kg DM ha-1 and constituted 95% or more of the available plant material throughout the experiment. Diets selected by the sheep contained significant amounts of grain or green plant material only during the first six weeks, while the proportion of dead plant material increased from 66% to 98% of the diet as the experiment progressed. Supplementation had no effect on diet selection. All sheep gained some weight during the first six weeks of stubble grazing, and thereafter lost weight. This loss was reduced from 0.66 kg week-1 to 0.47 kg week-1 with a mineral block supplement, and to 0.37 kg week-1 with supplements of a mineral/urea block, or molasses or molasses/urea licks. Significant differences in mean liveweight occurred between unsupplemented sheep and those offered a mineral/urea block, or a molasses lick. These differences were reduced by half after five weeks on green pasture, due to compensatory gain. Supplementation had no effect on wool production, or on the amount of dead plant material utilized for animal production, which amounted to a mean of about 10% of the quantity initially available. Mean intakes of supplement by groups were close to the desired amounts, i.e. 10 g urea or 50 g molasses sheep-1 day-1, or both, but for all supplements intake varied widely among individual sheep, with the coefficient of variation exceeding 40% in more than half of the recordings. Apart from special circumstances where reduced rates of weight loss may be important, it seems that little benefit will be gained from feeding urea, molasses or mineral supplements to sheep grazing crop stubbles.

The production of young crossbred wethers grazing oat, barley and wheat stubbles was measured in each of three years at stocking rates ranging from 15 to 30/ha. In one year, production on 'weedy' stubbles was compared with that of 'clean' (weed-free) stubbles, and also the effect of a wheat–urea–mineral supplement on the production of sheep was measured on oat stubble. Liveweight change and wool production were significantly influenced by the availability of green plant material and by stocking rate, but not by supplementation. The maximum liveweight loss in any year was 7.5 kg and the maximum gain 6.0 kg, both recorded over 11 weeks' grazing. Mean daily clean wool production was 9.9 g/sheep at the lower stocking rate and 6.6 g/sheep at the higher rate, but production per hectare was 10–60% higher at the heavier stocking rate. The ranking of the crop stubbles with respect to animal production was not consistent from year to year. Intense selection for green plant material by sheep resulted in the proportion of green in the diet being nearly always greater than 80%, when the weight of this material on the plots was more than 40 kg dry matter/ha. It appeared that a low intake of nitrogen was not the main limitation to animal production. A maximum of only 36% of the crop residue which disappeared during the experiment could be accounted for as animal intake. Thus it is unlikely that the potential of cereal residues as a source of food for animal production will be realized with grazing sheep.