Effects of dietary lysine intake during lactation on blood metabolites, hormones, and reproductive performance in primiparous sows

Effects of three dietary lysine (protein) concentrations during lactation o n metabolic state, protein metabolism, reproductive hormones, and performan ce were investigated in 36 primiparous sows. Sows were assigned randomly to one of three diets containing .4% (low lysine, LL), 1.0% (medium lysine, M L), or 1.6% (high lysine, HL) total lysine from intact protein sources. All diets contained 2.1 Meal NE/kg and exceeded the recommended requirements f or all other nutrients. Actual lysine intakes over an 18-d lactation were 1 6, 36, and 56 g/d for sows fed LL, ML, and HL, respectively. Fractional bre akdown rate of muscle was determined on d 4 and 15 of lactation by using a three-compartment kinetic model of 3-methylhistidine metabolism.. Increasin g lysine intake during lactation did not affect fractional breakdown rate o f muscle on d 4 of lactation but decreased it on d 15 (P < .05). Sows fed L L had a reduced number of LH pulses on d 12 and 18 (P < .05) and reduced se rum estradiol (E-2) concentration on d 18 of lactation compared with sows f ed ML and:HL treatments. However, LH pulses and E-2 concentrations were sim ilar between ML and HL treatments (P > .35). Increasing lysine intake incre ased serum urea nitrogen (SUN) and postprandial insulin concentrations (P < .05) during lactation but had no effect on plasma glucose concentrations ( P > .20). Sows fed HL had greater serum IGF-I on d 6 and 18 than sows fed M L (P < .05). Number of LH peaks was correlated with serum insulin concentra tion 25 min after feeding on d 6 and 18 (r = .31 to .41; P < .1) and pre- ( r =.33 to .46) and postprandial (r = .30 to .58) SUN concentrations (P < .0 5) during different stages of lactation. Results indicate that, compared wi th medium lysine intake, low lysine intake increased muscle protein degrada tion and decreased concentrations of insulin, SUN, and estradiol and LH pul satility. In contrast, high lysine (protein) intake increased SUN, insulin, and IGF-I, but did not increase secretion of estradiol and LH compared wit h medium lysine intake. Furthermore, nutritional impacts on reproduction ma y be mediated in part through associated effects on circulating insulin con centration.