No abstract

Microalgal biomass can be used for biodiesel, feed, and food production. Collection and identification of local microalgal strains in the Northern Territory, Australia was conducted to identify strains with high protein and lipid contents as potential feedstock for animal feed and biodiesel production, respectively. A total of 36 strains were isolated from 13 samples collected from a variety of freshwater locations, such as dams, ponds, and streams and subsequently classified by 18S rDNA sequencing. All of the strains were green microalgae and predominantly belong to Chlorella sp., Scenedesmus sp., Desmodesmus sp., Chlamydomonas sp., Pseudomuriella sp., Tetraedron caudatum, Graesiella emersonii, and Mychonastes timauensis. Among the fastest growing strains, Scenedesmus sp. NT1d possessed the highest content of protein; reaching up to 33% of its dry weight. In terms of lipid production, Chlorella sp. NT8a and Scenedesmus dimorphus NT8e produced the highest triglyceride contents of 116.9 and 99.13 μg mL−1 culture, respectively, as measured by gas chromatography–mass spectroscopy of fatty acid methyl esters. These strains may present suitable candidates for biodiesel production after further optimization of culturing conditions, while their protein-rich biomass could be used for animal feed.

-The live weight gain of cattle on tropical pastures is reviewed and found to be low and dependent on the length of the growing season. Supplements may be added to address the primary limiting nutrient, which, in the dry season, is crude protein. The response relationships of live weight gain to level of supplement (protein or energy) that have been developed for animals on pasture in Brazil and Australia have been compared and found to be very similar. This gives confidence in recommending a supplementation strategy for cattle on tropical pastures. Response in the wet season was very low and likely to be uneconomic compared with dry season supplementation. Supplementation is costly and should only be used as a last resort, but the strategy needs to be viewed in the context of a growth path to a defined market or slaughter weight. In Australia, high inputs in the first dry season are risky as subsequent compensatory growth can reduce or eliminate the weight advantage of a supplement. There is less financial risk in using supplements towards the end of the growth path. Growth paths can follow many forms and there is no need to maximise live weight gain in each period. Targeted supplements in the second dry season, leucaena based systems, other special-purpose pastures or crops, and feedlots offer the most economical way for cattle to meet market targets. The expected annual live weight gain and weaning weight are other major factors which determine the growth path, target market which can be achieved, and the level of intervention (supplements, legumes, feedlots, etc) which are required and when. Some recent results on growth paths in Australia are presented.