Genetic parameter estimates for reproductive traits of male and female littermate swine

Reproductive traits of purebred and crossbred pigs produced in a four-breed diallel mating system using the Duroc, Landrace, Spotted and Yorkshire breeds were collected for five consecutive farrowing seasons (two farrowing seasons/year) beginning in fall 1976. Paternal half-sib heritabilities and genetic correlations for testicular traits (120 boars from 36 sires), serum testosterone (TE) and luteinizing hormone (LH) concentrations before and after treatment with gonadotropin releasing hormone (GnRH; 131 boars from 37 sires) and breeding performance traits (151 boars from 38 sires) were estimated. Heritability estimates were generally small to moderate except for sperm/gram testis (SGT), LH concentrations before (LHO) and at 3 h (LH3) after treatment with GnRH (.73 +/- .48, .61 +/- .46 and 1.19 +/- .45, respectively). A large positive genetic correlation was found for LHO with LH3 (.94 +/- .39), while a negative relationship existed for LH3 with TE concentrations at 3 h after GnRH injection. The genetic correlation between a boar's average first service conception rate and average conception rate also was significant (.82 +/- .54). Genetic correlations among littermate traits would suggest that selection for decreased age at puberty in gilts could cause an increase in LH concentrations in boar offspring, before and after GnRH injection, and may also have adverse effects on their ability to settle females. Selection for increased weight at puberty of gilts could cause TE concentrations of boar offspring to increase while having little effect on their breeding performance.     

Influence of manure gases on puberty in gilts

To determine whether manure gases can influence onset of puberty in gilts, 42 crossbred gilts were reared from 10 to 40 wk of age on concrete slats over a 1.22-m deep pit that was drained and refilled with clean water biweekly (clean group). Forty-one gilts were reared over a similar type pit where manure was allowed to accumulate (control group). Treatments were in two separate rooms of the same building with similar feeding, water, floor space, lighting and room temperature. Ventilation fans with timer controls in each room were set so fans in the clean environment ran twice as long as fans in the control environment. Aerial concentrations of ammonia in the control room were fourfold higher than in the clean room (21 vs 5 ppm), while aerial concentrations of hydrogen sulfide were similar. Average daily gain and feed efficiency were similar for both groups [.69 vs .72 kg/d (P = .31) and 1.61 vs 1.54 kg feed/kg gain (P = .52)]. From 20 to 40 wk of age, all gilts were exposed to a mature boar three times weekly, utilizing four boars in rotation. Blood samples were collected weekly from each gilt by venipuncture and analyzed for progesterone to establish time of first ovulation. A greater proportion of gilts in the clean group attained puberty by 24 to 26 wk (P less than .05) and 27 to 29 wk of age (P less than .10) compared with the control group.(ABSTRACT TRUNCATED AT 250 WORDS)     

Hormonal patterns of boars exposed to natural or supplemental lighting during pubertal development

Thirty-two crossbred boars (Hampshire X Duroc X Yorkshire) were reared under natural lighting (35 lx) or supplemental lighting (1,400 lx) beginning at 4 wk of age. Boars received supplemental lighting from six 40-W fluorescent bulbs between 0530 and 2030 in a nursery unit. From 9 to 32 wk of age, boars received either natural lighting (30 lx) or supplemental lighting (100 lx) in a growing-finishing unit. Blood samples were collected from indwelling cannulae at 20-min intervals for 6 h every 2 wk from 2.5 to 7 mo of age. Libido scores were evaluated during alternate weeks when intensive blood samples were not taken. Libido scores were not different between natural and supplemental lighting treatments (P greater than .30). However, at 122 d of age, libido scores of boars exposed to supplemental lighting tended to be higher (P = .10) than those exposed to natural lighting. Although mean serum concentrations of luteinizing hormone (LH) were higher (P less than .05) in boars at 75, 89, 103 and 131 d of age reared under supplemental lighting than boars of the same age reared under natural lighting, the number of LH secretory spikes was similar between the treatment groups (P = .39). Serum concentrations of LH decreased in both treatment groups as boars became older (P less than .05). However, the incidence of LH spikes was similar across ages and between treatment groups from 2.5 to 7 mo of age. Mean serum concentrations of follicle stimulating hormone and testosterone were similar between treatments (P greater than .75).     

Influence of daily injections of porcine somatotropin on growth, puberty, and reproduction in gilts

To determine whether recombinant porcine somatotropin (rpST) alters reproduction, 40 crossbred gilts weighing 59.1 +/- .5 kg at 125 +/- 1 d of age were assigned randomly to an experiment arranged as a 2 x 2 factorial. Eight gilts were given daily injections of diluent until they reached 104 kg BW (DW), and eight received diluent injections until puberty (DP). Twelve gilts were given rpST (4 mg/d) until 104 kg BW (PW) and 12 were given rpST injections until puberty (PP). All gilts were individually fed on an ad libitum basis an 18% CP corn-soybean meal diet (1.2% lysine and 3.1 Mcal/kg of ME). Beginning at 5 mo of age, gilts were exposed 20 min daily to mature boars. Serum concentrations of progesterone were measured weekly from 5 to 8 mo of age to verify age of puberty. Gilts observed in pubertal estrus were mated to two different boars 10 h apart. At 47 +/- 1 d of gestation, gilts were slaughtered to assess fetal development. After 60 d of treatment, serum LH and FSH profiles were determined in blood samples drawn at 20-min intervals for 4 h from eight diluent- and eight rpST-treated gilts fitted with indwelling jugular catheters. By 28 d, feed intake, feed/gain, and blood urea nitrogen were decreased (P less than .005) by rpST. Treatments did not affect (P greater than .05) the proportion of gilts attaining first ovulation (DW = 6/6; DP = 10/10; PW = 7/9; PP = 14/14) or conception rate (DW = 5/6; DP = 7/10; PW = 4/6; PP = 11/12).(ABSTRACT TRUNCATED AT 250 WORDS)     

The effect of castration, estradiol and LHRH on LH secretion of lambs fed different levels of dietary energy

To examine the effect of diet on luteinizing hormone (LH) secretion, basal and luteinizing hormone releasing hormone (LHRH)-induced LH release was compared in intact or castrated-estradiol-17 beta implanted Finn-Dorset lambs. Ten to 12 wk old ram (n = 20) and ewe lambs (n = 20) were maintained under a 8L:16D photoperiod and fed for high (HG, 163 to 168 g/d) or low (LG, 76 to 103 g/d) rates of gain. Eight to 10 wk later, baseline LH concentrations were determined in blood samples collected at 20 min intervals for 7 h. The following day, lambs were given an iv injection of 5 micrograms of estradiol-17 beta followed within 4 h by LHRH (.5 or 2.5 micrograms). Baseline concentrations of LH for HG ewes were threefold greater than for LG ewes (4.2 vs 1.4 ng/ml), respectively. Time to peak response was inversely related to dietary energy level (P less than .025). Basal LH levels were similar across diets in rams. Total LH release following LHRH was dose-dependent (P less than .005). Effects of gonadal feedback were tested in a second group (n = 24) of castrated lambs. Changes in LH secretion were not different between diets within 3 to 4 wk after castration. A subcutaneous silastic implant (22 mm) of estradiol-17 beta inhibited (P less than .01) LH concentrations across diets in both ewes and rams. No differences in estradiol feedback on LH secretion (at the dose of steroid tested) were detected between HG and LG lambs. Within 8 d, however, basal LH concentrations were 60% lower (P less than .01) in HG vs LG ewes. Furthermore, peak LHRH-induced LH release was greater (P less than .025) in LG vs HG lambs of both sexes. Estradiol inhibited basal LH secretion in ewes and rams but facilitated LH release in lambs with a reduced rate of gain.     

The influence of duration of photoperiod and hemicastration on growth and testicular and endocrine functions of boars

Yorkshire boars were used to evaluate the influence of duration of photoperiod and hemicastration on growth and testicular and endocrine functions. At 10 wk of age, 5 hemicastrate (HC) and 5 intact (I) boars were assigned to either 8 or 16 hr of light daily until 6 mo of age. Body weights were recorded biweekly throughout the experiment. Venous cannulae were placed in all boars at 6 mo of age, and serum was collected at 30 min intervals from 0800 to 2000 hr. Gonadotropin releasing hormone (GnRH) was infused at 2000 hr (50 micrograms) and at 2030 hr (250 micrograms), and samples of serum were collected until 2400 hr. The following day, all boars were castrated, and the weights and sperm content of the testes and epididymides were determined. At castration, all pigs were given implants containing testosterone. Two weeks later, pigs were again canulated, and serum was obtained at 15 min intervals for 2 hr. Growth of boars was not significantly affected by duration of photoperiod or number of testes. Duration of photoperiod did not affect weight or sperm content of testes or epididymides. Hemi-castrated boars had greater testicular (P less than .01) and capita-corpora (C-C) epididymal weights (P less than .05) and more testicular and C-C sperm (P less than .01) per testis. Neither average concentrations of luteinizing hormone (LH) nor number and amplitude of pulses of LH were affected by photoperiod treatment. However, HC boars had greater average concentrations of LH (P less than .05) than I boars (.71 +/- .05 vs .52 +/- .05 ng/ml). Hemicastrated boars in 16 hr light daily had greater concentrations of FSH in serum (P less than .05) than 8I, 8HC, and 16I boars. Intact and HC boars had similar concentrations of prolactin (PRL) and testosterone. Similarly, concentrations of PRL and testosterone were not affected by duration of photoperiod. Secretion of LH and testosterone after treatment with GnRH was not significantly affected by duration of photoperiod. In general, HC boars released more LH in response to GnRH treatment than I boars. Concentrations of LH were greater (P less than .05) in HC than I boars at .5, 1, 2, and 3 hr after GnRH and tended (P less than .10) to be elevated at 1.5, 2.5, 3.5 and 4 hr after GnRH. The FSH response to GnRH was greater (P less than .05) for 16HC than 8I, 8HC, or 16I boars.(ABSTRACT TRUNCATED AT 400 WORDS)     

Effect of purified zearalenone on early gestation in gilts

Purified zearalenone (Z) was added to the diet of gilts from d 2 to 15 postmating. Gilts received either 0, 5, 15, 30, 60 or 90 ppm Z (three to five gilts per dose) in 1.8 kg of feed daily. Serum concentrations of progesterone and estradiol-17 beta were determined weekly. On d 13 to 15 and 40 to 43 postmating, blood samples were drawn from a cannula at 20 min intervals for 4 h and analyzed for luteinizing hormone (LH), follicle-stimulating hormone (FSH) and prolactin (PRL). Gilts were killed 40 to 43 d postmating and embryonic development was assessed. Treatment with 5, 15 or 30 ppm Z had no effect on embryonic development when compared with 0 ppm. No fetuses were present in gilts fed 60 to 90 ppm Z, but two gilts given 60 ppm Z had remnants of fetal membranes in the uterus. The histologic appearance of reproductive tract tissues from the gilts given 60 ppm Z was similar to that from pregnant gilts. Tissues from gilts given 90 ppm Z appeared to be stimulated by both estrogen and progesterone. Serum concentrations of progesterone were decreased at 2, 3 and 6 wk postbreeding in gilts fed 60 and 90 ppm Z. Serum concentrations of estradiol-estradiol-17 beta were decreased at 4 wk postbreeding in gilts fed 60 and 90 ppm Z.(ABSTRACT TRUNCATED AT 250 WORDS)     

Serum concentrations of IGF-I, estradiol-17beta, testosterone, and relative amounts of IGF binding proteins (IGFBP) in growing boars, barrows, and gilts

The purpose of this research was to determine whether serum concentrations of steroids, IGF-I, and relative amounts of serum IGF-binding proteins (IGFBP) differ in growing boars (n = 11), barrows (n = 11), and gilts (n = 12) from 70 to 140 d of age. Pigs of similar age and weight were housed in pens of three or four and given ad libitum access to a 17% CP corn-soy diet and water. Pigs were weighed and blood samples were collected every 14 d beginning at 70 d of age. Serum concentrations of IGF-I and steroids were determined by RIA and relative amounts of IGFBP were determined by ligand blot analysis. By 84 d of age and continuing through 140 d of age, mean serum concentrations of IGF-I were greater (P < .05) in boars than in barrows or gilts. Relative amounts of 46-kDa IGFBP3 and 28-kDa IGFBP-4 were similar (P > .05) among pigs at 70 d of age; however, boars and barrows had greater (P < .05) relative amounts of 24-kDa IGFBP-4 and 41-kDa IGFBP-3 than gilts. Relative amounts of IGFBP-2 were greater (P < .01) in barrows than in gilts or boars at 70 d of age. From 84 d of age through 140 d of age, relative amounts of both forms of IGFBP-3 and the 28-kDa IGFBP-4 were greater (P < .05) in boars than in gilts or barrows. Relative amounts of IGFBP2 were greater (P < .05) in barrows than in gilts or boars at 98 d of age, but by 140 d of age relative amounts were greater (P < .05) in boars and barrows than in gilts. Mean serum concentrations of estradiol-17beta were similar (P > .05) between gilts and boars at 70 d of age, but by 98 d of age, and continuing through 140 d of age, mean serum concentrations of estradiol-17beta were greater (P < .05) in boars than in gilts. Mean serum concentrations of testosterone in boars increased (P < .05) with increasing age and were greatest at 128 and 140 d of age. Serum concentrations of testosterone were negatively correlated (P < .01) with relative amounts of serum IGFBP-2 but positively correlated (P < .01) with serum concentrations of IGF-I and estradiol-17beta. Serum concentrations of estradiol-17beta were positively correlated (P < .01) with serum concentrations of IGF-I in boars. Changes in serum concentrations of IGF-I and relative amounts of IGFBP resulting from changes in serum concentrations of estradiol-17beta and testosterone may contribute to growth differences observed among sexes.     

Characterization of gonadotropic and ovarian steroid hormones during the periovulatory period in high ovulating select and control line gilts

Cyclic gilts from Control (C, randomly selected, n = 11) and Relax Select (RS, nine generations of selection for increased ovulation rate followed by seven generations of relaxed or random selection, n = 9) lines of the University of Nebraska Gene Pool population (derived from 14 different breeds) were utilized to characterize differences in gonadotropic and ovarian steroid hormones during preovulatory and postovulatory phases of the estrous cycle. Blood samples were collected during four periods (0500, 1100, 1700 and 2300) daily beginning 2 d prior to anticipated estrus (d -2, d 18 of a 20-d estrous cycle), and continuing through d 4 postestrus (d 0 = 1st of standing estrus). Sampling within a period consisted of five blood samples at 15-min intervals. All plasma samples were analyzed for concentrations of follicle stimulating hormone (FSH) and luteinizing hormone (LH). Neither mean LH nor peak concentration of LH during the preovulatory surge differed between genetic lines (P greater than .10). Concentrations of FSH increased faster (line X period, P less than .05) and tended (P less than .1) to peak at a higher concentration in RS (.88 ng/ml) than in C (.54 ng/ml) gilts (P less than .05) during the 12 h preceding the FSH and LH preovulatory peaks. The second FSH surge began approximately 24 h after the preovulatory FSH peak. Peak FSH concentrations were observed at 42 h in both lines (1.46 vs 1.74 ng/ml for C and RS gilts, respectively). The higher FSH concentration in RS gilts established during the preovulatory surge was maintained through the second FSH surge (P less than .01). No line differences were detected in plasma concentrations of estradiol-17 beta and progesterone.     

Follicular fluid concentrations of estradiol-17 beta and progesterone and secretory patterns of LH and FSH in prepubertal gilts reared in confinement or outdoor lots

One-hundred-twenty crossbred gilts from two experiments were assigned randomly to a 2 X 5 factorial experiment. Gilts were reared in two environments (confinement or outside) and assigned to be slaughtered at 4, 5, 6, 7 or 8 mo of age. Beginning at 6 mo of age, blood samples were taken at weekly intervals from each gilt via venipuncture. Serum concentrations of progesterone were analyzed to determine when gilts attained puberty. On the day prior to slaughter, six pigs within a treatment group were cannulated and blood samples were taken at 20-min intervals for 4 h. At slaughter, follicular fluid (FF) was aspirated and the volume determined from those follicles having a diameter of at least 4 mm. No effect of environment was found on the proportion of gilts that attained puberty by 8 mo of age. For the 12 gilts that reached puberty during the study, the age at puberty for gilts reared in outdoor lots (202 +/- 5 d) was less (P less than .05) than those reared in confinement (224 +/- 8 d). Mean concentrations of serum luteinizing hormone (LH; P = 98) and number of secretory spikes of LH (P = .76) were similar between gilts reared in confinement and those reared in outdoor lots. No differences in average serum concentrations of follicle stimulating hormone (FSH) or number of secretory spikes of FSH were found between gilts subjected to these environments (P = .95). Concentrations of estradiol-17 beta in FF were not affected by environment or age (P greater than .25).(ABSTRACT TRUNCATED AT 250 WORDS)     

Serum profiles of progesterone, LH, FSH and prolactin immediately preceding induced puberty in gilts

Two experiments were conducted to determine if the secretory patterns of luteinizing hormone (LH), follicle stimulating hormone (FSH) and prolactin (PRL) and serum concentrations of progesterone change immediately preceding induced puberty in gilts. To help predict when prepubertal gilts would attain puberty, gilts were induced into puberty by relocation from confinement housing to an outdoor lot and exposure to mature boars. In Exp. 1, 17 prepubertal gilts were bled on two successive days from 0800 to 1200 h before relocation and boar exposure and until the second day of estrus or for 8 d in gilts that failed to exhibit estrus. Blood samples were collected from indwelling cannulas at 20-min intervals for 4 h. In Exp. 2, blood samples were collected from 20 prepubertal gilts at 20-min intervals from 0800 to 1200 h and from 2000 to 2400 h until the second day of estrus or for 6 d if the gilt failed to exhibit estrus. In each experiment, 11 gilts exhibited pubertal estrus 3 to 6 d after relocation and boar exposure. When the frequency of LH spikes in each gilt was normalized to the day of her preovulatory surge of LH (d 0), a decline in the frequency of LH secretory spikes was observed as gilts approached puberty. However, neither the average magnitude of LH spikes nor mean LH concentrations were different among these days. Mean serum concentrations, frequency of spikes or average magnitude of secretory spikes of FSH or PRL did not change on the days preceding the preovulatory peak of LH.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effect of castration on plasma luteinizing hormone concentrations in prepubertal boars

Mean concentrations and the occurrence of pulsatile release of luteinizing hormone (LH) were determined in 14-wk-old crossbred boars (50.5 +/- 1.5 kg) after bilateral or unilateral castration at 10 wk of age. Blood was collected at 10-min intervals for 5 h. Then gonadotropin releasing hormone (GnRH; 40 micrograms) was given and sampling was continued at 5-min intervals for 1 h. Compared with intact boars, bilateral castration increased (P less than .001) mean LH (982 +/- 56 vs 389 +/- 56 pg/ml), pulsatile releases of LH (7.0 +/- .6 vs 2.0 +/- .6 pulses/5 h) and LH pulse amplitude (617 +/- 29 vs 360 +/- 58 pg/ml). Unilaterally castrated boars did not differ from intact boars in any of the above measures of LH secretion. Testis weight increased more between 10 and 14 wk of age in the unilateral castrates than in the intact boars (432 +/- 42 vs 245 +/- 34%; P less than .05). Thus, compensatory hypertrophy occurred within 4 wk of castration. Plasma testosterone was lower for bilateral castrates than for intact animals (.1 +/- .8 vs 3.6 +/- .9 ng/ml; P less than .05) while unilateral castrates (3.8 +/- 1.0 ng/ml) and intact boars did not differ. Plasma estradiol concentrations in bilateral and unilateral castrates were not different from levels found in intact boars (1.8 +/- 1.8, 8.8 +/- 2.1 and 6.0 +/- 1.8 pg/ml, respectively).(ABSTRACT TRUNCATED AT 250 WORDS)     

Prolactin and luteinizing hormone secretion in the pregnant pig.

Four pregnant, primiparous, crossbred gilts and six gilts from the same population that had been ovariectomized (OVX) for approximately 3 wk were placed in individual pens in an enclosed building. Blood samples were collected every 30 min for 12 h from all gilts via an indwelling jugular vein cannula when the pregnant gilts were at d 30, 50, 70, 90, and 110 of gestation. Serum was quantified for LH and prolactin (PRL) by RIA. The OVX gilts served as controls to ensure that any variations in serum LH and PRL concentrations observed in the pregnant animals were not due to environmental factors unrelated to pregnancy. Within the pregnant gilts, mean serum LH concentrations, mean basal serum LH concentration, and mean serum LH peak height were similar on all days; however, number of LH peaks on d 30, 50, and 70 were greater (P < .05) than on d 90 and 110, and number of LH peaks on d 50 was greater (P < .05) than that on d 70. Within the pregnant gilts, mean serum PRL concentration, mean basal serum PRL concentration, and mean PRL peak height were greater (P < .001) on d 110 than on all other days; however, number of PRL peaks were similar among days. Parameters of LH and PRL secretion in the OVX and pregnant gilts varied independently. Results of this study indicated that 1) LH secretion does not vary appreciably throughout pregnancy and 2) PRL secretion does not vary significantly during the first 90 d of pregnancy, after which it increases markedly on or before 110 d.     

Effect of vitamin supplements on some aspects of performance, vitamin status, and semen quality in boars

The aim of the present study was to determine the effects of dietary supplements of vitamins on vitamin status, libido, and semen characteristics in young boars under normal and intensive semen collection. Sixty Landrace, Yorkshire, and Duroc boars were allocated randomly from 6 to 10 mo of age to one of the following diets: 1) basal diet (industry level) for minerals and vitamins (Control, n = 15); 2) basal diet supplemented with vitamin C (ASC, n = 15); 3) basal diet supplemented with fat-soluble vitamins (FSV, n = 15); and 4) basal diet supplemented with water-soluble vitamins (WSV, n = 15). After puberty (approximately 12 mo of age), semen was collected at a regular frequency (three times every 2 wk) for 5 wk. Thereafter, all boars were intensively collected (daily during 2 wk). A recovery period (semen collection three times every 2 wk) followed and lasted for 10 wk. Sperm quality (percentage of motile cells and percentage of morphologically normal cells) and quantity (sperm concentration, semen volume, and total sperm number) were recorded as well as direct and hormone related measurements of boar libido. Blood and seminal plasma samples were taken to monitor vitamin status. High concentrations of B6 (P < 0.05) and folic acid (P < 0.05) were observed in the blood plasma of WSV boars, whereas greater concentrations of vitamin E (P < 0.01) were obtained in FSV boars. In the seminal plasma, folic acid concentrations tended to be greater in WSV boars (P < 0.08). During the intensive collection period, there was a tendency (P < 0.06) for semen production to be greater in WSV boars, the effect being less pronounced (P < 0.10) in FSV boars. During the recovery period, the percentage of motile sperm cells was greater in WSV boars (P < 0.03) and, to a lesser extent, in FSV boars (P < 0.10) compared with Control boars. Sperm morphology and libido were not affected by treatments. These results indicate that the transfer of vitamins from blood to seminal plasma is limited and the dietary supplements of water-soluble and fat-soluble vitamins may increase semen production during intensive semen collection.     

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 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)     

Release of luteinizing hormone after administration of naloxone in pre- and peripuberal heifers.

This study was conducted to investigate regulation of LH release by opioid peptides during puberal development in beef heifers. Fourteen heifers were randomly assigned to receive naloxone (opioid antagonist) i.v. at dosages of either 1 mg.kg BW-1.wk-1 (Dose 1) or .25 mg.kg BW-1.wk-1 (Dose 2) for 13 wk or until puberty. Blood was sampled (one sample every 15 min) 6 h before (prenaloxone) and 2 h after naloxone administration. Two hours after naloxone administration, GnRH (10 ng/kg BW) was administered and blood was sampled for 1 h. Nine heifers attained puberty during the study. There were no differences between naloxone dosage groups for any measured variables. Therefore, heifers were grouped dependent on the attainment of puberty. Prenaloxone concentrations of serum LH and LH pulse frequency were normal for prepuberal heifers. Serum LH concentrations increased within 30 min after naloxone 135 of 139 times it was administered (P less than .05). Serum LH concentrations during the hour after naloxone were higher (P less than .05) than those during the hour before naloxone in both puberal and nonpuberal heifers. In puberal heifers, serum LH pulse height during the hour after naloxone was greater (P less than .02) at 5 wk before puberty and lower (P less than .02) the week before puberty than at other times during the trial. There was no effect of week on serum LH pulse height after naloxone in heifers that failed to attain puberty during the study. Response of LH to GnRH was similar between groups.(ABSTRACT TRUNCATED AT 250 WORDS)     

Nutritionally-induced anestrus in gilts: metabolic and endocrine changes associated with cessation and resumption of estrous cycles

Two experiments determined how feed restriction and realimentation altered metabolism and ovarian function in gilts. In Exp. 1, cyclic (INTACT-R, n=6) and ovariectomized (OVEX-R, n=6) gilts were fed restricted diets (.23 kg feed.d-1) or ovariectomized (OVEX-C, n=6) gilts were fed control diets (1.81 kg.d-1). Estrous cycles stopped after 46 +/- 9 d of feed restriction. Average weight (WT), backfat thickness (BF) and concentrations of insulin (INS) were lower and free fatty acids (FFA) were greater in OVEX-R than in OVEX-C gilts. Frequency of luteinizing hormone (LH) release (peaks.6 h-1) was reduced by feed restriction (.2 +/- .2, 1.8 +/- 1.0 and 5.8 +/- .2 in INTACT-R, OVEX-R and OVEX-C gilts, respectively). Patterns of secretion of LH and follicle stimulating hormone (FSH) after gonadotropin releasing hormone (GnRH) or estradiol benzoate were not altered by feed restriction. Feed intake was then increased in INTACT-R and OVEX-R gilts beginning on d 80 and 82, respectively. Resumption of estrous cycles in INTACT-R gilts occurred on d 116.0 +/- 4.0 and was preceded by a significant increase in WT, but not BF, and a linear increase in concentration and frequency of release of LH. Increasing feed intake in OVEX-R gilts increased WT and frequency of LH release, while FFA decreased and INS increased to concentrations not different from those of OVEX-C gilts. The hypothesis that nutritionally-induced anestrus resulted from decreased activity of the hypothalamic pulse-generator was evaluated in Exp. 2 by providing 144 hourly pulses (iv) of saline (n=3), GnRH (n=3) or LH (n=4) to nutritionally-anestrous gilts.(ABSTRACT TRUNCATED AT 250 WORDS)     

Ovarian function and hormone secretion of gilts actively immunized against androstenedione

Fifty crossbred gilts immunized against bovine serum albumin (BSA) or androstenedione conjugated to BSA (AD) were used in three experiments. Primary immunizations were given at 120 d of age and boosters at 148 and 176 d. Gilts were moved to pens containing four to five animals each and exposed to boars beginning at 180 d of age. Immunization against AD did not affect age at puberty, percentage of gilts exhibiting estrus or duration of first estrous cycle. Over the three experiments, ovulation rate was 24% greater for AD-immunized gilts than for controls, and the number of corpora lutea was related positively (r = .82) to the log of the antibody titer. Number of ovulations decreased as interval from booster immunization to onset of estrus increased. During diestrus of the first estrous cycle, gilts immunized against AD had more follicles 5 to 10 mm in diameter, more total ovarian follicles and more total ovarian structures (corpora lutea plus follicles) than controls. Immunization against AD increased the frequency of LH pulses on d 16 but not on d 17 or 18, of the estrous cycle. However, average serum concentrations of LH, FSH and estradiol from 5 d before until 2 d after expected estrus were not different between treatment groups. Concentrations of AD in follicles 4 to 6 and greater than 7 mm in diameter were greater in gilts immunized against AD. Mean serum progesterone was higher on d 9 and 12 after mating in AD immunized gilts than in controls. Immunization against AD had no effect on maintenance of pregnancy or embryo survival rate.     

Contact with oestrous female pigs stimulates and synchronises puberty in gilts.

Three experiments, using a total of 132 pre-pubertal gilts, were carried out to investigate the influence of contact with oestrous female pigs on the attainment of puberty by gilts. Experiment 1 compared the effect of removing the gilts from their groups as they reached puberty in response to exposure to a boar, with leaving the gilts in their groups for five to 15 days after puberty or five to 15 days after second oestrus. All the groups exposed to boars reached puberty significantly earlier than controls (P less than 0.05) but there was no difference between these groups in their mean age at puberty. However, the synchrony of puberty was significantly greater among the gilts which remained in their groups after puberty (P less than 0.01) or second oestrus (P less than 0.001) than among the gilts which were removed at puberty. Experiment 2 investigated the influence of housing pre-pubertal gilts with penmates induced into puberty with injections of oestradiol benzoate. Puberty was significantly advanced by the presence of penmates regularly exhibiting oestrous periods. Experiment 3 compared the effect of daily exposure to an anoestrous ovariectomised sow, an oestrous ovariectomised sow or a boar, on the attainment of puberty by gilts. Gilts exposed to either an oestrous sow or a boar were significantly younger at puberty than isolated control animals (P less than 0.05) whereas the mean age at puberty of gilts exposed to an anoestrous sow was not significantly different from that of controls.(ABSTRACT TRUNCATED AT 250 WORDS)