Seasonal serum concentrations of melatonin in cycling and noncycling mares.

To determine whether secretory patterns of melatonin change throughout the seasons in mares, blood samples were drawn byvenipuncture from nine mares at noon and midnight for five successive days at monthly intervals from August through July at the University of Missouri in Columbia, MO. In addition, during September, December, March, and June, blood samples were drawn from indwelling catheters at 2-h intervals for 48 or 72 h. Mares were predominantly Quarter Horses weighing approximately 450 kg and ranged from 3 to 12 yr of age. Mares were housed in outdoor paddocks with three-sided run-in sheds for shelter. During the noon and midnight bleeding period, mares were placed in a larger open-sided barn with outside runs. Mares remained outdoors with the barn being used as a shelter in the event of inclement weather. All lights in the shed were converted to red light. Often, moonlight provided enough illumination to collect blood samples. Mares were returned to their normal paddock after each sampling period. For analysis of data, a mare was considered to be cycling if serum concentrations of progesterone were greater than 1 ng/ mL. For a mare to be classified as exhibiting a nocturnal rise of melatonin, serum concentrations of melatonin had to be at least two times greater at midnight than at noon. By month, a relationship did not exist (chi2; P > 0.05) among mares that were exhibiting estrous cycles and exhibiting nocturnal rises of melatonin. Likewise, examination of serum profiles of melatonin taken at 2-h intervals for 48 h revealed considerable variation among mares throughout the seasons. A nocturnal rise in serum melatonin was observed only in June (P < 0.02). In March and December, serum melatonin was greater in cycling mares than noncycling mares, but the elevation was not associated with light-dark periods (P < 0.01). Two of the mares exhibited estrous cycles throughout the seasons but melatonin secretion in these two mares were similar to that observed in the seven mares that demonstrated seasonal anestrous. From these results, it does not appear that changes in serum concentrations of melatonin are used as a cue to regulate cyclic activity in the mare throughout the seasons.

Effects of lactation length and an exogenous progesterone and estradiol-17beta regimen during embryo attachment on endogenous steroid concentrations and embryo survival in sows.

The hypotheses that short lactation lengths increase embryo mortality by altering endogenous post-weaning steroid concentrations, and that an exogenous steroid regimen during embryo attachment might increase embryo survival were tested using 36 s parity sows assigned randomly to a 2 x 2 factorial. Sows were subjected to either a short lactation (SL, 13.0 days, n = 25) or a long lactation (LL, 31.5 days, n = 11), artificially inseminated at first estrus and treated daily with 2 ml i.m. of either 25 mg progesterone (P4) and 1.25 pg estradiol-17beta (E2) (steroid treatment, ST, n = 17) or the vehicle alone (control treatment, CT, n = 17) on Days 14-20 post-insemination. Blood samples were collected by jugular venipuncture from weaning to 24 days post-insemination on alternate days. Sows subjected to the SL compared to the LL tended to have a longer weaning-to-estrus interval (WEI) (5.3 versus 4.6 days; P < 0. 10), but did not have a significantly reduced conception rate (CR) (71 versus 90%; P > 0.10). The SL and LL sows had a similar ovulation rate (19.9 versus 21.3 corpora lutea, CL; P > 0.05), but SL sows had fewer viable embryos than LL sows (11.5 versus 15.3; P < 0.05) when reproductive tracts were recovered 28-32 days post-insemination. In addition, even after correction for the difference in number of embryos between groups, viable embryos from the SL versus the LL group weighed less (1.63 versus 1.79 g; P < 0.05), had a decreased amnion volume (1.02 versus 1.22 ml; P < 0.05) and apparently produced less estrogens since estrone sulfate concentration was decreased at 24 days post-insemination in SL versus LL sows (4.3 versus 6.3 ng/ml; P < 0.05). Embryo survival (percentage of CL represented by a viable embryo) however, was not different between SL and LL sows (60 versus 74%; P > 0.05) and no differences in post-weaning P4 or E2 concentrations were apparent. Sows that received the ST only tended to have increased P4 concentrations at 16 days post-insemination compared to CT sows and neither the number of viable embryos, nor embryo survival, was increased in ST versus CT sows (14.7 versus 12.2; P > 0.05 and 66 versus 68%; P > 0.05, respectively). These data suggest that short lactations do not increase embryo mortality by inducing aberrant endogenous post-weaning P4 or E2 concentrations. It is unclear whether or not small, repeated doses of exogenous P4 and E2 during attachment can increase embryo survival.

Pregnancy, parturition, and lactation in hypophyseal stalk-transected beef heifers.

Progesterone secretion is crucial for maintaining pregnancy to parturition in mammalian species, and in cattle the corpus luteum is the primary source of this hormone. This study determined the roles of prolactin (PRL), growth hormone (GH) and luteinizing hormone (LH) in the luteotropic process in beef heifers hypophyseal stalk-transected (HST, n=7) or sham operated (sham operated controls, SOC, n=9) during midgestation. The main finding was that endogenous PRL and GH maintained progesterone secretion in HST heifers in a similar manner to that in SOC throughout pregnancy. Serum PRL averaged 37 vs 187 and GH 2 vs 4 ng/ml in HST heifers compared with SOC, whereas LH abruptly decreased to undetectable levels after HST compared with a modest 0.4 ng/ml in SOC heifers. The second finding was that parturition and lactation occurred in HST heifers with calf delivery induced to occur at the same time as SOC. Milk production in HST animals was severely limited, and postpartum estrus obliterated compared with SOC. The suckling stimulus sustained milk ejection in HST heifers in spite of diminished PRL, GH, thyroid stimulating hormone, thyroxine and tri-iodothyronine secretion. The results suggest that PRL, GH and possibly placental lactogen are luteotropic during pregnancy in cattle.

Failure of vitamin A to increase litter size in sows receiving injections at various stages of gestation.

To determine the effectiveness of a single injection of vitamin A to increase litter size, 1,375 sows were assigned randomly to 11 treatment groups (125 sows per treatment). Treatments included injection of 1 x 10(6) IU of vitamin A dissolved in corn oil at weaning or on d 0, 2, 6, 10, 13, 19, 30, 70, or 110 after breeding. Sows in the control group were injected with corn oil on corresponding days. A total of 396 sows were removed from the study following treatment or treatment assignment. Therefore, farrowing data were collected for 979 sows. Injection of vitamin A did not influence (P > . 10) total litter size, live litter size, litter weight, pig weight, number of runts, or number of mummies. Mean live litter size was 10.1 +/- .1 for all sows that farrowed in the experiment. Parity group affected total litter size, live litter size, live litter weight, and number stillborn (P < .01) but not pig weight, number of runts, number of mummies, or gestation length (P > . 10). In this study, a single injection of vitamin A at any time from weaning to farrowing did not increase litter size in sows.

Health and growth performance of barrows reared in all-in/all-out or continuous flow facilities with or without a chlortetracycline feed additive.

OBJECTIVE: To compare health and growth performance in barrows reared in all-in/all-out (AIAO) or continuous flow (CF) management systems. ANIMALS: 400 barrows. PROCEDURE: Barrows (approx 2 months old) were allotted to 4 replications (100 barrows each); barrows were housed in AIAO or CF rooms (10 pens/room), and 50 pigs/replicate received chlortetracycline (CTC, 110 mg/kg of feed). Barrows from each pen were slaughtered at 3, 4, 5, and 6 months old. RESULTS: Barrows in the AIAO room had greater total daily gain (TDG) and lean daily gain (LDG) than did barrows in the CF room. Addition of CTC did not improve TDG or LDG in either environment. Barrows in the AIAO room reached body weight of 104.5 kg in 169.7 days, compared with 177.3 days for barrows in the CF room. Feed-to-gain ratio was not affected by management or CTC. Lungs from barrows reared in AIAO facilities had a lower percentage of lesions than did lungs of barrows reared in CF facilities (1.74% vs 9.52%). Addition of CTC did not affect prevalence and extent of lung lesions. Extent of lung lesions was positively correlated with change in serum optical density (OD) to Mycoplasma hyopneumoniae (r = 0.35), but not with change in serum OD to Actinobacillus pleuropneumoniae. Lean growth and serum OD to M. hyopneumoniae and A. pleuropneumoniae were not correlated. CONCLUSIONS: Health and growth performance were better for barrows in an AIAO facility, compared with a CF facility, but addition of CTC to feed failed to enhance health or performance of barrows in either facility.

Seasonal regulation of prolactin secretion in hypophyseal stalk transected beef calves.

Seasonal regulation of prolactin secretion was investigated in crossbred beef heifer calves. Calves were randomly assigned to hypophyseal stalk transection (HST, n = 6) or sham-operation control (SOC, n = 6) groups and fitted 1 day before surgery with an indwelling external jugular catheter. Prolactin (PRL), growth hormone (GH), thyroid stimulating hormone (TSH), thyroxine (T4), and tri-iodothyronine (T3) in peripheral serum were measured by radioimmunoassay in samples obtained before and after HST or SOC. During the first 8 days after HST, PRL concentrations remained significantly greater than SOC, but then decreased in both HST and SOC calves to 4 +/- 2 (+/- SE) and 10 +/- 3 ng/ml, respectively (P < 0.001). PRL remained low in both HST and SOC groups for three months after surgery. By four months, HST calves had lower basal PRL (5 +/- 1 ng/ml) than observed in SOC (40 +/- 4 ng/ml), and seasonal changes in PRL blood concentration also were attenuated by HST. Although HST reduced PRL secretion, it did not abolish the effect of seasonal changes (P < 0.01); circulating PRL concentration increased six-fold by shifts in photoperiod and temperature from winter to summer in these stalk-transected calves. The SOC group had higher serum GH during the winter (3.8 +/- 0.8) than in July (1.3 +/- 0.03 ng/ml). The HST group had the opposite profile of GH concentration, however, with concentrations being higher during May through July. Thyroid stimulating hormone secretion was partly sustained after stalk transection possibly by negative feedback of reduced circulating thyroxine and tri-iodothyronine. These results in both hypophyseal stalk-transected and sham-operated beef calves maintained in a natural environment strongly suggest that hypothalamic regulation of PRL secretion by adenohypophyseal cells is extremely sensitive to seasonal changes throughout the year. Additionally, immediately after HST, PRL blood concentration remains significantly greater than in SOC calves but eventually decreases to low blood concentration in HST calves, and unlike that seen after HST in primates. Regardless, basal PRL serum concentration responds to seasonal changes, but a less distinct change in basal GH serum concentration in HST calves than seen in the SOC calves.

Lack of a nocturnal rise in serum concentrations of melatonin as gilts attain puberty.

Twenty prepubertal crossbred gilts (Yorkshire x Hampshire x Duroc) weighing 98.1 +/- 4.2 kg at 5 mo of age were placed in an environmentally controlled room having a temperature of 18 degrees C and light:dark cycle of 12 h:12 h. Light intensity measured 700 lx at eye level to the gilts. Three mature ewes were penned adjacent to the gilts to serve as positive controls for the light-dark cycles. After a 30-d acclimation period, 10 gilts from the pool determined to be prepubertal (serum progesterone < 500 pg/mL) were fitted with surgically implanted jugular catheters. Blood samples were drawn at 1100 (4 h after onset of light), 1130, 1200, 2300 (4 h after onset of darkness), 2330, and 2400 for 4 d. On d 5 of sampling, gilts were transported in an open-bed truck for 15 min, returned to their original environment, and exposed to boars for 20 min. Boar exposure was repeated every day throughout the remainder of the experimental period. Blood samples were drawn from each gilt until 7 d after estrus or for 12 d in those gilts that did not exhibit estrus. Blood samples were drawn by venipuncture from the ewes during the entire experimental period. For each sampling day, within an individual gilt or ewe, means of serum concentrations of melatonin (MEL) for night (scotophase) and day (photophase) samples were calculated. After three replications were conducted, four classes of animals were obtained: ewes (n = 9); nonpubertal gilts (n = 10); and two classes of gilts that ultimately reached puberty (prepubertal [n = 16] and postpubertal [n = 16]). Across all gilts, only 65 of 406 bleeding periods (16.0%) had a nocturnal (scotophase) rise in serum MEL. The proportion of gilts expressing a nocturnal rise in serum MEL did not differ as gilts approached puberty (P > .05). Incidence of nocturnal rises of MEL was similar (P > .05) in gilts that attained puberty and gilts that did not attain puberty. Nocturnal rises in MEL were observed in 86.2% of the bleeding periods of ewes housed in the same environment. These data indicate clearly that nocturnal rises in serum MEL are not necessary for a gilt to attain puberty.

Failure of melatonin implants to alter onset of puberty in gilts.

Forty crossbred gilts (Hampshire x Yorkshire x Landrace x Duroc) weighing 55.4 +/- 0.5 kg at 4.2 +/- 0.1 months of age received either melatonin implants (N = 20) or served as controls (N = 20). Gilts were housed in a temperature controlled room (21 degrees C) with a light (L):dark (D) cycle of 10L:14D. Initially, four implants (12 mg melatonin each, Wildlife Pharmaceuticals, Ft. Collins, CO) were placed in one ear subcutaneously. At 2-week intervals, five, six, seven or eight implants were placed in ears of the gilts (one implant per 11.8 kg body weight). Throughout the trial, blood samples were collected twice weekly by jugular venipuncture. All gilts were exposed to mature boars for 15 min on alternate days. Age of puberty was determined from serum concentrations of progesterone and visual observations of estrus. Serum concentrations of melatonin were elevated (5-10 fold) throughout the trial in those gilts that received melatonin implants. Average daily gain (P = 0.51) and age at puberty (P = 0.57) were similar between gilts that received melatonin implants or no implants. Even though gilts continued to receive melatonin after they attained puberty, elevated serum concentrations of melatonin did not alter the length of subsequent estrous cycles (P = 0.90). These data indicate that elevation of serum concentrations of melatonin via implants did not alter the onset of puberty or length of subsequent estrous cycles.

Serum concentrations of melatonin in prepubertal or postpubertal gilts exposed to artificial lighting or sunlight.

To determine if the type of environmental lighting or reproductive status influences secretory patterns of serum melatonin, gilts were exposed to artificial light or full sunlight during the summer months. In Experiment 1, eight prepubertal and eight postpubertal gilts (Hampshire x Yorkshire x Duroc) were exposed to light intensity of 700 lux in an environmentally controlled room from 0730 to 1900 h daily. An additional eight prepubertal and eight postpubertal gilts were reared outdoors in an open modified-front gestation building and fed on a concrete apron outdoors where light intensity approached 50,000 lux in full sunlight. After 2 mo of acclimating to these environmental conditions, blood samples were drawn from each gilt at 2-h intervals from 1000 to 0200 h. Serum concentrations of melatonin were assayed utilizing Guildhay antisera. The experiment was repeated during the same months of the following year utilizing different gilts (Experiment 2). During both replications, neither light intensity nor reproductive status affected the secretory patterns of melatonin during the sampling period (P >0.05). In both prepubertal and postpubertal gilts, serum concentrations of melatonin were not reduced (P >0.05) by exposure to direct sunlight. Since baseline concentrations of serum melatonin were not reduced by sunlight during the day, the incidence of nocturnal rises of melatonin was not increased (P >0.05) in either prepubertal or postpubertal gilts.

Maternal recognition of pregnancy in swine. I. Minimal requirement for exogenous estradiol-17 beta to induce either short or long pseudopregnancy in cycling gilts.

Five experiments were conducted to determine the minimal requirement for estradiol-17 beta (E2) injections to induce either short pseudopregnancy (SPP) or long pseudopregnancy (LPP) in cycling gilts. In experiments 1 through 5, E2 was injected i.m. on combinations of days between 11 and 25 days postestrus. Exogenous E2 on Days 12 and 13 or on Days 12 through 19 was optimal for induction of SPP or LPP, respectively. The duration of E2-induced diestrus was clearly demarcated between SPP (n = 73, duration 23-35 days) and LPP (n = 23, duration > 50 days). A sixth experiment was conducted to determine the minimum dose of intrauterine E2 required to induce SPP, and these gilts received intrauterine infusions of 0, 4, 40, or 400 micrograms E2 per 24 h on Days 12 and 13 postestrus. Pseudopregnancy was induced in 0 of 12, 1 of 4, 1 of 11, and 4 of 7 gilts in the treatment groups, respectively. These data suggest that uterine exposure alone is not sufficient to induce SPP. The present results indicate that the optimal signal for inducing LPP in unmated cycling gilts, and perhaps also for maternal recognition of pregnancy in mated gilts, may occur in two phases with continuous exposure to E2 being required from Day 12 to Days 17-19.

Maternal recognition of pregnancy in swine. II. Plasma concentrations of progesterone and 13,14-dihydro-15-keto-prostaglandin F2 alpha during the estrous cycle and during short and long pseudopregnancy in gilts.

Two experiments were conducted to determine plasma progesterone (P4) and 13,14-dihydro-15-keto-prostaglandin F2 alpha (PGFM) concentrations in unmated gilts induced to have either short pseudopregnancy (SPP) or long pseudopregnancy (LPP). In experiment 1, estradiol-17 beta (E2) was injected on different combinations of days between Days 11 and 16 of the estrous cycle. For gilts induced to exhibit SPP, the interestrous interval averaged 27.0 +/- 0.4 days compared to the control interval of 20.0 +/- 0.4 days. In experiment 2, E2 injections were given on Days 12 and 13 or on Days 12 through 25. Interestrous intervals in SPP and nonpseudopregnant gilts were 25.6 +/- 0.2 and 19.9 +/- 0.6 days, respectively. Four of six gilts treated with E2 on Days 12-25 were induced to have LPP lasting more than 100 days. In both experiments, plasma P4 declined to baseline approximately 3 days before posttreatment estrus, regardless of type of pseudopregnancy induced. Plasma PGFM peaked 4-6 days before posttreatment estrus in gilts displaying each type of response. In gilts exhibiting LPP, plasma PGFM concentrations tended to increase steadily during pseudopregnancy. These data suggest that the mechanisms of luteolysis during the estrous cycle of unmated gilts and during estrogen-induced SPP and LPP may be similar. The present results suggest that luteal persistence during SPP and LPP may be due to delayed peak release of prostaglandin F2 alpha by the uterus.

Serum concentrations of melatonin in prepubertal gilts exposed to either constant or stepwise biweekly alteration in scotophase.

Melatonin (MEL), a hormone known to mediate photoperiodic cues, is secreted from the pineal gland in a circadian fashion in numerous species. The transduction of photoperiodic information into the secretion of MEL, however, remains controversial in the pig. To determine whether domestic pigs have a nocturnal increase in serum melatonin when exposed to equatorial photoperiods only, 24 prepubertal gilts (38.7 +/- 0.7 kg; 104.5 +/- 0.8 d) and 12 mature ewes, serving as positive controls, were randomly assigned to one of two environmentally regulated rooms. The light (L):dark (D) schedule in one room remained constant (10 L:14 D), while the other room scotophase (darkness duration) was decreased by 1 hr every 2 wk (Experiment 1). After a 2-wk acclimation to each new schedule, 6 ewes and 6 gilts in each room were bled by venipuncture at 2-hr intervals for 22 hr. Experiment 2 was conducted as described for Experiment 1, except that the LD schedule in one room remained constant (15L:9D) while length of scotophase in the other room was increased by 1 hr every 2 wk. In gilts that were exposed to constant 10L:14D, scotophase MEL in serum averaged 103 +/- 13 pg/ml as compared with 57 +/- 13 pg/ml in the photophase. Using each gilt's initial photophase value as a statistical covariate, scotophase MEL in the constant 10L:14D schedule was higher (P < 0.001) than photophase MEL. A similar analysis of MEL in gilts exposed to stepwise biweekly decreases in scotophase revealed a scotophase elevation (P < 0.05) in only certain LD schedules (i.e., 12L:12D and 13L:11D), but the same trend was present throughout all LD schedules. Subjective examination of individual gilt profiles revealed that 56% of gilts had a nocturnal increase in serum MEL in Experiment 1. However, only 10% of the MEL profiles were closely coupled to the environmental LD periods. Overall, mean serum MEL in gilts was of lesser magnitude and more variable than in ewes. Data from these two experiments suggests that the domestic pig has an inherently weak nocturnal elevation in serum MEL, and the ability to detect these rises is dampened by considerable pig-to-pig variability.

Growth and reproductive performance, during exposure to ammonia, of gilts afflicted with pneumonia and atrophic rhinitis.

From 2 to 4.5 months of age, 80 crossbred gilts were reared in a conventional grower unit where they were naturally exposed to mycoplasmal and bacterial pathogens that cause pneumonia and atrophic rhinitis. At 4.5 months of age, gilts were moved to environmentally regulated rooms (4.9 x 7.3 m) and assigned at random to 1 of 2 treatment groups: low aerial concentration of ammonia (4 to 12 ppm; mean, 7 ppm) or moderate aerial concentration of ammonia (26 to 45 ppm, mean, 35 ppm). Low concentration of ammonia was obtained by flushing of manure pits weekly, whereas moderate concentration of ammonia was maintained by adding anhydrous ammonia to manure pits that were not flushed. Gilts were weighed biweekly. Mean daily gain (MDG) was less (P < 0.01) for gilts exposed to moderate concentration of ammonia than for gilts exposed to low concentration of ammonia after 2 weeks in their respective environments. By 4 and 6 weeks, however, MDG was similar between the 2 treatment groups. After 6 weeks in these environments, 20 gilts from each treatment group were slaughtered, and prevalence and severity of lung lesions and snout grades were determined. At slaughter, body weight was greater (P < 0.01) in gilts exposed to low, rather than moderate, ammonia concentration (94.5 vs 86.8 kg; SEM, 3.3 kg). Percentage of lung tissue containing lesions (18 vs 12) and snout grade (2.8 vs 3.1) were similar between gilts exposed to low or moderate concentration of ammonia. The remaining 20 gilts in each treatment group were maintained in their respective environments, exposed daily to mature boars and bred at first estrus.(ABSTRACT TRUNCATED AT 250 WORDS)

Serum concentrations of immunoactive and bioactive luteinizing hormone (LH) in gilts. I. Biopotency of LH increases during prepubertal development.

The patterns of secretion of bioactive and immunoactive LH during prepubertal development were examined in four groups of 12 gilts each at approximately 3, 4, 5, and 6 mo of age. The rat interstitial cell testosterone assay was validated for the determination of bioactive LH (BLH) in porcine serum. Serum concentrations of immunoactive LH (ILH) were determined by RIA. Blood samples were collected via indwelling jugular catheters every 20 min for a 6-h period of spontaneous secretion. GnRH (0.5 microgram/kg BW) was injected i.v. and blood samples were taken for an additional 4 h at 20-min intervals. Mean serum and baseline concentrations of ILH and of BLH were greater (p < 0.05) in 3-mo-old gilts than in gilts of other ages. Three-month-old gilts also secreted more ILH and more BLH in response to GnRH than 6-mo-old gilts (p < 0.05), but the biopotency of GnRH-induced LH was reduced (p < 0.05) in 3-mo-old gilts. Elevated serum concentrations of ILH and of BLH in 3-mo-old gilts may be inherently necessary to give follicles the maximum opportunity to respond to LH. During the period of prepubertal development, estimates of ILH accurately reflected BLH concentrations except when LH release was stimulated by exogenous GnRH. The age-related increase observed in the biopotency of LH released in response to GnRH may reflect a maturational process whereby the biopotency of LH increases as gilts approach puberty.

Serum concentrations of immunoactive and bioactive luteinizing hormone (LH) in gilts. II. Biopotency of LH increases at puberty but remains constant throughout the estrous cycle.

To determine serum concentrations of immunoactive (I) and bioactive (B) LH during the pubertal surge of LH release, two groups of twelve prepubertal gilts were relocated and exposed to boars to stimulate the onset of puberty. Puberty was defined as the first sign of behavioral estrus and occurrence of a preovulatory surge of LH. Blood samples were taken every 2 h, beginning on the third or fifth day after boar exposure; sampling was continued for 24 h after each gilt had exhibited estrus, or for 7 days, or until two-thirds of the gilts in a group attained puberty. Fifty percent of the total number of gilts exposed to boars attained puberty within 7 days of first boar exposure. Total area under the ILH curve was greater (p < 0.01) than area under the BLH curve during the ovulatory rise in LH. A second experiment was conducted to compare serum concentrations of ILH and BLH during the luteal and follicular phases of the estrous cycle. Blood samples were collected every 20 min for a 6-h period of spontaneous secretion; then GnRH was injected and blood samples were collected every 20 min for 4 h from gilts during the luteal (n = 16) and follicular (n = 15) phases, respectively. BLH baseline tended to be greater (p = 0.07) during the follicular phase than during the luteal phase. Mean peak amplitude of naturally occurring peaks of ILH and BLH was greater (p < 0.05) during the luteal phase than during the follicular phase.(ABSTRACT TRUNCATED AT 250 WORDS)

Influence of porcine somatotropin on endocrine and histological variables in gilts.

Thirty-six crossbred gilts (71.7 +/- .9 kg and 140.1 +/- .9 d) were assigned to one of three doses (0, 35, or 70 micrograms.kg BW-1 x d-1) of recombinant porcine somatotropin (rpST). The doses of rpST were adjusted weekly, and i.m. injections continued until d 50. Gilts were pen fed (six gilts/pen) a 17% CP corn-soybean diet (1.2% lysine and 3.2 Mcal of ME/kg). At d 50, feed intake, feed:gain ratios (P = .02), and blood urea nitrogen were decreased (P < .001) by increasing rpST doses, whereas ADG was increased (P = .04) by increasing rpST doses. Injections of rpST did not affect (P > .05) conception rate, age, or weight at puberty. Numbers of blastocysts or corpora lutea observed at d 10.4 +/- 1.5 of gestation (42.2 d after final rpST injection) were unaffected (P > .05) by rpST treatment. Anterior and posterior pituitary weights were increased (P < or = .003) linearly with rpST dose. However, liver, adrenal, and heart weights were unaffected (P > .05) by rpST. After a withdrawal period of 42.2 +/- 2.0 d, rpST increased (P < or = .02) the estimated percentage of lean by 5.8% and longissimus muscle area by 10.4%. Eighteen hours before the initial rpST injection (d 0), 10 gilts per rpST dose were catheterized. Catheterizations were repeated on d 40. The rpST or diluent was given i.m. in the extensor muscle of the neck 1 h after initiation of blood collection. Adrenocorticotropic hormone (1.4 IU/kg BW) was administered through the catheter 3 h after initiation of blood collection.(ABSTRACT TRUNCATED AT 250 WORDS)

Mycotoxins and reproduction in domestic livestock.

Molds are parasitic plants that are ubiquitous in livestock feedstuffs. Even though molds themselves reduce the quality of grains, their synthesis of chemical substances termed mycotoxins causes the greatest monetary loss to the animal industry. Five major mycotoxins that impair growth and reproductive efficiency in North America are aflatoxins, zearalenone, deoxynivalenol, ochratoxin, and ergot. Aflatoxins are produced by Aspergillus flavus and Aspergillus parasiticus. Consumption of grains containing aflatoxins by swine affects reproduction indirectly by reducing feed intake and growth. In swine, aflatoxins impair liver and kidney function, delay blood clotting, increase susceptibility to bruising, and interfere with cellular humoral immune systems. Ruminants are comparatively resistant to aflatoxicosis, but presence of aflatoxins in milk of dairy cows is closely monitored for human safety. Depending on environmental conditions, Fusarium roseum can produce either zearalenone or deoxynivalenol. Days 7 to 10 postmating seem to be a critical period of gestation for zearalenone to exert its detrimental actions on early embryonic development. Presence of deoxynivalenol in swine feedstuffs decreases feed intake, causes feed refusal, and induces occasional vomiting. Several species of Penicillium and Aspergillus produce ochratoxin, a mycotoxin that causes necrosis of kidney tissue. Ergot alkaloids produced by Claviceps purpurea on wheat can cause reproductive problems and are associated with lactational failure in swine. Various methods have been developed to remove mycotoxins from infected feedstuffs. Chemical analyses in laboratories as well as diagnostic kits suitable for use at the elevator or farm can be used successfully to identify which mycotoxins are present in suspect feedstuffs.

Lack of a nocturnal rise of serum melatonin in prepubertal gilts.

Experiments were conducted to determine if a nocturnal rise in serum melatonin occurs in prepubertal gilts and whether acute exposure of gilts to light during the dark period abruptly reduces serum concentrations of melatonin. In experiment 1, 12 prepubertal crossbred gilts (Duroc x Hampshire x Chester White x Yorkshire) weighing 96.4 + 1.3 kg at 5.1 + .1 mo of age were housed in an LD cycle of 10:14. Following a 3-wk acclimation period, blood samples were drawn at 1-hr intervals from indwelling jugular catheters. Serum concentrations of melatonin were similar (P greater than .05) among blood samples collected during light and dark periods. In experiment 2, serum concentrations of melatonin did not change (P greater than .05) when gilts were abruptly exposed to light during the normal dark period. In experiment 3, serum concentrations of melatonin were similar (P greater than .05) in blood samples collected at 2-hr intervals under 700 lux of light or in total darkness from gilts maintained in either LD 9:15 or LD 24:0. Data from experiment 4 demonstrated that serum melatonin could be detected in nighttime samples if exogenous melatonin was ingested by gilts at night. Together, these experiments clearly indicate that prepubertal gilts do not exhibit a nocturnal rise in serum melatonin when maintained under short daylengths (10L:14D or 9L:15D), and serum melatonin concentrations are unaffected by abrupt changes in light/dark conditions.

Forebrain sites of estradiol-17 beta action on sexual behavior and aggression in female Syrian hamsters.

The effects of intracranial implants of estradiol in the ventromedial hypothalamus (VMH), the anterior hypothalamus (AH), or the medial amygdala (AMG) on aggression, sexual behavior, and serum estradiol were examined in female Syrian hamsters. Estradiol implants in the VMH, followed by systemic progesterone, stimulated sexual behavior and inhibited aggression. Estradiol implants in other intracranial sites activated sexual behavior but did not reliably inhibit aggression. Intracranially implanted and systemically treated animals had equivalent peripheral estradiol concentrations at sacrifice. These results suggest that: (a) the VMH is an important neural site for estradiol actions on sexual and aggressive behavior, (b) the caudal AH and AMG also may be sites of estradiol action on sexual behavior, and (c) these intracranial implants may only be effective given systemic estradiol exposure or the concurrent stimulation of multiple brain areas.

Effect of zearalenone on days 7 to 10 post-mating on blastocyst development and endometrial morphology in sows.

First litter sows in naturally occurring post-weaning estrus were hand mated to proven boars and were fed a diet supplemented with zearalenone, an estrogenic mycotoxin (1 mg zearalenone/kg body weight), or a control diet on days 7 through 10 after mating. Embryos (blastocysts) and endometrial biopsies were collected from control and treated sows on days 9, 11, and 13 after mating. All blastocysts harvested on day 9 were spherical; treatment of sows with zearalenone had no effect on blastocyst development. Blastocysts collected from treated sows on day 11 were in stages of elongation comparable to those of blastocysts from control sows but had mild degenerative changes in the embryonic disks, characterized by slightly retarded development and an increase in the number of necrotic cells. Blastocysts collected from treated sows on day 13 were in an advanced stage of degeneration, characterized by circumferential constrictive division, fragmentation, and degeneration and disorganization of the embryonic disk. Feeding zearalenone to pregnant sows had no effect on the normal decrease in height of the endometrial luminal epithelium on days 9 through 13 after mating and no effect on morphologic appearance of secretory vesicles in the endometrial glandular epithelium. The dosage scheme of zearalenone used in this study did not cause any morphologic changes in the endometrium that could be associated with hyperestrogenism.