title: Maternal protein reserves and their influence on lactational performance in rats. 3. The effects of dietary protein restriction and stage of lactation on milk composition.
abstract: The effects of severe protein restriction following parturition on the changes in rat milk composition during lactation were investigated using multiparous female Sprague-Dawley rats caged individually following mating and offered a high-protein diet (H; 215 g crude protein (N x 6.25; CP)/kg dry matter (DM)) ad lib. until parturition. Following parturition, half the females continued to receive diet H, whilst the remainder were offered a diet low in protein (L; 90 g CP/kg DM) ad lib. On days 2, 4, 8 and 12 of lactation groups of females from both dietary treatments were used to provide a milk sample. Milk samples were analysed for their lactose (enzymically), protein (binding to Coomassie blue), lipid (gravimetrically) and mineral (spectrophotometrically) contents. The milk lactose concentration of group H increased with stage of lactation (r2 0.85, P < 0.001). Such an increase was prevented by diet L, and from day 8 of lactation the milk lactose of group L was lower (P < 0.05) than in group H. Group H milk protein concentration did not change during lactation and averaged 90.7 mg/g. Dietary protein restriction reduced the milk protein concentration of group L so that on days 2, 4 and 12 of lactation it was lower (P < 0.05) than that of group H. On day 8 of lactation the milk protein concentration of group L had increased (P < 0.05) and was comparable with that of group H. For group H, milk lipid averaged 166.8 mg/g and was generally unchanged during lactation. Diet L increased (P < 0.01) the milk lipid concentration (205.5 mg/g) compared with diet H and this was also significant on days 4 and 8 of lactation (P < 0.05). Group L milk lipid concentration also increased between days 4 and 8 of lactation (P < 0.05). Milk Na concentration declined during lactation in both dietary groups (P < 0.01) but was unaffected by dietary treatment. Both milk Ca and P concentrations increased (P < 0.01) during lactation in both dietary groups, whilst protein restriction also increased the Ca and P concentrations (P < 0.05). Milk K and Mg concentrations were unaffected by dietary treatment or stage of lactation. This significant alteration in the milk composition of severely protein-restricted dams, while possibly favouring the disposal of greater quantities of energy-yielding nutrients, suggests that equations developed for the estimation of milk production in rats cannot be used under such conditions.
authors: Institute of Ecology and Resource Management, University of Edinburgh.
authors: A P
authors: AP
authors: Pine
authors: N S
authors: NS
authors: Jessop
authors: J D
authors: JD
authors: Oldham
mesh_terms: D000818:Animals; D001835:Body Weight; D004044:Dietary Proteins / Q000008:administration & dosage* / Q000378:metabolism; D004435:Eating; D005260:Female; D007774:Lactation / Q000502:physiology*; D007785:Lactose / Q000032:analysis; D008055:Lipids / Q000032:analysis; D008321:Mammary Glands, Animal / Q000033:anatomy & histology; D008892:Milk / Q000737:chemistry*; D008894:Milk Proteins / Q000032:analysis; D008903:Minerals / Q000032:analysis; D011247:Pregnancy; D051381:Rats; D017207:Rats, Sprague-Dawley; D013997:Time Factors
chemical_list: D004044:Dietary Proteins; D008055:Lipids; D008894:Milk Proteins; D008903:Minerals; D007785:Lactose