Werner G. Jaffé
Instituto Nacional de Nutrición, Caracas, Venezuela
Reproduction studies with mice and rats kept on whole plant rations have been in progress in this laboratory for several years. In the first experiments, poor reproduction performance was observed (1), but later much more satisfactory results were obtained with a slightly modified diet (2). The only difference in the composition of the diets was that the salt mixture supplement used originally did not contain cobalt, whereas in the later experiments 0.2% CoCl2 was added to the salt complement. Because of the apparent influence of this small amount of dietary Co on reproduction, the present study was undertaken.
The rats used were of the Sprague-Dawley strain, raised in our laboratory; the mice were of the same albino strain used in the previous experiments. The rats had been kept on a whole plant ration for at least 3 generations prior to the start of the present experiments, and the mice for at least 5 generations. The animals were kept on the basal ration in common cages until females became pregnant. These were put in single screen-bottomed cages and given the respective experimental diets and water ad lib. Litters were reduced by random selection to 6 and weaned at the age of 28 days.
The composition of the basal diet was: solvent extracted soybean meal, 46; cornmeal, 46; sesame oil containing 0.2% percol11orphum oil and 0.2% wheat germ oil, 5; salt mixture II USP, 2; thiamine, 0.3 mg; riboflavin, 0.3 mg; calcium pantothenate, 2 mg; pyridoxin, 0.2 mg; choline hydrochloride, 100 mg; nicotinic acid, 2 mg; folic acid, 0.025 mg; biotin, 0.01 mg; inositol, 10 mg; PABA, 25 mg. The diet has been analyzed by microbiological methods and found to contain about 0.5ug/100g of vitamin B12 activity (2). Cobalt was supplied in the diet by adding 0.2% CoCl2 to. the salt mixture, or in the drinking water in a concentration of 0.2 mg% of CoCI2; when cobalt was injected, a 0.1% solution of CoCl2 in physiological saline solution was used, of which 0.2 ml was injected in each female 2-6 days prior to giving birth. A total of 130 litters of mice and 64 litters of rats was used in the present study.