SynopsisWe report flow birefringence observations of polyethylene oxide solutions in a four roll mill where the flow field in the central region of the mill approximates well to that of pure shearing flow. When flow birefringence is observed it is seen to be highly localized within a region close to the "outgoing" asymptotic plane of flow. The phenomenon can be explainer! in terms of the flow birefringence corresponding to high extension of some polymer chains where the localization is caused by the chains requiring sufficient time in the flow field to become extended. This explanation has important consequences in all "persistently extensional flows" and can explain the origin of previously published results of localized flow birefringence observed for polyethylene solutions in axial compression and axial extensional flows.

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Three experiments were conducted with ewes during late gestation (last 4 weeks) to examine metabolic and lamb birth weight responses to supplements. In a metabolism experiment, 18 ewes were divided into 2 groups and offered 800 g chopped Rhodes grass (Chloris gayanu, 1.1% N) with or without a supplement of 150 g cottonseed meal + 50 g molasses, daily until parturition. Supplementation was associated with significant increases in intake of digestible dry matter (37%) and crude protein (121%). Supplemented ewes had significantly greater liveweight gain (173 v. 39 g/day), plasma glucose (2.9 v. 2.5 mmol/L), glucose entry rate (20.6 v. 12.3 mmol/h), udder measurements (e.g. circumference, 548 v. 443 mm), and milk yields (measured at day 2 post-partum, 1748 v. 627 mL/day), and had heavier lambs at birth (3.9 v. 2.9 kg). In a second experiment, 10 ewes were pen-fed chopped Rhodes grass ad libitum, and 5 received individually 150 g cottonseed meal + 100 g molasses administered daily. Supplemented ewes were significantly heavier (47.8 v. 45.0 kg) in the last week before parturition. Supplementation was associated with improved ewe liveweight change (48 v. -33 g/day) and lamb birth weight (3.4 v. 2.4 kg). In a third experiment, 42 ewes grazed a 80-ha paddock during a dry season and received daily 1 of 3 individually administered treatments: control (20 mL water drench); 7 g urea + 4 g sulfate of ammonia in a 20 mL drench; 100 g meat and bone meal + 100 g molasses + 3 g urea administered as a slurry in a single drench. Performance and metabolic parameters for the 3 groups were ewe liveweight gain (38, 80, 131 g/day), rumen ammonia concentration (7.1, 10.0, 8.6 mmol/L), plasma glucose (2.6, 2.6, 2.1 mmol/L), plasma hydroxybutyrate (0.6, 0.5, 0.4 mmol/L), and lamb birth weight (3.5, 3.7, 4.0 kg). Differences were significant between the protein-supplemented and control groups for all parameters except rumen ammonia concentration. The data support the conclusion that protein supplements provide a production response in pregnant ewes that is sufficient to improve lamb survival rates when the nutrition from grass diets is inadequate.

The impact of heat stress on the feed intake, milk production, water intake and urine output of undernourished lactating ewes and on the growth rate and water intake of their lambs was measured both in a climate chamber and during exposure to natural high ambient temperature conditions. Similar liveweight increases occurred in both stressed and unstressed lambs. Feed intake was depressed in heat-stressed ewes in the climate chamber but not under natural heat-stress conditions. During the first and second weeks of lactation calculated milk yield (200-500 mljday) and composition were unaffected by heat stress per se. However, undernutrition due to the poor quality roughage offered apparently depressed milk production of all ewes. Increased water intake (27 %) and plasma prolactin concentrations (220 %) were recorded in heat-stressed ewes, but daily urine output (27-36 mljkg body wt) was unaffected. No relationship between prolactin concentrations, milk production and antidiuretic activity was obvious. At the age of 5-6 weeks water intake accounted for 67 % (500 mljday) and 80 % (1000 mljday) of total fluid intake (water plus milk) of unstressed and heat-stressed lambs respectively. These data indicate the importance of making water freely available to lambs subjected to extensive grazing systems of tropical regions.

Urea supplementation of lambing Merino ewes increased milk yield and lamb growth and survival rates in both pen and paddock studies. These productivity gains occurred in a semi-arid environment characterized by poor reproductive efficiency in Merinos. In pens, urea supplenlents fed to lactating ewes at the rate of c. 12 g/day stimulated intake of poor quality pasture hay (0.9 %nitrogen) by c. 30% and increased total nitrogen intake by c. 100%. Milk yield was improved by c. 50% and lamb growth rate by c. 140%. Sorghum grain supplements stimulated milk yield and lamb growth to a lesser extent than urea. The correlations found in pen studies between nitrogen intake and milk yield of ewes (r � 0.85; P < 0.05), and between ewe milk yield and lamb growth (r % 0.80; P < 0.01), prompted further investigations under paddock conditions. Ewes grazing dry pastures and supplemented with urea (8-10 glday) via drinking water yielded more milk (11-32%) than unsupplemented counterparts. Similarly, there were improvements in lamb growth (80-100%) and survival (c. 10%) in the supplemented groups.