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Low-selenium corn-soya diets (.04 ppm Se) supplemented with 0, .1, or .2 ppm was selenium (as Na2SeO3), in the presence or absence of 10 IU of supplemental vitamin E per kilogram, were fed to progeny of selenium-depleted breeder ducks. Ducklings from nondepleted breeders received selenium-adequate diets supplemented with 0, .1, or 1.0 ppm selenium from Na2SeO3. High mortalityyy, extensive muscle necrosis, and depressed early weight gain occurred in ducklings fed the low-selenium diets without added selenium. These effects were not prevented by supplemental vitamin E. None of the above manifestations of selenium deficiency were observed in ducklings fed the low-selenium diets supplemented with .1 or .2 ppm selenium. The addition of up to 1.0 ppm selenium to the adequate-selenium diet had no significant effect on mortality or weight gain. The selenium content of kidney, liver, and muscle increased with the addition of .1 ppm selenium to the low-selenium diet. Relatively small increases in tissue selenium concentrations resulted from the addition, to either diet, or levels of selenium in excess of the nutritional requirement. Glutathione peroxidase in plasma varied directly with selenium additions to the low-selenium diets. Plasma vitamin E increased as dietary vitamin E and selenium were increased. Dietary treatment had no significant effect on the concentration of ascorbic acid in plasma.

In a series of experiments, various chemotherapeutic agents administered in feed were evaluated for their efficacy against experimental Pasteurella anatipestifer (PA) infection in White Pekin ducklings. The feeding of medicated diets was started 3 days prior to challenge and continued throughout each experiment. Novobiocin and lincomycin, when fed at adequate concentrations, were the most effective medicaments tested. Mortality in treated groups was 0-18% compared with 45-92% mortality in controls. Sulfadimethoxine-ormetoprim, sulfaquinoxaline, and lincomycin-spectinomycin were moderately effective. Drugs that were not effective included chlortetracycline, tylosin-sulfamethazine, fosfomycin, furazolidone, nihydrazone, penicillin, bacitracin, and erythromycin. Six antibiotics were tested parenterally against experimental PA infection in another series of experiments. A single dose of an antibiotic was injected subcutaneously 5 to 6 hr after infection except in one experiment in which treatment was delayed until 24 hr after infection. When given 5 to 6 hr after infection, lincomycin-spectinomycin, penicillin-streptomycin, penicillin, oxytetracycline, and spectinomycin significantly reduced mortality. Gentamicin tested under the same conditions was ineffective. Drugs injected 24 hr after infection were not effective.

E ARLIER studies conducted in this laboratory have dealt with energy, protein and vitamin requirements of ducklings (Scott and Heuser, 1951, 1952;and Scott et al., 1959); little information is available on mineral requirements. Since rickets is uncommon in commercial ducks, it appears likely that the calcium and phosphorus levels used in commercial diets are adequate. These levels usually have been set somewhat higher than the 1.0% Ca and 0.45% available P which are the recommended levels for chickens. In view of the possible detrimental effects of excessive calcium and phosphorus levels, or improper ratios of calcium to phosphorus, not only upon the occurrence of rickets but also as etiological factors in leg weaknesses, it was considered desirable to determine the calcium requirement of young ducklings. The results of four experiments on the calcium requirement, conducted during the past four years, are presented in this report. EXPERIMENTALWhite Pekin ducklings were distributed at one day of age into pens with wire floors in an enclosed building equipped with forced-air heating. In experiments 1 and 2 which continued until the ducklings were 56 days of age, the ducklings were moved at 28 days to an unheated shed type building, open to the south where they were al-