Non-pregnant Sows Research Articles

Lysine vasopressin-induced increases in porcine myometrial contractility and intracellular Ca2+ concentrations of myometrial cells: involvement of oxytocin receptors.

The present study was undertaken to investigate whether lysine vasopressin (LVP) induces porcine myometrial contractions by activating vasopressin or oxytocin (OT) receptors. Both LVP (3 x 10(-9)-10(-6) M) and OT (3 x 10(-11)-10(-8) M) increased contractility dose-dependently in myometrium from both the luteal phase and prepartum period. Comparison of EC50s showed that OT was 75 and 57 times more potent than LVP in increasing myometrial contractility in pregnant and nonpregnant sows, respectively. L-366,948 (10(-8), 3 x 10(-8), 10(-7) M), a highly selective OT receptor antagonist, inhibited LVP- and OT-induced increases in myometrial contractility dose-dependently in both pregnant and nonpregnant tissues with similar antagonist affinity values (pA2). The V1 antagonist d(CH2)5[D-[Tyr(Me)2]AVP also antagonized both LVP- and OT-induced increases in myometrial contractility, but higher concentrations (10(-7) and 10(-6) M) were required to achieve the antagonism. The V2 antagonist Aaa-D-Tyr(Et)-Phe-Val-Asn-Abu-Pro-Arg-Arg-NH2 (10(-6) M) did not alter this effect of LVP and OT. LVP (10(-9)-10(-6) M) and OT (10(-10)-10(-7) M) also increased intracellular Ca2+ ([Ca2+]i) concentrations in porcine myometrial cells from sows during the prepartum period in a dose-dependent manner, with OT being 14 times more potent than LVP. L-366,948 (10(-9)-3 x 10(-8) M) antagonized the effect of OT (10(-7) M) and LVP (10(-6) M) in a similar dose-dependent manner.(ABSTRACT TRUNCATED AT 250 WORDS)

Follicular development during early pregnancy and the estrous cycle of the sow

The objective of this study was to monitor and compare follicle populations and follicular development in pregnant and nonpregnant sows from Day 3 to Day 20 after breeding. Twenty-four sows were paired within parity on the day of artificial insemination and were randomly allocated within pair for insemination with either killed (n=12) or live spermatozoa (n=12). All the sows were artificially inseminated with the pooled ejaculate of the same boar. From Day 3 through Day 20 post estrus, ovarian follicles were scanned daily by ultrasonography. Ultrasound images were recorded on videotape and were retrospectively analyzed. Follicles were mapped to indentify the existence of follicular waves. The follicles were then classified as small (< 3 mm), medium (3–5 mm), or large (≥5 mm). Pregnancy diagnosis was performed on Day 21 by ultrasonography. Pregnant sows maintained a constant proportion of the follicle population in the small, medium and large follicle categories. However, in the nonpregnant sows, the proportion of follicles in the various size categories remained constant until Day 15. Thereafter, the proportion of small follicles decreased (P < 0.05) from Day 15 to 20, and the proportions of medium and large follicles increased (P < 0.05). The predictability of pregnancy status on Day 20 based on follicle populations in any of the 3 follicle categories was low. Moreover, there was no evidence of follicular waves during the estrous cycle or early pregnancy. In conclusion, the proportion of small follicles decreased while medium and large follicle increased from Day 15 through Day 20 of the estrous cycle, but not during a similar stage of pregnancy. This latter finding concurs with follicle recruitment from the pool of small follicles for ovulation following PGF2α secretion to induce luteolysis, which reduces progesterone concentrations and thereby allows for the stimulation of the pool of small follicles by gonadotropins.

Pregnancy diagnosis in sows: enzyme immuno assay measurement of oestrone sulphate in plasma on day 25–30 after insemination in comparison to ultrasound scanning on day 28

The overall accuracy of plasma oestrone sulphate (E 1S) and ultrasound pregnancy diagnosis in a group of 953 inseminated sows was 99.0% and 91.2%, respectively. The accuracy of pregnancy diagnosis based on E 1S (day 25–30) for pregnant sows (test sensitivity) as well as that for non-pregnant sows (test specificity) was high (99.4% and 96.9%, respectively). For A-mode ultrasound pregnancy diagnosis (day 28) the test sensitivity was also high (96.2%), but the test specificity was low (55.0%). Litter size at farrowing (total born) was significantly correlated with the E 1S concentration on days 25–28, but the correlation coefficients were rather low (0.20–0.42). It is concluded that pregnancy diagnosis based on E 1S measurement between days 25 and 30 is highly sensitive and specific, but the E 1S concentration can not be used to predict litter size accurately. Especially the high test specificity, together with the ease and rapidity of performance of the EIA procedure, adds considerable to the potential value of E 1S measurement for routine pregnancy diagnosis in pigs.

Ameliorative Effect of Folic Acid on Pyrimethamine Teratogenesis in Pigs

The effects of oral dosing of folic acid (FA) on pyrimethamine (PYR) teratogenesis were examined in Goettingen minipigs. PYR (3.6 mg/kg/day) was orally administered in the feed to sows with or without FA (2.5, 10 or 50 mg/kg/day) for 12 days, (days 11 - 22 of gestation). Major malformations, such as cleft palate, cleft lips, micrognathia and clubfoot, were observed in all treated groups. The incidence of malformed fetuses decreased dose-dependently as the FA level was raised. This new finding suggests FA administration may prevent newborns from PYR induced malformations. This result contrasts in the observations in rats, in which PYR teratogenesis was potentiated by the concurrent oral dosing of FA. Neither PYR blood concentrations nor plasma protein binding was significantly affected by FA dosing in nonpregnant sows. These results suggest a mechanism other than pharmacokinetic modification was responsible for the protective effect of FA on PYR teratogenesis in minipigs.

Identification and characterization of 19-nortestosterone in urine of meat-producing animals

To monitor the illegal use of 19-nortestosterone as an anabolizing agent in meat-production, the Belgian Institute of Veterinary Expertise applies a strategy of urine control by radioimmunoassay, positive samples being confirmed by thin-layer chromatography. We have evaluated this control strategy, using gas chromatography—mass spectrometry to confirm the presence of 19-nortestosterone, or its metabolite oestrane-diol, in positive samples from radioimmunoassay. Our results show that the effective way of proceeding remains reliable in cattle, for mature and immature males as well as non-pregnant females, and in pigs, for pregnant and non-pregnant sows. The possible presence of endogenous 19-nortestosterone in cattle, in pregnant cows urine, and in pigs, in boars and in cryptorchid pigs, impedes the control of the use of 19-nortestosterone on these samples. False-positive (not confirmed by gas chromatography—mass spectrometry) results were produced by radioimmunoassay in the urine of castrated pigs and sheep.

Use of an on-farm progesterone assay kit to determine pregnancy in sows.

Blood samples taken from the ear vein of 1037 sows two to three weeks after service were assayed the same day using Ovucheck 'Sowside' kits. Colour development was compared with oestrous and pregnancy controls. Reliable data on reproductive performance were obtained from 908 sows sampled 17 to 20 days after service. The accuracy of identification of 796 pregnant and 12 non-pregnant sows was 94.6 per cent and 35.7 per cent, respectively. Excluding animals which returned outside the normal range of 18 to 24 days, 52.1 per cent of 48 empty sows were identified by the test. Problems with blood sampling were reported on seven of 18 farms and this may explain the low accuracy of the kit on some farms.

Inhibitory effect of oxytocin and vasopressin on steroid release by cultured porcine luteal cells.

Previously, we have demonstrated the presence of substances reacting like arginine vasopressin (AVP) and oxytocin (OXT) in acid extracts of corpora lutea (CL) of pigs by RIA. The present study examined purified extracts of CL by using HPLC. The results of these experiments show that CL of nonpregnant sows contain AVP and OXT. Little is known about possible auto- and paracrine effects of AVP and OXT in the ovary. Therefore, we investigated the influence of AVP and OXT on progesterone, estradiol, and androstenedione secretion in porcine luteal cell cultures from nonpregnant sows. Progesterone and androstenedione secretion increased significantly (P less than 0.05) in the presence of ovine LH (oLH), whereas no change in basal estradiol levels could be observed under the same conditions. When AVP or OXT was added to the culture system a dose-dependent inhibition of basal as well as oLH-stimulated progesterone secretion was measured. Under basal conditions, a dose of 1 pg AVP/ml decreased progesterone secretion significantly (P less than 0.05), but to reach the same effect in the presence of OXT a dose of 100 ng/ml was necessary. In the presence of oLH the addition of as little as 0.01 pg AVP/ml inhibited progesterone secretion significantly (P less than 0.05). On the other hand, 10 ng OXT/ml or higher doses were needed to decrease oLH-stimulated progesterone release. In the presence of specific peptide antagonists the inhibitory effect on progesterone release was abolished. These results suggest that AVP and OXT effects are mediated through specific receptors. OXT and AVP also inhibited androstenedione secretion, but had no effect on estradiol secretion. Calculation of the ED50 data from dose-response curves of both peptides show that AVP is about 10(4)-fold more active than OXT in inhibiting in vitro progesterone and androstenedione secretion. This suggests that AVP as well as OXT may play an important role in the regulation of ovarian function.

Pregnancy diagnosis in sows by estimation of oestrogens in blood, urine or faeces

Concentrations of oestrone sulphate in blood and of total unconjugated oestrogens in faeces were measured during the oestrous cycle and early gestation. The level of these hormones in blood and faeces was consistently higher (blood, 100%; faeces, 69–100%) between Days 24 and 30 in pregnant than in non-pregnant sows. Therefore, early pregnancy diagnosis based on the concentration of oestrogens in blood, urine and faeces was performed on Day 27, 28 or 29 after service for a total of 290 sows. Blood samples (25 μl) were taken from the tail vein of 289 sows. One hundred urine samples (1 ml) were collected by inserting a cellulose sponge into the vagina and faeces samples (2 g) were taken from the rectum of 290 sows. Pregnancy diagnosis was made on the assumption that more than 2.79 ng oestrone sulphate/ml blood, 19.7 ng oestrogens/g faeces and 65.6 ng oestrogens/ml urine indicated a pregnant animal. The efficiency of the tests was determined by comparing the diagnosis based on oestrogen concentrations with the farrowing results. The oestrone sulphate concentration in blood, as measured by enzyme immunoassay on microtitre plates, showed that 265 of the examined sows were correctly diagnosed, an accuracy of 91.7%. Seven results were false negative and 17 false positive. The determination of oestrogens in urine by radioimmunoassay (RIA) showed that 98 of 100 examined sows were correctly diagnosed and 2 were false negative. According to the oestrogen concentration in faeces, measured by RIA, 271 sows (93.5%) were correctly diagnosed, 16 were false negative and 3 false positive.

Measurement of urinary and plasma estrone sulphate concentrations from pregnant sows

The accuracy of urinary estrone sulphate (E 1S) concentrations as an indication of pregnancy was compared to that of plasma E 1S concentration. Urine and plasma were collected from 145 sows 18 to 30 days after mating. Concentrations of E 1S in urine were indexed to creatinine concentration (CR) and specific gravity (SG) to correct for urine dilution. There was no significant difference in E 1S concentration between urine corrected for CR or SG and uncorrected urine (UN) from pregnant sows. Urinary E 1S concentrations were 20 to 100 times higher than plasma E 1S concentrations. The E 1S test was accurate in the detection of pregnancy in sows using both plasma and urine (test sensitivity, 98.8% vs. 96.4%, respectively) during the optimal sampling period of 20 to 30 days post mating. The test was slightly more accurate (NS) using plasma than urine in detecting non-pregnant sows (test specificity, 100.0% vs. 91.9%, respectively) 20–30 days after mating. Urinary E 1S concentrations could be used to predict litter size, but the precision was poor (± 3 piglets), and thus could only be used to predict small (<5 piglets), medium (6–10 piglets) and large (>11 piglets) litters.

Influence of food intake during late gestation on serum lipids of sows and their progeny.

Serum and lipoprotein lipids were quantified in pregnant and nonpregnant sows allowed restricted and ad libitum access to a low-fat cholesterol-free diet, and in the progeny of these sows. Pregnant sows exhibited a mild increase in serum triglycerides in the third trimester, reflecting an increase in very low density lipoprotein (VLDL)-triglyceride concentration. Ad libitum feeding enhanced this increase. Free fatty acids were depressed in mid-pregnancy (60 days gestation), but were normal or elevated in the final trimester. Total cholesterol was similar in all groups. Pregnancy and level of food intake interacted to increase VLDL-cholesterol in pregnant sows fed ad libitum. Pregnancy decreased high density lipoprotein cholesterol. Level of food intake by sows had no influence on serum lipid concentrations of newborn pigs. Distribution of cholesterol and triglyceride between lipoprotein classes was different in newborn pigs when compared to sows. These results imply fetal self-regulation of lipid metabolism during late gestation. Sow serum lipids are not identical to those in humans. However, when fed a modified diet that resembles a human diet, sows may be useful as a model for humans in studies of lipid metabolism during pregnancy.

Use of ultrasound scanning in swine for detection of pregnancy and some pathological conditions

The adaptation of ultrasound scanning to the diagnosis of pregnancy and other physiological conditions in swine was examined. The scanner was equipped with a 3.5-MHz transducer. The probe was placed against the skin in the area of the abdominal flank of a standing sow and moved between the first and third posterior teats. The 2,257 sows were all presumed to be pregnant and underwent a single echography examination between 18 and 90 d post-insemination. For pregnant sows, the accuracy rate of diagnosis averaged 98.7 %. The majority of errors were made between 18 and 21 d of pregnancy in sows which subsequently gave birth to fewer than five piglets. This technique allowed us to detect only 54 % of non-pregnant sows. Nevertheless, a high accuracy rate was obtained when examination was performed within 7 d before the return of estrus (80 %). Conditions at the time of the examination were also an important factor. Ultrasound scanning opened up possibilities for observing other conditions such as cystic ovaries and metritis.

Oestrus synchronization and fixed-time artificial insemination in the weaned sow

Reproductive performance was assessed in multiparous weaned sows in which double fixed-time AI was used in association with the injection of oestradiol benzoate (OB) to synchronize post-weaning oestrus. After weaning (day 0), groups of 25 sows were either injected with ethyl oleate (group 1, controls), or 10μg OB/kg body weight (b. wt.) (group 2) on the morning of day 2, or 10μg OB/kg b.wt. on the morning of day 3 (group 3). Group 1 sows were inseminated 8–16 h after the onset of behavioural oestrus and again 24 h later. Group 2 and 3 sows were inseminated on the afternoons of days 4/5 and 5/6, respectively. Sows were allocated to treatment with respect to parity and litter-size born, and no differences existed in pre-treatment reproductive performance between groups. The mean weaning-to-oestrus interval in group 1 sows was 5.66 ± 0.14 days; 49/50 OB-treated sows were in oestrus when inseminated, indicating the efficacy of OB in promoting an early and synchronous return to oestrus. Conception rates were 19/25, 8/25 and 14/25 for groups 1, 2 and 3, respectively, and the difference between groups 1 and 2 was significant (ifP< 0.01). Ovulation rates, assessed in pregnant sows at 28 to 40 days of gestation, were not significantly different (18.32 ± 0.76, 17.00 ± 0.93 and 16.64 ± 0.83 for groups 1, 2 and 3, respectively) but embryonic survival was affected by OB treatment and was significantly lower (ifP< 0.01) in group 2 (36.8%) than in control (64.4%) sows. In non-pregnant sows the ovulation rate at slaughter was similar in all groups, indicating that there was no residual effect of OB treatment on ovarian function. Five of the group 2 sows had cystic follicles at slaughter. It is concluded that the time of oestrogen treatment after weaning has a critical effect on reproductive performance in the sow. Work on further refinements of the dose and mode of administration of oestrogen, as well as the timing of injection in individual herds is, therefore, needed in order to determine whether treatment with oestradiol can be effectively used for oestrus synchronization in association with fixed-time mating or AI.

Evaluation of a rosette inhibition test for pregnancy diagnosis in pigs

A rosette inhibition test was developed using pig lymphocytes and sheep red blood cells. Antilymphocyte serum (ALS) in the presence of complement inhibited rosette formation by greater than 95% at 1/250 declining to no inhibition at 1/8000. Sera obtained from a total of 14 pregnant sows before and 1, 2, 3 and 4 wk after mating were tested for their ability to augment the rosette depression caused by ALS. In one experiment in which the responses of 4 pregnant sows were compared to 4 non-pregnant sows by discriminant analysis, sera were classified correctly in 83% of the samples taken from either pregnant or non-pregnant sows. When the more usual method of calculating the rosette inhibition titre was used, the responses of sera from pregnant pigs were classified with 31% accuracy and those from non-pregnant pigs with 80% accuracy. In a second experiment, sera from 10 pregnant sows were classified with 25% accuracy using the rosette inhibition titre. Thus 4 of these pigs were classified as non-pregnant by this method. Data from the second experiment were not suitable for discriminant analysis. It was concluded that there was some factor present in the sera of pregnant pigs, particularly by 3 or 4 wk post-mating, which could be detected by the rosette inhibition test. However, the test is not sensitive enough to allow specific diagnosis of early pregnancy in pigs.

Stress and summer infertility in pigs.

A serious year-round fertility problem on a commercial piggery was investigated. The problem was characterised by a high proportion of non-pregnant sows and gilts which showed a delayed return or failure to return to oestrus after a normal mating to a fertile boar. Several factors were identified that we considered to be placing undue stress on the breeding stock from wearning through mating and early pregnancy. When steps were taken to reduce the influence of these stressors there was a marked improvement in the herd farrowing rate. Across all months this improvement was largely due to a reduction in the number of sows showing delayed return or failure to return to oestrus after mating. There were no concomitant changes in other indices of performance. In conclusion this study has shown that stressful factors other than summer heat stress can cause a syndrome of delayed or failure to return to oestrus, this syndrome is commonly and perhaps wrongly called 'summer or seasonal infertility'. When given the appropriate combination and/or intensity of stressful stimuli, it can be manifest at any time of the year.

Seasonal influence on fecundity and litter performance characteristics in Iberian pigs

The Iberian breed was developed in an extremely adverse environment. Data recorded in an experimental herd in Oropesa (Spain) are used to study the seasonal influence on productive performance. Results of 2621 planned matings, classified according to year, mating season, strain and fecundity, have been analysed through a log-linear model. Significant effects of year and strain on fecundity have not been detected, while mating season shows a marked effect. Percentages of non-pregnant sows are 23.5, 22.9, 35.5 and 28.7 in winter, spring, summer and autumn. Least-Squares Anovas carried out on litter recordings, show that farrowing season has clear effects on litter size at birth and piglets' survival and development. Constant estimates and their standard errors coresponding to winter, spring, summer and autumn are 0.29 ± 0.11, −0.19±0.10, −0.01±0.11 and −0.09±0.10 piglets in litter size at birth, −0.50 ±0.19, 0.00±0.18, 0.49±0.19 and 0.01±0.18 piglets in litter size at 3 weeks and −1.53 ±0.31, 0.96±0.30, 1.36±0.29 and −0.79±0.32 kg in litter weight at 3 weeks.

Concentrations of progesterone in the backfat of pigs during the oestrous cycle and after ovariectomy

Small samples of backfat were taken daily during one oestrous cycle and more frequently after ovariectomy from 12 gilts by means of a simple biopsy technique and the levels of progesterone were determined. Compared to the levels of progesterone in peripheral plasma changes in backfat levels during the oestrous cycle were delayed by 1-2 days. Maximal levels with 89.7 +/- 9.2 (mean +/- s.e.m) ng progesterone/100 mg backfat were recorded on Day 15 of the oestrous cycle. It was estimated that, on this day, a total amount of about 36 mg progesterone is stored in the adipose tissue, which is approximately 200 times that present in total blood and corresponds to the daily production of the corpora lutea of the sow on Day 11. Initial half-life of progesterone in backfat after ovariectomy was estimated to be about 34 h compared to an initial half-life of plasma progesterone of about 120 min. The exact calculation of half-lives was, however, confounded by an obvious effect of anaesthesia or surgery on progesterone levels. Changes in backfat or plasma progesterone concentrations were not affected by the fat-to-lean ratio of the gilts. Fat progesterone levels determined in 44 additional pregnant and non-pregnant sows 17 or 20 days after mating indicated that reliable diagnosis of non-pregnant sows was possible on Day 20. It is concluded that the endocrinology of the oestrous cycle in pigs is related to the enormous storage of progesterone in the fat.

Direct estimation of urine estrone conjugate for a rapid pregnancy diagnosis in sows

A rapid and direct radioimmunoassay of urine estrone conjugate (E 1C) was developed. Urine samples were taken from Large White sows by inserting sponges in the vagina which were expelled during micturition. Analysis of samples collected daily from 13 sows between 2 and 40 days after service showed that high urine E 1C levels occurred between day 20 and 30 after insemination in pregnant sows; maximum concentrations were observed on day 25 (79.4 ± 11.7 ng/ml, X ± s.e.m. ). In this period E 1C levels never exceeded 1 ng/ml in nonpregnant sows. A single urine sample was then taken from 84 sows, 25 days after insemination, to check the accuracy of E 1C estimation as a test for early pregnancy diagnosis. Seventy-six of the examined animals were correctly diagnosed, giving an overall accuracy of 90.4%. No relationship was found between litter size and urine E 1C levels.

Ovarian blood flow throughout the estrous cycle and early pregnancy in sows.

The association between ovarian arterial blood flow (OBF), as measured with electromagnetic blood-flow transducers, and the concentrations of progesterone, estrone and estradiol-17 beta in systemic blood were determined throughout the estrous cycle and the first 21 days of pregnancy in four sows (first day of estrus or mating=Day 0). Changes in OBF were positively correlated (P less than 0.01) with the concentrations of progesterone in systemic blood throughout the estrous cycle (requal+0.63) and early pregnancy (requal+0.65) and negatively correlated (P less than 0.01) with estrone (r=-0.53) and estradiol-17 beta (r=-0.51) during the estrous cycle, but not (P greater than 0.10) during early pregnancy. In nonpregnant sows, OBF was lowest at estrus, highest during the luteal phase, and declined precipitously after Day 14 in association with declining concentrations of progesterone and increasing concentrations of estrogens in systemic blood. Patterns of OBF and progesterone during the subsequent pregnancy of each sow were similar to those observed during the estrous cycle until Day 12. Between Days 12 and 15 of pregnancy, blood flow to the ovary and progesterone in systemic blood exhibited transient rises of 26% (P less than 0.01) and 20% (P less than 0.05), respectively. Both an ovarian vasodilatory and luteotropic effect of the conceptuses was demonstrated on days critical for maintenance of the corpora lutea during early pregnancy in this species.

Local and systemic effects of intrauterine estradiol-17 beta on luteal function of nonpregnant sows.

This study was conducted to determine if intrauterine injections of estradiol-17 beta (E2 beta) could maintain luteal function in nonpregnant sows. Eight sows were assigned to surgery on d 8 or 9 of the estrous cycle (first day of estrus = d 0). At surgery, cannulas were inserted bilaterally into the uterine artery (UA) and common utero-ovarian vein (UOV), as well as into the lumen of each isolated uterine horn. Electromagnetic blood flow transducers were placed around the middle uterine artery supplying each horn of four sows. After surgery, sows were assigned randomly to receive either intrauterine injections of vehicle (.9% NaCl) into both uterine horns (control sows) or E2 beta into one uterine horn (375 ng/injection) and vehicle into the other (treated sows) every 6 h from 1200 h on d 11 to 1200 h on d 15. Uterine blood flow (UBF) was quantified, and blood was sampled from the UA and UOV, periodically, from d 11 to 18. On d 18, sows were ovariectomized and corpora lutea (CL) were weighed. Blood plasma was subsequently analyzed for progesterone (P4) and prostaglandin F (PGF) by radioimmunoassay. Control sows had smaller (P less than .05) CL than treated sows on d 18 (3,046 +/- 614 vs 4,451 +/- 324 mg). Progesterone concentrations in UOV blood of treated sows tended to increase from d 11 (469 +/- 110 ng/ml) to 18 (626 +/- 209 ng/ml) while P4 in UOV blood of control sows decreased markedly (P less than .01) from d 11 (579 +/- 79 ng/ml) to 18 (14 +/- 5 ng/ml). In addition, UOV P4 concentrations on the E2-beta-injected side of treated sows were higher (P less than .05) than those on the vehicle-injected side from d 14 to 18. The UBF of two treated sows increased eightfold to 10-fold within 12 h of the first E2 beta injection and remained elevated through d 17, while UBF of two control sows remained constant. Prostaglandin F concentrations in UOV blood of treated sows were lower (P less than .05) than in UOV blood of control sows on d 14 and 15. There was no effect of side of E2 beta injection on PGF concentrations, which were similar in UOV blood draining both uterine horns of treated sows. Thus, the local effect of E2 beta in stimulating P4 secretion by the ipsilateral ovary is not due to reduced PGF concentrations in UOV blood draining the E2 beta-injected horn.

Reproductive development in young boars exposed to sexually mature, nonpregnant sows and gilts

Thirty Yorkshire boars were allotted by litter to one of two treatment groups. Fifteen boars were reared, from 14 to 22 wk of age, in fenceline contact with mature sows and gilts that were randomly exhibiting estrus. Fifteen littermates of these boars, reared without exposure to females, served as controls. Boar-to-boar sexual behaviors were observed 1 hour daily from 16 to 22 wk of age. At ages 14 to 30 wk, boars were weighed at 4-wk intervals. Five boars per treatment were slaughtered when 22 wk old and twelve others (six per treatment) when 30 wk old. Vesicular gland, bulb of the prostate gland, bulbourethral gland, and each testis, cauda epididymis, and combined caput and corpus epididymis were closely trimmed and weighed. Left cauda epididymal sperm and left testis elongated spermatids were determined by homogenization and hemacytometer counting. At 26, 30, and 38 wk of age, boars were tested for mating efficiency by exposure to an estrous gilt. Boars exposed to females tended to be lighter at 22 wk and were lighter at 30 wk (P<.05). Total male-to-male sexual acts from 16 to 22 wk were correlated with mating-efficiency score at 26 and 30 wk (r = .69 and .68, respectively; (P<.05)). Correlation between testicle size and total testicle elongated spermatids was high at 30 wk of age (r = .92; P<.001). Results indicated that exposing young boars to mature females had limited effects on the boars' reproductive development; however, there were strong indications of a relationship between boar behavior during rearing and postpuberal mating performance.