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The purpose of the study was to develop a realistic method of determining the optimum replacement time of steers in a feedlot in which there are sequential feeding cycles. There are two models for steers developed and discussed in this paper. The first model optimizes the length of stay in the feedlot assuming that feedlot capacity is the limiting constraint. The second model optimizes the length of stay in the feedlot when working capital is the limiting constraint. A third model is developed to determine the optimum length of feeding time for market hogs in a feeding barn. An evaluation of each model is made. It is concluded that the cattle models have a limited use because of the high variability in performance. The hog replacement model is quite valid and can be used in a modern hog feeding enterprise. / Land and Food Systems, Faculty of / Graduate

Soybean meal-protected tallow has been commercially available in Canada for use in dairy rations, since 1975. The reported effects of feeding protected tallow to dairy cows have been variable and the prices of protected tallow supplements have been high. In view of the lower cost of canola meal relative to soybean meal in Canada, a study was undertaken to investigate the efficacy of feeding protected tallow made either from soybean meal or canola meal, to dairy cows in early lactation. Secondly, a comparison was made between the soybean meal-protected tallow and the canola meal-protected tallow. Twenty-seven cows from the University herd, comprised of 12 first-calf Holstein heifers, 3 Holsteins in their >2nd lactation, 4 Ayrshire heifers and 8 ≥2nd lactation Ayrshires, were used in a continuous feeding trial which was conducted from day of calving until the end of week 20 of lactation. Cows were randomly assigned within breed and lactation category (9 cows per treatment) to one of 3 isonitrogenous (16 % crude protein) concentrates: a) no protected tallow (control); b) 8 % soybean meal-protected tallow; or c) 8 % canola meal-protected tallow, which they received during weeks 1-15 (inclusive). From the beginning of week 16 until the end of week 20 all cows were fed a 16 % crude protein, post-treatment concentrate (no protected tallow). Throughout the 20-week trial the ratio of concentrates to cubes offered was maintained at 70:30 with feed intakes being ad libitum. Between weeks 13 and 16, 4 cows per treatment were assigned to a digestibility trial involving a 7-day total Collection of faeces and urine. Protected tallow rations produced significant increases over the control ration (P<.05) in the yields of milk, 4 % fat-corrected milk and milk fat, and protected tallow rations increased the efficiencies of conversion of gross energy, digestible energy, crude protein and digestible protein to milk, 4 % fat-corrected milk, solids-corrected milk and milk energy (P<.05). The apparent digestibility of ether extract and the concentration of plasma non-esterified fatty acids were significantly higher on rations with protected tallow (P<.05). Milk protein % was significantly reduced below the control level with rations containing protected tallow and rumen acetate and the acetate:propionate levels were also decreased. Protected tallow rations had no significant effect on the intakes of dry matter, gross energy, digestible energy, crude protein or digestible protein or on the apparent digestibilities of dry matter, organic matter, gross energy, nitrogen, acid-detergent fibre, ash, calcium, phosphorus or magnesium (P>.05). Also the yields of solids-corrected milk, milk gross energy and milk protein, the plasma glucose concentration and average daily gain were not significantly different, on rations containing protected tallow, compared with the control ration. There was no significant difference between the soybean meal-protected tallow ration and the canola meal-protected tallow ration for any parameter measured except apparent digestibility of ether extract which was significantly higher for the canola meal-protected tallow ration (P<.01). / Land and Food Systems, Faculty of / Graduate

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