Estradiol feedback inhibition of luteinizing hormone concentrations in the anestrous sow

The suppressive effects of exogenous 17 beta-estradiol (E2) on LH concentrations in sows that remained anestrus following weaning and in those that returned to estrus were evaluated. Four anestrous and four cyclic sows were treated subcutaneously with silastic implants containing E2 at 13 d after ovariectomy (d 0). Three anestrous and six cyclic sows received silastic implants without E2. Blood was collected at 6-h intervals from d -1 to d 12 and at 15-min intervals for 8 h on d -1, 2, 7 and 12. Sows were treated with 1 microgram GnRH/kg BW at the completion of each 8-h frequent sampling period. Blood was collected at intervals of 10 to 30 min for 3 h after GnRH treatment. Concentrations of E2 remained less than 5 pg/ml in sham-treated sows and were between 20 and 25 pg/ml in E2-treated females. Pulsatile LH concentrations was similar between anestrous and cyclic sows prior to implant treatment. Sham-treated anestrous sows had greater (P less than .05) pulse frequency and mean LH concentrations than E2-treated anestrous sows on d 2, 7 and 12. Differences in pulsatile LH concentrations between E2-treated and sham-treated cyclic sows were not detected. Pulse frequency was less (P less than .05) in E2-treated anestrous sows than in E2-treated cyclic sows on d 7 and 12. Peak LH concentrations were greater (P less than .05) in E2-treated cyclic sows than in E2-treated anestrous sows at each GnRH challenge. These results suggest that the hypothalamo-hypophyseal axis is more sensitive to the negative feedback effects of E2 in anestrous sows than in cyclic sows. In addition, chronic E2 treatment reduces pituitary responsiveness to GnRH to a greater extent in anestrous than in cyclic sows. Failure to return to estrus in swine may be due, at least in part, to an increased sensitivity of the hypothalamo-hypophyseal axis to the negative feedback effect of estradiol.     

Impact of amino acid nutrition during lactation on luteinizing hormone secretion and return to estrus in primiparous sows.

The impact of the dietary amino acid regimen of primiparous sows on LH secretion and weaning-to-estrus interval was evaluated. Thirty-six sows, nursing litters of 13 pigs, were allocated daily 6 kg of a corn-soybean meal diet containing a high (HP, 1.20% lysine) or low (LP, .34% lysine) protein content during a 23-d lactation. Dietary lysine concentration was achieved by altering the ratio of corn and soybean meal in the diet. Plasma LH, ACTH, and estradiol-17beta were evaluated at 15 min, hourly, and at 6-h intervals, respectively, during 6-h periods on d 0, 5, 10, 15, and 20 of lactation. Sows were checked daily for estrus from weaning to 45 d postweaning. Sows fed the LP and HP diets consumed 4.41 and 4.98 kg of feed daily during lactation. The LP sows weighed less (P < .05), had lighter (P < .05) litters at weaning, and had (P < .05) extended weaning-to-estrus intervals. Mean and baseline LH concentrations and LH pulses/6 h were lower (P < .01) in LP sows, and the differences between LP and HP sows were established by d 10 of lactation. Plasma estradiol and ACTH concentrations were not altered by diet. Mean LH concentrations on d 5 and 10 of lactation were correlated (r = -.54 and -.56, respectively, P < .01) with weaning-to-estrus interval. Also, mean LH concentrations on d 10 were correlated (P < .05) with the magnitude of dietary lysine deficiencies relative to demand for milk synthesis on d 0 to 5 and d 5 to 10 (r = -.39 and -.49, respectively). Inadequate dietary amino acid intake in sows during early lactation results in lower LH secretion by d 10 postpartum and is associated with increased weaning-to-estrus interval.     

Dietary energy source at two feeding levels during lactation of primiparous sows: I. Effects on glucose, insulin, and luteinizing hormone and on follicle development, weaning-to-estrus interval, and ovulation rate

Our objective was to study the effects of dietary-induced insulin enhancement during and after lactation on the reproductive performance of primiparous sows. During a 21-d lactation period, 48 sows were allotted to a 2x2 factorial experiment. Treatments were feeding level (high or low; 44 MJ or 33 MJ NE/d) and dietary energy source (fat or starch). After weaning, all sows received the same amount of feed (31 MJ NE/d from weaning to estrus and 17.5 MJ NE/d from breeding until slaughter) of the same energy source as fed during lactation. On d 7, 14, and 21 of lactation and d 22 (weaning), blood samples were taken every 12 min for 12 h and analyzed for plasma glucose, insulin, and LH. Sows were slaughtered on d 35 of the subsequent pregnancy, and ovulation rate was assessed. During lactation, postprandial plasma glucose and insulin concentrations were higher for sows fed the starch diet than for those fed the fat diet (P<.001), whereas feeding level had no effect. Basal and mean LH concentrations were not affected by treatments. The LH pulse frequency on d 7 of lactation was greater for sows fed the starch diet than for those fed the fat diet (.52 vs .17 pulses/12 h; P = .03). The high compared with the low feeding level resulted in a greater LH pulse frequency on d 21 of lactation (.89 vs .47 pulses/12 h; P = .05) and on d 22 (8.63 vs 5.77 pulses/12 h; P = .02), in a higher percentage of sows that exhibited estrus within 10 d after weaning (96 vs. 63%; P = .01), and a tendency for a higher ovulation rate (18.0 vs. 16.2; P = .09). Plasma glucose and insulin concentrations were not related to any of the LH traits. The LH pulse frequency after weaning was related to the weaning-to-estrus interval (WEI) and was best explained by a linear-plateau model. In sows fed the low feeding level, follicle size after weaning was correlated with LH pulse frequency after weaning and with the WEI, whereas in sows fed the high feeding level these correlations were not significant. Our results indicate that an improved dietary-induced insulin status during and after lactation does not overcome the inhibitory effects of lactation on subsequent reproduction at any of the feeding levels.     

Dietary energy source at two feeding levels during lactation of primiparous sows: II. Effects on periestrus hormone profiles and embryonal survival

Our objective was to study the effects of dietary energy source (fat or starch) on periestrus hormone profiles and embryonal survival in primiparous sows. During lactation, 48 primiparous sows were fed either a starch-rich or a fat-rich diet, at either a high (44 MJ NE/d) or a low (33 MJ NE/d) feeding level. After weaning, all sows received the same amount of feed (31 MJ NE/d from weaning to estrus and 17.5 MJ NE/d from breeding to slaughter) of the same dietary energy source fed during lactation. Around estrus, blood samples were taken to analyze the preovulatory LH surge, estradiol (E2), and progesterone (P4). Sows were inseminated on each day of standing estrus. On d 35 after last insemination, all 35 pregnant sows were slaughtered and their reproductive tracts were removed. The number, weight, and length of the embryos and placentas were determined as well as the weight and length of the uterus. The LH, E2, and P4 profiles were similar for the treatment groups, except for the E2 levels at 16, 12, and 8 h before the LH surge, which were lower in the sows fed the fat-rich diet at a low level. Ovulation rate tended to be higher in sows fed the high compared to the low feeding level during lactation (18.0 vs. 16.2; P = .09), but the number of total and viable embryos as well as embryonal survival rate were not influenced by the treatments. Neither uterine length and weight nor length and weight of the embryos and placentas were affected by treatments. However, after removal of the embryo-placental units, uterine weight was greater in sows fed the high than in those fed the low feeding level during lactation (1.8 vs. 1.6 kg; P = .03). Plasma insulin concentration during lactation was not related to any of the uterine, placental, or embryo traits. Mean progesterone concentration between 24 and 250 h after the LH surge was positively correlated with embryonal survival. Differences in progesterone concentration between sows with high and low embryonal survival were evident from 172 h after the LH surge. From the present study, we conclude that altering feeding level during lactation or dietary energy source from farrowing until d 35 of subsequent pregnancy did not affect embryonic development and embryonal survival.     

Reproductive, metabolic, and endocrine responses to feed restriction and GnRH treatment in primiparous, lactating sows

The current experiment was carried out to determine whether exogenous GnRH treatment in primiparous, lactating sows undergoing feed restriction would improve reproductive performance after weaning. Sows were allocated to one of three treatments: AA sows (n = 8) were fed to appetite throughout a 28-d lactation, AR (n = 12) and AR + GnRH (n = 12) sows were fed as AA sows from farrowing to d 21 of lactation, and feed intake was reduced to 50% of the ad libitum intakes from d 22 to 28. The AR + GnRH sows received 800 ng of GnRH i.v. every 6 h from d 22 to 28 of lactation, and AA and AR sows received saline. Sow weight, backfat, and litter weight were recorded weekly. Within 2 d after farrowing, litter size was standardized to 8 to 10. At d 17 of lactation, an indwelling jugular catheter was surgically implanted in each sow. Blood samples were taken for characterization of plasma LH, FSH, insulin, IGF-I, and leptin by RIA at d 21 and before and after weaning on d 28 of lactation. After weaning, all sows were given ad libitum access to feed, checked for onset of standing estrus twice daily with mature vasectomized boars, and inseminated 12 and 24 h after onset of standing estrus with pooled semen from the same fertile boars (3 x 10(9) sperm/AI). After breeding, feed allowance was reduced to NRC (1988) requirements for gestation. At d 28 +/- 3 of gestation, sows were killed and ovulation rate and embryo survival were determined. Restricted sows lost more weight during lactation than AA sows (P < .02). During the period of feed restriction, plasma IGF-I and postprandial insulin and leptin in AR and AR + GnRH sows, and LH pulse frequency in AR sows, were lower than those in AA sows (P < .04). Associations (P < .004) between plasma insulin and leptin and between leptin and mean LH concentrations were established. The LH pulse frequency in AR + GnRH sows did not differ from that in AA sows before weaning. After weaning, maximum, mean, and minimum LH concentrations in the AA and AR sows, and FSH concentrations in AR sows, increased (P < .05) in response to weaning. Paradoxically, GnRH treatment in lactation seemed to suppress the expected LH and FSH responses to weaning. Ovulation rate and embryo survival were not different among the three groups. In conclusion, although exogenous GnRH therapy restored LH secretion in feed-restricted sows, it did not improve overall reproductive performance.     

Steroid hormone and luteinizing hormone concentrations in the anestrous sow.

This investigation characterized serum concentrations of luteinizing hormone (LH), estradiol-17 beta (E2), progesterone (P4) and cortisol (C) in anestrous sows. Twenty-two sows that had not returned to estrus within 45 days after weaning (anestrous sows), and ten sows that had returned to estrus within seven days following weaning (cyclic sows) were nonsurgically fitted with indwelling jugular vein cannulae. Blood samples were collected at 6 h intervals for seven days and at 15 min intervals for 8 h on the fifth day after cannulation. Serum LH concentrations were determined in all samples, while C, E2 and P4 levels were quantitated in serum collected at 6 h intervals. Serum P4 concentrations in anestrous sows were consistently less than 0.5 ng/mL, and E2 levels ranged from 10 to 19 pg/mL. Concentrations of LH remained less than 1.0 ng/mL in anestrous sows, whereas a preovulatory LH surge was observed in five of ten cyclic sows. There was a circadian rhythm in mean C levels with C peaks occurring at 0600 or 2400 h and nadir levels observed at 1200 and 1800 h. Few differences in C levels were detected between anestrous and cyclic sows. It was evident that anestrous sows did not exhibit cyclic or predictable variations in steroid hormone concentrations. Unfortunately, the results of this study failed to elucidate the endocrine pathogenesis of the anestrous sow.     

Influence of litter size on metabolic status and reproductive axis in primiparous sows

This study on primiparous sows was designed to 1) determine the impact of nursing a large litter on LH secretion and follicular development, and 2) investigate the metabolic adaptations by which milk yield increases with litter size. At farrowing, crossbred, primiparous sows were assigned to 1 of 3 experimental groups differing in litter size and feed allowance. Sows with 13 or 14 piglets (13AL, n = 7) were fed ad libitum. Sows with 7 piglets were fed ad libitum (7AL, n = 6) or were feed-restricted (7R, n = 8). The restriction was based on the estimated energy deficiency for the 13AL sows. On d 9 +/- 1 of lactation, a jugular catheter was surgically implanted. Serial blood samplings and glucose tolerance tests were performed in mid- and late lactation. Sows were slaughtered 3 d after weaning, and ovarian characteristics were recorded. During lactation, the 7AL sows lost no or little body reserves, and their estimated energy balance was near zero. The 13AL and 7R sows exhibited similar negative energy balances and similar losses of backfat and estimated lipid content. Litter growth rate was greater (P < 0.05) in the 13AL than in the 7AL and 7R groups. After weaning, the volume of the largest 14 follicles was smaller (P < 0.05) in sows nursing 13 or 14 piglets than in sows with 7 piglets. Plasma concentrations of LH and LH pulse frequency did not differ between groups (P > 0.1). The longer glucose half-life on d 16 than on d 27 of lactation (22.5 vs. 18.8 min; P < 0.05) indicated a lower glucose tolerance in mid- than in late lactation. The area under the insulin curve was greater in the 7AL than in the 13AL sows (P = 0.08) and intermediate in the 7R group, with no differences in glucose profiles. This led to the suggestion that the 7AL sows were more resistant to insulin than the 13AL sows. In all groups of sows, follicular development after weaning was correlated with LH secretion in midlactation. Active follicular development was associated with prolonged secretion of insulin in response to glucose challenge. Our results show that besides litter size, a sow's metabolic status in lactation influences follicular maturation after weaning and also indicate that the metabolic adaptations by which primiparous sows nursing large litters increase litter growth rate and body reserve mobilization do not involve an accentuated peripheral insulin resistance.     

Duration of lactation,endocrine and metabolic state,and fertility of primiparous sows

The objectives of this study were to determine factors affecting the reproductive performance of primiparous sows early weaned (EW; n = 35) at d 14 or conventionally weaned (CW; n = 35) at d 24 of lactation. Sow BW and backfat were recorded at farrowing, weekly until weaning, and at standing heat. Feed intake was controlled throughout lactation to standardize nutritional effects on subsequent reproductive performance. Litter size was standardized across treatments within 48 h after farrowing, and litter weight was recorded until weaning. In subsets of sows, blood samples were collected from 10 h before to 10 h after weaning, and then every 6 h until ovulation. Sows were heat checked twice daily and bred at 24-h intervals during standing heat using pooled semen. Ultrasonography every 6 h determined time of ovulation. Sows were either slaughtered within 24 h after ovulation to assess ovulation rate, fertilization rate, and embryonic development in vitro, or at d 28 of gestation to determine ovulation rate and embryonic survival. Compared with CW sows, EW sows had more backfat at weaning (15.9 +/- 0.5 vs. 14.7 +/- 0.5 mm; P < 0.001). Also, CW sows tended to lose more BW and to have lower IGF-I concentrations, indicating poorer body condition. Duration of lactation did not affect ovulation rate (EW = 17.6 +/- 0.7; CW = 18.7 +/- 0.6), fertilization rate (EW = 96.0 +/- 2.2; CW = 88.2 +/- 4.7%), or embryo survival to d 28 (EW = 62.5 +/- 4.5; CW = 63.1 +/- 5.0%). There was a marginal effect of duration of lactation on weaning-to-estrus interval (EW = 120 +/- 3; CW = 112 +/- 3 h; P < 0.06) and duration of estrus (EW = 52.4 +/- 2.3; CW = 46.3 +/- 2.2 h; P < 0.08). Overall, embryonic survival, not ovulation rate, seems to be the limiting factor for potential litter size in the second parity. Although fertility in both EW and CW sows studied was compromised, endocrine and metabolic data indicate that the mechanisms affecting reproductive performance may differ between the two weaning systems. The LH, FSH, and estradiol data from the EW sows are characteristic of animals with limited follicular development and incomplete recovery of the hypothalamic-pituitary-ovarian axis; consequently, the integrity of the uterine environment may be adversely affected and limit embryonic survival. In CW sows, variability in metabolic state seemed to be the key factor limiting the fertility, again adversely affecting embryonic survival.     

The influence of ovariectomy on luteinizing hormone concentrations in anestrous and cyclic sows

In an effort to determine whether anestrus in swine is due to aberrant ovarian feedback control of gonadotropin release, this study contrasted the influence of ovariectomy on LH concentrations in serum of anestrous sows and in sows that returned to estrus following weaning. Blood samples were collected at 6-h intervals from 7 d prior to until 4 d after ovariectomy of 22 anestrous and 24 cyclic sows. Blood samples also were collected at 15-min intervals for 8 h at 2 d prior to and 2 d after ovariectomy. Sampling at 6-h intervals continued until 12 d after ovariectomy and additional 8-h windows of 15-min samples were taken at 7 and 12 d after ovariectomy of seven anestrous and nine diestrous sows. Mean LH concentrations and LH pulse frequencies were greater (P less than .05) 2 d after ovariectomy than 2 d prior to ovariectomy in both anestrous and diestrous sows. Mean pulse amplitude had increased by 2 d after ovariectomy in anestrous sows but did not change in cyclic sows. Baselines as determined from the mean of all LH measurements excluding pulses, remained the same in both anestrous and diestrous sows at 2 d after ovariectomy. Pulse frequency, pulse amplitude, and mean LH concentration were greater (P less than .05) in both anestrous and diestrous sows at 7 and 12 d after ovariectomy than at 2 d prior to and 2 d after ovariectomy. Pulse amplitude on d 7 and 12 after ovariectomy decreased (P less than .05) in both anestrous and diestrous sows relative to those observed at earlier times.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effect of lactation and rebreeding phase energy intake on primiparous and multiparous sow performance

Fifty-three primiparous sows were used to study the effects of a high-energy, fat-supplemented diet on sow lactation and rebreeding performance. Sows received either a low [Lo, 12.5 Mcal metabolizable energy (ME)/d] or high (Hi, 16.0 Mcal ME/d) energy sorghum-soybean diet during a 28-d lactation. At weaning, sows were randomly allotted, within lactation treatment, to a low (lo, 5.54 Mcal ME/d) or high (hi, 9.61 Mcal ME/d) energy sorghum-soybean diet until the day of first postweaning estrus. Primiparous sows fed Lo weaned larger (P less than .05) litters than sows fed Hi; however, average pig weight was not affected by lactation treatments. Primiparous sows fed Hi had more backfat at weaning (P less than .01) than Lo sows. In contrast, sow weight was not affected by dietary treatments. Neither lactation nor rebreeding treatments influenced days to rebreeding; however, an interaction (P less than .01) was observed. Mean days from weaning to rebreeding for Lolo, Lohi, Hilo and Hihi sows were 10.0, 7.6, 6.9 and 17.1, respectively. Forty sows were maintained on the same dietary treatments during their second parity. Sows receiving Lo during their second parity farrowed and weaned more (P less than .05) pigs than Hi sows. Multiparous sows fed Hi nursed heavier (P less than .05) pigs on d 21 of lactation and at weaning compared with Lo sows. Sows fed Hi were heavier (P less than .05) and had more (P less than .01) backfat at weaning of their second litter compared to Lo sows. Days to postweaning estrus were not affected by lactation or rebreeding diets. Mean length of the second parity rebreeding interval for Lolo, Lohi, Hilo and Hihi sows was 6.2, 10.2, 7.0 and 10.5 d, respectively. These results suggest that feeding levels during lactation of 12.5 Mcal ME/d or higher supported adequate rebreeding performance. Postweaning feeding levels did not influence days to first estrus. Feeding a high energy diet continuously throughout the lactation and rebreeding phases in primiparous sows may lengthen the postweaning interval to estrus.     

Effects of Feeding Level During Lactation on FSH and LH Secretion Patterns, and Follicular Development in Primiparous Sows

In the primiparous lactating sow undernutrition affects LH, but the effect on FSH is less clear. This study was conducted to investigate the effect of ad libitum (AL; n = 5) and restricted (RE; 70% of the AL feed; n = 5) feeding on the secretion patterns of FSH and LH, and on follicular development in primiparous lactating sows. Body side fat thickness (BSFT) was measured prior to farrowing and at weaning on day 21 postpartum (pp). Sows had an intravenous catheter fitted on day 6 or 7 pp. Blood samples were taken on days 12, 15 and 18 pp, every 15 min starting at 0700 h for 11 h, and plasma analysed for FSH and LH by radioimmunoassay (RIA). Daily transcutaneous ultrasonography of the ovaries was performed between days 10 and 20 pp to monitor follicular growth. Reduction in BSFT was higher in RE than in AL sows (p < 0.05). Mean and basal LH were significantly higher in AL than in RE sows on days 12 and 15 pp. (p < 0.05), and LH pulse frequency tended to be higher (p < 0.1). Mean FSH was higher in AL than in RE sows on days 15 and 18 (p < 0.05), and had a tendency to be higher on day 12 (p = 0.1). Follicle size increased in AL sows between days 10 and 20 of lactation (p < 0.05; r = 0.71), but remained unaffected in RE sows. In conclusion, the study demonstrates that feed restriction of primiparous sows during lactation affects not only LH, but also FSH, as well as lactational follicular growth. An association between those events is suggested.     

Effect of dietary energy intake during lactation on performance of primiparous sows and their litters

A total of 146 primiparous sows was used in four replications of an experiment to investigate the effect of energy intake during a 28-d lactation on sow and litter performance. Dietary treatments consisted of three energy intakes; 10, 12 or 14 Mcal of metabolizable energy (ME) X sow-1 X d-1. All sows were fed equal amounts of crude protein, vitamins and minerals daily, which met or exceeded standard recommendations. The experiment was initiated at parturition. Sow weight and backfat loss during lactation decreased linearly (P less than .001) as energy intake increased. There were no differences in litter size at either 14 d of lactation or weaning. Pig weights on d 14 increased linearly (P less than .05) and litter weights tended to increase linearly (P = .13) as energy intake increased. At weaning, pig weights and litter weights increased (P less than .05) as sow energy intake increased. There were no significant differences in the percentages of sows in estrus by 7, 14, 21 and 70 d postweaning, but sows fed 10 Mcal ME/d had a slightly longer interval from weaning to first estrus than sows fed higher energy intakes. Serum urea concentrations of sows were inversely related to energy intake during lactation. Serum creatinine concentrations were not affected by energy intake. An intake of 10 Mcal ME/d by primiparous sows during a 28-d lactation resulted in reduced sow and litter performance; there was little difference between sows fed 12 and 14 Mcal ME/d.     

Influence of duration of litter separation and boar exposure on estrous expression of sows during and after lactation

The influence of litter separation (LS) that included a change in housing environment and social status of sows, boar exposure (BE), and parity on estrous expression by sows during and after lactation was examined in two experiments utilizing 140 crossbred sows. In Exp. 1 (Yorkshire X Duroc sows), limiting duration of LS to 6 or 3 h/d during the last 8 d of lactation in two trials, while maintaining 1 h BE, resulted in similar proportions of sows in estrus during lactation (65 vs 79% for 3- and 6-h sows). However, 6-h LS tended to reduce (P = .08) the interval to estrus by .6 d for those sows that expressed a preweaning estrus. Postweaning intervals to estrus were unaffected by duration of LS in the remaining sows. In Exp. 2, sows (Yorkshire X Duroc X Chester White) were assigned to four treatment groups during the last 8 d of lactation: 1) BE (1 h/d), 2) LS (6 h/d), 3) LS + BE and 4) no LS + no BE (control). Only nine sows expressed estrus during lactation; four of 28 LS sows and five of 28 LS + BE sows. No sows were in estrus before weaning during August 1985 and only one sow (LS group) was in estrus before weaning during October 1986. Postweaning intervals to estrus were reduced (P less than .05) by .9 d after preweaning BE compared with controls.(ABSTRACT TRUNCATED AT 250 WORDS)     

Characterization of luteinizing hormone secretion in the primiparous, lactating sow: relationship to blood metabolites and return-to-estrus interval.

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)     

Reproductive traits of sows penned individually or in groups until 35 days after breeding

We compared estrous and farrowing traits in 274 Duroc X Yorkshire sows penned either in individual gestation stalls or in groups (four or five sows/group) during the intervals from weaning to breeding and from breeding to 30 to 35 d after breeding. Sows were assigned to treatment by parity (primiparous vs multiparous), checked twice daily for estrus from 3 to 10 d after weaning and artificially inseminated (AI) twice during estrus. Ovaries of anestrous sows were examined at laparotomy. No major treatment effects on estrous response were detected and 88% (45/51) of anestrous sows had only small ovarian follicles. Litter traits were not affected by penning treatments. However, penning sows in groups postbreeding resulted in a 50% reduction (P less than .05) in early pregnancy losses as indicated by low serum progesterone 19 to 23 d after AI or return to estrus by 23 d after AI. This resulted in a 12 percentage point higher (P less than .05) farrowing rate for group-penned (78%) than for individually penned sows (66%).     

Relationship between body fat and postweaning interval to estrus in primiparous sows

Twenty-two primiparous Yorkshire sows were used to determine whether a minimal threshold of body fat exists below which the return to estrus is delayed. A second objective was to examine the relationship between body fat and interval from weaning to estrus in restricted-fed sows. During lactation (28 d), sows received 7, 9, 11 or 13 Mcal of ME daily to produce a range of sow body fatness at weaning. Intake of all dietary essentials except ME was similar for all sows. Litter size was adjusted to 10 pigs for all sows by d 3 postpartum. Each day from weaning to estrus, sows received 110 kcal ME per kg metabolic body weight plus 1,359 kcal ME per sow. Body fat was estimated at weaning and at first postweaning estrus by deuterium oxide dilution. Last rib backfat depth was determined ultrasonically 24 h postpartum and at weaning. Irrespective of dietary ME intake, percentage body fat at weaning (R2 = .24; P less than .05) and first postweaning estrus (R2 = .03; P greater than .50) accounted for only a small portion of variation in interval from weaning to estrus. Likewise, loss of backfat depth during lactation was not an accurate predictor of interval from weaning to estrus (R2 = .24; P less than .05). The low coefficients of determination (less than .25) suggest that body fat is a minor controller of postweaning interval to estrus. In contrast, dietary ME intake during lactation accounted for the largest portion of the variation (R2; = .48; P less than .01) in postweaning interval to estrus. We conclude that timing of postweaning estrus in primiparous sows is not dependent on a minimal threshold of body fat. Furthermore, effects of lactational ME intake on the postweaning interval to estrus are more pronounced than the effects of body fat.     

Effects of postweaning dietary energy source on reproductive traits in primiparous sows

An experiment was conducted to study the effects of major dietary energy source fed from weaning to ovulation or from ovulation to d 35 of pregnancy on reproductive traits in primiparous sows. Dietary energy sources were used to manipulate the plasma insulin concentration. One hundred thirteen sows were used in a split-plot design. From weaning to ovulation sows were fed at two times maintenance either a diet with tallow (Fat) or maize starch plus dextrose (Starch) as the major energy source. From ovulation onward, sows within each dietary group were alternately reassigned to either the Fat or the Starch diet and were fed at 1.25 times maintenance. Estrus detection was performed three times a day from d 3 to 9 after weaning and sows were inseminated each day of standing estrus. On d 35 of pregnancy, the sows were slaughtered and their reproductive tracts were removed. Plasma insulin concentration was higher in sows fed the Starch-rich diet than in sows fed the Fat-rich diet on d 4 after weaning (1.30 vs 0.97 ng/mL, P = 0.08) and on d 32 of pregnancy (1.20 vs 0.51 ng/mL, P < 0.001). Plasma glucose and IGF-I concentration on d 4 after weaning and d 32 of pregnancy did not differ between sows on the two dietary energy sources. The percentage of sows exhibiting estrus within 9 d after weaning was 52 and 67% for the Fat and Starch diet before ovulation, respectively (P = 0.11), whereas the weaning-to-estrus interval was 134 vs 123 h, respectively (P = 0.12). Survival analysis showed that sows fed the Fat-rich diet had a 1.6 times higher risk to remain anestrous until d 9 after weaning than sows fed the Starch-rich diet (P = 0.04). No effect of dietary energy source, either before or after ovulation, on uterine, placental, or embryonal development on d 35 of pregnancy was found. It can be concluded that the dietary energy source provided after weaning can affect the risk of sows to remain anestrous but does not affect uterine, placental, or embryonic traits.     

Factors affecting the reproductive performance of the weaned sow.

The majority of sows return to estrus within 2 weeks after weaning. Swine practitioners attempt to optimize production by reducing the WEI. Some sows fail to resume estrous cyclicity after weaning; however, the endocrinologic pathogenesis of these anestrous sows is speculative. The average WEI is influenced by numerous factors, including season, environmental temperature, photoperiod, nutrition, stress, facility design, lactation length, and management practices. It is evident that the majority of these factors have a more profound influence on primiparous sows than on multiparous sows. Optimum protein and energy consumption by sows during lactation and after weaning and effective utilization of breeding facilities reduce the WEI. The precise roles of photoperiodic changes, elevated environmental temperatures, and stress in seasonal infertility remain poorly understood. Fortunately, current management techniques have reduced the WEI on most farms without instituting therapeutic measures.     

Ovarian follicular changes after weaning in sows.

Three experiments investigated ovarian follicular development in sows whose litters were weaned at 28 to 31 d of lactation. Unilateral ovariectomy near the time of weaning was used to assess early follicular characteristics and to identify those sows that would not return to estrus within 10 d after weaning. This allowed segregation of and exclusion from the study those sows that had a prolonged interval from weaning to first estrus. In Exp. 1, 82 and 72% of the large follicles that were marked at 48 or 72 h after weaning (10 sows per time point) were subsequently identified as corpora lutea. In Exp. 2, sows (seven to nine per time point) were unilaterally ovariectomized at 0, 6, 12, 18, 24, or 48 h after weaning, and follicular fluid was evaluated for changes in steroid concentrations. Progesterone concentrations in fluid from medium-sized (4 to 6 mm) follicles increased by 6 h after weaning and then declined through 24 h concomitant with increases in testosterone and estradiol. For Exp. 3, follicular fluid and granulosa cells from individual follicles were obtained from sows (seven to nine per time point) at 0, 6, and 24 h after weaning. In follicular fluid, insulin-like growth factor I (IGF-I) concentrations were not correlated (P greater than .05) with concentrations of progesterone, testosterone, or estradiol, or with granulosa cell production of estradiol during culture in androstenedione-supplemented medium.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effect of feeding thyrotropin-releasing hormone to lactating sows

Two experiments were conducted to assess the effects of feeding thyrotropin-releasing hormone (TRH) during lactation on sows. In Exp. 1, sows were fed 0, 1, 10, 100 or 1,000 mg TRH on d 10.8 +/- .4 (mean +/- SE) after parturition. Blood samples were taken from sows every 30 min from -2 h to 8 h and at 10, 12 and 18 h from feeding. Consumption of 100 or 1,000 mg TRH increased mean serum concentrations of thyroxine (T4; P less than .001), 1,000 mg TRH increased growth hormone (GH; P less than .06) and 100 or 1,000 mg TRH increased prolactin (PRL; P less than .01), but insulin (INS; P greater than .10) was unaffected by TRH. Serum concentrations of T4 were elevated within 2 to 4 h after feeding TRH and remained elevated for 12 to 18 h. Concentrations of GH and PRL began to increase immediately after feeding 100 or 1,000 mg TRH and remained elevated for 6 and 8 h, respectively. In Exp. 2, sows were fed 0 or 200 mg TRH from d 111 of gestation to weaning at 27.1 +/- .3 d of lactation. Consumption of TRH elevated concentrations of T4 at all stages of lactation and increased respiration rate on d 10 and d 20, heart rate on d 20, and milk production on d 20 of lactation. Consumption of TRH did not influence number of pigs born, number born alive, survival rate during lactation, sow body weight, heartgirth, backfat depth, feed disappearance, or milk production on d 10 of lactation. Piglets nursing sows fed TRH were similar in weight to piglets nursing sows not fed TRH on d 0 and 5 of lactation, but they were heavier on d 10 (P less than .07), 15 (P less than .001), 20 (P less than .001) and 27 (P less than .0001). Sows fed TRH took longer (P less than .001) to return to estrus after weaning than control sows. Results indicated that feeding TRH elevated T4, GH and PRL and that feeding TRH for the duration of lactation increased milk production on d 20 of lactation and increased weaning weights, but it delayed estrus after weaning.