The effect of breed and intrauterine crowding on fetal erythropoiesis on day 35 of gestation in swine

In a previous report, it was suggested that intrauterine crowding impaired fetal erythropoiesis and that fetal erythropoiesis was accelerated in Meishan pigs during early pregnancy. Because these conclusions were based on limited numbers of observations, the present experiment was undertaken to provide a more extensive investigation of these phenomena. Intact white crossbred gilts, unilaterally hysterectomized-ovariectomized (UHO) white crossbred gilts, and intact Meishan gilts (n = 13 to 16 per group) were mated after at least one estrous cycle of normal duration (17 to 23 d). Gilts were laparotomized at d 35 of pregnancy, the uterine horns were exteriorized and opened near each fetus, and a blood sample was collected from each fetus. The uterine horn was then surgically removed, and each fetus and placenta was weighed. All fetal blood samples were measured for hematocrit, red blood cell number, and hemoglobin. Erythropoietin and the percentages of nucleated cells and reticulocytes were also measured in blood samples from the largest and smallest living fetus in each litter. Fetal hematocrits were not affected by treatment. Blood cell counts were greater (P < 0.01) in fetuses of Meishan gilts than in White crossbred intact or UHO gilts. Hemoglobin was less (P < 0.01) in fetuses of Meishan gilts than in fetuses of White crossbred intact or UHO gilts. The percentages of nucleated (immature) cells and reticulocytes were both less (P < 0.01) in fetuses of Meishan intact gilts. Erythropoietin was also lower (P < 0.01) in fetuses of Meishan gilts. As observed previously, fetal weight was correlated (r = 0.38; P < 0.01) with blood hemoglobin concentration. These results confirm that fetal erythropoiesis in Meishan gilts is accelerated compared with White crossbred gilts. These results are consistent with the hypothesis that faster blood cell development could be beneficial to fetal survival in swine.     

Interrelationships among conceptus size, uterine protein secretion, fetal erythropoiesis, and uterine capacity

The interrelationships among d-11 conceptus size, d-105 placental weight, placental efficiency (the ability of the placenta to support fetal growth and development), fetal erythropoiesis, and uterine capacity were examined in 1/2 Meishan, 1/2 White crossbred gilts that were unilaterally ovariohysterectomized at 90 to 100 d of age. In Exp. 1, gilts were mated after at least one normal estrous cycle and then slaughtered at 105 d of gestation and number of fetuses and CL, placental weights, fetal weights, hematocrits, fetal plasma iron, and fetal plasma folate were measured. In Exp. 2, gilts were mated and plasma progesterone was measured on d 2 and 3 of gestation. On d 11, the length of the remaining uterine horn was recorded and the uterine horn was flushed with minimal essential medium. Number of CL, conceptus number, conceptus diameters, and total uterine flush retinol-binding protein (tRBP), acid phosphatase (tAP), and folate-binding protein (tFBP) were measured. Gilts were mated again and slaughtered at 105 d of pregnancy and the same traits measured in Group 1 were recorded. Plasma progesterone concentrations on d 2 and 3 were correlated with average conceptus diameter on d 11 (r = 0.60, P < 0.01, for each day). In contrast, tRBP (r = 0.49, P < 0.01), tAP (r = 0.53, P < 0.01), and tFBP (r = 0.51, P < 0.01) in uterine flushings on d 11 were only correlated with d-3 plasma progesterone concentrations. No correlations between d-11 average conceptus diameter or d-11 uterine length with d-105 uterine capacity were observed. Uterine capacity was negatively correlated with placental weight, fetal weight and fetal hematocrit (r = -0.36, P < 0.01; r = -0.44, P < 0.01; r = -0.32, P < 0.01; respectively). Hematocrits were correlated with fetal plasma iron (r = 0.50, P < 0.01) and folates (r = 0.44, P < 0.01). Hematocrit, plasma iron, and plasma folate were each correlated with residual fetal weights after adjusting for placental weight (a measure of placental efficiency), and accounted for 11% of the variation in this trait. These data suggest that conceptus diameter and uterine protein secretion on d 11 may be influenced by the onset of progesterone secretion by the CL, but do not support an influence of conceptus growth during early pregnancy on uterine capacity. These results also suggest that reducing placental and fetal weights will likely result in increased uterine capacity.     

Reduction in age of puberty in gilts consuming melatonin during decreasing or increasing daylength

Two experiments were conducted to determine whether oral administration of melatonin alters the onset of puberty in gilts during naturally increasing or decreasing daylength. In Exp. 1, 20 crossbred prepubertal gilts weighing 77.5 +/- .5 kg at 171.8 +/- 1.0 d of age were assigned randomly to receive either a daily oral dose of 3 mg of melatonin (MEL) or ethanol vehicle (ETH) at 1530 from August 31 to December 1, 1987 (decreasing daylength). Gilts were exposed to mature boars for 20 min thrice weekly and blood samples were collected twice weekly. Serum concentrations of progesterone were used to establish age at puberty and length of estrous cycle. In Exp. 2, 20 crossbred prepubertal gilts weighing 67.7 +/- .7 kg at 143.8 +/- 1.1 d of age received either MEL or ETH treatment from February 1 to May 15, 1988 (increasing daylength). Age of puberty was less in gilts that received MEL than in gilts that received ETH in both Exp. 1 (198 +/- 3 vs 228 +/- 7 d; P less than .01) and Exp. 2 (183.8 +/- 2.7 d vs 194.3 +/- 3.3 d; P less than .05). Gilts that received MEL reached puberty at a lighter weight than gilts that received ETH in Exp. 1 (95.6 +/- 2.1 vs 112.4 +/- 3.9 kg; P less than .01) and Exp. 2 (88.1 +/- 1.5 vs 96.0 +/- 1.8 kg; P less than .01). Serum concentrations of LH and FSH, length of estrous cycles, and percentage of muscle of carcasses were similar between MEL and ETH gilts.(ABSTRACT TRUNCATED AT 250 WORDS)     

Endocrine relationships of Meishan and White composite females after weaning and during the luteal phase of the estrous cycle

Endocrine differences between European crossbred and Chinese Meishan females have been somewhat modest. Indwelling jugular cannulas were placed in Meishan (n = 7) and White composite (n = 6) multiparous sows before weaning, and blood was sampled from 4 h before to 240 h after removal of litters. Temporal changes in FSH, triiodothyronine (T3), and tetraiodothyronine (T4) after weaning differed between Meishan and White composite sows. Plasma cortisol concentrations were higher in Meishan sows than in White composite sows (P < 0.01), but there were no temporal differences between breeds after weaning. Other hormones monitored (prolactin, GH, IGF-I, and inhibin) were not different between breeds. In the second experiment, Meishan gilts (n = 7) and sows (n = 7) and White composite sows (n = 9) were cannulated during the luteal phase of the estrous cycle and sampled after treatments consisting of GnRH (15 and 150 ng/kg BW), ovariectomy, estradiol cypionate challenge after ovariectomy (10 microg/kg BW), and GnRH antagonist. In response to GnRH challenge, White composite sows had elevated (P < 0.05) concentrations of gonadotropins compared with Meishan. Cortisol concentrations were elevated in Meishan as compared with White composite females (P < 0.01) but unaffected by GnRH treatment. After ovariectomy, LH concentrations increased 3 h sooner in White composite than in Meishan females. After GnRH antagonist, declines in gonadotropins were comparable in both breeds, but LH increased in Meishan females by 20 h but not until after 54 h in White composite females. White composite females demonstrated only a short decline in FSH in response to the GnRH antagonist, but Meishan females had a prolonged decline in FSH concentrations. Consistently elevated cortisol concentrations in Meishan females may positively impact ovarian function; thus, the assumption that high plasma cortisol concentration as an index of stress that impairs reproductive function should be reevaluated in swine. There were few endocrine differences that would relate to or explain increased ovulation rates found in the Meishan breed; thus, other mechanisms must exist to explain the increase in ovarian function in the Meishan breed.     

Effect of estradiol-17beta administration during the time of conceptus elongation on placental size at term in Meishan pigs

Meishan embryos transferred to recipient females on d 2.5 are larger, contain greater numbers of trophectoderm cells, and secrete greater amounts of estradiol-17beta (E2beta) when gestated in a Yorkshire as compared with Meishan uterus to d 12. Additionally, placentas of Meishan conceptuses are larger when gestated in a Yorkshire as compared with Meishan uterus throughout gestation. Embryonic E2beta secretion during elongation on d 12 to 13 of gestation is temporally associated with endometrial secretion of growth factors, including IGF-I, which has been shown to increase mitotic rate in the trophectoderm of pig embryos. This experiment was conducted to determine whether E2beta administration to Meishan gilts at the time of conceptus elongation would increase placental size at term. Meishan gilts (n = 12) were checked twice daily for estrus (0700 and 1900), and each was bred to a Meishan boar at 0 and 24 h after the onset of estrus (d 0). Gilts were randomly assigned in equal numbers to receive injections of sesame oil (VEH) starting on d 12 (control), 1 mg of E2beta in VEH starting on d 12 (E212), or 1 mg of E2beta in VEH starting d 13 (E(2)13). The injections were initiated at 0700 or 1900 (corresponding to the time of day they first exhibited estrus) and continued at 6-h intervals for 48 h, resulting in 8 mg of E2beta given in eight injections. Pregnant gilts were killed on d 112 of gestation, and ovulation rate, litter size, implantation site length, fetal weight, crown-rump length, placental weight, and placental surface area were quantified. There were no differences among E(2)12, E(2)13, and control females in ovulation rate or litter size, which averaged 16.3 +/- .7 and 11.8 +/- .7, respectively. Fetal weight and crown-rump length were not different (P > .10) among E(2)12, E(2)13, and control females, averaging 802 +/- 26 g and 24.3 +/- .3 cm. Placentas were markedly heavier (176 +/- 14 and 174 +/- 16 vs 134 +/- 10 g, P < .05) and larger (1,337 +/- 97 and 1,520 +/- 70 vs 978 +/- 29 cm2, P < .001) for E(2)12 and E(2)13 vs control gilts, respectively. Placental efficiency (estimated as fetal weight:placental weight) was greater (P < .05) in the control than in the E(2)12 and E(2)13 gilts (5.8 +/- .2 vs 4.8 +/- .2 and 5.1 +/- .4). These data demonstrate that the amount of E2beta exposure around the time of elongation affects placental size at term. Additionally, the difference in placental efficiency between control and E2beta groups indicate that E2beta-induced increases in placental size led to a reduced placental efficiency.     

A radioimmunoassay for porcine intrauterine folate binding protein.

A RIA was developed for porcine intrauterine folate binding protein (FBP). Displacement of [125I]FBP caused by increasing dilutions of uterine flushings collected from either d-15 pregnant or nonpregnant gilts or media from culture of endometrial tissue from d-15 pregnant or nonpregnant gilts was parallel to the displacement caused by the standard curve. Addition of known amounts of purified allantoic fluid FBP to dilutions of either intrauterine flushings or endometrial culture medium were measured accurately with the RIA. To test specificity, 2-mL samples of uterine flushings collected from d-15 pregnant and nonpregnant gilts were preincubated with 10 microCi of [3H]folic acid and then chromatographed using Sephadex G-100 (Sigma Chemical Co., St. Louis, MO). The fractions were subsequently assayed for radioactivity by liquid scintillation spectrophotometry and for FBP by RIA. The [3H]folic acid and FBP peaks coincided, indicating that the RIA is specific for FBP. Uterine flushings were collected on d 10, 11, 12, 13, 14, and 15 of the cycle or pregnancy from 1) White crossbred, 2) progesterone-treated White crossbred (200 mg of progesterone at 48 and 72 h after estrus), and 3) Meishan gilts and assayed for FBP. Total FBP increased 140-fold from d 10 to 15, and the pattern of change across day did not differ between pregnant and nonpregnant gilts. Progesterone treatment increased intrauterine FBP content on d 10 and 11. No difference in FBP concentrations was detected between White crossbred and Meishan gilts. These results indicate that the RIA for FBP is valid, allowing measurement of this protein in uterine flushings and endometrial culture medium. The onset of FBP secretion by the uterus between d 10 and 15 of the cycle or pregnancy is influenced by the timing of onset of progesterone influence in a manner similar to the endometrial proteins uteroferrin and retinol binding protein. In contrast to these endometrial proteins, FBP concentrations are similar in Meishan and White crossbred gilts.     

Uterine contractions in nonpregnant and early pregnant mares and jennies as determined by ultrasonography

Uterine contractions in 8 nonpregnant and 13 pregnant mares were studied using ultrasonography. A 1-min video tape recording was made of longitudinal real-time images of the uterine body. An overall uterine contractile activity score (0 = no or minimal activity to 4 = maximal activity) was assigned to each video tape segment. There was a day effect (P less than .01) and an interaction (P less than .01) of reproductive status X day. Uterine activity scores were highest on d 14 to d 18 (d 0 = day of ovulation) for nonpregnant mares and on d 10 to d 14 for pregnant mares. Uterine activity scores on d 10, d 12, and d 14 were greater (P less than .02) for pregnant mares (2.5 +/- .3, 3.1 +/- .3, and 3.2 +/- .1, respectively) than for nonpregnant mares (1.2 +/- .3, 1.5 +/- .3, and 2.6 +/- .3). Uterine activity scores for six pregnant and five nonbred jennies were assigned daily from d 0 to d 24. There were main effects of reproductive status and day (P less than .01) and an interaction of status X day (P less than .01). Uterine activity scores for pregnant jennies were highest on d 13 and d 14 and then declined. In the nonbred jennies, scores were highest on d 14 to d 20. The mean score on d 13 was greater (P = .05) in pregnant jennies (2.8 +/- .2) than in nonbred jennies (1.9 +/- .5).(ABSTRACT TRUNCATED AT 250 WORDS)     

Consequences of different patterns of feed intake during the estrous cycle in gilts on subsequent fertility

The impact of different patterns of feed restriction between d 1 and 15 of the estrous cycle on subsequent reproductive performance of 23 trios of littermate gilts was tested. Some gilts were fed a high plane of nutrition (HH gilts) throughout the cycle, in contrast to HR gilts, which were restricted from d 8 to 15, and RH gilts, which were restricted from d 1 to 7. During feed restriction, weight gain in RH gilts (2.5 +/- .7 kg) was lower (P = .006) between d 1 and d 7 than in their HH and HR littermates (5.6 +/- .7 and 5.6 +/- .8 kg, respectively) and it was lower (P = .0001) in HR gilts (5.5 +/- .5 kg) between d 8 to d 15 than in their HH and RH counterparts (8.5 +/- .4 and 9.4 +/- .5 kg, respectively). There were no differences in backfat changes among groups. Embryonic survival in HR gilts at d 28 of gestation (68.3 +/- 4.8%) was lower (P < .05) than in HH and RH gilts (83.6 +/- 4.3 and 81.7 +/- 4.5%, respectively). Plasma progesterone concentrations in HR gilts were lower (P < .05) at 48 and 72 h after onset of standing estrus (.82 +/- .2 and 3.6 +/- .5 ng/mL, respectively) than in HH and RH gilts (1.44 +/- .2 and 1.24 +/- .2 ng/mL, 5.0 +/- .4 and 5.0 +/- .5 ng/mL, respectively at 48 and 72 h). No differences in ovulation rate were observed among treatments. Placental area was positively correlated to embryo size at d 28 (embryo size = .0003 x (area) + 18.35; r = .28, P = .03) but placental volume was negatively correlated to the number of embryos in utero (placental volume = -4.317 x (number) + 207.55, r = -.39, P = .002). These data demonstrate that the timing of feed restriction during follicular development has important consequences for subsequent embryo survival, possibly mediated by differences in progesterone concentrations in early pregnancy.     

The effects of recombinant porcine somatotropin on reproductive function in gilts treated during the finishing phase.

The objective of this study was to determine the effects of recombinant porcine somatotropin (rpST) treatment during the finishing phase on subsequent reproductive function in crossbred gilts. Forty gilts weighing 50 kg and housed in a swine finishing facility were randomly assigned to control or rpST treatment. Four control and four rpST-treated gilts were allotted per pen. Twenty rpST-treated gilts received 6 mg of rpST.gilt-1.d-1 in 1 ml of buffered carrier and 20 control gilts received 1 ml of buffered carrier.gilt-1.d-1. Injections were administered daily at 1400 in the extensor muscle of the neck. All gilts received an 18% CP diet containing 1.2% lysine. Treatment was terminated when the average weight in each pen reached 110 kg. Gilts treated with rpST gained more weight (P less than .05) than control gilts (59.8 +/- 1.0 vs 53.5 +/- 1.0 kg). Age at puberty was not different (rpST, 182.2 +/- 3.3; control 181.4 +/- 3.1 d). Prior treatment with rpST did not significantly affect length of estrus (rpST, 1.9 +/- .1; control, 1.8 +/- .1 d) or estrous cycle length (rpST, 20.6 +/- .4; control, 20.4 +/- .4 d). Ovulation rates at second estrus were similar for rpST gilts (15.1 +/- .5) and control gilts (14.4 +/- .5). More embryos (P = .10) were recovered on d 9 to 12 of gestation from rpST-treated gilts than from control gilts (13.1 +/- .9 vs 10.7 +/- .9).(ABSTRACT TRUNCATED AT 250 WORDS)     

Expression of the uterine Mx protein in cyclic and pregnant cows,gilts, and mares

Pregnancy and interferon-tau (IFN tau) upregulate uterine Mx gene expression in ewes; however, the only known role for Mx is in the immune response to viral infection. We hypothesize that Mx functions as a conceptus-induced component of the anti-luteolytic mechanism and/or regulator of endometrial secretion or uterine remodeling during early pregnancy. This study was conducted to determine the effects of early pregnancy on uterine Mx expression in domestic farm species with varied mechanisms of pregnancy recognition. Endometrium from cows, gilts, and mares was collected during the first 20 d of the estrous cycle or pregnancy, and total messenger RNA (mRNA) and protein were analyzed for steady-state levels of Mx mRNA and protein. Northern blot analysis of Mx mRNA detected an approximately 2.5 Kb of mRNA in endometrium from each species. In pregnant cows, steady-state levels of Mx mRNA increased 10-fold (P < 0.05) above levels observed in cyclic cows by d 15 to 18. In cyclic gilts, slot blot analysis indicated that endometrial Mx mRNA levels did not change between d 5 and 18 of the cycle. However, in pregnant gilts, Mx levels tended (P = 0.06) to be elevated two-fold on d 16 only, and in situ hybridization indicated that this increase occurred in the stroma. In mares, Mx mRNA was low, but detectable, and did not change between ovulation (d 0) and d 20, regardless of reproductive status. Western blot analysis revealed multiple immunoreactive Mx protein bands in each species. One band was specific to pregnancy in cows. As in ewes, in situ hybridization analysis indicated that Mx mRNA was strongly expressed in the luminal epithelium, stroma, and myometrium by d 18 in cows. However, on d 14 in gilts, Mx was expressed primarily in the stroma, and on d 14 in mares, low levels of Mx expression were confined largely to the luminal epithelium. The uteruses of cows, gilts, and mares express Mx, and expression is upregulated during pregnancy in cows and gilts--animals whose conceptuses secrete interferons during early pregnancy, but that possess different mechanisms for pregnancy recognition.     

Dietary energy intake affects fetal survival and development during early and middle pregnancy in Large White and Meishan gilts

This experiment was designed to determine the effects of variations in dietary energy intake on reproductive performance and gene expression of luteal and endometrium tissues in Large White(LW)and Meishan(MS) gilts during early and middle pregnancy. After insemination, 32 LW gilts were assigned to high and low(HE_Land LE_L, 14.23 and 12.56 MJ DE/kg, respectively) diet treatment groups,while 32 MS gilts were allocated to HE_M and LE_M(12.56 and 10.88 MJ DE/kg) groups. Gilts were slaughtered on days 35, 55 and 90 of gestation. The fetal survival and luteal progesterone(P_4) concentration in the HE_Lgroup were higher on day 35 but lower on day 90 of gestation compared with the LE_L group(P 0.05) for LW gilts. However, fetal survival and luteal P_4 concentration on day 35 of gestation were greater(P 0.05) in the LE_M group than in the HE_M group for MS gilts, but no significant difference in mid-gestation was showed. The fetal weights of both breeds were higher for the high energy diets compared with the respective control group on day 90 of gestation(P 0.05). In addition,the m RNA levels of P_4 synthesis-related proteins had correlated with luteal P_4 concentration in both breeds. Further, endometrial levels of uteroferrin(ACP5), retinol-binding protein 4(RBP_4) and secreted phosphoprotein 1(SPP1) m RNA were upregulated in the HE_Lgroup on day 35 of gestation but ACP5 and SPP1 were downregulated on day 55 of gestation compared with the LE_Lgroup(P 0.05) for LW gilts. In MS gilts, diet only affected the expression of SPP1(P 0.05). Our results revealed the differential sensitivity of LW and MS breeds to variations in dietary energy intake. For LW gilts, the HE_Lgroup improved fetal survival on day 35 but a sustained high energy diet decreased fetal survival on day 90 of gestation. The differences in dietary energy intake did not influence fetal survival on day 90 of gestation but the higher energy diet did increase fetal weight in the MS breed compared with the lower energy intake diet. These results may be due to differential luteal secretion activity and endometrium gene expression in these two breeds.     

Uterine clearance mechanisms during the early postovulatory period in mares

Uterine response to inoculation with Streptococcus zooepidemicus organisms, 51Cr-labeled 15-microns microspheres, and charcoal was evaluated in 9 mares (4 resistant and 5 susceptible to endometritis) to determine mechanical and cellular clearance rates during the early postovulatory period. Mares were inoculated at estrus prior to ovulation during estrous cycles 1, 3, and 5. Uterine swab specimens for aerobic and anaerobic bacteriologic culture and serum for progesterone determination were obtained on postovulation day 3 during estrous cycle 1, on the day of ovulation during estrous cycle 3, and on postovulation day 5 during estrous cycle 5. Immediately thereafter, the uterus was irrigated with 50 ml of sterile physiologic saline solution containing tracer amounts of 125I-labeled human serum albumin. Streptococcus zooepidemicus was isolated from 10 of 15 (67%) uterine specimens collected from susceptible mares and incubated aerobically. Escherichia coli also was isolated from 2 of the 10 specimens incubated aerobically. Anaerobic bacteriologic culture of specimens from all mares yielded no growth. Chromium-labeled microspheres were recovered twice from 2 susceptible mares, on day 0 and day 5. Charcoal was retained in 5 specimens collected from 3 susceptible mares. Bacteriologic culture of specimens from resistant mares did not yield growth. On day 0, chromium-labeled microspheres and charcoal were recovered once from 1 resistant mare. Mares susceptible to endometritis accumulated more fluid within the uterine lumen after ovulation than did resistant mares (mean +/- SEM, 52.73 +/- 15.22 ml and 7.41 +/- 1.96 ml, respectively; P less than 0.01). From this study, it appeared that uterine cellular and bactericidal mechanisms are dysfunctional during the early postovulatory period. However, there appeared to be no disruption of the mechanisms responsible for mechanical clearance of materials inoculated in the uterus.     

Cortisol-binding globulin and meat quality in five European lines of pigs

The gene (Cbg) encoding cortisol-binding globulin (CBG) has been proposed as a candidate gene to explain genetic variation in cortisol secretion and carcass composition in pigs. The objective of this study was to evaluate the association between CBG and pork quality in 5 European breeding lines, Piétrain, Large White (LW), and Landrace purebred lines, a Duroc synthetic line, and a Meishan (MS) x LW advanced intercross. Cortisol-binding globulin maximum binding capacity (CBG-Bmax) was twice as high (P < 0.05) in MS x LW pigs compared with the other lines. There was no (P > or = 0.364) association between CBG-Bmax and carcass quality traits in Piétrain gilts, but CBG-Bmax was associated with increased loin yields in LW (P = 0.010) and Landrace (P = 0.103) gilts, decreased ham yields (P = 0.082) in Duroc gilts, and increased fat depth (P = 0.064) and leaf fat (P = 0.001) in MS x LW gilts. There was no association between CBG-Bmax and pork quality traits in Piétrain (P > or = 0.269) and Duroc (P > or = 0.114) gilts. Conversely, CBG-Bmax was associated with lighter (higher L* values; P < 0.05) pork in Land-race gilts, as well as lower (P < or = 0.055) ultimate pH in the LM and semimembranosus, and a tendency for lower (P = 0.095) L* values of pork from LW gilts. Within MS x LW pigs, CBG-Bmax was associated with increased drip loss (P = 0.001) and decreased i.m. fat in the semimembranosus (P = 0.005). Because drip loss is an economically important pork quality trait, results of this study could be used in the selection of improved water-holding capacity of pork from synthetic lines involving the MS breed.     

Interestrous interval of cyclic gilts is decreased by systemic but not intrauterine administration of exogenous oxytocin

Oxytocin (OT) stimulates pulsatile secretion of uterine prostaglandinF2alpha in ruminants, but the role of OT in the estrous cycle regulation of pigs is not clear. These studies were performed to determine the effect of exogenous OT on interestrous interval of intact cyclic gilts. Intrauterine infusion of 80 USP units three times daily on d 10 to 16 after estrus did not decrease interestrous interval (24.5+/-1.3 d) compared with control gilts (22.5+/-1.3 d). In contrast, i.m. injections of 20 USP units of OT twice daily or 80 USP units of OT three times daily on d 10 to 16 after estrus decreased (P < 0.05) interestrous interval (20.0+/-0.3 or 19.5+/-0.4 d, respectively) compared with control gilts (20.5+/-0.3 d). When gilts received a single i.m. injection of 0 or 1 mg of estradiol valerate on d 11 and twice daily i.m. injections of 0 or 20 USP units OT on d 10 to 16 after estrus, an interaction (P = 0.05) between OT and estradiol valerate was detected. In the absence of exogenous estradiol valerate, injection of OT decreased interestrous interval (19.0+/-0.5 d) compared with injection of vehicle (20.4+/-0.5 d). However, when gilts were injected with 1 mg of estradiol valerate to inhibit luteolysis, OT did not prevent the increase in interestrous interval (25.4+/-0.5 d) compared with injections of vehicle (24.7+/-0.5 d). These results indicate that 1) exogenous OT administered by intrauterine infusion on d 10 to 16 did not decrease interestrous interval of intact cyclic gilts, 2) exogenous OT administered i.m. on d 10 to 16 shortened interestrous interval, and 3) exogenous OT did not prevent the increase in interestrous interval induced by estradiol valerate.     

Interval to first postweaning estrus and causes for leaving the breeding herd in Large White, Landrace, Yorkshire and Chester White females after three parities

Three hundred and five Large White (LW, 93), Landrace (L, 92), Yorkshire (Y, 69) and Chester White (CW, 51) gilts produced at the Roman L. Hruska U.S. Meat Animal Research Center over 3 yr with 15 to 41 gilts per breed group per year were housed in total confinement and mated to farrow at 1 yr of age. After 28 to 30 d lactation, piglets were weaned and all females were observed for estrus daily for 30 d. During the year that each gilt initially farrowed, she was mated to produce a second and third litter if she returned to estrus within 30 d after piglet removal. Interval from weaning (d 0) to estrus and reason for leaving the breeding herd were recorded for each animal. Interval from weaning to estrus was influenced by breed (P less than .01), parity (P less than .01) and interaction between breed and parity (P less than .01). Intervals from weaning to estrus, in first parity females which exhibited estrus, were 7.8, 6.6, 9.3 and 14.0 d for the LW, L, Y and CW breeds. Intervals for all females after the second litter were 6.8, 4.9, 8.0 and 9.1 d, and after the third litter 6.4, 5.2, 8.3 and 10.1 d for the LW, L, Y and CW breeds. Breed, parity and year (P less than .01) affected the number of females not exhibiting estrus. Percentages of females not exhibiting estrus were 6.5, 18.7, 37.7 and 23.5 for the LW, L, Y and CW breeds and 16.1, 2.3 and 2.0 for sows after the first, second and third parities.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effects of active immunization against growth-hormone releasing factor on puberty and reproductive development in gilts.

Hormones within the somatotropin cascade influence several physiological traits, including growth and reproduction. Active immunization against growth hormone-releasing factor (GRFi) initiated at 3 or 6 mo of age decreased weight gain, increased deposition of fat, and delayed puberty in heifers. Two experiments were conducted to investigate the effects of GRFi on puberty and subsequent ovulation rate in gilts. Crossbred gilts were actively immunized against GRF-(1-29)-(Gly)2-Cys-NH2 conjugated to human serum albumin (GRFi) or against human serum albumin alone (HSAi). In Exp. 1, gilts were immunized against GRF (n = 12) or HSA (n = 12) at 92 +/- 1 d of age. At 191 d of age, antibody titers against GRF were greater (P < .05) in GRFi (55.5 +/- 1.3%) than in HSAi (.4 +/- 2%) gilts. The GRFi decreased (P < .05) BW (86 +/- 3 vs 104 +/- 3 kg) by 181 d of age and increased (P < .05) backfat depth (15.7 +/- .4 vs 14.8 +/- .4 mm) by 130 d of age. At 181 d of age, GRFi reduced the frequency of ST release (1.0 +/- .5 vs 5.0 +/- .5, peaks/24 h; P < .0001) and decreased (P < .01) ST (1.1 +/- .06 vs 1.7 +/- .06 ng/mL), IGF-I (29 +/- 2 vs 107 +/- 2 ng/mL), and insulin concentrations (3.5 +/- .2 vs 6.3 +/- .2 ng/mL). The GRFi decreased (P < .05) feed conversion efficiency but did not alter age at puberty (GRFi = 199 +/- 5 d vs HSAi = 202 +/- 5 d) or ovulation rate after second estrus (GRFi = 10.7 +/- .4 vs HSAi = 11.8 +/- .5). In Exp. 2, gilts were immunized against GRF (n = 35) or HSA (n = 35) at 35 +/- 1 d of age. The GRFi at 35 d of age did not alter the number of surface follicles or uterine weight between 93 and 102 d of age, but GRFi decreased (P < .05) ovarian weight (.41 +/- .08 vs 1.58 +/- .4 g) and uterine length (17.2 +/- 1.1 vs 25.3 +/- 2.3 cm). Immunization against GRF reduced (P < .05) serum IGF-I (GRFi = 50 +/- 4 vs HSAi = 137 +/- 4 ng/mL) and BW (GRFi = 71 +/- 3 vs HSAi = 105 +/- 3 kg) and increased (P < .05) backfat depth (GRFi = .38 +/- .03 vs HSAi = .25 +/- .02 mm/kg). Age at puberty was similar in GRFi and HSAi gilts, but ovulation rate was lower (P < .05) after third estrus in GRFi (11.3 +/- .8) than in HSAi (13.8 +/- .8) gilts. Thus, GRFi at 92 or 35 d of age decreased serum ST, IGF-I, and BW in prepubertal gilts without altering age of puberty. However, GRFi at 35 d of age, but not 92 d of age, decreased ovulation rate. These results indicate that alterations in the somatotropic axis at 1 mo of age can influence reproductive development in pubertal gilts.     

Endocrine changes associated with a dietary-induced increase in ovulation rate (flushing) in gilts

Effects of an increased level of dietary energy (flushing) on plasma concentrations of FSH, LH, insulin, progesterone and estradiol-17 beta and ovulation rate were studied in 16 gilts. Gilts received 5,400 kcal ME/d for one estrous cycle and the first 7 d of a second. On d 8 of the second estrous cycle, gilts received either 5,400 kcal ME/d (control [C], n = 8) or 11,000 kcal ME/d (flushed [F], n = 8) for the remainder of the estrous cycle. Blood was collected daily at 15-min intervals for 6 h from d 8 through estrus. Gilts were examined by laparotomy 6 d after estrus. Ovulation rate was greater (P less than .05) in F than C gilts (16.0 vs 9.4). Mean daily concentrations of FSH were greater (P less than .05) in F gilts at 5 d, 4 d and 3 d prior to estrus compared with C females. In both C and F gilts, FSH decreased (P less than .05) prior to estrus. Mean daily concentrations of LH and LH pulse amplitude were not different (P greater than .05) between treatments. Mean number of LH pulses/6 h at 4 d, 3 d and 2 d prior to estrus were greater (P less than .05) in F than in C gilts. In both treatments, LH pulse amplitude decreased (P less than .05) and pulse frequency increased (P less than .07) prior to estrus. Mean plasma concentrations of insulin tended to be higher (P less than .07) in F than in C females during the 7-d period before estrus.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effect of intrauterine bacterial infusions and subsequent endometritis on prostaglandin F2 alpha metabolite concentrations in postpartum beef cows.

Multiparous Angus and crossbred Angus cows were used to determine the effect of induced endometritis on plasma concentrations of 13,14-dihydro-15-keto-prostaglandin F2 alpha (PGFM) and progesterone (P4) and on duration of the estrous cycle of treatment. Beginning on the day of calving (d 0), blood samples were collected on alternate days. On three consecutive days, ranging from d 8 to 14 of the first postpartum estrous cycle, uterine horns were inoculated transcervically with either 3 x 10(9) colony forming units (cfu) of Actinomyces pyogenes and 1.5 x 10(9) cfu of beta-hemolytic Escherichia coli (treated; n = 9) in sterile PBS or with sterile PBS alone (control; n = 9). Samples of uterine fluid were collected by transcervical aspiration twice weekly from just before the start of each series of inoculations until the end of the experiment. Endometrial biopsies were collected transcervically between d 4 to 6 and 11 to 13 after inoculation. Based on clinical observations and results of bacterial cultures, all treated cows developed acute uterine infections. Controls did not develop uterine infections. Endometrial biopsies indicated that there were no significant diffuse or focal cellular reactions in response to the infection. The interestrous interval was greater (P less than .0003) for treated (27.7 +/- 1.0 d) than for control (20.6 +/- 1.0 d) cows, but P4 concentrations were similar between the two groups. Mean PGFM concentration and PGFM profiles were similar (P greater than .10) between treated and control cows before bacterial infusions. Bacterial infusions increased mean PGFM concentration (P less than .0001) and changed the shape of the PGFM profile (P less than .02).(ABSTRACT TRUNCATED AT 250 WORDS)     

Behavior and pituitary-adrenal function in large white and Meishan pigs

Six-wk-old piglets of both sexes from European Large White (LW, n = 36) and Chinese Meishan (MS, n = 24) breeds were individually exposed to a novel environment, a stressful stimulation. Behavioral and pituitary-adrenal reactivity were investigated. When compared with LW, MS pigs displayed low locomotion (18.5 ± 2.2 vs. 41.0 ± 3.8 squares crossed/10 min; P < 0.0001), and defecation scores (0.58 ± 0.15 vs. 4.86 ± 0.37 fecal boli; P < 0.0001). Basal concentrations of cortisol were higher in MS (96.1 ± 1.1 vs. 44.9 ± 1.1 ng/ml; P < 0.0001), although no differences between breeds were found in basal concentrations of adrenocorticotropic hormone (ACTH). In response to novel environment exposure, the ACTH increase was greater in LW than in MS, but the cortisol response was not different on a log scale. To further investigate the pituitary-adrenal differences between the two breeds, the 24-hr profile of ACTH and cortisol plasma concentrations, a corticotropin-releasing factor (CRF) and a coupled dexamethasone-ACTH test were studied. Five castrated male 9-wk-old piglets from each breed were fitted surgically with a jugular vein catheter. A classic marked circadian rhythm of cortisol and a weak nycthemeral variation of ACTH were found. Cortisol concentrations were approximately twice higher in MS exclusively during the early light phase (from 0800–1200 hr) of the cycle, but no significant interbreed difference was found in the circadian rhythm of ACTH. Administration of CRF (1 μg/kg iv) induced the same significant increase in plasma ACTH and cortisol concentrations in both breeds. Administration of ACTH (10 μg/kg iv) increased significantly cortisol concentrations and revealed no difference in plasma cortisol response to ACTH. These data suggest that the hypercortisolism of MS pigs is of adrenal origin, and related to extrapituitary factors that control the adrenal sensitivity during the light phase of the diurnal cycle.