Boar Effect Research Articles

Selective sperm binding to pig oviductal epithelium in vitro

The sperm reservoir in the caudal isthmus of the oviduct of a number of species is created by binding of spermatozoa to oviductal epithelium. The sperm reservoir fulfills a number of functions such as control of sperm transport, maintenance of sperm viability and modulation of capacitation. The initial capacities of ejaculated and epididymal boar spermatozoa to bind to oviductal epithelium were investigated using a modified pig oviductal explant assay. The number of spermatozoa that bound to 0.01 mm(2) of explant surface was used as the parameter of binding capacity. Binding of spermatozoa to oviductal epithelial explants was dependent in a linear manner on the number of spermatozoa added (P < or = 0.05). No difference was found in initial sperm binding between isthmic and ampullar explants. There was no effect of the stage of the oestrous cycle or the reproductive status of the female donor. There was a significant effect (P < or = 0.05) of the individual boar on the binding index. The binding index correlated negatively with the percentage of spermatozoa with cytoplasmic droplets and the percentage of morphologically abnormal spermatozoa (P < or = 0.05). Epididymal spermatozoa showed significantly lower initial binding capability than did ejaculated spermatozoa from the same boars (P < or = 0.05); therefore, components of seminal plasma may play a role in the binding process. The individual differences revealed by this study and their relation to morphology and contact of spermatozoa with seminal fluid indicate a selective function of sperm-oviduct binding.

Management and Genetic Factors Affecting Fertility in Sows

Contents The purpose of this article is to summarize the current knowledge on genetic and management methods for improving fertility in sows. Fertilization rate, litter size and the interval between weaning and oestrus are traits that can be monitored on farms. These traits are heritable but can also be influenced by management. Age at puberty and the interval between weaning and oestrus are genetically linked (rg = 0.3) and a shorter weaning‐to‐oestrus interval is related to a longer duration of oestrus. Consequently, selection may be used to simplify detection of oestrus but because of variation in duration of oestrus between lines/breeds, farm‐specific insemination strategies are needed. The direct boar effect on fertilization is small, probably due to the superabundance of sperm cells that is available in each dose of semen. Consequently, the use of a large number of sperm cells per dose is the best management tool for avoiding fertilization problems in sows. Health status of the boars, both for artificial insemination and natural mating, is of importance in order to produce a large number of sperm cells/doses of good quality per ejaculate. It is concluded that factors that influence fertility in sows, particularly prior to and during fertilization, are mainly related to oestrus and the optimal timing of insemination. Selection for adequate symptoms of oestrus, together with farm‐specific insemination strategies are needed.

Effect of freezing and thawing rates on the post-thaw viability of boar spermatozoa frozen in FlatPacks and Maxi-straws

The effects of different freezing and thawing rates on the post-thaw motility and membrane integrity of boar spermatozoa, processed as split samples in Maxi-straws or flat PET-plastic packages (FlatPack) were studied. A programmable freezing device was used to obtain freezing rates of either 20, 50 or 80°C/min. Thawing of the samples was performed in a bath of circulating water; for 40 s at 50°C or 27 s at 70°C for Maxi-straws and 23 s at 35°C, 13 s at 50°C or 8 s at 70°C for the FlatPacks. Sperm motility was assessed both visually and with a computer assisted semen analysis (CASA) apparatus, while plasma membrane integrity was assessed using the fluorescent probes Calcein AM and ethidium homodimer-1. Temperature changes during freezing and thawing were monitored in both forms of packaging. Values for motile spermatozoa, sperm velocity and lateral head displacement variables were significantly ( p<0.05) higher for samples frozen in FlatPacks than in Maxi-straws, with superior results at higher thawing rates. Freezing at 50°C/min yielded better motility than 20 or 80°C/min, although the effect was rather small. Neither freezing rate nor thawing rate had any effect on membrane integrity ( p>0.05). A significant boar effect was seen for several parameters. The most striking difference in temperature courses between containers was a 4–5-fold lowering of the thawing rate, between −20 and 0°C, in the center of the Maxi-straw, compared with the FlatPack. This is apparently due to the insulating effect of the thawed water in the periphery of the Maxi-straw. The improvement in sperm motility seen when using the FlatPack appears to be related to the rapid thawing throughout the sample, which decreases the risk of cell damage due to recrystallization during thawing. Since sperm motility patterns have been reported to be correlated with fertility both in vitro and in vivo it is speculated that the use of the FlatPack might improve the results when using frozen-thawed boar spermatozoa for artificial insemination.

A note on the effects of contact frequency and time of day of boar exposure on the efficacy of the boar effect.

Sixty-four Large White/Landrace crossbred gilts were used in this study, 16 gilts being allocated to each of four treatments to compare the effects on puberty attainment of exposure to boar contact either 0, 1 or 2 times daily. The once-daily exposure occurred in either the morning or the afternoon (AM vs. PM). Treatments were of 20-min duration starting at a mean gilt age of 160 days and continuing for 60 days. Boar exposure significantly increased the proportion of gilts attaining puberty within 60 days of the commencement of treatments (P < 0.05) compared with gilts not receiving boar contact. Gilts receiving boar exposure twice daily attained puberty significantly earlier than did gilts in the two treatment groups (AM and PM, respectively) given a single daily boar exposure period (mean gilt ages at puberty 176.4 vs. 192.7 and 189.2 days of age, respectively, P < 0.05). It is concluded that (a) twice-daily boar contact enhances the efficacy of the boar effect in gilts above that seen with a single daily boar exposure period and (b) this enhanced response of the gilt is due to the frequency of boar contact and not to the time of day at which the contact occurs.

In vitro production of pig embryos: Comparisons of culture media and boars

The utilization of in vitro produced pig embryos for commercial production or research is dependent upon the development of improved methodology. Our objective was to establish a consistent in vitro embryo production (IVP) system and subsequently utilize the procedures to evaluate culture system components and boar effects. To summarize the IVP system, 403 inseminated oocytes from a total of 2243 were analyzed across 17 replicates for maturation and fertilization efficiency, while 1838 zygotes were cultured in 26 replicates for developmental data. Penetration, cleavage and blastocyst development rates were determined at 18, 44 and either 144 or 168 h post insemination, respectively. Monospermic penetration averaged 31.8±7.3% while polyspermy was 30.8±17.2%. Cleavage rate was 44.9±16.1%, with 21.8±7.5% of fertilized oocytes and 51.9±15.9% of cleaved embryos developing to blastocysts. For culture medium comparison, fertilized oocytes were cultured in either BECM-6, BECM-7, NCSU-23 or NCSU-23aa and supplemented on Day 5 post insemination (pi) with 10% FCS. These treatments resulted in 4.0, 4.9, 19.8 and 13.6% (± 3.2%) blastocysts by Day 7 pi, with an average cell number of 44.4±9.0, 65.1+8.2, 61.3±4.5 and 64.4±4.8, respectively. These IVP procedures consistently produced zygotes from semen of several different boars, capable of forming blastocysts in vitro. Comparison of developmental rates among the boars indicated that this system is variable among boars but not strictly boar-dependant. Culture media comparisons suggest that NCSU-23 yielded a higher percentage of blastocysts than the other media in this IVP system.

Maturation, fertilization and complete development of porcine oocytes matured under different systems

This study was designed 1) to determine the effectiveness of 2 in vitro maturation systems commonly employed to produce nuclear and cytoplasmicly mature pig oocytes, 2) to assess the effects of boar, sperm concentration and maturation system on oocyte penetrability and male pronucleus formation and 3) to determine the ability of the in vitro matured oocytes to be fertilized in vivo by artificial insemination (AI) of sows. The differences examined between the 2 maturation systems included the culture medium (Waymouth vs TCM199), hormones, additives, culture conditions (static vs gentle agitation) presence or absence of porcine follicular fluid (PFF) and presence or absence of follicular shells. The results showed that nuclear maturation rate was similar in both systems (83.3 ± 3.5 vs 86.4 ± 2.5%), and intracellular content of glutathione was 5.21 ± 0.73 vs 3.5 ± 0.39 pmol/oocyte, although no correlation between these parameters was observed. The penetration rate and number of sperm cells per oocyte were dependent on the boar, maturation system and sperm concentration, but the rate of male pronuclear formation seemed to be influenced only by the boar and the maturation system but not by sperm concentration. In vivo fertilization of in vitro matured oocytes showed that both maturation systems could yield viable oocytes since 3 of 4 gilts and 2 of 4 gilts, respectively, became pregnant. Failure to become pregnant was not associated with inadequate oocyte maturation since control gilts, which received their own ovulated oocytes rather than in vitro matured oocytes at transfer, also did not become pregnant. We conclude that polyspermy may be an inherent problem in the IVF but not in the IVM systems.

Effects of vertebrate herbivores on soil processes, plant biomass, litter accumulation and soil elevation changes in a coastal marsh

1 Submergence of coastal wetlands in Louisiana is currently rapid and widespread. A number of factors contribute to this loss of habitat, including the activities of herbivores. The objective of this study was to examine the effects of large mammals, predominantly nutria and wild boar, on processes controlling soil elevation in coastal marshes. 2 Effects of herbivores on soil and vegetation were assessed by the use of paired fenced and unfenced plots over two successive growing seasons. Above‐ground biomass, litter production, changes in soil elevation, vertical soil accretion, shallow subsidence, below‐ground production of roots and rhizomes, the thickness of the root zone, soil bulk density, and soil organic matter were measured. 3 Above‐ground biomass, below‐ground production, soil elevation and the expansion of the root zone decreased due to herbivore activity. Litter production, the rate of soil surface accretion and shallow soil subsidence were all higher in grazed compared to ungrazed plots, while soil organic matter and bulk density did not differ significantly between treatments. 4 The results indicate that herbivores can have a negative effect on soil building processes, primarily by reducing below‐ground production and expansion of the root zone. Where natural rates of mineral sediment deposition are high, coastal marshes are expected to persist, despite herbivore activities. However, where sediment inputs are substantially less, herbivores may lead to destruction of habitat.

In vitro maturation and fertilization techniques for assessment of semen quality and boar fertility.

The reliability of using different in vitro-derived measures of sperm quality to predict boar fertility was examined. On three occasions during a 20-wk period of breeding, special collections of the first sperm-rich fraction of the ejaculate from six boars were carried out. After in vitro capacitation procedures, three dilutions (5 x 10(5), 1.25 x 10(5), and 3.125 x 10(4) sperm/mL) of these semen samples were used in a standardized in vitro fertilization (IVF) test with oocytes recovered from prepubertal slaughterhouse ovaries and matured in vitro. Routine assessments of sperm motility, concentration, and morphology were also carried out for all collections used for AI during the 20-wk period. Semen from the same ejaculate, processed according to normal commercial practice using the AndroHEP extender, was used to inseminate equal numbers of recently weaned sows with either 3 x 10(9) or 2 x 10(9) total sperm, three times during the estrous period. Data from a total of 444 sows were used to determine boar fertility; between 12 and 54 sows were bred with each semen dose across the six boars. All measures of sperm fertilizing ability in vitro were different among boars (all P < .05) and use of different semen dilutions for IVF allowed further discrimination of apparent sperm quality among boars. The laboratory evaluation of semen collected during the period of breeding indicated effects of boar on ejaculate volume, total number of sperm per ejaculate, motility, and the percentage of sperm with normal morphology (all P < .01). Sperm dose used in AI had no effect on farrowing rate (80.7 vs 81.5%), but the lower AI dose resulted in a reduction (P < .05) in total numbers born (10.8 vs 10.0). For all three semen dilutions, estimated potential embryo production rate accounted for up to 70% of the variation in litter size obtained with 3 x 10(9) sperm per AI dose, and the number of sperm attached per oocyte was a major factor accounting for variation in litter size obtained with 2 x 10(9) sperm per AI dose. These IVF variables may, therefore, be effective indicators of boar sperm quality for use in AI. With 2 x 10(9) sperm per AI dose, the percentage of sperm with normal morphology also explained a large part of the variance in litter size born (R2 = .59), indicating that morphological characteristics are a useful measure of semen quality.

In vitro penetration assay of boar sperm fertility: Effect of various factors on the penetrability of immature pig oocytes

The present study was designed 1) to examine the influence of cumulus cells, ovary storage time and oocyte size on the penetrability of immature pig oocytes, and 2) to investigate the effect of 2 methods of treating the semen from different boars on the inter-assay variability of homologous in vitro penetration tests of boar sperm fertility. In Experiment 1, cumulus oocyte complexes, oocytes with spontaneous loss of the cumulus cells during collection, and oocytes mechanically stripped of cumulus cells were used. No differences were observed in oocyte penetrability among the 3 types of oocyte, although mechanical removal of the cumulus caused an increase (P < 0.005) in the degeneration rate compared with the other oocyte types. In Experiment 2, the oocytes were recovered from ovaries kept in PBS (30 °C) for 2, 4 or 6 h after slaughter of prepuberal gilts. Ovary storage did not modify the penetrability of oocytes but increased (P < 0.02) their degeneration rates. In Experiment 3, the diameters of fresh oocytes were determined after co-incubation with spermatozoa. They were classified into 4 groups according to diameter: A) < 105 μm, B) 105–115 μm, C) 116–120 μm and D) > 120 μm. Oocytes from Groups C and D exhibited higher (P < 0.05) penetrability than oocytes from the other groups. In Experiment 4, stored, diluted spermatozoa from 4 boars were pretreated by centrifugation at 50 × g for 3 min and subsequent concentration of the supernatants at 1,200 × g for 3 min. The pellets were treated (washed twice and preincubated for 40 minutes) before co-incubation with immature oocytes or used directly as untreated samples (unwashed and non-preincubated). A boar effect (P < 0.001) was evident for the parameters of in vitro penetration, independently of sperm treatment. When the oocytes were inseminated with untreated spermatozoa, the effects of the replicate and the boar-by-replicate interaction on the variability in oocyte penetrability were not significant. The results of this study indicate that the use of standardized immature pig oocytes and stored untreated, diluted spermatozoa can provide a useful method for optimizing the homologous in vitro penetration (hIVP) assay of boar fertility.

In vitro fertilization of in vitro matured pig oocytes: Effects of boar and ejaculate fraction

Ejaculates from 3 young boars were collected on 4 occasions as a series of separate 15-ml fractions. The contribution of different fractions of these ejaculates to observed variability in the quality of the semen when used for IVF was then determined. On the basis of sperm concentration, 3 fractions representing the first peak concentration (Fraction 1), the lowest sperm concentration after Fraction 1 (Fraction 2), and the second peak concentration (Fraction 3) were selected for analysis in vitro. Oocyte-cumulus-granulosa cell complexes were obtained by dissection from slaughterhouse ovaries. In vitro matured oocytes were randomly assigned for fertilization by the 3 semen samples from each boar. Sperm concentration was the same in all the samples during prefertilization incubation, while the final concentration for fertilization was 5 × 10 5 sperm/ml. Data were analysed using ANOVA for a split-plot design. In the presence of fraction effects, Student-Newman-Keuls (SNK) test was used for multiple comparison of treatment means. Oocyte penetration rates differed among fractions (P = 0.001) and varied from 69 to 100% (mean 95.7%) for Fraction 1, from 0 to 100% (mean 53.3%) for Fraction 2, and from 50to 100% (mean 89.9%) for Fraction 3. There were also differences in male pronuclear formation rate (P = 0.028; mean 27.6, 9.3 and 16.4% for Fractions 1, 2 and 3, respectively); in the rate of polyspermy (P = 0.0001; mean 92.3, 31.9 and 76.3% for Fractions 1, 2 and 3, respectively); and in the number of penetrated spermatozoa per oocyte P = 0.002; mean 5.58, 1.94 and 4.07 for Fractions 1, 2, and 3, respectively). The first peak concentration of semen (Fraction 1) showed superiority in fertilizing ability and less variability in penetration rate from replicate to replicate compared with the other 2 fractions. By multiple comparison, Boar 1 showed higher rates of penetration (P < 0.05), male pronuclear formation (P < 0.05) and polyspermy (P < 0.05) than the other 2 boars. There was no fraction-by-boar interaction. The IVM-IVF system adopted proved to be a promising method for boar semen evaluation.

The effects of contact frequency and season on the efficacy of the boar effect

One hundred and twenty eight Large White/Landrace crossbred gilts were used in this study. The study was conducted in four replicates (spring, summer, autumn and winter), eight gilts being allocated to each of four treatments in each replicate. The treatments compared the effects on puberty attainment of exposing gilts to boar contact either daily (D), twice daily (2D) or three times daily (3D). Puberty attainment by gilts in the boar exposure regimens was compared with puberty attainment in a non-boar exposed control group of gilts (C). Boar exposure began at a mean gilt age of 160 days and continued for 60 days. The duration of boar contact was for 60 min, 30 min and 20 min per exposure period respectively for treatments D, 2D and 3D (i.e. all boar-exposed gilts received a total of 60 min of boar contact per day). There was no significant effect of season on the timing of gilt puberty attainment. Boar exposure significantly increased the proportion of gilts attaining puberty within 60 days of the commencement of treatments ( P < 0.001) compared with control gilts. Boar exposure three times daily significantly reduced mean gilt age at puberty relative to once-daily boar exposure (183.2 vs. 196.0 days of age respectively, P < 0.01). Twice-daily boar contact resulted in an intermediate mean gilt age at puberty (190.3 days). There was also a trend towards a higher proportion of gilts reaching puberty earlier with increasing frequency of boar contact. However, this difference was only significant ( P < 0.05) between once- and three times-daily boar contact at day 20 of treatment. It is concluded that the pubertal response of the gilt to the boar effect is enhanced when boar contact occurs several times each day compared with a single boar contact period. While the efficacy of these treatments may vary with season this effect was not evident in the present results.

PS-17-3 Influence of cholecystokinin (CCK-8) and yohimbine on supraspinal modulation of nociceptive process

This study was designed 1) to determine the effectiveness of 2 in vitro maturation systems commonly employed to produce nuclear and cytoplasmicly mature pig oocytes, 2) to assess the effects of boar, sperm concentration and maturation system on oocyte penetrability and male pronucleus formation and 3) to determine the ability of the in vitro matured oocytes to be fertilized in vivo by artificial insemination (AI) of sows. The differences examined between the 2 maturation systems included the culture medium (Waymouth vs TCM199), hormones, additives, culture conditions (static vs gentle agitation) presence or absence of porcine follicular fluid (PFF) and presence or absence of follicular shells. The results showed that nuclear maturation rate was similar in both systems (83.3 ± 3.5 vs 86.4 ± 2.5%), and intracellular content of glutathione was 5.21 ± 0.73 vs 3.5 ± 0.39 pmol/oocyte, although no correlation between these parameters was observed. The penetration rate and number of sperm cells per oocyte were dependent on the boar, maturation system and sperm concentration, but the rate of male pronuclear formation seemed to be influenced only by the boar and the maturation system but not by sperm concentration. In vivo fertilization of in vitro matured oocytes showed that both maturation systems could yield viable oocytes since 3 of 4 gilts and 2 of 4 gilts, respectively, became pregnant. Failure to become pregnant was not associated with inadequate oocyte maturation since control gilts, which received their own ovulated oocytes rather than in vitro matured oocytes at transfer, also did not become pregnant. We conclude that polyspermy may be an inherent problem in the IVF but not in the IVM systems.

The Weaning Process of Free‐ranging Domestic Pigs: Within‐ and Between‐litter Variations

AbstractTo determine variations within and between litters in the weaning process and behavioural development, the behaviour of four focal piglets from each of nine litters was recorded at the ages of 4, 6, 8 and 10 wk in a 12.5‐ha semi‐natural environment. The piglets were weighed at birth, at 7–11 d and at 7 wk. Activities and nearest‐neighbour distances were recorded instantaneously and social interactions continuously during 4 times 11 min/piglet at all ages. Within‐litter comparisons were obtained by transforming raw data to standard scores within litters. There were significant age effects on all behavioural variables except aggression, which, however, was very rare. There were also significant effects of sow and boar on several behavioural variables, as well as interactions between sow/boar and age, indicating a possible genetic influence on the behavioural development. Within‐litter variations did not relate to sex or weight. Within litters, some individuals tended to be more associated with their families and to rely more on milk for nutrients whereas others tended to affiliate with other families and spend more time feeding on solids. The latter group could be conceived of as piglets starting the weaning process earlier.

In vitro fertilization of in vitro matured pig oocytes: effects of boar and ejaculate fraction

In vitro fertilization of in vitro matured pig oocytes: effects of boar and ejaculate fraction

The efficacy of the boar effect when conducted in a modified detection-mating area (DMA)

Fifty-six Large White/Landrace crossbred gilts from 14 litters were allocated to four treatments by litter and liveweight in a 2x2 factorial experiment. The two factors tested were boar contact v. no boar contact and exposure to a modified Detection-Mating Area (DMA) v. no DMA exposure. All treatments began at a mean gilt age of 160 days and continued on a daily basis for 60 days. Daily boar exposure significantly reduced mean gilt age at puberty (196.2�3.88 v. 216.6�3.26 days respectively, P &lt; 0.01) and increased the proportion of gilts attaining puberty within 60 days of commencement of treatment (0.79 v. 0.30 respectively, P &lt; 0.01), compared with gilts receiving no boar exposure. In contrast, daily exposure to a modified DMA failed to significantly reduce mean gilt age at puberty (202.8�4.63 v. 209.7� 3.35 days respectively) or to increase the proportion of gilts attaining puberty within 60 days of commencement of treatment (0.50 v. 0.59 respectively) compared with gilts receiving no DMA exposure. However, daily exposure to a modified DMA did significantly increase the proportion of gilts pubertal over a 2-day period (days 27-28 of treatment) relative to gilts not exposed to a DMA. It is concluded that (1) daily boar exposure is a potent stimulus for early puberty attainment in gilts, (2) full physical contact with the boar must occur in order to achieve the boar effect, and (3) the current recommendation that gilt puberty stimulation can be adequately achieved by exposing them to a DMA on a daily basis should be re-examined.

The role of contact frequency in modifying the efficacy of the boar effect

Sixty-four Large White-Landrace crossbred gilts were used in each of two experiments in this study. The two experiments compared the effects on puberty attainment of exposing gilts to boar contact on either alternate days (ADB), daily (DB) or twice daily (2DB) in Experiment 1, and daily (D), twice daily (2D) or three times daily (3D) in Experiment 2. In each experiment, puberty attainment by gilts in the boar exposure regimens was compared with puberty attainment in a non-boar exposed control group of gilts. Boar exposure began at a mean gilt age of 160 days and continued for 60 days. The duration of boar contact was for 20 min per exposure period in Experiment 1, and for 60 min, 30 min and 20 min per exposure period, respectively, for Treatments D, 2D and 3D in Experiment 2. Experiment 1 commenced in the summer whereas Experiment 2 began in the winter months. All boar exposure regimens significantly increased the proportion of gilts attaining puberty within 20, 40 and 60 days of the commencement of treatments ( P<0.05) compared with control gilts in both experiments. In Experiment 1, twice daily boar contact resulted in a significantly higher proportion of gilts reaching puberty in the first 20 days of treatment than for either daily or alternate day boar contact (0.86 vs. 0.21 and 0.07 for Treatments 2DB, DB and ADB, respectively, P<0.01). No significant effect of boar contact frequency was observed in Experiment 2, although there was a tendency for three times daily boar contact to increase the proportion of gilts pubertal within 20 days of the start of treatments (0.25, 0.27 and 0.62 for Treatments D, 2D and 3D, respectively). Both the mean days taken to reach puberty after the imposition of treatments and mean gilt age at puberty were significantly reduced by increasing boar contact frequency in both experiments. It is concluded that the pubertal response of the gilt to the boar effect is enhanced when boar contact occurs several times each day compared with a single boar contact period. Preliminary data suggest that the actual frequency of daily boar contact required to maximise puberty stimulation in the gilt may be dependent on season.

The influence of boar libido on the efficacy of the boar effect

Eighty-one Large White/Landrace crossbred gilts were used in three replicates in this study. These gilts were allocated to one of three treatments, these being (1) control—no boar contact, (2) daily exposure to a low-libido boar, and (3) daily exposure to a high-libido boar. All treatments began at a mean gilt age of 160 days and continued for 60 days. The ‘libido’ boars used were designated as high or low on the basis of their sexual behaviour at 9–10 months of age in three 15-min mating tests, the variables measured being total number of copulations achieved and mean time to first mount an oestrous female. Results from the combined data of the three replicates show that gilts in both boar exposure treatments were younger at puberty than were nondashboar exposed gilts ( P<0.05). Exposure to a high-libido boar stimulated puberty at a significantly earlier age than did exposure to a low-libido boar (179.6 vs. 194.1 days, P<0.05). These data demonstrate that differences in the stimulus value of mature boars to prepubertal gilts do occur. However, the causes of these differences remain to be identified.

Evaluation of boar spermatozoa penetrating capacity using pig oocytes at the germinal vesicle stage

We evaluated the ability of immature pig oocytes (at germinal vesicle stage) to detect differences in the in vitro penetration rates of boar spermatozoa. In Experiment 1, immature and ovulated oocytes (n=303) were exposed to capacitated boar spermatozoa to determine if the penetrability of immature pig oocytes was comparable to that of ovulated oocytes. The percentages of penetrated oocytes and the mean number of spermatozoa per oocyte were similar for immature (88.82 and 7.42±0.41) and ovulated oocytes (90.97 and 7.95±0.34, respectively). In Experiment 2, immature oocytes (n=1230) were inseminated with semen from 2 boars (A and B) with satisfactory semen characteristics to establish the variability of in vitro penetrating capacity between the boars. Semen was examined for motility, movement quality, acrosome integrity and plasma membrane integrity at various stages of the in vitro procedure. Although the sperm evaluation results were similar between boars, Boar A exhibited a significantly higher (P<0.001) penetration rate (91.49%) and number of spermatozoa penetrated per oocyte (5.90±0.25) than Boar B (52.87% and 2.03±0.12, respectively). Increasing the sperm concentration at insemination from 1×10 6 to 10×10 6 cells/ml resulted in an increased penetrating capacity for both boars, and the differences in the number of spermatozoa per oocyte between boars also increased. These results indicate that immature pig oocytes can be used in a homologous in vitro fertilization assay, and that despite similarities in semen characteristics a significant boar effect is evident for parameters of in vitro penetration of oocytes.

The effects of duration of boar exposure, number of gilts in the exposure group and size of the exposure pen on the efficacy of the boar effect

Forty-eight Large White×Landrace gilts were allocated to treatment in each of three 3×2 factorial experiments within this study. The three experiments used boar exposure durations of either 20, 12.5 or 5 min day −1. The factors examined were number of gilts in the boar-exposure group (8, 4 or 2) and size of the exposure pen (large — 22.2 m 2, small — 11.1 m 2). Boar exposure began at a mean gilt age of 160 days and continued on a daily basis for 80 days. The frequency of boar-gilt interactions was assessed in the replicate employing 5 min day −1 of boar exposure by video-recording the exposure period for all treatment groups on Days 1–3 and 6–8 of treatment. Increasing group size significantly decreased boar-gilt interactions ( P<0.05) as did increasing the size of the exposure pen ( P<0.01). Twenty minutes day −1 of boar exposure significantly reduced gilt age at puberty ( P<0.05) and increased the proportion of gilts attaining puberty in response to boar exposure within 21 days of commencement of treatment ( P<0.01) compared with 12.5 or 5 min day −1 of boar exposure. Neither group size nor exposure pen area exerted a significant influence on gilt puberty attainment when boar exposure occurred for either 5 or 20 min day −1. However, at 12.5 min day −1 of boar exposure gilts reached puberty significantly earlier in pairs than in groups of four or eight ( P<0.001) and the proportion of gilts reaching puberty within 21 days of commencement of treatment was significantly higher for pairs than for groups of four ( P<0.001) or eight ( P<0.05). Additionally, when 12.5 min day −1 of exposure was allowed those gilts receiving boar contact in the large exposure pen attained puberty significantly earlier ( P<0.05) than did those gilts exposed in the small pen. It is concluded that daily boar exposure is required for at least 12.5 min day −1 to maximise the boar effect. Furthermore, when the adequacy of boar contact duration is marginal (approximately 12.5 min day −1) both group size and exposure pen area may influence the efficacy of boar-induced puberty stimulation in the gilt.

Effects of Duroc, Meishan, Fengjing, and Minzhu boars on productivity of mates and growth of first-cross progeny

Meishan, Fengjing, Minzhu, and Duroc boars were mated by AI to crossbred gilts to compare the sire breeds for effects on productivity of their mates and performance of their progeny. Gilts were derived from a four-way cross of Chester White, Landrace, Large White, and Yorkshire. At weaning, litters sired by Meishan boars averaged 1.69 and 1.32 more pigs than those sired by Duroc and Minzhu boars, respectively (P less than .05). Pigs sired by Meishan and Fengjing boars averaged 1.2 to 1.8 more nipples than pigs sired by Duroc and Minzhu boars (P less than .05). Minzhu-sired pigs had a lower (P less than .05) survival rate to 14 and 28 d of age than did those sired by Meishan, Fengjing, and Duroc. Fengjing-sired pigs were heavier than Minzhu-sired pigs at birth and heavier than Minzhu- and Duroc-sired pigs at 14, 28, and 56 d of age (P less than .05). At 70 d of age, Meishan-sired pigs were heaviest, followed in order by Fengjing-, Duroc-, and Minzhu-sired pigs. At 98 d of age, Meishan-sired pigs were significantly heavier than all other breed groups and Duroc-sired pigs were significantly heavier than Minzhu-sired pigs. At 126 and 154 d of age, Duroc-sired pigs were heaviest, followed in order by Meishan-, Fengjing-, and Minzhu-sired pigs; all differences were significant. Average backfat thickness of gilts at 99.7 kg was least for Duroc-sired gilts and highest for Meishan-sired gilts. Sire breed groups did not differ significantly in feed efficiency from 70 to 98 d of age. Duroc-sired pigs were the most efficient (P less than .05) from 98 to 126 and 126 to 154 d of age. Results indicate that use of these Chinese breeds in crossbreeding programs will decrease performance traits. This decrease would have to be offset by increases in reproductive efficiency of Chinese sows, use of repartitioning agents, or other management techniques if Chinese pigs are to improve overall production efficiency of a crossbreeding program.