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Nutritional Studies on Rats on Diets Containing High Levels of Partial Ester Emulsifiers¹

II. Reproduction and Lactation

Food Research Laboratories, Inc., Long Island City, New York

Breeding studies were undertaken in successive generations of rats on diets containing partial ester emulsifiers (Myrj 45 and 52, Span 60, and Tween 60, 65 and 80) to determine whether their chronic ingestion at levels up to 20% might induce cumulative or subtle effects manifested only under the conditions of physiological stress thus imposed. The responses were assessed, inter alia, in terms of indexes representing the proportions of matings resulting in pregnancy (fertility), pregnancies resulting in live litters (gestation), young remaining alive at 4 days (viability), nurslings weaned in relation to the number alive at 4 days and their weights at weaning (lactation).

On the average, 7 out of 10 matings were successful in both control and emulsifier groups, regardless of the level of dietary supplementation. Practically all pregnant rats cast live litters. The reproduction and lactation responses in all emulsifier groups at the 5% level were no different from those of the controls. Probably because of maternal neglect, survival of newborn litters was somewhat diminished in several of the emulsifier groups at the 10% level (Myrj 45, Span 60, and Tween 65) and in all of them at 20%. At the highest level some impairment in lactation efficiency was evidenced in most groups by the lower weaning weights; and in the Myrj 45, Tween 65, and mixed emulsifier groups also by greater mortality of the nurslings.

Similar responses with respect to survival and lactation were noted in the two succeeding generations. Despite the fact that the general level of reproductive performance (in the Primex as well as emulsifier series) was somewhat lower in the third generation, the effects noticeable particularly at the 20% dosage levels of emulsifiers were not markedly more severe in the third than in the initial generation.

Increasing the fat level in the basal diet from its original concentration of 4% by adding 9% of Primex, had little if any effect on the proportion of successful matings in the 20% emulsifier groups. However, better survival of the young was observed in the Myrj 45, Span 60, Tween 60, and Tween 80 groups following the addition of fat. This suggests that the presence of more nearly normal levels of dietary fat would diminish such adverse effects as might be induced by the excessively high concentration of "undiluted" emulsifier in these experimental diets.

Manuscript received 9 March 1956.