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To summarize, I have attempted to present evidence that the unselected thymocyte TCR repertoire has such a propensity to recognize MHC/peptide at high affinity that it is likely that, were tolerance induction to be invariably dominant over positive selection, all T cells would be deleted or anergized. If this is true it follows that positive selection must in fact be capable of being the dominant process. I have further suggested that the existence of peptides capable of antagonizing T-cell activation in the thymus could inhibit deletion, and that this might correspond to positive selection.

Pregnant beef cows were winter-fed (November 15 to calving) hay (24 cows), red clover silage (21 cows) or grass silage (52 cows). Blood samples were taken from each cow in December and February. A condition of congenital joint laxity and dwarfism was observed in 38% and 28% of calves born to cows fed red clover silage and grass silage, respectively. None of the calves born to hay-fed cows were affected by the condition. The congenital joint laxity and dwarfism was associated with a lower serum manganese concentration in silage-fed cows than in hay-fed cows. However, manganese concentrations were similar in red clover silage, grass silage and in hay. A lower bioavailability of manganese in silages other than in hay, resulting in an apparent manganese deficiency in silage-fed cows, is suggested as a possible factor contributing to the etiology of congenital joint laxity and dwarfism in calves.

Intramuscular injections of various levels of prostaglandin F(2alpha) were administered to 116 pregnant swine in three commercial herds and the University research unit on Day 111, 112 or 113 of gestation. Sixty-three percent of the treated animals farrowed during the working day immediately following treatment. The parturition time, birth weight, litter size, number of piglets weaned, growth of the piglets to weaning and subsequent rebreeding of the dams were comparable with the expected performance in the herds. The results indicated that prostaglandin F(2alpha) in doses ranging from 5 to 12.5 mg per animal were effective for induction of parturition in a substantial proportion of the treated animals. Successful induction of parturition could reduce the farrowing interval for batches, allow more supervision of farrowing, facilitate transfer of piglets from large to small litters and generally increase efficiency in the farrowing unit. This technique could have practical application in intensive swine production units.

Ten Yorkshire gilts were fed either 1.36 or .45 kg of a gestation diet per day from day 85 of gestation to farrowing for determination of the effect of feed restriction during late gestation on reproductive performance. All gilts consumed 1.36 kg/day from day of breeding to day 85. Feeding level of affected (P < .001) gestation weight during the experimental period such that the restricted gilts lost 3.2 kg while control gilts gained 15.0 kilograms. Gestation period tended to be shorter (115.4 vs 113.6 days) and total litter weight tended to be lower (10.6 vs 8.6 kg) in the restricted group although the differences were not statistically significant. Litter size was similar (9.6 vs 9.4 pigs/litter). Restriction of gestation feed significantly reduced individual piglet birth weight (1.1 vs .9 kg), liver weight (32.9 vs 26.0 g) and skeletal muscle weights (8.9 vs 7.1 and 2.1 vs 1.6 g for the longissimus and semitendinosus muscles, respectively). Piglets born to restricted dams also had reduced liver and muscle glycogen concentrations (15.1 vs 13.9, 10.1 vs 9.4 and 9.9 vs 9.4 g/100 g of wet tissue for the liver and longissimus and semitendinosus muscles, respectively), lower (P < .05) blood pH (7.31 vs 7.23) and higher (P < .01) blood lactate levels (43.8 vs 71.3 mg/100 ml).

Levels of lactoferrin, an Fe-binding protein with bacteriostatic properties, were determined in the colostrum and milk of Yorkshire sows during a 21-d lactation. Lactoferrin levels averaged 1,100 to 1,300 micrograms/ml near the time of farrowing, then declined sharply during the first week of lactation. Concentration of lactoferrin showed considerable variation among sows, but not among teat positions (anterior to posterior). A method for isolating high purity swine lactoferrin is described.

Pregnant gilts and sows were given a single intramuscular injection of from 5-10 mg of prostaglandin F2alpha-tromethamine salt (dependent on liveweight) on day 111, 112 or 113 of pregnancy (first day of estrus = day 0) to induce parturition. When injected on day 111, 44% of the pigs farrowed within 40 hours compared with 93% injected on days 112 or 113. The mean time to the induced parturition was 27.3 +/- 4.7 hours. Signs of discomfort were observed during the first hour posttreatment but there were no apparent effects on lactation or on the mothering ability of the dams after farrowing.

During the harvesting of the 1980 Ontario white winter wheat crop, producers noticed pink discoloration on kernels; this was attributed to Fusarium mold. Grain elevator and boatload samples were analyzed for mycotoxin contamination. Vomitoxin levels up to 8 ppm were detected in samples from southwestern Ontario. Other suspected mycotoxins were either nondetectable or present in trace amounts. Fusarium-contaminated wheat and clean wheat were added to swine and poultry diets for feeding trials. Feed refusal and decreased weight gains were observed in pigs fed diets containing 0.3 and 0.7 ppm vomitoxin, but there was no vomiting or other ill effects. Adult roosters and laying hens fed diets containing vomitoxin levels similar to those of the pig diets did not show any overt toxicological effects. Chemical analysis of suspected field cases of vomitoxin-contaminated feed did not reveal high vomitoxin levels.

The effect of nutritional restriction and rehabilitation imposed between 5 and 35 d and 35 and 166 d of age, respectively, on body and tissue growth were investigated in 96 Yorkshire pigs from 12 litters. One-half of the pigs were allowed to suckle continuously until weaning (fully fed, FF); the remainder were removed from the sow for 16 h of each 24 h period (1600 to 0800 h), during which time they received only water (restricted feeding, RF). All pigs were fed ad libitum from 35 d of age. Although significantly lower body and tissue (liver, kidney and gastrocnemius muscle) weights were observed in the RF pigs at 35 and 70 d of age, by 166 d, because of compensatory growth between 35 and 166 d, the difference in body and muscle weights between the two groups of pigs (RF and FF) was reduced to 5%, but the difference in kidney and liver weight remained as high as 15 and 9%, respectively. Total DNA, RNA and protein in the tissues examined were also lower in the RF pigs at 35 and 70 d of age, but increased after ad libitum feeding to more than 90% of the corresponding value in the FF pigs by the time they reached 166 d of age. The results of these measurements and the comparison of the protein: DNA ratios of the tissues indicated that growth retardation in the RF pigs was associated with reduced cell proliferation in liver and kidney and nuclear proliferation in muscle rather than any decrease in cell (or fiber) volume. Percentage of fat was lower while percentage of protein was higher (on a dry matter basis) in the RF pigs than in the FF pigs at 35 d of age. No significant difference in fat and protein content in the carcasses between the RF and FF pigs at 70 or 166 d of age or 90 kg body weight was noted. The carcass of intact males had more protein and less fat than that of females.