No abstract

Digestible organic matter (D.O.M.) intakes of sheep grazing various pastures were measured by faecal index methods in three 4- to 6-week experiments. No correlation could be found between the weight of pasture available (over the range 150–2900 Ib dry weight per acre of green herbage) and the D.O.M. intake of sheep. During two experiments the sheep were shorn. Shortly after, voluntary D.O.M. intakes rose significantly by 42–62%. Concurrently the hay intake of other sheep yarded nearby rose by 20–51% following shearing. Cold stress is probably responsible for these increases.

Barnyard millets (Echinochloa utilis and E. frumentacea), maize (Zea mays) and a sorghum hybrid (Sorghum bicolor x S. sudanense) were grown as spaced plants at temperature regimens from 15/10 to 33/28�C (dayhight). Leaf and stem dry weight, leaf area and leaf number were recorded every 2 weeks and the dry matter analysed for nitrogen, sulfur, sodium and in vitro digestibility. Tolerance to low temperatures was in the order maize > E. utilis >sorghum >E. frumentacea. At mean temperatures above 25�C, relative growth rates were similar for all species. Differences in leaf area, for which individual leaf size was mainly responsible, accounted for most of the dry weight responses to temperature, although net assimilation rate responses were also apparent. The dry weight response to temperature became negligible after adjusting for differences in stage of development. Dry matter digestibility decreased with temperature; it also decreased with time because of deteriorating stems, except in sorghum. Maize leaves were of low digestibility, similar to stems. The nitrogen : sulfur ratio of all species remained steady with age; in sorghum at low temperature it exceeded the 15: 1 maximum considered desirable for animals. Sodium was highest in E. utilis stems and increased with temperature, in contrast to sorghum. Maize had a marginal nitrogen: sulfur ratio and unacceptably low sodium concentration. It was concluded that more attention should be given to E. utilis as a forage for cool climates.

During three summers a sorghum-Sudan grass hybrid (Sorghum bicolor x S. sudanense) and S. almum were grown at three levels of nitrogen fertilizer (0, 84, or 168 kg N/ha) in a cool temperate environment at Armidale, N.S.W. A pearl millet (Pennisetum typhoides) was included in the experiment during one summer and Japanese millet (Echinochloa crus-galli var. frumentacea) in two summers. Differences in dry matter production were non-significant except in one summer when Japanese millet produced almost twice as much as the sorghums. The forages were grazed by young sheep on the put-and-take method. Carrying capacity as judged by this technique was high on all crops except pearl millet but average daily gains were low, the performance on S. almum being generally the poorest. Total production (expressed as metabolizable energy intake) was significantly higher for S. almum than for the hybrid or pearl millet in the first year but there were no significant differences thereafter. Pre-sowing application of anhydrous ammonia did not increase the dry matter available at the first grazing and tended to depress animal performance. Liveweight gain per hectare was significantly reduced by nitrogen in one of the three summers. Residual soil nitrogen subsequently assessed by an oat crop was substantial on plots that had received ammonia. Crop performance measures were computed in various ways and differences between them are discussed. It is tentatively concluded that, of the four crops, Japanese millet has the most potential for use by sheep in this environment.

Two experiments on the efficiency of utilization of oats by Merino sheep are reported. In the first experiment eight plots with a range from 2730 to 4850 kg dry matter per ha were stocked at c. one sheep per 40 kg of forage. In the second, five plots with approximately equal quantities of forage oats were stocked at c. one sheep per 18, 29, 38, 44, and 50 kg of forage. The data were analysed by regression, ordination, and canonical analysis. Over the range of availabilities examined in experiment I there was no indication that increased dry matter availability reduced the efficiency of utilization. In experiment II, however, increased grazing pressure was associated with an increase in the total liveweight gain and metabolizable energy harvested from a constant quantity of forage; this implied lower efficiency at the lower stocking pressures. The higher digestibility of the forage on some plots in the first experiment was associated with an increased rate of dry matter intake and a reduction in wastage; this effect appeared to be independent of the original planned comparison. It was concluded that within the range of availability studied, forage digestibility and stocking pressure were probably more important determinants of the efficiency of utilization of oats than was the quantity of forage available.