Milk yield, suckling behaviour and milk ejection in the lactating rat nursing litters of different sizes.

Abstract

SUMMARY1. The quantitative relationship between the suckling stimulus and several sucklingdependent variables was studied in lactating rats.2. The intensity of the suckling stimulus, measured as the product of duration and number of pups suckling was in proportion to litter size for litters of one, ten or twenty-two pups.3. Pups in the litters of ten grew fastest. Single-pup litters grew most slowly, some not at all. Litter weight gain, corrected for inevitable losses, was used to estimate milk yield. Total milk yield was greater for litters of twenty-two to twentyfour pups than for litters of ten pups only in the first week. Milk yield for single pups was up to 7 % of the yield for ten pups. Milk yield per mammary gland sucked was similar for the larger litters but less for single pups.4. The number of milk ejections, measured as pup stretch reactions, in observation periods of 225 min, was similar for litters of ten and twenty-two to twenty-four pups, but less for single-pup litters.5. The suckling stimulus applied by single-pup litters inhibited ovarian growth less effectively than did the stimulus applied by larger litters.6. There was no change in serum osmolality during lactation. 7. It is concluded that litters of ten or twenty-two to twenty-four pups applied suckling stimuli of different intensities, but these had similar effects on the daily secretion rate of oxytocin, milk production and suppression of ovarian growth. Single-pup litters were less effective.

Limits to sustained energy intake VI. Energetics of lactation in laboratory mice at thermoneutrality

“…At the same time, warmer ambient temperatures provide a smaller gradient for the heat flow and, therefore, increase the duration of each nest absence (Scribner and Wynne-Edwards, 1994a). Frequent and prolonged maternal nest absence would affect the suckling behaviour involved in stimulation of milk production (Epstein, 1978;Russel, 1980;Knight et al, 1986). Consequently, the amount of milk produced would decrease.…”

Limits to sustained energy intake VII. Milk energy output in laboratory mice at thermoneutrality

“…The suckling stimulus induces the release of oxytocin and prolactin from the pituitary gland via a neuroendocrine reflex. Oxytocin is responsible for milk let-down and ejection, whereas prolactin, which is the most important lactogenic hormone, activates the transcription of RNAs for milk proteins and enzymes involved in the synthesis of milk fats and sugars (Russel, 1980;Barber et al, 1992;Flint and Knight, 1997). Consequently, frequent suckling (or milking) increases milk production, whilst forced weaning, or a gradual cessation of milk removal that occurs during natural weaning, initiates the process of mammary gland involution (e.g.…”

Developmental origins of obesity: a sympathoadrenal perspective

“…The exact role of pup nutrition per se, however, is uncertain as litter size influences both the quantity and the quality of milk produced by the mother. 53,54 The impact of litter size on SNS function in young adult animals was reported several years ago from this laboratory. 35 Although the animals reared in small litters were bigger than those reared in large litters, the impact on tissue NE levels (adjusted for differences in wet weight of tissue) was noted in some, but not all tissues.…”