A new method for encapsulating low-molecular weight, water-soluble substances in lipid-walled microcapsules (LWMs) for delivery to marine bivalves was developed, characterized, and tested. LWMs produced by a spray technique (spray microcapsules, SMs) were demonstrated to encapsulate both aqueous (polymeric dye or oxytetracycline hydrochloride) and particulate (riboflavin) core materials within a capsule wall composed of triacylglycerides. Core materials were most effectively delivered in a capsule wall composed of tripalmitin. Addition of lower melting point lipids to soften the capsule wall significantly reduced (up to a nine-fold reduction) delivery of aqueous core materials, but did not significantly affect particulate riboflavin delivery. The composition of the capsule wall was demonstrated to affect the digestibility of LWMs. Addition of 40% w/w fish oil to the tripalmitin wall was required for Manila clam spat (Tapes philippinarum) enzymatically digest LWMs (convert triaclyglycerides to free fatty acids). Delivery of aqueous and particulate core materials by microcapsules was assessed by feeding clams LWMs containing an aqueous core of polymeric dye or a particulate core of oxytetracycline hemicalcium salt (OTC.HEM). The physical appearance and absence of core material in capsules observed in clam fecal strands suggested release and delivery of core materials in the clam's digestive system. Optimal methods for encapsulating and storing oxytetracycline were assessed. Oxytetracycline hydrochloride was most efficiently encapsulated (3.2 mg core/ 100 mg lipid) and retained (30%) as an aqueous core in LWMs produced by a double-emulsion process (double-emulsion microcapsules, DEMs). OTC.HEM was most efficiently encapsulated (7.4 mg core/l00 mg lipid) and retained (66% of initial encapsulated core material remained after 24 hours suspension in seawater) as a particulate in SMs. SMs containing OTC.HEM were most stable in storage, retaining 86% of their core after 5 weeks of storage as a wet paste. Freeze-drying of SMs containing particulate OTC.HEM increased initial leakage losses of core material, but did not the affect the stability of capsules during long-term storage. Freeze-drying of DEMs containing aqueous OTC.HCl also increased initial leakage loses of core material, but improved the stability of DEMs during long-term storage. / Graduation date: 1995

Ranchers in the high desert area of Eastern Oregon traditionally market their calves when they are weaned in late fall. This is the time when the market prices for calves are at a seasonal low. In this study the economic feasibility of various alternative management and marketing strategies for the utilization of range forage with a spring calving operation is determined. The operational objectives were (1) to determine the most profitable time and weight to market the spring-born calves, (2) to determine whether supplementary feeding of yearlings is economically feasible, (3) to explore the competitive relationship between cows and yearlings for limited range forage, and (4) to determine the combination of beef production and growing activities which will provide the highest net returns. Linear programming was used to determine the combination of activities that would maximize net returns subject to the constraint of forage quality and quantity. The quality and quantity of the range forage was determined by using data provided by the Squaw Butte Experiment Station, Burns, Oregon. All the basic data pertaining to the high desert area were obtained from Squaw Butte. The initial L. P. solution indicated the heifers should be sold March 1 at 600 pounds having been fed to gain 1.5 pounds per day while the steers were sold April 16 at 780 pounds, gaining 2.0 pounds per day. The cows earned a higher MVP for the limited resource, range forage, than could the yearlings either with or without supplementary feeding. In the second solution barley price was reduced from $50 to $45 per ton and the steers were sold April 16 at 780 pounds (same as initial solution). The heifers were sold June 16 weighing 900 pounds having been fed to gain 2.0 pounds per day. Supplementary feed was provided on the range for these heifers from April 16 to June 15. The study shows that the traditional management and marketing practice is not the most profitable alternative. The feed costs are less than the increase in income from feeding the animals to heavier weights. / Graduation date: 1972

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