MATERNAL PROTEIN RESERVES AND THEIR INFLUENCE ON LACTATIONAL PERFORMANCE IN RATS

To determine the contribution of tissue protein reserves to lactationa l performance, multiparous female Sprague-Dawley rats were mated, cage d individually and offered a diet high in protein (215 g crude protein (N x 6.25; CP)/kg dry matter (DM);H) nd lib. until day 12 of gestatio n. subsequently half the rats continued to receive diet H while the re mainder were offered a diet low in protein (65 g CP/kg DM;L) until par turition. This treatment aimed to produce a difference in carcass prot ein at parturition. On day 1 of lactation females were allocated to ei ther diet H or a low-protein diet (90 g CP/kg DM;L(2) offered until da y 13 of lactation, giving four lactation treatment groups HH, HL(2), L H and LL(2). Groups of females were slaughtered on days 2 and 12 of ge station and days 1 and 13 of lactation and carcass and major organs we re analysed. Weight gain of standardized litters was used as an indica tor of lactational performance. Maternal carcass protein contents at p arturition were 43.5 (SE 1.2) and 38.7 (SE 0.8) g (P < 0.01) for diets H and L respectively. During lactation there wits little change in ca rcass protein content of HH rats while LH rats appeared to replenish t heir depleted reserves. Food intake or lactational performance did not differ between these two groups. HL(2) and LL(2) rats lost carcass pr otein with HL(2) rats losing more than LL(2) rats (P < 0.05). Intake a nd lactational performance were reduced compared with that on diet H ( P < 0.05) but for the first 6 d of lactation were both greater (P < 0. 05) for diet HL(2) than for diet LL(2). All four groups showed a consi derable loss of body fat during Lactation which was not affected by di et. The ability of HL(2) rats to catabolize more protein and consume m ore food allowed them to sustain a greater lactational performance. Pr evious maternal protein depletion had no influence on lactational perf ormance as long as an adequate supply of dietary protein was provided.