Interactive environmental and genetic effects on longevity in the male rat: litter size, exercise, electric shocks and castration.

The effects on longevity of manipulating litter size during rearing and of postweaning forced exercise were observed in intact and castrated male rats. Random-bred sib quintets of newborn littermates were reared in reduced litters or normal litters (5 or 6, or 10-12 young, respectively). The quintets were split into five postweaning treatments: untreated (control), exercised (forced to run by electric shocks), shocked (without exercise), castrated, and castrated and exercised. Reduced litter size increased weaning weight from 46 to 56 g and diminished mean longevity from 724 to 620 days. The decrease in longevity due to reduced litter size was greater in the control (204 days) than in the other postweaning treatments (42 to 142 days). The postweaning treatments affected longevity only in the reduced-litter males; in these, exercise and mere shocks appeared to increase longevity. The variation in longevity among quintets was large and the expression of genetic longevity interacted with the treatments. The regression of individual on mean sib longevity was .89 in the castrates but only .10 in the controls; in exercised and shocked males it was .58 in normal-litter but only .09 in reduced-litter sibs indicating an interaction between pre- and postweaning treatments. The implications of the results on the interpretation of longevity studies are discussed.

Effects of selenium and vitamin E on incidence of retained placenta.

In a series of experiments over 3 yr, relatively low doses of selenium and vitamin E were injected intramuscularly 3 wk prepartum to pregnant Israeli-Holstein dairy cows in a high-producing herd (9000 kg milk/yr) with a history of retained placenta in 17% of the primiparous and 28% of the multiparous animals, as recorded for the 12 mo preceding the study. Selenium ranged from .035 to .109 ppm in the prepartum diet and from .160 to .200 ppm in the postpartum diet. Doses of selenium ranging from 2.3 to 23.0 mg reduced the incidence of retained placenta in 186 primiparous and in 428 multiparous to 7 and 15%, which was half of that of controls. Low doses of selenium (2.3 to 4.6 mg) tended to be more effective than higher ones. Selenium alone was at least as effective as a combination of selenium and vitamin E. Dosage, timing, mechanism, and interactions of selenium with other factors in reducing the incidence of retained placenta need clarification.

The effect of sodium chloride ingestion on food intake and on fat deposition in male rats.

1. A 21 d slaughter trial was done using weanling male rats offered sodium chloride added at 10, 20 and 30 g/kg to a nutritionally adequate, control diet containing 13 g NaCl/kg, or added to the drinking-water at 5, 10 or 15 g NaCl/l. Food and drinking-water with or without NaCl were offered ad lib. and their intakes were measured. 2. NaCl in the food reduced food intake by 10-15%; NaCl in solution reduced food intake only when added at the 15 g/l level; the reduction was 25%. 3. NaCl increased the fluid intake of the rats; for NaCl in the food the increments ranged from 23 to 44%; for NaCl in the drinking-water they ranged from 44 to 229%. 4. Body fat was significantly reduced by 20 and 30 g NaCl/kg added to the control diet, indicating a reduction in the efficiency of fat synthesis. Comparable amounts of NaCl taken in the drinking-water had a negligible effect on fat deposition. 5. It is suggested that NaCl in the food produces hypodipsia, i.e. a failure to drink an optimal amount of water, causing changes in the electrolyte balance which reduce food intake and progressively reduce the efficiency of fat synthesis.