Effect of social conditions during rearing on mating behaviour of gilts

The mating behaviour of 28 gilts was studied. The gilts were reared under two different social conditions known to affect both their puberty attainment and reproductive parameters during early pregnancy. The different social conditions were applied from an average age of 137 days onwards. Ten gilts were housed individually, having neither tactile nor visual contact with other pigs. The remaining gilts (n=18) were housed pairwise, having additional contact with gilts in adjacent pens and daily boar contact from 180 days of age onwards. At third oestrus, the gilts were artificially inseminated and subsequently introduced to one of three vasectomized boars for a period of 20 min. The gilts were slaughtered 10±1 days after insemination.

The mating behaviour varied considerably between individual gilts, partly because of differences in mating behaviour between the two groups of gilts. More (P<0.05) individually housed gilts showed a standing response latency upon introduction of the boar. During this latency period, the individually housed gilts initiated contact with the boar. Once the standing response was elicited, mating behaviour was similar in gilts of both social groups. One individually housed gilt did not show a standing response and consequently was not mated. The mating behaviour of the boars did not differ for the gilts of the two social conditions.

It was concluded that the social conditions of gilts during rearing affected their introductory sexual behaviour. The relationship with reproductive performance during early pregnancy is discussed.     

The effects of PG600 and boar exposure on oestrus detection and potential litter size following mating at either the induced (pubertal) or second oestrus

Within gilt pools, incidences of delayed puberty attainment, failure to exhibit regular oestrous cycles and low first litter size are often high. Boar exposure is an effective method of accelerating puberty; however, the timing of gilt response can vary greatly. Although, PG600 (400 IU of PMSG and 200 IU of hCG; Intervet) can induce a rapid and synchronous ovulatory response, thus providing an alternative to boar contact, the quality of the response is often variable. This study compared the effect of PG600, either alone (NBC) or in conjunction with boar exposure (BC), on puberty attainment and maintenance of oestrous cyclicity. The effects of first mating these gilts at the hormonally induced (pubertal) or second oestrus on ovulation rate and early embryo survival were also studied. Eighty Large White cross terminal (Duroc) line gilts were used in this study. The study was conducted in two blocks, with 10 gilts allocated to each of the four treatments in each block. Gilts were artificially inseminated at the allocated oestrus, with the reproductive tracts collected at 26.5+/-0.29 days after first mating (mean+/-S.E.M.), and the number of corpora lutea and viable embryos recorded. Mean days-to-puberty was significantly reduced (P<0.05) when gilts received both PG600 and boar exposure as opposed to PG600 alone (5.7+/-0.15 versus 6.9+/-0.37 days; P<0.01). The proportion of gilts exhibiting an ovulatory response to PG600 was similar for the BC and NBC treatment groups (0.88 and 0.84); however, the proportion of gilts exhibiting visible signs of oestrus in response to PG600 was significantly higher for the BC compared to the NBC treatment groups (0.81 versus 0.49; P<0.05). Boar contact resulted in a numerical, but not significant, increase in the proportion of gilts exhibited a second oestrus (1.00 versus 0.76). There was no significant effect of boar contact on ovulation rate, embryo number or survival. Although ovulation rate was unaffected by oestrus at mating, embryo number was significantly increased (P<0.05) following mating at the second compared to the first oestrus (11.2+/-0.96 versus 7.8+/-1.17). In conclusion, the current data indicate that the timing of puberty attainment and oestrus detection are significantly improved when PG600 treated gilts receive full boar contact. Further, it is evident that mating gilts at their second as opposed to the hormonally induced oestrus significantly increases embryo number at day 26 post-mating.     

The effect of early contact with mature boars on reproductive efficiency in the gilt

The effect of first contact of gilts with a mature boar at 23 or 28 weeks of age on their subsequent reproductive efficiency was studied over a 12-month period at a large intensive piggery in southern Australia. Following this contact, the gilts entered the mating shed at 29 weeks of age and were checked daily for oestrus, as assessed by the back-pressure test in the presence of the boar. Gilts that showed moderate or high responses were taken to a boar for mating. Sexual receptivity was then assessed by the time taken to “stand” after the first mount by the boar. Gilts that remained unmated at 35 weeks of age were culled, and their ovaries were examined.Of the 2660 gilts in the study, 2349 were mated and they had a farrowing rate of 88.2% with a mean litter size of 9.5 piglets, of which 0.7 piglets (7.4%) were born dead. The reproductive efficiency of the gilts following earlier contact with the boar was consistently higher than that of gilts exposed later. The mating rate of the week 23 gilts was greater than that of the week 28 gilts (70.1 vs 66.0%, P < 0.01), more appeared to show a high level of sexual receptivity (97.0 and 94.6%, N.S.) and fewer failed to mate when put to a boar (6.1 vs 9.5%, P < 0.01). The percentage of prepubertal gilts at 35 weeks of age was also lower (1.46 vs 3.03%, P < 0.01). The improved reproductive performance was estimated to be equivalent to 0.24 extra piglets born per gilt.     

Effectiveness of frozen boar semen under practical conditions of artificial insemination

A technique of boar semen deep-freezing and frozen semen use was tested in practice. 338 sows and 43 gilts belonging to small herds with less than 10 females each were inseminated without oestrus detection by a teaser boar. About 58 % of the inseminated females produced 9.3 piglets per litter. But there were differences between parities. The sows had the highest fertility rate, whereas the gilts showed a significantly lower farrowing rate (59.8% vs 41.9%; P < 0.05). The standing reaction of the female to the back pressure test made by the inseminator and the behaviour of the female during insemination had an effect on the farrowing rate. The best result was obtained after a standing reaction and a behaviour score of 1 (64.5% and 9.6 piglets for farrowing rate and litters size respectively). Farrowing rate for inseminators ranged from 44.3% to 62.4% among inseminators. Farrowing rate for females inseminated with frozen semen from Large-White, Landrace, Pietrain boars was not different, but there were significant differences between the boars. Results showed that insemination with deep-frozen boar semen could be used under practical conditions as an additional technique to the use of fresh semen.     

Attainment of puberty in female pigs: Influence of boar stimulation

The object of the present study was to investigate whether the presence of a boar is of importance for the age at puberty and the expression of external heat symptoms in female pigs. Altogether 60 crossbred gilts were purchased at an age of 12 weeks and grouped, three or four per pen, in three separate barns (treatment groups A, B and C). Treatment group A: Boars were kept in adjacent pens to the gilts during the whole period. One vasectomized boar was penned with the gilts daily for 20 min during the experimental period, which started at a mean age of 142 days. Treatment group B: Boars were kept in adjacent pens to the gilts during the whole period. Treatment group C: No boars were kept in the barn at any time.The study was performed six times. Daily heat control was carried out during the experimental period, which was terminated when the gilts had passed at least two oestrous cycles. Blood samples for progesterone analysis were taken once a week. Laparoscopy was performed in all gilts after their first observed heat. The gilts were slaughtered after their third or fourth heat. The effects of treatment group were estimated by the method of least squares analysis.All gilts except one showed external heat symptoms at regular intervals during the experimental period. A few gilts did not stand for the boar at each oestrous period, regardless of oestrous number. Gilts belonging to group A showed their first oestrus on average 20 days earlier than gilts in group B and 35 days earlier than gilts in group C. These differences were highly significant (P < 0.001). The stimulatory effect of the boar on the age at puberty varied between the six experimental groups and the interaction between treatment and experimental groups was significant (P < 0.01).     

Effect on oestrus and ovulation of exposing creole goats to the male at three times of the year

The characteristics of the oestrous and ovarian cycles of local goats were studied over 2 years, on 96 females in March, 60 in July and 100 in November. After 3 weeks of separation between sexes, the females with inactive ovaries were identified and harnessed males were introduced. Detection of oestrus was undertaken daily and the date and rate of ovulation were checked at laparoscopies. The proportion of females with non-cyclic ovaries before the mating period varied according to the season and whether the females were nulliparous or suckling. Among the females with inactive ovaries before the mating period, 97% ovulated 2 . 8 days after the introduction of males; 68% of these initial ovulations were accompanied by oestrus and 76% resulted in short luteal phases (5 . 3 days) followed by a second ovulation accompanied by oestrus 89% of the time. The proportions of initial ovulations with oestrus and of initial ovulations followed by a short luteal phase were in linear relationship with the proportion of females with non-cyclic ovaries before the mating period. For the females with cyclic ovaries before the mating period, the distribution of first oestrus during the 8 days after the introduction of males was significantly different from the expected uniform distribution. A possible luteolytic action of teasing was suspected. The fertility of females in all groups was high (greater than 79%). Litter size was not different for non-cyclic and for cyclic females.     

The effect of modified eros centre, outdoor raising or conventional group housing on breeding gilts and its effects on reproductive performance over four parities

The present study was conducted in a large Croatian "built up unit". The objective of the study was to determine if an indoor modified eros centre (MEC) compared to indoor or outdoor group housing of gilts, influenced the onset of puberty of gilts and the reproductive performance of the evaluated females (n = 783) over four parities. The gilts were from the same nucleus herd. Gilts of same age (140-150 days of age), body condition (body condition score of 3-4) and similar genetics (four-way cross females), during the same season (January to April 1999), were randomly divided at arrival into three groups and treated as follows:MEC gilts (n = 279): These were placed into indoor MEC pens in groups of 8-10. The gilts had continuous fenceline contact to boars (one boar to two groups of gilts, boars were changed daily) and to shortly weaned oestrous sows. Gilts were regrouped and dislocated at 10-day intervals. Outdoor gilts (n = 263): These were kept in groups of 8-10 on a large pasture (80-100 m2 per group). The animals had fenceline contact to mature boar for 5-10 min daily. Control indoor gilts (n = 241): These were housed indoors in large pens in groups of 8-10. The animals had fenceline contact to mature boars for 5-10 min daily. Each outdoor group had an insulated hut with straw bedding. All gilts were fed ad libitum with the same commercial diet. Housing gilts in MEC resulted in earlier (P < 0.001) onset of estrus (MEC: 174.8 +/- 2.4 days, indoor group housing: 207.6 +/- 4.1 days, outdoor group housing: 187.4 +/- 2.1 days) and lower (P < 0.001) farrowing rate to first service (MEC: 70.97%, indoor group housing: 89.73%, outdoor group housing: 89.62%). Farrowing rate of regularly returning MEC gilts to second service was 95.00%. First total-born litter size, first liveborn litter size, first wean-to-estrus interval (WEI), percent of sows bred after first weaning, second total-born litter size, second liveborn litter size, average third and fourth total-born and liveborn litter size, number of sows having four litters, number of litters per sow, total number of pigs per sow, total number of liveborn pigs per sow showed no significant differences between the groups. More (P < 0.05) sows were culled in outdoor group. Compared to MEC and outdoor housing, indoor housed sows suffered higher (P < 0.05) percentage of anoestrus.     

The effect of repeated boar exposure on cortisol secretion and reproduction in gilts

It has been proposed that short-term activation of the hypothalamo-pituitary adrenal axis, with a consequent increase in the secretion of cortisol, may disrupt the endocrine events prior to ovulation and thereby impair reproduction in females. We investigated this concept in gilts in which oestrus was detected by introduction to boars, where intense physical contact is possible, or by applying pressure to the back of gilts (back-pressure test) during fence-line exposure to boars, where intense physical contact is prohibited. We expected that there would be a greater release of cortisol and that reproduction would be inhibited in gilts introduced to boars compared to gilts in which the back-pressure test was used. As expected, introduction of gilts to boars resulted in a significant transient increase in plasma concentrations of cortisol while there was no significant effect of using the back-pressure test on plasma cortisol. Nevertheless, introduction of gilts to boars did not impair reproduction and there was no effect of method of detecting oestrus on duration of oestrus, sexual receptivity, fertility or fecundity. The length of the oestrous cycle was decreased and ovulation rate increased in gilts that were introduced to boars compared to gilts that underwent the back-pressure test, indicating that introduction of gilts to boars may have stimulated these aspects of reproduction. These stimulatory effects may have been due to an increased exposure of gilts to sexual behaviour and stimuli from boars when introduced to boars and/or to stimulatory effects of the hypothalamo-pituitary adrenal axis on some aspects of reproduction.     

Impact of boar exposure on puberty attainment and breeding outcomes in gilts

We examined the most effective method of boar exposure for the attainment of puberty in 89 gilts. At 160 days of age, we allocated gilts to daily direct contact with a vasectomized boar after movement of pen groups of gilts to a detection-mating area (DGB: n = 30); daily direct contact with boars in the gilt home pens (DBG: n = 31); or daily fenceline contact between boars and gilts housed in individual gilt stalls (FBG: n = 28). DGB gilts were younger (P < or = 0.05) than FBG gilts at puberty. Direct boar contact reduced the interval from initial boar contact to puberty in DGB and DBG gilts, compared to fenceline contact in FBG gilts (P < 0.05). There was no difference (P > or = 0.05) between treatment for pubertal weight, backfat, lifetime growth rate, or duration of first pubertal estrus. Backfat depth and leptin concentration at 160 days of age were positively correlated (P < or = 0.05). We detected no relationships between leptin or IGF-1 concentration at 160 days of age and the interval from initial exposure to a vasectomized boar to puberty (P > 0.05). Based on objective criteria, fenceline contact with a boar (BC) during artificial insemination improved the quality of artificial insemination compared to no boar contact (NC) (P < 0.05).     

Clinical,Morphological and Endocrinological Studies in Gilts with Delayed Puberty

Thirty-six gilts which had not shown oestrus at about 8 months of age or more were transported from the pig research station to the clinic, a journey of 12 km. The gilts were examined by laparoscopy and those which had only small follicles in the ovaries were catheterized and placed in pens, with sexually mature boars kept in adjacent pens. Oestrus detection was done twice daily and blood was sampled three times a day. After 7 days the laparoscopy was repeated and gilts which still had only small follicles in their ovaries were given 250 μg GnRH intravenously the following day. Blood samples were taken frequently before and after GnRH treatment. One week. after administration of GnRH the ovaries were inspected by laparoscopy once more. The first laparoscopic examination showed that 42 % of the gilts were sexually mature. One gilt had no uterus or ovaries. Twenty gilts had only small follicles in the ovaries and fourteen of these gilts showed ovulatory oestrus 5.5 days (4-7.5 days) after arrival. In these fourteen gilts a rise in the oestradiol-17B level (>30 pmol/1) was seen at an average time of 1.9 days and a rise in LH (preovulatory peak) was seen at an averaged 4.5 days after the start of blood sampling. Six gilts were given 250 ug GnRH. An immediate rise in LH could be seen in all the gilts (mean peak level was 6.18 μg/l) and the elevated levels had a duration of 4 hours. None of the GnRH-treated gilts responded with oestrus symptoms or increased ovarian activity.     

The influence of conditions at the time of mating on reproduction of commercial pigs

The objective of this study was to compare a new mating system, called the Detection-Mating Area (DM Area), and a conventional mating system on the long-term reproductive performance of commercial pigs. The DM Area treatment basically involved detecting oestrous females in an arena closely surrounded on two sides by boars and mating these females in this arena. This mating system was designed to improve the physical and sexual environments of the pigs at mating. In contrast, the conventional treatment involved conducting oestrus detection and mating in the boar's accommodation pen. The study was conducted over an 18-month period at a commercial farm that housed 2400 breeding female pigs.

In order to control for the effects of the stockperson, an analysis was conducted on the reproductive performance of female pigs in which one stockperson assisted the matings in both treatments over a 12-month period. Gilts mated in the DM Area treatment had a higher (P<0.05) total litter size and a higher (P<0.01) litter size born alive than gilts mated in the conventional treatment (10.31 vs. 8.96 and 9.50 vs. 8.29, respectively). Although gilts in the DM Area treatment had a higher farrowing rate (93.2 vs. 87.9%), this difference was not significant (P>0.05). There were no significant (P>0.05) differences found between the reproductive performance of sows in the two treatments; however this comparison was confounded by sows in the DM Area treatment having a lower number of matings per oestrus than those in the other treatment. Observations on the sexual behaviour of pigs at 145 matings indicated that the boars in the DM Area treatment displayed a higher (P<0.05) number of bouts of courting behaviour directed towards the female than boars in the conventional treatment (8.3 and 6.4, respectively). These very limited observations on sexual behaviour suggest that changes in the courting behaviour of bears may be associated with changes in litter size. While there was some indication from the results of progesterone analysis of blood samples taken from unmated gilts that there may have been some differences between treatments in the sexual age of gilts at matings, these differences are unlikely to explain the differences in litter size between treatments. Further research is required to identify the component (s) of the DM Area treatment that are responsible for the improvement in litter size in gilts and to further examine the effects of the two treatments on the reproductive performance of sows.     

Influence of the presence of a mature female on puberty attainment in gilts

At 90 days of age, 40 Large White gilts were assigned to one of two treatments. At 155 days, a mature female which was left intact (Treatment I) or ovariectomized (Treatment O) was placed in each pen of five experimental gilts. From 180 days, estrus was checked daily with the back pressure test, and the occurrence of ovulation was detected by measuring the concentration of plasma progesterone at weekly intervals. From 240 days, a mature boar was introduced, for 5 minutes daily, into each pen during estrus detection. Gilts were slaughtered within 12 days after ovulation or at 270 days of age if they were not cyclic earlier. The percentage of gilts reaching puberty before 225 days of age was significantly higher in Treatment I (7 19 ) than in Treatment O (0 19 ) even though the average age at puberty was similar (I, 231 +/- 24 days; O, 243 +/- 12 days; mean +/- SD). Age at puberty and the number of days between mature female introduction and puberty differred significantly between the pens of gilts in Treatment O but not in Treatment I. Ovarian weights, ovulation rate and percentage of gilts with silent estrus were similar in the two treatments. Thus, the occurrence of pubertal estrus may be influenced by contact with an older, cyclic female or with other contemporary females raised in the same pen.     

Effect of sexual stimulation on concentrations of 5α-androstenone and testosterone in the peripheral plasma of boars reared individually

Six Yorkshire boars were reared from 107 days of age in individual pens. No female pigs were housed in the same building. When the boars were 200 days old, sows in oestrus were introduced to the pens of five boars and remained with the boars for 2 days. No oestrous sow was introduced to the pen with the sixth boar. Plasma 5α-androstenone and testosterone concentrations were low between 107 and 200 days of age in all boars. The maximum mean concentrations of these two steroids during this period were 6.18 ± 0.72 and 3.04 ± 1.02 ng/ml, respectively. Plasma 5α-androstenone concentrations increased with advancing age (P < 0.01). A similar trend was not seen for plasma testosterone concentrations. Plasma concentrations of 5α-androstenone and testosterone increased by 247 ± 27% (P < 0.02) and 1212 ± 204% (P < 0.001), respectively, in the samples drawn 24 h after the introduction of the sexually receptive sows. The maximal mean concentrations recorded following sexual stimulation were 12.90 ± 1.80 and 17.51 ± 1.96 ng/ml for 5α-androstenone and testosterone, respectively. The control boar also showed increases in plasma 5α-androstenone (221%) and testosterone (751%) concentrations in the same period, probably in response to auditory and olfactory stimuli originating in the pens nearby with introduced oestrous sows.     

Modification of the zona-free hamster ova bioassay of boar sperm fertility and correlation with in vivo fertility

These studies were designed to evaluate the ability of the zona-free hamster ova bioassay to detect differences in fertility of boar sperm. In the first study, sperm from two previously infertile boars were compared to sperm from seven previously fertile boars. The percentage of zona-free hamster ova penetrated by sperm from the previously infertile boars was significantly lower than the percentage of ova penetrated by sperm from previously fertile boars (18% of ova penetrated vs. 83%, P < .001). In the 14 ejaculates from the previously infertile boars that had ejaculate motilities of 50% or greater, the percentage of zona-free hamster ova penetrated continued to be lower than in ejaculates from the fertile boars. One of the two previously infertile boars consistently had a normal semen analysis. The only two observed manifestations of his reduced fertility were his zero conception rate and the limited ability of his sperm to penetrate zona-free hamster ova. In the second study, females were inseminated with equal numbers of sperm from two previously fertile males and the paternity of offspring determined at birth. The experiment was replicated with four combinations of six boars. A high correlation was observed between the percentage of offspring sired and the ability to penetrate zona-free hamster ova (R = .89). Neither morphology nor the ability of the sperm to undergo an acrosome reaction during in vitro incubation was correlated with fertility in the competitive mating situation. These results suggest the zona-free hamster ova bioassay can improve the in vitro fertility assessment of fresh boar semen.     

Effects of social environment on welfare status and sexual behaviour of female pigs. II. Effects of space allowance

This study examined the effects of housing groups of adult female pigs (6 pigs per group) with a space allowance of 1, 2 or 3 m² per pig on sexual behaviour and welface status, determined by plasma free-corticosteroid concentrations. A lower percentage of gilts was detected in oestrus and a lower percentage of gilts was mated when housed with a space allowance of 1 m² per gilt than with a space allowance of either 2 or 3 m² per gilt (oestrus detection rate of 79, 88 and 100%, respectively, and a mating rate of 77, 85 and 97%, respectively). There was a significant increase in plasma free-corticosteroid concentrations when gilts were housed with a space allowance of 1 m² per gilt. The elevated free corticosteroid levels of gilts in the 1 m² per gilt treatment suggests that a chronic stress response due to crowding may have been responsible for the apparent impairment in the sexual behaviour of these animals.     

The involvement of boar submaxillary salivary gland secretions in boar-induced precocious puberty attainment in the gilt

The involvement of secretions from boar submaxillary salivary glands in mediating the induction of precocious puberty in the gilt was investigated as follows. Forty-eight Large White × (Large White × Landrace) prepubertal gilts from 12 litters were randomly allocated within litters by weight, to four treatment groups of six, in two replicates, at 145 days of age. Treatments commencing at a mean group age of 165 days, were: (1) control (no boar exposure); (2) gilts exposed to a mature sialectomised boar (submaxillary salivary glands were removed at 9 weeks of age); (3) gilts exposed to a mature sham-operated boar; (4) gilts exposed to a mature unoperated boar.Boar exposure occurred for 30 min per day for 75 days, or until pubertal oestrus was observed. Gilts showing pubertal oestrus were removed and slaughtered. Ovaries were examined to confirm reproductive status. Gilts failing to exhibit oestrus by 240 days of age were slaughtered and nominally ascribed a pubertal age of 245 days. Age at puberty was significantly earlier in all three boar-exposed treatments than in the control treatment (P<0.05 for treatments 2 and 3, P<0.001 for treatment 4; median ages at puberty being 227.0, 203.5 , 202.0 and 179.0 days for treatments 1 to 4 respectively). No frothy saliva was ever produced by the sialectomised boar, and chromatographic analysis of saliva produced by the sham-operated boar during mating revealed very low levels of 16-androstene pheromones, while levels in the unoperated boar's saliva were normal. These results provide further evidence for an important role of boar salivary pheromones in the induction of precocious puberty attainment in the gilt.     

Selection of impubertal gilts by ultrasonography optimizes their oestrus, ovulatory and fertility responses following puberty induction by PG600

In a group of gilts, occurrence of puberty is spread over several weeks. The optimal time to apply puberty induction is therefore difficult to define, as treatment of puberal gilts is meaningless. Changes in uterine aspect around puberty can be detected by ultrasonography. Two experiments were carried out to assess the effect of PG600(?) (400 UI of eCG and 200 UI hCG) administration to 6 months old gilts shown to be impubertal by ultrasonography on cyclicity and reproductive performance. Impubertal Large White gilts (n=94) were treated with either PG600 or solvent (controls). Administration of PG600 to impubertal gilts increased significantly the proportion of females displaying pubertal uterine ultrasound images 3 days after treatment (100% versus 65% in controls). The number of days to puberty was significantly reduced in gilts injected with PG600 (3.3 days) versus controls (4.7 days). In gilts of the PG600 group, ovulation rate was higher at the 1st oestrus compared to the 2nd, while this did not happen in controls. Progesterone concentrations were higher at mid-luteal phase in the PG600 treated gilts compared to controls (significant treatment by time interaction). Similar proportions of gilts returned to oestrus (89% versus 74% for controls). Following insemination at the 2nd oestrus, pregnancy rate and number of live embryos were unaffected by treatment. The combination of ultrasonography and PG600 optimizes the use of exogenous hormones by targeting treatment to gilts that need it, therefore facilitating the introduction of gilts into all in/all out system.     

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.     

Sexual motivation in relation to social rank in pair-housed sows

The influence of social subordination on sexual motivation during oestrus was studied using 36 sows of which 24 treatment sows were housed in pairs and 12 control sows were housed individually in 12 and 6 m(2) pens, respectively. Video recordings were made from 07:00 h to 19:00 h during the first 2 days after grouping, which took place 3 days after weaning of the piglets. Based on the aggressive interactions between the pair-housed sows, their rank was determined. From day 4 after weaning, a test for sexual proceptive behaviour was carried out twice daily and back-pressure test was carried out four times daily in order to detect standing oestrus. When standing oestrus had occurred, transrectal ultrasonographical scans were also carried out in order to determine if ovulation took place. The proceptivity test took place in a T-maze with a 2 m x 10 m runway ending in two 1.5 m x 1.5 m goal boxes each adjacent to a stimulus compartment. One compartment contained an adult sexually experienced boar and the other was empty. Latency to and duration of time spent close to the boar and time spent presenting were recorded during the 10-min test period. On the first day that standing oestrus had been detected, a test for sexual receptivity was also carried out by introducing the sow to a mature boar in his home pen (9 m(2)). Sexual- and fear-related behaviour of sow and boar were recorded until mating was terminated or the sow had spent 5 min in the pen without mating being initiated. During oestrus the proceptivity test showed a significant increase (P < 0.05) in the time spent standing close to the boar and in presenting for single-housed sows and for pair-housed dominant sows, but not for subordinate sows. During oestrus subordinate sows spent significantly less time standing close to the boar than the dominant sows (P = 0.01) and the same tended to be the case for presenting (P = 0.07). In the receptivity test more subordinate sows than dominant sows fled (40% versus 0%, P = 0.001) and more subordinate sows than dominant sows squealed (58% versus 15%, P = 0.02) as a response to boar stimulation. In both tests, the single-housed sows differed neither from the dominant nor the subordinate sows. There was however no difference between the groups in the weaning to oestrous interval, duration of oestrus and number of piglet born. In addition, all the sows ovulated. The results indicate that social subordination can have significant consequences for sexual motivation in sows. Subordinate sows showed fear-related behaviour in response to boar stimulation even when they were in standing oestrus. Thus, both heat detection and mating may be impaired in subordinate sows. The results emphasise the importance to alleviate the social stress experienced by subordinates as well as the need for stock people to pay special attention to these animals when they are to be mated or inseminated.     

Attainment of puberty in female pigs: Clinical appearance and patterns of progesterone,oestradiol-17β and LH

The object of the study was to investigate the clinical and endocrine patterns of progesterone, oestradiol-17β and LH during the peripubertal period in female pigs. Crossbred gilts were penned in groups at an age of 10–12 weeks and boars were kept in adjacent pens during the entire experimental period. Daily oestrous checks started at 4.5 months of age and the gilts were slaughtered after their third heat. At the age of 4.5–5 months a permanent catheter was inserted in the cephalic vein and blood samples were collected from the gilts once daily until either the first or second oestrus. In three gilts hourly blood samples were taken during their first and second oestrus, beginning at early pro-oestrus.The gilts showed their first oestrus at the average age of 183 days. No corpora lutea from earlier ovulations were observed in gilts laparoscoped after their first detected oestrus. During the 30-day period before first oestrus the mean daily progesterone levels varied between 32 and 329 pmol/l. The average levels of oestradiol-17β varied between 15.6 and 30.8 pmol/l. There was no tendency for the oestradiol-17β level to rise before onset of first pro-oestrus. The average levels of LH varied between 0.15 and 0.94 μg/l. The statistical analyses revealed no significant relationship between the level of the hormones studied and onset of first oestrus. The mean progesterone levels during the first and second oestrous cycles were almost identical, however. Oestradiol-17β increased gradually during pro-oestrus, reaching maximum levels before onset of oestrus and thereafter decreasing sharply to values around 30 pmol/l. The oestradiol-17β levels were higher at the second than at the first pro-oestrous period. The concentrations of plasma LH rose sharply with declining plasma levels of oestradiol-17β. The duration of elevated plasma LH levels (> 1 μg/l) was, on average, 26 h and the LH levels were higher during the first oestrus than during the second oestrus. The first rise in progesterone was observed 11–29 h after the LH levels had decreased to concentrations below 1 μg/l.