Applied Animal Nutrition-I

EFFECTS OF PROLONGED UNDER OR OVER FEEDING OF BREEDING ANIMALS

• Animals given a sub-maintenance ration eventually show some reduction in fertility.
• In males this may be brought about by a decreased output of spermatozoa or by a smaller output of the accessory secretions.
• In females continued underfeeding leads to a cessation of ovarian function; the farm animals most likely to suffer in this way are heifers kept on inadequate rations during the winter feeding period. It should be stressed, however, that underfeeding has to be severe and prolonged to exert its full effect.
• Thus a bull kept on a starvation ration and losing weight at the rate of 0.9 kg/day was at the end of 14 weeks still capable of producing semen containing normal spermatozoa, but the production of fructose and citric acid in the accessory secretion was much reduced by this treatment.
• The evidence for a causative association between overfeeding and impaired reproductive ability is less convincing.
• Very fat animals frequently are sterile, but the two conditions, fatness and sterility, may both be effects of an endocrine disturbance, rather than other cause.
• Fatness and sterility occur together most commonly in sows, and also occur together frequently in show animals.
• Over-fat sows may continue to produce ova while failing to show signs of oestrus; it has been suggested that the oestrogens intended to be responsible for the latter are absorbed in the fat depots.