Single Boar Research Articles

PSIII-9 Field fertility following the practice of post-cervical artificial insemination (PCAI) at multiple North American swine units

Abstract On a global scale, greater than 95% of sows are bred using artificial insemination (AI). As with most technologies, efficiencies improve over time and in the case of swine AI the industry is moving towards fewer sperm per dose in conjunction with a post-cervical deposition (PCAI). Nevertheless, little information is available stating the fertility of farms actively using PCAI. The objective of this research is to provide a retrospective report on the field fertility of multiple farms in North America utilizing PCAI. As a reference, information is provided for contemporary farms utilizing conventional AI (intra-cervical deposition in conjunction with a greater total sperm count per dose). Semen doses produced for PCAI (1.5 billion total cells in 40 mL volume) sourced from one boar stud located in Tennessee and are packaged as pooled semen in NUTRIXcell + extender. Semen was held overnight at 18°C and delivered to seven farms the next day. Semen doses produced for conventional AI (CONAI) also sourced from a single boar stud located in Michigan; packaged as pooled semen at 2.75 billion total cells in a 70 mL volume using the NUTRIXcell + extender and shipped to six farms the same day as semen production. Both PCAI and CONAI were used on 100% of gilts and multiparous sows in respective systems. Field fertility, reported as farrow rate (FAR) and mean total born (TB), is reported below for both PCAI (Table 1) and CONAI (Table 2) following use per individual farms during January 2022 to September 2023. Results suggest that PCAI can maintain acceptable levels of fertility and should enable cost savings in conjunction with increased dissemination of superior genetics.

Detection of inorganic elements in single boar spermatozoa by inductively coupled plasma mass spectrometry

Trace elements play an important role in the spermatogenesis, maturation, and fertilization of sperm. Accurate determination of elemental content of sperm cells, especially at the level of single sperm, is of great significance to evaluate the quality of boar semen, which affects the boar's reproductive health and eventually the pig breeding industry. Here we develop a simple method to determine trace elements in single boar's sperm cells by time resolved inductively coupled plasma mass spectrometry (ICP-MS). Effect of dwell time of ICP-MS on the signals of the sperms were investigated and optimized. Signal profiles of single sperm cells and elemental distributions of P, Mg, K, and Zn in normal sperm cells were obtained with dwell time at 0.1 ms. Experimental parameters affecting the adsorption of cisplatin by sperm cells were studied. Interestingly, the incubated Pt in sperm cells shows different signal trends to the endogenous P and Mg under the ultrasonic treatment that separated the sperm's head and tail, indicating elements with variable contents and locations in the sperm cells may be differentiated by the proposed method. The single-cell determination of sperm elements by ICP-MS would be useful for studying sperm signal transduction and relevant physiological topics.

Seasonal Changes of Nuclear DNA Fragmentation in Boar Spermatozoa in Spain.

Simple SummaryArtificial insemination is widely used in pig production and currently a boar performs several thousand matings per year. Traditionally sperm quality is focused on the number of spermatozoa, their motility and morphology. However, the quality of sperm DNA, which contains genetic information, is also related to fertility problems. The aim of this research was to study the effect of natural light hours and age of the boar on the status of the sperm DNA. After a powerful statistical analysis, it was found that the percentage of spermatozoa with fragmented DNA decreases within the observed age range as the boar gets older. On the other hand, the amount of spermatozoa with fragmented DNA was the lowest in autumn while it was the highest in summer. This study demonstrates the remaining seasonality of boars in Spain and highlights the importance of controlling the environmental conditions in the farms. Sperm DNA testing provides a basis for improving the selection of AI boars by excluding males with higher DNA fragmentation due to their very young reproductive age that may pose a potential subfertility.There are numerous cases when conventional spermiogram parameters are all within an acceptable range but boar subfertility persists. The total sperm nuclear DNA fragmentation index (tDFI) is a trait related to fertility and prolificacy problems that is not routinely evaluated in commercial AI boars. The aim of this research was to study the effect of the photoperiod, season and reproductive age of the boar on tDFI (measured by SCSA) of 1279 ejaculates from 372 different boars belonging to 6 different breeds located in 6 AI studs in Spain. tDFI data ranged from 0.018% to 20.1%. Although there was a significant single boar effect in the tDFI occurrence, a negative correlation between the tDFI and the age of the boar was found (p < 0.001). tDFI would decrease due to aging of the boar 0.66% each year old within the observed age range. After including age as a covariate in the ANCOVA, no differences were found in tDFI between photoperiods when the sperm collection date was evaluated. However, when the date of the production of semen in the testis was evaluated, the total percentage of spermatozoa with fragmented nuclear DNA was 1.46% higher in the increasing photoperiod in comparison to the decreasing photoperiod (p < 0.0001). On the other hand, for both dates, the lowest tDFI values corresponded to minimum day length for decreasing photoperiod phase (autumn), while the highest tDFI values were found in summer (maximum day length for decreasing photoperiod phase).

Sertoli cell proliferation in juvenile boars and microRNA

Sertoli cell numbers are a major influence on sperm production capacity. Increased use of artificial insemination and the limited number of insemination doses from a single boar ejaculate provide the incentive to increase Sertoli cell numbers for potential increases in sperm production and pig production efficiency. Although the number of Sertoli cells can be at least temporarily manipulated in vivo, the mechanism for the increased proliferation is poorly understood and critical for development of practical production practices. MicroRNAs are recognized to regulate many genes during development. Recent work suggested specific microRNAs were involved with regulation of Sertoli cell lines maintained in monoculture. In order to evaluate the relationship of specific microRNAs (miR-26a, miR-196a, miR-499, miR-638 and miR-1285) to in vivo Sertoli cell proliferation, three in vivo models of increased Sertoli cell proliferation (hemicastration, reduced androgen signaling, and reduced endogenous estrogen synthesis) were evaluated in young juvenile boars. Hemicastration was associated with slightly decreased miR-26a, similar to the decrease associated with in vitro Sertoli cell monoculture but none of the other microRNAs were affected by hemicastration nor were any affected by the blockade of androgen signaling with flutamide. Decreased expression of miR-638 followed reduced endogenous estrogen synthesis consistent with in vitro results although expression of miR-1285 was the converse from the in vitro results. Alterations in specific microRNAs are associated with increased Sertoli cell proliferation. However, altered expression of microRNAs was specific to the particular model system, suggesting unique molecular pathways are involved.

Improving accuracy of direct and maternal genetic effects in genomic evaluations using pooled boar semen: a simulation study1.

Pooling semen of multiple boars is commonly used in swine production systems. Compared with single boar systems, this technique changes family structure creating maternal half-sib families. The aim of this simulation study was to investigate how pooling semen affects the accuracy of estimating direct and maternal effects for individual piglet birth weight, in purebred pigs. Different scenarios of pooling semen were simulated by allowing the same female to mate from 1 to 6 boars, per insemination, whereas litter size was kept constant (N = 12). In each pooled boar scenario, genomic information was used to construct either the genomic relationship matrix (G) or to reconstruct pedigree in addition to G. Genotypes were generated for 60,000 SNPs evenly distributed across 18 autosomes. From the 5 simulated generations, only animals from generations 3 to 5 were genotyped (N = 36,000). Direct and maternal true breeding values (TBV) were computed as the sum of the effects of the 1,080 QTLs. Phenotypes were constructed as the sum of direct TBV, maternal TBV, an overall mean of 1.25 kg, and a residual effect. The simulated heritabilities for direct and maternal effects were 0.056 and 0.19, respectively, and the genetic correlation between both effects was -0.25. All simulations were replicated 5 times. Variance components and direct and maternal heritability were estimated using average information REML. Predictions were computed via pedigree-based BLUP and single-step genomic BLUP (ssGBLUP). Genotyped littermates in the last generation were used for validation. Prediction accuracies were calculated as correlations between EBV and TBV for direct (accdirect) and maternal (accmat) effects. When boars were known, accdirect were 0.21 (1 boar) and 0.26 (6 boars) for BLUP, whereas for ssGBLUP, they were 0.38 (1 boar) and 0.43 (6 boars). When boars were unknown, accdirect was lower in BLUP but similar in ssGBLUP. For the scenario with known boars, accmat was 0.58 and 0.63 for 1 and 6 boars, respectively, under ssGBLUP. For unknown boars, accmat was 0.63 for 2 boars and 0.62 for 6 boars in ssGBLUP. In general, accdirect and accmat were lower in the single-boar scenario compared with pooled semen scenarios, indicating that a half-sib structure is more adequate to estimate direct and maternal effects. Using pooled semen from multiple boars can help us to improve accuracy of predicting maternal and direct effects when maternal half-sib families are larger than 2.

Impact of holding and equilibration time on post-thaw quality of shipped boar semen

Cryopreservation of boar semen is of growing interest for breeding companies. Overnight-shipping of pre-diluted ejaculates to specialized laboratories offers a practicable method, but requires fine-tuned protocols. In this study, the impact of holding post shipping at 17°C for 2 or 24h (n=10 samples) and of equilibration in lactose-egg yolk extender without glycerol at 5°C for 2, 4, 24 or 48h (n=11 samples) before freezing was investigated. Sperm-rich fractions of ejaculates from 21 mature Pietrain boars were collected at a single boar stud. After pre-dilution (1+1, v:v) with Beltsville thawing solution, samples were sent to the laboratory. Temperature profiles during transport and initial equilibration time were recorded. Semen quality post-thaw (PT) was evaluated using CASA and flow cytometry. Holding of 2h after shipping resulted in higher sperm motility (P=0.013) and beat cross frequency (BCF; P=0.047) compared to 24h. Differences between both groups vanished with prolonged incubation at 38°C PT. Equilibration at 5°C for 4h yielded the highest motility and BCF, whereas the equilibration for 48h impaired sperm motility. Membrane integrity, mitochondrial activity and DNA fragmentation index were not affected by any protocol modification. In conclusion, processing of pre-diluted boar semen shipped overnight within 2h after arrival at the laboratory is preferred to 24h of additional holding at 17°C. Extending the equilibration period in lactose-egg yolk extender without glycerol at 5°C from 2h to 4h before freezing is recommended.

Spermometer: electrical characterization of single boar sperm motility

To study single sperm boar motility using electrical impedance measurements in a microfluidic system. Comparison of the optical data and electrical impedance data. Research laboratory at a university. Boar semen sample were used. A microfluidic system is developed that is able to spatially confine single boar sperm cells and allows noninvasive analysis of their motility on the single cell level. Using this system, the single sperm motility was affected by changing the temperature or adding chemical stimuli (caffeine). The retrieved electrical impedance and video data were processed using Matlab. The sperm beat frequency and amplitude determined from the electrical impedance and video data. The electrically measured sperm beat frequency was verified by optical analysis and in correspondence. Furthermore the microfluidic platform allowed single sperm analysis by altering the sperm by temperature and chemical stimuli. This platform could be exploited as a potential tool to study sperm cells on the single cell level and to perform advanced sperm selection for intracytoplasmic sperm injection (ICSI) applications.

Evidence that periweaning failure-to-thrive syndrome (PFTS) has a genetic predisposition

Genetic susceptibility or resistance to diseases is currently drawing increasing attention. This work describes two different breeding herds showing signs of periweaning failure-to-thrive syndrome (PFTS), an emergent swine disease. The...

Effect of using frozen-thawed boar sperm differing in post-thaw motility in the first and second inseminations on pregnancy establishment, litter size, and fetal paternity in relation to time of ovulation1

Frozen-thawed boar sperm (FTS) has reduced motility and viability compared to cooled semen. Motility of FTS is related to in vitro and in vivo fertility, but this effect has not been determined in relation to the timing of ovulation. To test the effect of variable FTS motility in a multiple-AI system, ejaculates from 38 boars were collected and frozen in 0.5-mL straws. Upon thawing, samples were classified (mean ± SEM) by motility as poor (P, 20.2% ± 1.1%), moderate (M, 31.3% ± 0.9%), or good (G, 43.5% ± 0.8%). In replicates, mature gilts were synchronized and checked for estrus at 12-h intervals and assigned (n = 207) to receive 4.0 billion total sperm in each AI at 24 and 36 h after onset of estrus using the treatments: 1) P and M (P-M), 2) M and P (M-P), 3) G and M (G-M), and 4) M and G (M-G). For each treatment combination, a set of 3 boars was randomly selected within motility class for their allelic distinction with M sperm from a single boar represented across all treatments and sires used in both first and second inseminations. The insemination to ovulation interval (IOI) was determined using ultrasound every 12 h. Reproductive tracts were collected at approximately d 32 after AI. Treatment did not interact with IOI (P > 0.10) and did not affect (P > 0.10) pregnancy rate (57%, 67%, 71%, 76% ± 7.2%, pooled SEM) or total number of fetuses (9.2, 9.1, 9.5, 10.0 ± 0.8) for P-M, M-P, G-M, and M-G treatments, respectively. Treatment did affect (P < 0.05) the number of fetuses sired from the first AI (3.1, 7.2, 6.4, 6.3 ± 1.2) and second AI (5.7, 2.6, 3.0, 3.6 ± 0.9) for the P-M, M-P, G-M, and M-G treatments, respectively. The IOI also influenced (P < 0.05) the proportion of offspring sired by the second AI (30.0%, 57.7%, 51.3%, 18.3% ± 6.5%), as well as the number of fetuses sired by each AI. These results indicate FTS motility had no effect on pregnancy rate or litter size but did affect the number of fetuses sired from the first and second inseminations. The first AI appears to sire most of the litter except when P sperm was used. Number of fetuses sired was reduced when P sperm was used in either insemination compared to M, although no difference was evident between M and G. Fetal paternity appears to be a more sensitive marker for identifying the effects of sperm quality and IOI in a multiple-AI system with use of FTS. These results suggest that use of semen of various qualities can be used in combinations to aid in pregnancy establishment and contribute to litter size.

Polymorphisms in DMRT1 coding and promoter regions are probably not causative for swine sex reversal (XX,SRY-negative) syndrome

SRY-negative XX sex reversal is an inherited or sporadically occurring disorder, where testis development appears in the absence of the SRY gene. Although the molecular background of this intersexuality syndrome in pigs is unknown, it was proposed that familial cases might be inherited as a single autosomal recessive trait. Because DMRT1 (Doublesex and Mab-3 related transcription factor 1) is an autosomal locus in pig (SSC1q21), shows sexually dimorphic expression in swine gonads and has strong significance in vertebrate testis development, the molecular analysis of this gene was performed in previously reported three intersexes (38,XX, SRY-negative), the progeny of a single boar from a Polish farm. The first two exons encoding functional DM (double sex and mab-3) domain and the promoter region (the 5'flanking sequence) (altogether 3894 bp) were sequenced and compared with male and female control pigs (n = 16) and with publicly available sequences. Three different polymorphisms were found in the coding region, one Indel type polymorphism (DNA 142_144indelAGC) causing a deletion of an amino acid (protein S47_G48indelS) and two silent SNPs (DNA G432A and G492A). The promoter region seems to be highly polymorphic, since 17 SNPs and 5 indels were detected. However, the sequences of control males and females were concordant with those of the intersexes. These results indicate that DMRT1 is an unlikely candidate gene for SRY-negative XX sex reversal in pig.

Modeling Inheritance of Malignant Melanoma With DNA Markers in Sinclair Swine

Cutaneous malignant melanoma in Sinclair swine is a hereditary disease that develops in utero or during the first 6 weeks of life. In many cases, the tumors regress and piglets survive the disease. Two different sets of gene(s) might be involved in the disease: tumor initiator (suppressor) locus or loci and loci affecting the aggressiveness of the disease (number and stage of tumors). We develop maximum-likelihood methods for interval mapping for both types of loci. The experimental design consisted of a boar mated to tumor-bearing sows with recording of tumor status and number of tumors in the 6 weeks of life of the offspring. The model to search for the tumor initiator locus (with alleles T and t) was tested by computer simulation. Estimates of penetrances (Psi(TT) and Psi(Tt) for genotypes TT and Tt, respectively) were accurate even for small family sizes. Statistical power was >99% for a family size of 70 with Psi(TT) = 1 and Psi(Tt) = 0. The models to test for number of tumors incorporated genotype information for the tumor initiator locus. All models were tested with data from a single boar family of 72 piglets over swine chromosomes 6 and 8 (SSC6 and SSC8). No tumor evidence for initiator loci was found associated with these chromosomes. However, association of a QTL affecting number of tumors at birth near microsatellite SW1953 on SSC8 was chromosomewise significant (P<0.0124).

300 IMMUNO-EXPRESSION OF POTENTIAL FACTORS REGULATING SERTOLI CELL PROLIFERATION IN THE PREPUBERTAL BOAR

Today's pork production is very dependent on reproductive efficiency. Any improvements in the production capability (e.g., number of sperm produced) of the animals involved would be invaluable. Many researchers have examined methods to improve oocyte production, but have not focused on the concentration of sperm produced from a single boar used for artificial insemination (AI). The benefit of using AI is that a greater number of females can be bred to a single boar; thus the total amount of sperm per ejaculation is the main factor in the efficiency of AI. An increase in the number of Sertoli cells leads to an increase in testis size and the number of sperm produced because there are a finite number of germ cells that can be supported by the Sertoli cell during spermatogenesis. Therefore, by examining the factors that control the growth and differentiation of Sertoli cells, the amount of sperm per ejaculation in an individual boar can be increased. The purpose of this research is to begin a systematic analysis of cell cycle regulators expressed in the Sertoli cell during testicular development in the pig. By using pigs of different ages, we will establish a baseline of what regulatory factors are present at different time points in the developing Sertoli cell. Identification of certain factors could lead to an increase in sperm production by enabling the growth of Sertoli cells or inhibition of the natural reduction of these cells. Immunohistochemistry (IHC) analysis was performed on testis tissues from different males (n = 2) at various ages (3, 7, 14, 25, and 50 days) prior to puberty. Tissues were fixed in modified Davidson's fixative, embedded in paraffin, and sectioned; slides were processed for IHC. After antigen retrieval, endogenous hydrogen peroxidase was blocked with 0.6% H2O2 and sections were incubated overnight at 4°C with the appropriate antibody. The following antibodies were used to examine the factors controlling Sertoli cell proliferation: GATA-4 (transcription factor specific for developing and adult pig Sertoli cells), Ki67 (a nuclear protein present in all phases of the cell cycle except G0), cyclin-dependent kinase inhibitor p27 (Kip1), and steroid receptors AR (androgen receptor) and LH2 (estrogen receptor). The slides were then incubated with an appropriate secondary antibody, visualized with DAB chromagen, and counterstained with Mayer's hematoxylin. Immunostaining using p27 (Kip1) revealed no positive staining in any of the days tested, as there is cell division during all of these time points. Protein expression for Ki67 stained mildly after Day 25, suggesting that Sertoli cells became more active at this stage of development. The AR weakly stained and GATA-1 stained intensely at all time points. The data for LH2 were inconclusive and the procedure needs to be performed again. These experiments only give a glimpse of the regulatory factors involved in Sertoli cell proliferation in the developing boar testis. Further studies are being planned to explore other potential factors involved.

Familial occurrence of pig intersexes (38,XX; SRY-negative) on a commercial fattening farm

Occurrence of sex-reversal (38,XX; SRY-negative) cases in the progeny of a single boar was observed. Altogether 11 intersexes, originating from nine litters, given by nine sows were found. The breeder classified the sex-reversal individuals as females with enlarged clitoris. In addition, it was noticed that the anus was joined with the vulva. Moreover, in the scrotum-like structure one or two gonads were present. Cytogenetic evaluation was carried out for the sire, five dams and seven intersexes. The study revealed the normal male karyotype (38,XY) in the sire and the normal female karyotype (38,XX) in the dams and the intersexes. Molecular detection of the presence of the SRY gene was carried out for the sire, five dams, 10 intersexes and 28 phenotypically normal siblings. The SRY gene was present in the genotype of the sire and the male siblings. Three intersexes were subjected to detailed anatomical and histological examinations, after slaughter in a local slaughterhouse. Gonads were classified as testes with well-developed epididymis, however, without spermatogenetic activity. The presence of a properly developed uterus and ducti deferens was observed, but oviducts were not found. The collected data indicate that the sex-reversal status was caused by an unknown autosome, recessive mutation. Genetic background of this type of intersexuality is discussed in this study.

Mammalian Sperm Contain a Ca2+-Sensitive Phospholipase C Activity That Can Generate InsP3 from PIP2 Associated with Intracellular Organelles

We have previously described a phospholipase C (PLC) activity in mammalian sperm cytosolic extracts. Here we have examined the Ca2+ dependency of the enzyme, whether there is enough in a single sperm to account for Ca2+ release at fertilization, and finally where in the egg is the phosphatidyl 4,5-bisphosphate, the substrate for the enzyme. As for all PLCs examined so far in vitro, we found that the boar sperm PLC activity was Ca2+ dependent. Specific activity increased when free Ca2+ levels were micromolar. However, even at nanomolar free Ca2+ concentration the boar sperm PLC activity was considerable, being two orders of magnitude greater than PLC activities in other tissues. We calculated that PLC activity of a single boar sperm in a mammalian egg is enough to generate 400 nM inositol 1,4,5-trisphosphate (InsP3) in 1 min, which may be sufficient to account for the observed Ca2+ changes in an egg at fertilization. We fractionated sea urchin egg homogenate and examined the ability of boar sperm extract to generate InsP3 from these fractions. The sperm PLC activity triggered InsP3 production from a PIP2-enriched nonmicrosomal egg compartment that contained yolk platelets. We propose that this sperm PLC activity, which is active at nanomolar Ca2+ levels and hydrolyzes PIP2 from intracellular membranes, could be involved in the Ca2+ changes observed at fertilization.

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.

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.

Detection of linkage between genetic markers and genes that affect growth and carcass traits in pigs.

Segregation of paternal marker alleles in the progeny of a single boar was used to estimate linkage between the marker genes and associations of these genes with quantitative trait loci (QTL). The sire was heterozygous at four polymorphic marker loci, haptoglobin (HP), glucosephosphate isomerase (GPI), phosphogluconate dehydrogenase (PGD), and esterase D (ESD), and sired 30 litters during an 8-mo period. Glucosephosphate isomerase and PGD were linked (theta = .09; P less than .005). The phase of these two loci in the sire was determined to be GPI A-PGD B, GPI B - PGD A. NO other linkages were detected. Growth (135 less than or equal to n less than or equal to 172) and carcass data (70 less than or equal to n less than or equal to 80) were analyzed assuming a fixed linear model. Least squares means were compared for differences in growth and carcass traits between pigs that inherited alternative paternal marker alleles. Pigs that inherited the GPI A allele from the sire had a 22-g higher daily live weight gain postweaning and reached 103 kg live weight in 2.6 fewer days than did pigs that inherited the GPI B allele (P less than .05), indicative of the presence of gene(s) that affect rate of gain linked to the GPI locus. Pigs that inherited the PGD B allele had a .14 unit higher score for muscle firmness (score ranged from 1 to 3 units) than pigs that inherited the PGD A allele (P less than .05). Pigs that inherited the HP 3 allele had a .06-kg higher weaning weight and a .11 lower ham muscle mass score than did pigs that inherited the HP 2 allele from the sire (P less than .05). No associations with quantitative traits were detected for ESD.

Risk factors associated with transmissible gastroenteritis in swine

Summary Commercial production data base records from 2 Illinois farms, on which epizootic or enzootic transmissible gastroenteritis (tge) was experienced, were accessed for an epidemiologic study. Risk factors investigated were sow parity, source of sows, location of farrowing crates, and breeding practices. At farm 1, an epizootic was experienced; at farm 2, an epizootic of tge followed by enzootic tge was experienced. Initially, crude risk ratios were calculated for these risk factors, and the crude risk ratios were subsequently adjusted for confounders and interactions, using multiple logistic regression techniques. After adjustment, parity-3 sows were 2.3 times more likely to have litters with tge than were sows of all other parities on farm 1, and parity-1 sows were 2.6 times more likely to have litters that experienced tge than were sows of all other parities on farm 2. A single boar on each farm was linked to increased likelihood of a sow's litter contracting epizootic tge on each farm. Enzootic tge was maintained by the periodic influx of outside-source gilts on farm 2; these gilts were 2.2 times more likely to have litters with TCE than were sows derived from farm 2. Sows housed in farrowing crates located under the cold air inlet of farm 2 were 1.7 times as likely as sows located in other rows to have litters with enzootic tge.