Swine fertility in a changing climate

Climate change has been linked to increasing temperatures and weather extremes. Certain regions around the world become more susceptible to environmental hazards that limit pig production and reproductive fertility. Environmental measures that link to pig fertility are needed to assess change, risk and develop solutions. Sub-populations of pigs display lower fertility in summer and are susceptible to heat stress. In the context of a warming climate, elevated temperatures and number of heat stress days increase body temperature and change the physiology, behavior, feed intake, and stress response of the pig. These changes could alter follicle development, oocyte quality, estrus expression, conception and litter size. In boars, sperm quality and production are reduced in response to summer heat stress. Nevertheless, while temperature increases have occurred over the years in some warmer locations, other regions have not shown those changes. Perhaps this involves the measures used for heat stress assessment or that climate is buffered in more temperate areas. Reductions in pig fertility are not always evident, and depend upon climate, year, genotype and management. This could also involve selection, as females more susceptible to heat stress and fertility failure, are subsequently culled. In the years from 1999 to 2020 when increases in global temperature from baseline occurred, measures of female fertility improved for farrowing rate and litter size. Progressive reduction in fertility may not be apparent in all geo-locations, but as temperatures increases become more widespread, these changes are likely to become more obvious and detectable.

Welfare of pigs on farm

This scientific opinion focuses on the welfare of pigs on farm, and is based on literature and expert opinion. All pig categories were assessed: gilts and dry sows, farrowing and lactating sows, suckling piglets, weaners, rearing pigs and boars. The most relevant husbandry systems used in Europe are described. For each system, highly relevant welfare consequences were identified, as well as related animal-based measures (ABMs), and hazards leading to the welfare consequences. Moreover, measures to prevent or correct the hazards and/or mitigate the welfare consequences are recommended. Recommendations are also provided on quantitative or qualitative criteria to answer specific questions on the welfare of pigs related to tail biting and related to the European Citizen's Initiative 'End the Cage Age'. For example, the AHAW Panel recommends how to mitigate group stress when dry sows and gilts are grouped immediately after weaning or in early pregnancy. Results of a comparative qualitative assessment suggested that long-stemmed or long-cut straw, hay or haylage is the most suitable material for nest-building. A period of time will be needed for staff and animals to adapt to housing lactating sows and their piglets in farrowing pens (as opposed to crates) before achieving stable welfare outcomes. The panel recommends a minimum available space to the lactating sow to ensure piglet welfare (measured by live-born piglet mortality). Among the main risk factors for tail biting are space allowance, types of flooring, air quality, health status and diet composition, while weaning age was not associated directly with tail biting in later life. The relationship between the availability of space and growth rate, lying behaviour and tail biting in rearing pigs is quantified and presented. Finally, the panel suggests a set of ABMs to use at slaughter for monitoring on-farm welfare of cull sows and rearing pigs.

Productivity analysis of 70 farrow-to-finish swine farms in Japan from 2013 to 2018

Improving productivity is an urgent issue in the swine industry if it is to compete internationally. However, lack of data about recent productivity transition obstructs stakeholder planning. This study investigated the yearly productivity trends among farrow-to-finish swine farms in Japan using annual productivity data from 2013–2018 obtained for 70 farms in Japan. The productivity parameters analyzed were pigs born alive per litter (PBA), preweaning mortality (PRWM), pigs weaned per litter (PWL), litters per mated female per year (LMFY), pigs weaned per mated female per year (PWMFY), post-weaning mortality (POWM) and marketed pigs per mated female per year (MP). Data were classified into three groups based on the size of the average female inventory and compared among groups. Results presented the mean PBA increased continuously over the 6-year period (P<0.001), and the PWL, PWMFY, and MP means began increasing after 2015 (P<0.001). These upward trends were particularly remarkable on large farms. The mean PRWM increased sharply in 2014, thus inhibiting the increases in PWL, PWMFY, and MP for the same year. The LMFY and POWM means did not change during the study period. Altogether, productivity in Japan improved markedly during the study period, indicating highly prolific sows were well utilized with suitable breeding techniques among farmers these days. Continued genetic improvement and sow management would aid further development in Japan.

Effects of Weaning Age at 21 and 28 Days on Growth Performance, Intestinal Morphology and Redox Status in Piglets

The study objective was to assess effects of different weaning ages on growth performance, intestinal morphology and redox status in Duroc × Landrace × Large White piglets (n = 96) fed diets without antibiotic growth promoters. Piglets were selected from 24 litters based on similar body weight at 14 d of age. All piglets were allocated to two groups in a completely random design with six replicates and eight pigs per replicate (four barrows and four gilts), which were weaned at 21 (n = 48; BW = 6.87 ± 0.33 kg) and 28 (n = 48; BW = 8.49 ± 0.41 kg) days of age. After weaning, pigs were fed a corn-soybean meal-based diet. Average daily gain (ADG), average daily feed intake (ADFI), feed conversion (F:G), diarrhea incidence, gastrointestinal pH, intestinal morphology and redox status were determined. Pigs weaned at 28 d displayed increased ADG from d 8 to 14 (p < 0.01) compared with pigs weaned at 21 d. Pigs weaned at 28 d had a higher ADFI from d 0 to 7 (p < 0.01), d 8 to 14 (p < 0.01), d 15 to 28 (p < 0.05) and during the entire experimental period (p < 0.01) compared with pigs weaned at 21 d. Pigs weaned at 21 d had an improved F:G from d 15 to 28 (p < 0.05) compared with pigs weaned at 28 d. Pigs weaned at 28 d had decreased diarrhea incidence from d 8 to 14 (p < 0.01) and the entire experimental period (p < 0.01) compared with pigs weaned at 21 d. On d 28, the pH of the stomach contents in pigs weaned at 21 d was significantly higher compared with pigs weaned at 28 d (p < 0.01). On d 14, the morphology of the duodenum, jejunum and ileum in pigs weaned at 28 d was improved compared with pigs weaned at 21 d. During the experiment period, the antioxidant abilities of pigs weaned at 28 d of the heart, liver, kidney, intestinal and serum were better than pigs weaned at 21 d. In conclusion, intestinal morphology, pH of the stomach and antioxidant status of pigs weaned at 28 d were better than pigs weaned at 21 d. These factors supported better growth performance and decreased diarrhea incidence.

Timing and temperature thresholds of heat stress effects on fertility performance of different parity sows in Spanish herds

High temperature is an environmental factor that impairs sow fertility. In this study, we identified the critical weeks for heat stress effects on aspects of fertility performance, namely weaning-to-first-service interval (WSI) and farrowing rate (FR). We also examined the threshold temperatures above which the fertility performance deteriorated and whether there were any differences between parities regarding heat stress effects or thresholds. Performance data of sows in 142 herds from 2011 to 2016 were matched to appropriate weekly averaged daily maximum temperatures (Tmax) from weather stations close to the herds. Two types of ratios (i.e., ratio for WSI and odds ratio for FR) were used to identify the critical weeks for heat stress by comparing the respective measures for two sow groups based on Tmax in different weeks around weaning or service events. The ratios for WSI were calculated between groups of sows exposed to Tmax ≥ 27 °C or <27 °C in each week before weaning, with the Tmax cutoff value based on a recent review study. Similarly, the odds ratios for FR for the two groups were calculated in weeks around service. The weeks with the largest differences in the fertility measures between the two Tmax groups (i.e., the highest ratio for WSI and the lowest odds ratio for FR) were considered to be the critical weeks for heat stress. Also, piecewise models with different breakpoints were constructed to identify the threshold Tmax in the critical week. The breakpoint in the best-fit model was considered to be the threshold Tmax. The highest ratios for WSI were obtained at 1 to 3 wk before weaning in parity 1 and 2 or higher sow groups. The threshold Tmax leading to prolonged WSI was 17 °C for parity 1 sows and 25 °C for parity 2 or higher sows. Increasing Tmax by 10 °C above these thresholds increased WSI by 0.65, and 0.33 to 0.35 d, respectively (P < 0.01). For FR, the lowest odds ratios were obtained at 2 to 3 wk before service in parity 0, 1, and 2 or higher sow groups. The threshold Tmax leading to reductions in FR was 20, 21, and 24 to 25 °C for parity 0, 1, and 2 or higher sow groups, respectively. Increasing Tmax by 10 °C above these thresholds decreased FR by 3.0%, 4.3%, and 1.9% to 2.8%, respectively (P < 0.01). These results indicate that the critical weeks for heat stress were 2 to 3 wk before service for FR and 1 to 3 wk before weaning for WSI. The decreases in fertility performance in parity 0 to 1 sows started at temperatures 3 to 8 °C lower than in parity 2 or higher sows.

Effects of individual versus group housing system during the weaning-to-estrus interval on reproductive performance of sows

Selection of appropriate housing conditions for sows is critical for their physical health and long-term reproductive success. The present objective was to evaluate the influences of housing system postweaning (i.e., individual stalls (IS) or group pens (GP)), season and parity on piglet productivity of sows in a commercial setting. This study utilized 3 053 Polish Large White×Polish Landrace sows that were weaned at a rate of 20-30 animals per week at the median age of 4 weeks; 1 474 sows were moved into GP of seven to eight animals each, while 1 579 were placed in IS after weaning. Starting 2 days postweaning all animals were checked for estrus with a teaser boar and then artificially inseminated using 3×10⁹ spermatozoa per dose of an inseminate at the onset of heat and 24 h later. The proportion of sows showing the signs of standing heat at or before 6 days postweaning was greater (P < 0.05) for sows moved to GP compared with IS; this difference manifested mainly in second parity sows weaned in the summer and fall. Conception and farrowing rates were significantly higher (P < 0.01) and the weaning-to-estrus interval shorter in GP compared with IS sows in every season but autumn. Mean litter size was lower (P < 0.05) in IS groups in summer, autumn, and winter, and the number of live-born piglets/sow was lower (P < 0.05) for IS sows in the summer and fall. Beneficial effects of group housing on piglet productivity manifested up until the seventh consecutive farrowing and then began to wane. In summary, there was a significantly greater proportion of sows going estrus "on time" (i.e., <7 days) in group housing compared to single stalls but this effect was confined to the second parity sows during the summer and fall months; these results suggest the existence of a seasonal and age-related aspect to sow fertility worthy of further investigation. While both housing systems have their pros and cons, our present results indicate that, in commercial settings, group housing postweaning improved nearly all reproductive parameters of sows.

Effects of supplementing late-gestation sow diets with zinc on preweaning mortality of pigs under commercial rearing conditions

The objective of this experiment was to determine preweaning survival of pigs when sows were supplemented with 3 dietary levels of zinc (Zn) in late gestation. Gilts and sows (n = 339) were assigned to 1 of 3 dietary treatments based on parity. Dietary treatments were 1) Control—sows fed a corn–soybean meal-based diet containing 125 ppm total supplemental Zn supplied by ZnSO₄ (75 ppm Zn) and AvailaZn (50 ppm Zn, CON); 2) Intermediate—as Control + 240 ppm supplemental Zn as ZnSO₄ (INT); and 3) High—as Control + 470 ppm supplemental Zn as ZnSO₄ (HI). Final supplemental Zn concentrations of the 3 dietary treatments were 1) CON—125 ppm; 2) INT—365 ppm; and 3) HI—595 ppm. Sows received dietary treatments from about day 85 of gestation until farrowing. Individual piglet birth weights were recorded within 12 h of parturition. Instances of piglet mortality were recorded daily. The statistical model considered fixed effects of treatment and random effects of parity. Piglets from sows fed the INT diet had heavier (P < 0.05) birth weights than those fed CON (1.42 vs. 1.38 kg, respectively), while offspring from sows fed HI tended to have heavier (P < 0.10) birth weights (1.40 kg) than pigs from INT sows. Furthermore, incidence of low birth weight pigs was less (P < 0.05) for sows consuming INT compared with sows fed CON and HI. Despite differences in birth weight, there were no differences (P > 0.05) in total pigs born, born alive, or weaned, nor differences in individual piglet gain or weaning weight across treatments. Mortality of low birth weight pigs was lowest (P < 0.05) for offspring from sows fed HI (28.1%) compared with offspring from sows fed INT (36.1%) and CON (38.3%). Similarly, overall piglet mortality tended to decrease (P < 0.10) as dietary Zn content increased (CON: 15.0%, INT: 13.2%, and HI: 12.2%). A subset of pigs (n = 420, n = 140/treatment) were selected at weaning to evaluate effects of dietary treatment on postweaning performance. There were no significant effects of sow Zn supplementation on final body weight, days to market, or carcass characteristics of market pigs. Overall, effects of supplemental dietary Zn at 365 and 595 ppm in late gestation improved preweaning survival of low birth weight piglets and reduced overall preweaning mortality of piglets.

Herd-level factors associated with piglet weight at weaning, kilograms of piglets weaned per sow per year and sow feed conversion

To understand the production factors that affect conclusive parameters of sow herd performance can improve the use of the resources and profitability of farm. The objective of this study was to identify associations and quantify the effects of a set of factors related to piglet weight at weaning (PWW), kilograms of piglets weaned per sow per year (kgPWSY) and sow feed conversion (SFC). Data from 150 farms were collected, for a total study population of 135 168 sows, including gilt replacement, breeding (mating), gestation and farrowing/lactation phases. A questionnaire focusing on reproductive performance, management, facilities, feeding, health and biosafety was administered. Multiple linear regression models were used to assess associations among factors with each of the three dependent variables. Increased duration of lactation was positively associated with PWW, kgPWSY and SFC. The increase in the number of live born pigs per litter was positively associated with kgPWSY and with SFC. Farms with higher PWW had farrowing room humidifiers, did not surgically castrate male piglets and used quaternary ammonia compounds for farrowing room disinfection. Farms with higher kgPWSY used lined ceilings in farrowing rooms and winter feeds with higher CP percentages in gestation; they also had more farrowings per sow per year. Sow feed conversion was worse in farms with partly slatted floors during gestation, in farms feeding lactating sows six times a day or ad libitum and farms with a higher sow-handler ratio. This study indicates that farms can increase PWW and kgPWSY and improve the SFC by changing one or more management, biosafety and feeding practices or facilities as well as by focusing on improving several performance parameters, particularly increasing the duration of lactation and the number of live born pigs per litter.

Analysis of survey data of breeding herd for reproductive management practices in swine farms of Punjab

The present survey was performed to analyze standard operating procedures for swine development and fertility based on prevailing reproductive management practices among different swine farms of Punjab. The average farrowing rate, farrowing interval, weaning to estrus interval, weaning to conception interval and age at first breeding were 71.5±11.4%, 165.4±13.8 days, 8.3±2.1 days, 42.7±11.0 days and 8.1±1.3 months, respectively. Mean live litter size at birth and weaning were 9.9±3.6 and 8.1±3.3 piglets per farrowing, respectively. Most farmers (94.1%) kept pigs in loose housing system with a mixture of both stalls and pens, and used cement and brick as construction material for sties. Majority of farms (84.3%) functioned as farrow to wean with intensive production systems (75.5%). The labor to animal ratio of 1:50 was most common. Accurate and well maintained records were noticed at 66.7% farms. Start of boar exposure after weaning began within 1 day, occurring most often in morning, with exposure times varying from < 2–5 min/sow in 87.3% farms. Natural mating was allowed within minutes to hours after detection of estrus on 100% of farms. At all farms (100%), sows were allowed 􀁴1 chance for breeding after conception failure before culling. Summer infertility was observed on 56.9% of farms. Feeding method for lactating sows was divided between ad lib. and gradual daily increase of concentrate feed and kitchen waste. None of the farmer practiced docking in newborn piglets. These results suggest that reproductive management of farms in key areas related to weaning, breeding, gestation, feeding and health care could be a source of varying reproductive performance among swine.

Review: innovation through research in the North American pork industry

This article involved a broad search of applied sciences for milestone technologies we deem to be the most significant innovations applied by the North American pork industry, during the past 10 to 12 years. Several innovations shifted the trajectory of improvement or resolved significant production limitations. Each is being integrated into practice, with the exception being gene editing technology, which is undergoing the federal approval process. Advances in molecular genomics have been applied to gene editing for control of porcine reproductive and respiratory syndrome and to identify piglet genome contributions from each parent. Post-cervical artificial insemination technology is not novel, but this technology is now used extensively to accelerate the rate of genetic progress. A milestone was achieved with the discovery that dietary essential fatty acids, during lactation, were limiting reproduction. Their provision resulted in a dose-related response for pregnancy, pregnancy maintenance and litter size, especially in maturing sows and ultimately resolved seasonal infertility. The benefit of segregated early weaning (12 to 14 days of age) was realized for specific pathogen removal for genetic nucleus and multiplication. Application was premature for commercial practice, as piglet mortality and morbidity increased. Early weaning impairs intestinal barrier and mucosal innate immune development, which coincides with diminished resilience to pathogens and viability later in life. Two important milestones were achieved to improve precision nutrition for growing pigs. The first involved the updated publication of the National Research Council nutrient requirements for pigs, a collaboration between scientists from America and Canada. Precision nutrition advanced further when ingredient description, for metabolically available amino acids and net energy (by source plant), became a private sector nutrition product. The past decade also led to fortuitous discoveries of health-improving components in ingredients (xylanase, soybeans). Finally, two technologies converged to facilitate timely detection of multiple pathogens in a population: oral fluids sampling and polymerase chain reaction (PCR) for pathogen analysis. Most critical diseases in North America are now routinely monitored by oral fluid sampling and prepared for analysis using PCR methods.

Gilt Management for Fertility and Longevity

Simple Summary

Improving sow lifetime productivity, herd stability, and maximizing lifetime performance and longevity in the sow herd, represent significant challenges to the swine industry. Routine implementation of efficient gilt development unit (GDU) programs which deliver high quality, breeding-eligible gilts to the sow farm is still needed. Good gilt management starts at birth, because litter of origin, lactation management and the application of early selection strategies are early indicators of future performance and efficiency. A failure to select gilts with the greatest reproductive potential and inappropriate management of their physiological state and metabolic condition at service, are key risk factors for poor sow lifetime productivity (SLP). Management practices that deliver gilts with the greatest potential SLP are crucial to the productivity of conventional production systems.

Abstract

Substantial evidence supports successful management of gilts as an absolutely necessary component of breeding herd management and the pivotal starting point for the future fertility and longevity of the breeding herd. Therefore, gilt management practices from birth have the potential to influence the future reproductive performance of the sow herd. A good gilt management program will address several key components such as birth traits that determine the efficiency of replacement gilt production; effective selection of the most fertile gilts for entry to the breeding herd; effective management programs that provide a consistent supply of service eligible gilts; and appropriate management of weight, physiological maturity, and a positive metabolic state at breeding. Good gilt management can largely resolve the existing gap between excellent genetic potential and the more modest sow lifetime productivity typically achieved in the industry. Investment in good gilt development programs from birth represents a foundational opportunity for improving the efficiency of the pork production industry.

PHYSIOLOGY AND ENDOCRINOLOGY SYMPOSIUM: Factors influencing follicle development in gilts and sows and management strategies used to regulate growth for control of estrus and ovulation1

Factors that affect follicle health and growth can influence estrus, ovulation, conception, and litter size. Since the majority of the breeding herd is composed of sows, production schedules are established based on synchronized follicle growth following weaning. Insemination of sows over a 3- to 4-d period after weaning facilitates farrowing over fewer days and helps improve the uniformity of pigs at weaning. Synchronized inseminations of the group are reduced when disturbance to the follicular phase results in delayed estrus. The failure of >15 follicles to uniformly progress beyond the 6.0 mm size within 4 d during the follicular phase is associated with delayed estrus and ovulation, reduced ovulation rate, and reduced farrowing rate. In sows, the follicular phase is initiated at weaning by removal of the suckling inhibition, whereas in cycling gilts, luteolysis and clearance of progesterone begins the process. The timing and patterns of follicle-stimulating hormone and luteinizing hormone stimulation to the ovary determine follicle health and selection for ovulation. Interestingly, abnormal wean-to-estrus intervals in sows and deviations from a 19- to 22-d estrous cycle in gilts are associated with reduced fertility. However, in both cases, it is not entirely clear whether the abnormal intervals are a direct result of problems occurring prior to or only during the follicular phase. In prepubertal gilts, the signal for initiating the follicular phase remains elusive, but could reside in differential sensitivity and response to hormone signals at the level of the ovary and brain. Although the mechanisms are not clear, factors such as boar exposure, stress, feed intake, growth rate, and birthweight have been shown to stimulate an early follicular phase. In contrast, inhibitors to follicle growth have been associated with season, heat stress, photoperiod, negative energy balance, poor body condition, slow growth, fewer parities, and short lactation length. Hormonal aids for inducing and delaying the follicular phase, as well as for inducing ovulation are available to aid in synchronized breeding schedules.

The influence of azaperone treatment at weaning on reproductive performance of sows: altering effects of season and parity

Azaperone treatment can control aggression and decrease stress due to weaning, re-grouping and hierarchical fighting of gilts and sows. However, the effects of this butyrophenone neuroleptic and sedative administered at weaning on pig reproductive function are poorly characterized. In this year-long study, a total of 619 cross-bred sows (Polish Large White×Polish Landrace) kept on a commercial farm received an i.m. injection of azaperone (Stresnil®; 2 mg/kg BW) just before weaning and were artificially inseminated during the ensuing estrus with 3×109 spermatozoa per dose of an inseminate; 1180 sows served as untreated controls. Immediately after weaning, the sows were moved to four pens of seven to nine animals each. A teaser boar was used twice daily to check for estrus and sows were bred at heat detection. Subsequently, all sows stayed in individual stalls until pregnancy testing on day 30 post-artificial insemination and were then re-grouped until farrowing. The proportion of pigs that were in estrus within 6 days post-weaning was significantly lower in azaperone-treated groups of animals than in controls (71.4% v. 84.2%). Overall, the azaperone-treated sows had a significantly longer weaning-to-estrus interval (WEI; 8.7±10.1 v. 6.3±8.1 days; mean±SD) and a significantly larger litter size (LS: 11.8±3.0 v.11.3±3.2; azaperone-treated v. control sows). Treatment of the winter-farrowing sows was associated with increased LS (12.8±2.6 and 11.3±3.1 piglets/sow, respectively; P<0.05) and longer (P<0.05) weaning-to-effective-service intervals (11.7±19.3 and 8.4±12.3 days, respectively) as well as farrowing intervals (155.7±19.7 and 152.2±16.1 days, respectively) compared with untreated controls. In the summer months, significantly longer WEIs (12.1±21.0 v. 8.4±16.9 days) were accompanied by a significant decline in LS only in azaperone-treated sows that were inseminated within 6 days post-weaning (10.8±2.9 v. 11.5±3.3 piglets/sow; azaperone-treated v. controls). Azaperone-treated second parity sows had greater LS (P<0.001) along with prolonged WEIs (P<0.05) in comparison to their respective controls, regardless of the timing of estrus. An application of azaperone at weaning increased the annual piglet productivity of winter-farrowing animals and of second parity sows but depressed it significantly in summer. The extra cost and labor due to delayed onset of estrus may cancel out any reproductive benefits of azaperone treatment.

Sow housing associated with reproductive performance in breeding herds

Female pigs in breeding herds can be managed through four phases-gilt development, breeding, gestation, and lactation-during which they may be housed in group or individual pens, stalls, or on pasture. In this review, we focus on housing environments that optimize outcomes during gestation and lactation. Appropriate housing is important during early gestation, to protect embryos and to confirm pregnancy, and from mid-to-late gestation, to ensure sufficient nutrition to increase placental and fetal growth. No difference in the number of pigs born alive were reported between group housing and individual stall housing, although more risk factors for reproductive performance are associated with group housing than stall housing including genetics, bedding, floor space allowance, group size, social ranking, and parity. Furthermore, lameness in pregnant pigs is more frequent in group housing than in stall housing. Housing during lactation helps protect piglets from being crushed or from contracting disease, and can foster the transfer of enough colostrum from mother to piglets. Indeed, lactating sows in pen housing tend to have higher pre-weaning mortality and lighter litter weights than those in crated housing.

The relationship between mitochondrial DNA haplotype and the reproductive capacity of domestic pigs (Sus scrofa domesticus)

Background

The maternally inherited mitochondrial genome encodes key proteins of the electron transfer chain, which produces the vast majority of cellular ATP. Mitochondrial DNA (mtDNA) present in the mature oocyte acts as a template for all mtDNA that is replicated during development to meet the specific energy requirements of each tissue. Individuals that share a maternal lineage cluster into groupings known as mtDNA haplotypes. MtDNA haplotypes confer advantages and disadvantages to an organism and this affects its phenotype. In livestock, certain mtDNA haplotypes are associated with improved milk and meat quality, whilst, other species, mtDNA haplotypes have shown increased longevity, growth and susceptibility to diseases. In this work, we have set out to determine whether mtDNA haplotypes influence reproductive capacity. This has been undertaken using a pig model.

Results

To determine the genetic diversity of domestic pigs in Australia, we have sequenced the D-loop region of 368 pigs, and identified five mtDNA haplotypes (A to E). To assess reproductive capacity, we compared oocyte maturation, fertilization and development to blastocyst, and found that there were significant differences for maturation and fertilization amongst the haplotypes. We then determined that haplotypes C, D and E produced significantly larger litters. When we assessed the conversion of developmentally competent oocytes and their subsequent developmental stages to offspring, we found that haplotypes A and B had the lowest reproductive efficiencies. Amongst the mtDNA haplotypes, the number of mtDNA variants harbored at >25 % correlated with oocyte quality. MtDNA copy number for developmentally competent oocytes positively correlated with the level of the 16383delC variant. This variant is located in the conserved sequence box II, which is a regulatory region for mtDNA transcription and replication.

Conclusions

We have identified five mtDNA haplotypes in Australian domestic pigs indicating that genetic diversity is restricted. We have also shown that there are differences in reproductive capacity amongst the mtDNA haplotypes. We conclude that mtDNA haplotypes affect pig reproductive capacity and can be used as a marker to complement current selection methods to identify productive pigs.

Electronic supplementary material

The online version of this article (doi:10.1186/s12863-016-0375-4) contains supplementary material, which is available to authorized users.

The Fertility of Frozen Boar Sperm When used for Artificial Insemination

One of the limits to practical use of frozen boar sperm involves the lowered fertility when used for artificial insemination. Years of studies have shown that 5-6 billion sperm (approximately 3 billion viable) used in single or multiple inseminations results in pregnancy rates most often between 60 and 70% and with litter sizes between nine and 10 pigs. Yet today, it is not uncommon for studies to report pregnancy rates from 70 to 85% and litter sizes with 11-12 pigs. While global statements about the incidence and reasons for higher fertility are not conclusive, incremental fertility improvements appear independently associated with use of a minimum number of viable sperm (1-2 billion), insemination timing that increases the probability that sperm will be present close to ovulation for groups of females, selection for boar sperm survival following cryopreservation, and modification of the freeze and thaw conditions using additives to protect sperm from oxidative damage. Studies show that techniques such as intrauterine and deep uterine insemination can provide an opportunity to reduce sperm numbers and that control of time of ovulation in groups of females can reduce the need for multiple inseminations and improve the chance for AI close to ovulation. However, optimal and consistent fertility with cryopreserved boar sperm may require a multifaceted approach that includes boar selection and screening, strategic use of additives during the freezing and thawing process, post-thaw evaluation of sperm and adjustments in sperm numbers for AI, assessment of female fertility and ovulation induction for single insemination. These sequenced procedures should be developed and incorporated into a quality control system for improved fertility when using minimal numbers of cryopreserved boar sperm.

Artificial insemination in pigs today

Use of artificial insemination (AI) for breeding pigs has been instrumental for facilitating global improvements in fertility, genetics, labor, and herd health. The establishment of AI centers for management of boars and production of semen has allowed for selection of boars for fertility and sperm production using in vitro and in vivo measures. Today, boars can be managed for production of 20 to 40 traditional AI doses containing 2.5 to 3.0 billion motile sperm in 75 to 100 mL of extender or 40 to 60 doses with 1.5 to 2.0 billion sperm in similar or reduced volumes for use in cervical or intrauterine AI. Regardless of the sperm dose, in liquid form, extenders are designed to sustain sperm fertility for 3 to 7 days. On farm, AI is the predominant form for commercial sow breeding and relies on manual detection of estrus with sows receiving two cervical or two intrauterine inseminations of the traditional or low sperm doses on each day detected in standing estrus. New approaches for increasing rates of genetic improvement through use of AI are aimed at methods to continue to lower the number of sperm in an AI dose and reducing the number of inseminations through use of a single, fixed-time AI after ovulation induction. Both approaches allow greater selection pressure for economically important swine traits in the sires and help extend the genetic advantages through AI on to more production farms.

Current strategies for reproductive management of gilts and sows in North America

Many advances in genetic selection, nutrition, housing and disease control have been incorporated into modern pork production since the 1950s resulting in highly prolific females and practices and technologies, which significantly increased efficiency of reproduction in the breeding herd. The objective of this manuscript is to review the literature and current industry practices employed for reproductive management. In particular the authors focus on assisted reproduction technologies and their application for enhanced productivity. Modern maternal line genotypes have lower appetites and exceptional lean growth potential compared to females of 20 yr ago. Thus, nutrient requirements and management techniques and technologies, which affect gilt development and sow longevity, require continuous updating. Failure to detect estrus accurately has the greatest impact on farrowing rate and litter size. Yet, even accurate estrus detection will not compensate for the variability in the interval between onset of estrus and actual time of ovulation. However, administration of GnRH analogs in weaned sows and in gilts after withdrawal of altrenogest do overcome this variability and thereby synchronize ovulation, which makes fixed-time AI practical. Seasonal infertility, mediated by temperature and photoperiod, is a persistent problem. Training workers in the art of stockmanship is of increasing importance as consumers become more interested in humane animal care. Altrenogest, is used to synchronize the estrous cycle of gilts, to prolong gestation for 2–3 d to synchronize farrowing and to postpone post-weaning estrus. P.G. 600® is used for induction of estrus in pre-pubertal gilts and as a treatment to overcome seasonal anestrous. Sperm cell numbers/dose of semen is significantly less for post cervical AI than for cervical AI. Real-time ultrasonography is used to determine pregnancy during wk 3–5. PGF_2α effectively induces farrowing when administered within two d of normal gestation length. Ovulation synchronization, single fixed-time AI and induced parturition may lead to farrowing synchronization, which facilitates supervision and reduces stillbirths and piglet mortality. Attendance and assistance at farrowing is important especially to ensure adequate colostrum consumption by piglets immediately after birth. New performance terminologies are presented.

Effects of altering the dose and timing of triptorelin when given as an intravaginal gel for advancing and synchronizing ovulation in weaned sows

Previous studies have shown that triptorelin gel (TG) given intravaginally in gel form is effective for advancing the time of ovulation in weaned sows. Three experiments were performed to determine the effects of altering the dose and timing of administration of intravaginal TG for advancing and synchronizing ovulation in weaned sows. In all experiments, estrus was detected twice or three times daily and ultrasound was performed to determine ovulation at 8-hour intervals. In experiment 1, sows (n = 131) received intravaginal gel containing 0 (Placebo), 25, 100, or 200 μg of TG at 96 hours after weaning and sows were inseminated on each day of standing estrus. Wean-to-estrus interval and duration of estrus were correlated (P < 0.0001) with estrus duration longer in TG (P < 0.05) compared with Placebo. More sows ovulated (P < 0.001) by 48 hours after treatment with 200 (81%), 100 (64%), and 25 μg (63%) of TG compared with Placebo (42%). The farrowing rate and total pigs born did not differ (P > 0.10). In experiment 2, sows (n = 126) received 200 μg of TG at 72, 84, or 96 hours after weaning or were untreated (Control-96). Sows receiving TG were inseminated once 24 to 28 hours after treatment. Control-96 sows were inseminated on each day of standing estrus. Wean-to-estrus interval was not affected by treatment, but wean-to-ovulation interval was reduced (P < 0.05) by TG-72 and TG-84 compared with TG-96 and Control-96. More sows ovulated 40 hours after treatment (P < 0.001) with TG-72 (56.5%) and TG-84 (32.2%) compared with TG-96 and Control-96 (13%) and for all TG treatments 48 hours after treatment (64%) compared with Control-96 (34%, P < 0.05). The farrowing rate was lower (P < 0.05) for sows assigned to TG-72 and TG-84 compared with TG-96 and Control-96, whereas the number of liveborn pigs did not differ (P > 0.10). In experiment 3, sows (n = 113) were assigned to receive no treatment (Control), intravaginal gel alone (Placebo), or 200 μg of TG given intravaginally (OvuGel) at 96 hours after weaning. Wean-to-estrus interval did not differ, but the duration of estrus tended (P < 0.10) to be reduced with OvuGel compared with the other treatments. More sows ovulated (P < 0.001) by 48 hours after OvuGel treatment (79.1%) compared with Control (46.4%) and Placebo (37.9%) and by 56 hours (P < 0.05). The farrowing rate and the number of liveborn pigs did not differ among treatments. The results of these studies indicate that 200 μg of TG given intravaginally at 96 hours after weaning (OvuGel) synchronizes ovulation and results in fertility similar to Controls.

Effect of day of mixing gestating sows on measures of reproductive performance and animal welfare

Effects of day of mixing sows after breeding were measured for reproduction and welfare on a commercial research farm. Sows (n = 1,436) were weaned into stalls for breeding, and groups of sows were assigned to 1) no mixing and housed in individual stalls (STL), 2) mixed on d 3 to 7 after breeding (D3), 3) mixed on d 13 to 17 after breeding (D14), or 4) mixed 35 d after breeding (D35). Mixed sows were moved into pens (n = 58 sows/pen) with an electronic sow feeding station and maintained as a static group. In the first 12 d after mixing or movement into STL (period 1), sows were assessed for lameness and lesions every 3 d and then every 2 wk until farrowing (period 2). Cortisol and fights were measured in period 1. Conception rates were reduced (P < 0.005) in D3 (87.1%) and D14 (89.2%) compared to D35 (92.2%) and STL (96.2%). Farrowing rates were lower (P < 0.0001) in D3 (82.8%) compared to D35 (90.5%) and STL (96.2%), but litter size was not (P ≥ 0.20) affected by mixing. The proportion of sows bred within 10 d of weaning was reduced (P < 0.05) for D14 compared to STL, but D3 and D35 did not differ among treatments. Number of fights 24 h after mixing was less (P < 0.0001) for D14 compared to D3 and D35 groups, and serum cortisol was greater (P < 0.05) for D35 compared to STL and D3. From period 1 to 2, lameness increased in D3 and decreased in D35 but did not change for D14 and STL (treatment × period, P < 0.05), whereas leg inflammation did not differ (P > 0.10) among treatments. Head and body lesion scores declined from period 1 to 2 in all mix groups, whereas vulva lesions increased in the D3 and D35 but did not change in D14 and STL (treatment × period, P < 0.0001). These results suggest STL can improve most measures of welfare compared to mixing in groups. However, when mixing sows, assessments for reproductive performance and welfare may change from gestation to farrowing. The poorest reproductive performance and welfare was observed when sows were mixed 3 to 7 d after breeding. There were few differences between the D14 and D35 treatments in reproduction or welfare, but D14--not D35--differed from STL in weaned sows rebred. Overall, results of this trial suggest that, even though any of the mixing days can result in acceptable measures of reproduction, there are clear effects of day of mixing on fertility and welfare, and special attention should be focused on the long-term reproductive and welfare consequences.

Impact of swine reproductive technologies on pig and global food production

Reproductive technologies have dramatically changed the way pigs are raised for pork production in developed and developing countries. This has involved such areas as pigs produced/sow, more consistent pig flow to market, pig growth rate and feed efficiency, carcass yield and quality, labor efficiency, and pig health. Some reproductive technologies are in widespread use for commercial pork operations [Riesenbeck, Reprod Domest Anim 46:1-3, 2011] while others are in limited use in specific segments of the industry [Knox, Reprod Domest Anim 46:4-6, 2011]. Significant changes in the efficiency of pork production have occurred as a direct result of the use of reproductive technologies that were intended to improve the transfer of genes important for food production [Gerrits et al., Theriogenology 63:283-299, 2005]. While some technologies focused on the efficiency of gene transfer, others addressed fertility and labor issues. Among livestock species, pig reproductive efficiency appears to have achieved exceptionally high rates of performance (PigCHAMP 2011) [Benchmark 2011, Ames, IA, 12-16]. From the maternal side, this includes pigs born per litter, farrowing rate, as well as litters per sow per year. On the male side, boar fertility, sperm production, and sows served per sire have improved as well [Knox et al., Theriogenology, 70:1202-1208, 2008]. These shifts in the efficiency of swine fertility have resulted in the modern pig as one of the most efficient livestock species for global food production. These reproductive changes have predominantly occurred in developed countries, but data suggests transfer and adoption of these in developing countries as well (FAO STAT 2009; FAS 2006) [World pig meat production: food and agriculture organization of the United Nations, 2009; FAS, 2006) Worldwide Pork Production, 2006]. Technological advancements in swine reproduction have had profound effects on industry structure, production, efficiency, quality, and profitability. In all cases, the adoption of these technologies has aided in the creation of a sustainable supply of safe and affordable pork for consumers around the world [den Hartog, Adv Pork Prod 15:17-24, 2004].