The importance of tissue protein reserves to lactating females attempting to sustain milk output under conditions of severe dietary protein restriction was investigated using rats. Four experiments were carried out to study the effect of variation in repletion of tissue protein reserves on lactational performance, rates of body protein mobilisation and changes in tissue protein metabolism involved in promoting protein mobilisation. The extent to which body protein reserves were capable of maintaining milk quantity and quality under such conditions was also considered. The lactation performance of multiparous, female Sprague-Dawley rats, offered isoenergetic diets (21 MJ GE/kg DM), was assessed from growth of a standardised litter of 12 pups. Variation in repletion of protein reserves at parturition was achieved by applying a period of protein restriction during the latter half of gestation. Changes in body composition were estimated from carcass analysis and rates of protein mobilisation were derived from serial slaughter experiments. Tissue protein synthesis was estimated <i>in vivo</i> using a flooding dose of [<SUP>3</SUP>H] phenylalanine and tissue Na<SUP></SUP>+ , K<SUP></SUP>+ -ATPase activity was measured polarographically <i>in vitro</i>. Milk samples were obtained following injection of oxytocin. Females offered a high protein diet (215 gCP/kg DM) during lactation exhibited an increase in both feed intake and lactational performance while not utilising their body protein stores. However, in rats offered imbalanced feeds (low protein/high energy) such an increase in intake was not apparent and dams were forced to draw upon their endogenous protein reserves in an attempt to sustain milk production. Between 15 and 22% of body protein was lost by dams assumed to be 'Fully' protein replete at parturition. When dietary protein was limiting, reductions in the size of the protein reserve had a significant inpact on a female's ability to sustain milk production, and dams which were initially 'Fully' replete supported greater (P< 0.05) litter growth during early lactation, due to a greater endogenous protein supply and feed intake (P< 0.05), than their 'Depleted' contemporaries.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:660619 |
| Date | January 1993 |
| Creators | Pine, Andrew Paul |
| Publisher | University of Edinburgh |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://hdl.handle.net/1842/27194 |
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