Astrebla

Abstract: Some aspects of nitrogen metabolism of sheep given Mitchell grass (Astrebla spp.), Flinders grass (Iseilema spp.) and mixed native pasture were investigated. All diets were of low nutritive value as demonstrated by negative nitrogen and energy balances in sheep on these diets. Studies of urea metabolism demonstrated a significant relationship between plasma urea concentration, the rate of irreversible loss of urea from plasma and the rate of urea degradation in the digestive tract. On average, 81% of the urea synthesized in the body was transferred to the digestive tract and degraded to ammonia and carbon dioxide. The proportion of urea degradation occurring intraruminally was estimated during an intravenous infusion of 14C urea by measuring the rate of appearance of 14CO2 in ruminal fluid, the proportion degraded post-ruminally being obtained by difference. Urea degraded in the rumen accounted for 7–13% of the total quantity degraded in the digestive tract, and the rate of urea transfer (0.55 ± 0.13 g nitrogen/day) was not related to the rate of urea synthesis in the body. The lower digestive tract was the major site of urea degradation in sheep given these low protein diets, and the rate of urea transfer to this part of the digestive tract was linearly related to the rate of urea synthesis in the body. The implications of these findings are discussed in relation to nitrogen conservation in sheep given low quality diets.

Abstract: Budgerigars range and breed over most of the interior of Australia. During a year, budgerigars may experience a maximal change in day length of about 5 h, and temperatures range from well below to above their zone of thermo-neutrality. In the north of the budgerigar's range there is growth of pastures in summer and autumn and in the south there is growth in spring and early summer. In the arid interior, growth is irregular from year-to-year and varies from site-to-site. However, in northern arid regions growth tends to occur in summer and autumn; in southern arid regions in spring and early summer; and over most of the arid regions in most years there is some growth in run-on areas. In inland mid-eastern Australia budgerigars ate only seeds of ground vegetation. These seeds were from about 0.5 to 2.5 mm in length, weighed between about 0.3 and 1.3 mg and had an energy content of about 18.9 kJ g-1. Ata site on Mitchell grass plains Astrebla spp. were the main seeds eaten. At a site further inland the diet was more diverse: in the hot months of 1973–74 they ate mainly Boerhavia diffusa, Atriplex spp. and Astrebla pectinata, during the cold months of 1974 mainly Iseilema and an unidentified seed, and in spring 1974 mainly Atriplex spp. There was no evidence of special dietary requirements for breeding; in particular no requirements of soft, unripened seed or insect food to feed young. Males and females, adults and juveniles, and individuals in the same flock had similar diets. Information from the literature and my data suggest there is considerable stability and seasonal regularity in the budgerigar's food supply.