Effects of species, plant part, and plant age on the n-alkane concentrations in the cuticular wax of pasture plants

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.

Prime lamb production in relation to time of mating

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.

Monitoring the fate of dietary proteins in rumen fluid using gel electrophoresis

1. When fractionated by sodium dodecylsulphate-polyacrylamide gel electrophoresis (SDS-PAGE), strained rumen fluid from sheep fed on pelleted lucerne (Medicago sativa) hay showed no major protein components that stain with Coomassie Blue. This feature made it possible to monitor the fate of individual polypeptides within a protein mixture incubated in rumen fluid in vitro. 2. Extracts from a number of seed meals (sunflower (Helianthus annuus), lupin (Lupinus angustifolius), rape (Brassica napus) and pea (Pisum sativum L.)), as well as casein and bovine serum albumin, were examined in this system. The protein components of each seed type showed a wide range of resistances to degradation. One protein in pea seeds (pea albumin 1), which is particularly rich in cysteine, was almost as resistant to rumen degradation as bovine serum albumin. 3. Analysis of synthetic-fibre-bag experiments by SDS-PAGE showed that the rate of loss of total protein from solid meal residues does not provide an index of the resistance of individual protein components of the meal to rumen degradation. While there was no qualitative change in the protein profile of residual pea-seed meal inside a synthetic-fibre bag, there was considerable variation in the rate at which individual, solubilized protein components were degraded in the surrounding rumen fluid.

Responses to supplements by weaned lambs grazing mature pasture or eating hay in yards

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.

Feeding value of subterranean clover, lucerne, phalaris and Wimmera ryegrass for lambs

The feeding values of subterranean clover, lucerne, phalaris and Wimmera ryegrass were measured in three experiments using weaned lambs. With dried herbage, the voluntary intake of each species increased linearly with organic matter digestibility over the range tested (57-83%). Regressions for the two grasses did not differ from each other, nor did those for the two legumes; a common regression for the legumes had the same slope as that for the grasses but dry matter intake was about 190 g/d greater on legume diets. Digestibility accounted for 50 and 68% of variation in intake of legumes and grasses, respectively, but when cellulose concentration in the diet was used as the predictor, a single regression satisfied all the data and accounted for 76% of variation in intake. Energy retention by weaned lambs offered diets of dried subterranean clover or lucerne was 53% greater than that by lambs receiving the same intake of metabolizable energy from phalaris. When the intake of the two legume diets was unrestricted, this difference increased to 128%. Despite the 30% higher voluntary intake of the legume diets, the weight of digesta in the reticula-rumen at the end of a meal was the same as it was for the phalaris diet. When all four species were compared in the field, with herbage amply available, lambs grazing the two legumes retained 57% more energy than those on the grasses during the main spring period when the species were of comparable digestibility. As there was little or no difference, under the conditions of this experiment, in the intake of food from the four swards, it is concluded that the difference in feeding value resulted from more efficient use of metabolizable energy. Overall, subterranean clover had as high a feeding value for lambs as lucerne, and phalaris was not inferior to Wimmera ryegrass.

The accuracy of tritiated water turnover rate as an estimate of milk intake in lambs

The accuracy of water turnover measurement as an estimate of milk intake was evaluated, with special reference to the validity of the assumptions underlying the technique. Even when milk was the only source of water for penned lambs, water turnover measurement significantly underestimated known milk intake. The underestimates were greater over longer measurement periods. It is suggested that these underestimates occurred because changes in body water pool size were not considered in the calculation of water turnover, since estimates were improved by the incorporation of a pool size correction. In a second pen trial, it was demonstrated that the inhalation of vapour from tritiated water excreted by other lambs was not a source of error in the estimation of water turnover. .In a field trial, the turnover technique was successfully employed to estimate milk intake in the first 3–4 weeks of life. A method for accommodating changes in pool size is presented, and it is suggested that the effects of pool size changes on the accuracy of the estimate of milk intake are too large to be ignored. In later weeks of the experiment, it was obvious that lambs were consuming water in forms other than milk, so that milk intake estimates were inaccurate. .It is concluded that in animals consuming only milk, measurement of tritiated water turnover provides an accurate estimate of milk intake, but only if changes in body water pool size are taken into account.

An evaluation of cereal stubbles for sheep production

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.

Efficiency of lamb production in relation to the weight of the ewe at mating and during pregnancy

The intake of pasture by nine groups of 40 Border Leicester x Merino ewes was controlled to achieve three levels of liveweight at mating and three levels at the end of the 15th week of pregnancy. Over the last 6 weeks of gestation all groups gained about 7 kg per head, and after lambing the intake of pasture was unrestricted. Ewes that weighed 58 kg at mating produced 152 lambs per 100 ewes compared with a lambing percentage of 107 by ewes that weighed 44 kg. However, when the lambs reached 10 weeks of age there was little difference in their numbers. This was partly because of the higher death rate of young lambs when the liveweight of the ewe fell during mid-pregnancy, and partly because of the loss of single lambs following dystocia in ewes maintained at a high weight throughout pregnancy. The percentage of lambs reaching marketable weight (32 kg) before the end of the pasture season was related directly to the liveweight gain of the ewe during mid-pregnancy, and inversely to the proportion of lambs reared as twins. The weight of lamb marketed per unit weight of food eaten by the ewes over the autumn and winter was much greater from the ewes that increased from 51 to 58 kg during mid-pregnancy than from those that followed the reverse pattern. In general, a fall in ewe weight over this period led to inefficient use of food and a reduction in the weight and soundness of the fleece. These results suggest that in areas that are marginal for prime lamb production because of a short pasture season, it may be better to ensure a rising plane of nutrition throughout pregnancy than to aim for a high weight at mating.