No abstract

Effects of three dietary lysine (protein) concentrations during lactation on metabolic state, protein metabolism, reproductive hormones, and performance were investigated in 36 primiparous sows. Sows were assigned randomly to one of three diets containing .4% (low lysine, LL), 1.0% (medium lysine, ML), or 1.6% (high lysine, HL) total lysine from intact protein sources. All diets contained 2.1 Mcal NE/kg and exceeded the recommended requirements for all other nutrients. Actual lysine intakes over an 18-d lactation were 16, 36, and 56 g/d for sows fed LL, ML, and HL, respectively. Fractional breakdown rate of muscle was determined on d 4 and 15 of lactation by using a three-compartment kinetic model of 3-methylhistidine metabolism. Increasing lysine intake during lactation did not affect fractional breakdown rate of muscle on d 4 of lactation but decreased it on d 15 (P < .05). Sows fed LL had a reduced number of LH pulses on d 12 and 18 (P < .05) and reduced serum estradiol (E2) concentration on d 18 of lactation compared with sows fed ML and HL treatments. However, LH pulses and E2 concentrations were similar between ML and HL treatments (P > .35). Increasing lysine intake increased 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 ML (P < .05). Number of LH peaks was correlated with serum insulin concentration 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 < .05) during different stages of lactation. Results indicate that, compared with medium lysine intake, low lysine intake increased muscle protein degradation and decreased concentrations of insulin, SUN, and estradiol and LH pulsatility. In contrast, high lysine (protein) intake increased SUN, insulin, and IGF-I, but did not increase secretion of estradiol and LH compared with medium lysine intake. Furthermore, nutritional impacts on reproduction may be mediated in part through associated effects on circulating insulin concentration.

Lactating, primiparous Landrace x Yorkshire sows were used to characterize LH secretion during lactation in sows that experienced an early (less than 9 d; n = 14) or late (greater than 15 d; n = 9) return to estrous postweaning and to evaluate the relationship between LH secretion and blood metabolites. Twenty-three sows were fed one of nine corn-soybean meal diets to achieve a matrix of lysine (15 to 45 g/d) and energy (6.5 to 16.5 Mcal of ME/d) intakes and a range in metabolite concentrations and return-to-estrus intervals. Blood samples for LH analysis were collected every 15 min for 6 h on d 0, 7, 14, 21, and 28 of lactation. Circulating concentrations of glucose, amino acids, insulin, triglycerides, urea N, and nonesterified fatty acids also were measured on d 7 and 21. Mean LH concentrations were .27 and .42 ng/mL at farrowing for sows with an early and late return to estrus, respectively, but decreased (P less than .01) to .12 ng/mL by d 7 in both early and late groups. Mean LH and number of LH peaks per 6 h increased linearly (P less than .01) from d 7 to 28 for early sows. Early sows had a higher LH mean and more LH peaks per 6 h on d 14, 21, and 28 than did late sows (P less than .05). Early sows had higher serum insulin on d 7 (P less than .05) and d 21 (P less than .01) than did late sows. Concentrations of other metabolites did not differ (P less than .10) between early and late sows.(ABSTRACT TRUNCATED AT 250 WORDS)

In order to study the sequence of hormonal changes that accompany the onset of puberty in the female rat, immature animals were sacrificed by decapitation between days 32 and 38, and plasma titers of gonadotropins, prolactin, and LHRH, and the hypothalamic content of LHRH were determined by specific radoimmunoassays (RIA). Animals were decapitated at 10:00 and 16:00 h throughout the pubertal period, the uterine weight was recorded, and the ovaries were inspected for signs of ovulation. Animals with the vagina closed were grouped according to the condition of the uterus as anestrus (A), early proestrus (EP) and late proetrus (LP), the uterus being unstimulated, dilated with some fluid, or ballooned, respectively. Vaginal opening was usually associated with ovulation and in most cases occurred at the end of the late proestrous phase. Animals were studied up to 3 days after vaginal opening and were grouped according to vaginal cytology. Uterine weight, taken as an index of estrogen secretion, was low during A, increased during EP, and reached a peak at LP, declining thereafter. Plasma LH and FSH were low from A until the afternoon of LP. At this time, uterine weight was maximal and both gonadotropins increased dramatically. The following morning (estrus), LH but not FSH, had returned to basal values. FSH returned to basal levels on the afternoon of estrus. Plasma prolactin was low in the morning during the entire period, but showed peaks on the afternoon, which reached a maximum at LP and declined thereafter following the pattern of changes in uterine weight. Plasma LHRH was uniformly low throughout the entire pubertal period, whereas hypothalamic LHRH content declined on the morning of estrus (day of vaginal opening). We suggest that the onset of puberty in the female rat is brought about by a gradual increase in estrogen secretion which, acting at the CNS-pituitary level, triggers a preovulatory proestrus-like surge of gonadotropins and prolactin.