# Pig Breeding Cycle and Reproductive Management ## Key Takeaways - The porcine estrous cycle averages 21 days, with estrus (standing heat) lasting 2-3 days, during which ovulation occurs approximately 40 hours after onset; optimal artificial insemination timing is 12-24 hours after first detection of standing heat, followed by a second insemination if heat persists. - Gestation in sows lasts an average of 114 days (111-117 days range), requiring adjusted feeding regimens (increasing from 1.8-2.2 kg/day in the first trimester to 3.0-3.5 kg/day in the final two weeks) and consistent health monitoring to ensure optimal fetal development and sow condition. - Lactation typically spans 21-28 days, with sows requiring high-energy diets (increasing from 1.0-2.0 kg/day initially to 5.0-7.0 kg/day by weaning) to support milk production, while piglets are managed with creep areas and heat sources. - The weaning-to-estrus interval is a critical performance indicator, ideally 4-7 days, influenced by lactation length, sow body condition, and nutrition; flushing (increasing feed intake to 3.0-3.5 kg/day) and boar exposure are key management strategies to stimulate estrus. - Accurate record-keeping is paramount, including sow ID, breeding dates, boar IDs, insemination numbers, farrowing data (total born, born alive, stillborn), and weaning-to-estrus intervals, enabling monitoring of key performance indicators like farrowing rate (target 85-90%) and non-productive days (target <50). - Professional escalation to a veterinarian is indicated for farrowing rates below 75% for over a month, abortion rates exceeding 2%, pre-weaning mortality above 15%, or weaning-to-estrus intervals consistently over 10 days, suggesting systemic issues requiring diagnostic investigation. --- Swine breeders and farm managers responsible for sow reproduction must understand the complete breeding cycle to optimize farrowing intervals, litter sizes, and herd productivity. This article details the reproductive cycle of pigs, including estrus detection, artificial insemination timing, gestation length, and farrowing intervals, with practical management decisions based on observable signs and record keeping. ## At a Glance: Pig Reproductive Cycle Overview The pig breeding cycle follows a predictable sequence from estrus through gestation to farrowing and rebreeding. Understanding each phase allows managers to schedule breeding activities, anticipate farrowing dates, and identify problems early. | Phase | Duration | Key Management Actions | Observable Signs | |-------|----------|----------------------|------------------| | Estrus (heat) | 2-3 days (standing heat 1-2 days) | Estrus detection twice daily, insemination timing | Reddened vulva, mounting behavior, standing reflex | | Gestation | 114 days (range 111-117) | Feeding adjustments, vaccination, health monitoring | Weight gain, udder development, nesting behavior | | Farrowing | 2-6 hours | Supervision, assistance if needed, piglet care | Restlessness, milk letdown, contractions | | Lactation | 21-28 days (weaning age) | Sow feeding, piglet management, weaning | Milk production, piglet growth, sow body condition | | Weaning to estrus | 4-7 days | Flushing, boar exposure, estrus detection | Return to heat, vulva changes, standing reflex | The complete cycle from one farrowing to the next typically spans 145-155 days depending on lactation length and weaning-to-estrus interval. The pig gestation period averages 114 days, with most sows farrowing between 111 and 117 days after breeding according to the Merck Veterinary Manual [3]. ## Reproductive Anatomy and Physiology ### Female Reproductive Tract The sow reproductive tract includes the ovaries, oviducts, uterus, cervix, and vagina. Ovaries produce follicles containing ova and release them during ovulation. The uterus supports embryo implantation and fetal development. The cervix acts as a barrier and is the site for semen deposition during artificial insemination. Research on blood composition changes across the porcine breeding cycle provides insight into physiological shifts that occur during reproduction [7]. ### Estrous Cycle Gilts reach puberty between 5-8 months of age depending on breed, nutrition, and management. The estrous cycle averages 21 days (range 18-24 days). The cycle includes four phases: - Proestrus: 2-3 days of follicle development and estrogen rise - Estrus: 2-3 days of standing heat and ovulation - Metestrus: 1-2 days after ovulation - Diestrus: 14-16 days of corpus luteum activity Ovulation occurs approximately 40 hours after the onset of estrus and lasts 2-6 hours. Understanding this timing is critical for artificial insemination scheduling. Recent research has examined how gut microbiota-derived short-chain fatty acids promote follicular maturation through the gWAT-ovary axis in mammals, suggesting nutritional influences on reproductive function [5]. ### Boar Reproductive Function Boars reach sexual maturity at 6-8 months but should not be used for regular breeding until 8-10 months. Semen quality depends on age, nutrition, temperature, and collection frequency. The Merck Veterinary Manual provides guidance on boar management and semen evaluation [3]. ## Estrus Detection and Timing ### Visual Signs of Estrus Accurate estrus detection requires observation of multiple signs. Primary indicators include: - Vulva swelling and reddening - Clear mucus discharge from the vulva - Mounting other sows or standing to be mounted - Ears erect and tail raised - Reduced appetite - Restlessness and increased vocalization - Standing heat reflex when pressure is applied to the back The standing reflex is the most reliable indicator of estrus. A sow that stands rigidly when pressure is applied to her back or when a boar is present is in standing heat and ready for breeding. ### Detection Methods Estrus detection should occur twice daily, morning and evening, at 12-hour intervals. Methods include: - Visual observation of vulva changes and behavior - Back pressure test for standing reflex - Boar exposure using a mature boar in a pen or behind a barrier - Teaser boar introduction to stimulate estrus expression - Automated detection systems using cameras or sensors Boar exposure significantly improves estrus detection rates. Direct contact with a boar for 5-10 minutes twice daily is effective. The boar should be rotated to maintain interest. ### Timing of Insemination For optimal conception rates, insemination should occur during the latter half of standing heat. The standard recommendation is to inseminate 12-24 hours after first detection of standing heat, with a second insemination 12-24 hours later if the sow remains in standing heat. The Merck Veterinary Manual advises that sows should be inseminated twice during estrus, with the first insemination 12 hours after detection of standing heat and the second 12-24 hours later [3]. ## Artificial Insemination Process ### Semen Collection and Evaluation Semen is collected from boars using the gloved-hand technique. The gel fraction is removed, and the semen is evaluated for volume, concentration, motility, and morphology. Acceptable parameters include: - Volume: 150-300 mL per ejaculate - Concentration: 200-500 million sperm per mL - Motility: greater than 70% progressive motility - Morphology: greater than 70% normal sperm Semen is extended using commercial extenders to achieve a concentration of 2-4 billion sperm per dose. Extended semen can be stored at 15-20°C for 3-5 days depending on extender type. ### Insemination Technique Artificial insemination in swine uses a catheter inserted through the cervix into the uterus. The procedure involves: 1. Clean the vulva with a dry paper towel 2. Insert the catheter at a 45-degree angle upward into the vagina 3. Advance the catheter until resistance is felt at the cervix 4. Rotate the catheter gently to lock into the cervical folds 5. Attach the semen bottle and allow the sow to draw semen in by uterine contractions 6. Massage the sow's flanks or back to stimulate contractions 7. Allow 5-10 minutes for semen to be drawn in 8. Remove the catheter gently after semen is absorbed The sow should remain calm during insemination. Boar presence or pheromone spray can improve uterine contractions and semen uptake. ### Post-Insemination Care After insemination, sows should be kept in a quiet environment for 30-60 minutes. Avoid stress, excessive movement, or mixing with other sows. Record the insemination date, boar ID, and semen batch number. ## Gestation Management ### Gestation Length The pig gestation period averages 114 days, calculated as 3 months, 3 weeks, and 3 days. Most sows farrow between 111 and 117 days after breeding. Gestation length varies by breed, litter size, and parity. Smaller litters tend to have longer gestations. A gestation calendar or calculator helps predict farrowing dates. Sows that have not farrowed by day 117 should be examined by a veterinarian. ### Feeding During Gestation Gestation feeding affects litter size, piglet birth weight, and sow body condition. The Merck Veterinary Manual provides feeding recommendations for gestating sows [3]. General guidelines include: - First trimester (days 1-30): 1.8-2.2 kg per day of gestation feed - Second trimester (days 31-75): 2.0-2.5 kg per day - Third trimester (days 76-114): 2.5-3.0 kg per day, increasing to 3.0-3.5 kg in the last 2 weeks [Body condition scoring](/knowledge/animal-farming/farm-management/body-condition-scoring-a-tool-for-feed-management) should be done at weaning, breeding, and mid-gestation. Sows should maintain a condition score of 3 on a 5-point scale. ### Health Monitoring Gestation health checks include: - Daily observation for illness, injury, or lameness - Vaccination schedule according to herd health plan - Parasite control program - Hoof care and trimming as needed - Body condition assessment every 4 weeks Sows showing signs of illness, abortion, or abnormal discharge should be isolated and examined by a veterinarian. ## Farrowing and Lactation ### Farrowing Preparation Approximately 5-7 days before the expected farrowing date, sows should be moved to clean, disinfected farrowing crates or pens. The farrowing area should have: - Clean bedding or slatted flooring - Heat lamps or pads for piglets - Creep area for piglets - Clean water and feed - Farrowing kit with supplies Sows show nesting behavior 24-48 hours before farrowing, including rooting, pawing, and arranging bedding. ### Farrowing Process Farrowing typically lasts 2-6 hours, with piglets born every 15-30 minutes. Signs of impending farrowing include: - Restlessness and frequent position changes - Milk letdown from teats - Clear mucus discharge from vulva - Tail twitching and abdominal contractions - Nesting behavior Normal farrowing requires minimal intervention. Assistance is needed if: - More than 30 minutes between piglets - Strong contractions without piglet delivery - Visible piglet or placenta without progression - Sow appears distressed or exhausted After farrowing, ensure all placentas are expelled. Retained placentas require veterinary attention. ### Lactation Management Lactation length typically ranges from 21-28 days depending on farm management. Sows should be fed a high-energy lactation diet to support milk production and maintain body condition. Feeding guidelines during lactation: - Day 1-3: 1.0-2.0 kg per day, gradually increasing - Day 4-7: 3.0-4.0 kg per day - Day 7 to weaning: 5.0-7.0 kg per day, ad libitum if possible Sows should have constant access to clean water. Milk production peaks at 3-4 weeks of lactation. ### Weaning Weaning is typically done at 21-28 days of age. The weaning process involves: - Removing piglets from the sow - Moving sows to breeding area - Reducing sow feed for 1-2 days to reduce milk production - Monitoring sows for mastitis or other health issues Weaning triggers the return to estrus, with most sows showing heat within 4-7 days. ## Weaning to Estrus Interval ### Normal Return to Estrus After weaning, sows should return to estrus within 4-7 days. Factors affecting the weaning-to-estrus interval include: - Lactation length (longer lactation equals shorter interval) - Sow body condition (thin sows have longer intervals) - Nutrition during lactation - Season and temperature - Parity (gilts may have longer intervals) Sows that have not shown estrus by day 7 post-weaning should be evaluated for health or management issues. ### Flushing Flushing is the practice of increasing feed intake 10-14 days before breeding to improve ovulation rate. For weaned sows, flushing involves feeding 3.0-3.5 kg per day of a high-energy diet from weaning until breeding. Flushing is most effective in gilts and sows with moderate body condition. Overconditioned sows do not benefit from flushing. ### Boar Exposure Boar exposure after weaning stimulates estrus onset. Direct contact with a mature boar for 15-30 minutes twice daily improves the weaning-to-estrus interval and estrus expression. ## Records and Measurements ### Breeding Records Accurate breeding records are essential for managing the pig breeding cycle. Records should include: - Sow ID and parity - Breeding date and time - Boar ID or semen batch number - Number of inseminations - Estrus detection method and signs - Expected farrowing date - Actual farrowing date - Number of piglets born alive, stillborn, and mummies - Litter weight at birth and weaning ### Key Performance Indicators Monitor these reproductive performance metrics: | Metric | Target Range | Calculation Method | |--------|--------------|-------------------| | Farrowing rate | 85-90% | Number of sows farrowed divided by number of sows bred, multiplied by 100 | | Total piglets born per litter | 12-14 | Count all piglets at farrowing including stillborn and mummies | | Piglets born alive per litter | 11-13 | Count only live piglets at farrowing | | Pre-weaning mortality | Less than 10% | Number of piglets that die before weaning divided by number born alive, multiplied by 100 | | Weaning-to-estrus interval | 4-7 days | Days from weaning to first detected estrus | | Non-productive days per year | Less than 50 | Days when sows are not pregnant or lactating | | Sow longevity | 4-6 parities | Average number of litters produced before culling | ### Gestation Calendar A gestation calendar helps predict farrowing dates and plan management activities. Calculate expected farrowing date by adding 114 days to the breeding date. Many farms use wall calendars or software to track expected farrowing dates. ## Common Failure Patterns ### Failure to Show Estrus Sows that do not show estrus after weaning may have: - Poor body condition - Inadequate nutrition - Heat stress - Disease or infection - Ovarian cysts - Silent heat (estrus without visible signs) Management interventions include improving nutrition, reducing stress, increasing boar exposure, and veterinary examination. ### Low Conception Rates Low conception rates can result from: - Poor estrus detection timing - Low semen quality - Improper insemination technique - Uterine infection - Heat stress at breeding - Nutritional deficiencies Review breeding records and semen quality reports. Consult a veterinarian if conception rates remain below 80%. ### Abortion and Reproductive Failure Causes of abortion include: - Infectious diseases (PRRS, leptospirosis, parvovirus) - Toxins in feed - Heat stress - Trauma - Genetic abnormalities The USDA Animal and Plant Health Inspection Service provides information on swine disease surveillance and control [2]. Any abortion outbreak should be investigated by a veterinarian. ### Prolonged Weaning-to-Estrus Interval Sows with weaning-to-estrus intervals longer than 7 days may have: - Poor lactation nutrition - Excessive body condition loss - Disease or lameness - Seasonal infertility - Ovarian dysfunction Evaluate sow condition and nutrition. Consider culling sows with consistently long intervals. ## Welfare and Safety Considerations ### Sow Welfare Reproductive management affects sow welfare. Key welfare considerations include: - Housing systems that allow natural behaviors - Proper nutrition to maintain body condition - Pain management during farrowing and procedures - Social contact with other sows - Environmental enrichment The Merck Veterinary Manual addresses swine welfare and housing recommendations [3]. ### Worker Safety Working with breeding swine requires safety precautions: - Use proper handling techniques to avoid injury - Wear appropriate personal protective equipment - Be aware of boar aggression during breeding - Use safe equipment for insemination and farrowing - Follow biosecurity protocols ### Biosecurity Biosecurity measures protect herd health: - Quarantine new animals for 30-60 days - Limit visitor access to breeding areas - Use farm-specific clothing and boots - Clean and disinfect equipment between animals - Monitor for disease signs and report to veterinarian The USDA Agricultural Research Service provides information on animal production and protection [1]. ### [Food Safety](/knowledge/bacteria/livestock-bacteria/cooking-chicken-bacteria-prevention) Reproductive management affects food safety through: - Withdrawal periods for medications - Proper record keeping for treated animals - Clean farrowing and lactation environments - Prevention of disease transmission to piglets ## Professional Escalation Criteria Consult a veterinarian when: - Farrowing rate drops below 75% for more than one month - Abortion rate exceeds 2% of bred sows - Stillbirth rate exceeds 10% of total piglets born - Pre-weaning mortality exceeds 15% - Sows show signs of infectious disease - Individual sows have dystocia or retained placenta - Weaning-to-estrus interval exceeds 10 days for multiple sows - Semen quality declines significantly The USDA Animal and Plant Health Inspection Service provides resources for swine health management [2]. ## Record System for Breeding Cycle Interventions and Sow-Level Decision Thresholds A structured record system that links observed breeding cycle events to specific management interventions improves reproductive efficiency and reduces non-productive days. Many farms collect data but fail to translate records into timely decisions. The following framework provides decision thresholds based on days post-weaning, days post-breeding, and sow parity, with clear intervention triggers for each phase of the breeding cycle. ### Breeding Cycle Intervention Framework The framework organizes interventions into three phases: pre-breeding (weaning to estrus), breeding (estrus detection through insemination), and post-breeding (gestation confirmation). Each phase has defined observation windows, decision thresholds, and escalation criteria. **Phase 1: Pre-Breeding (Days 0-7 Post-Weaning)** Record the weaning date, sow parity, body condition score, and lactation length for every sow. Begin estrus detection twice daily starting day 3 post-weaning. The target weaning-to-estrus interval is 4-7 days. Sows that have not shown standing heat by day 7 post-weaning require intervention. Decision thresholds for delayed estrus: - Day 5 post-weaning: Increase boar exposure to 20 minutes twice daily. Verify that sows are receiving adequate feed intake (3.0-3.5 kg per day of lactation diet). - Day 7 post-weaning: Examine sows for health issues including lameness, vulva discharge, or poor body condition (score less than 2 on a 5-point scale). Record findings in the sow health log. - Day 10 post-weaning: Consult a veterinarian for sows that have not shown estrus. Potential causes include ovarian cysts, silent heat, or chronic infection. The Merck Veterinary Manual notes that sows with prolonged weaning-to-estrus intervals may require hormonal intervention or culling evaluation [3]. **Phase 2: Breeding (Days 0-2 of Standing Heat)** Record the time of first standing heat detection, the number of inseminations, boar ID or semen batch number, and the technician performing each insemination. Use a standardized breeding card for each sow that includes space for these observations. Decision thresholds during breeding: - First insemination timing: Inseminate 12 hours after first detection of standing heat. If standing heat is detected in the morning, inseminate that evening. If detected in the evening, inseminate the next morning. - Second insemination timing: Inseminate 12-24 hours after the first insemination if the sow remains in standing heat. Record the sow's response to the back pressure test before each insemination. - Semen quality check: Before each insemination session, verify semen motility under a microscope. Discard any doses with less than 70% progressive motility. Record the motility score for each batch used. - Sow behavior during insemination: Record whether the sow stood calmly, required restraint, or showed signs of stress. Sows that consistently resist insemination may have uterine infections or cervical abnormalities. **Phase 3: Post-Breeding (Days 18-24 Post-Insemination)** Begin estrus detection for bred sows starting day 18 post-insemination. Sows that return to estrus within 18-24 days are not pregnant. Record the return date and any observed signs of estrus. Decision thresholds for pregnancy confirmation: - Day 18-24 post-insemination: Observe for return to estrus. Sows showing standing heat during this window should be re-bred at the next estrus cycle. Record the return date and possible causes including poor timing, low semen quality, or uterine infection. - Day 25-30 post-insemination: Use a pregnancy detection method such as ultrasound or blood test. The Merck Veterinary Manual describes ultrasound as a reliable method for pregnancy diagnosis starting at day 25 [3]. Record the pregnancy status and any abnormalities detected. - Day 30-45 post-insemination: Sows that were pregnant at day 25 but show signs of abortion or reabsorption should be examined by a veterinarian. Record any observed discharge, weight loss, or behavioral changes. ### Sow-Level Record Card Template Each sow should have a permanent record card that tracks breeding cycle events across multiple parities. The card should include: - Sow ID and ear tag number - Breed and genetic line - Birth date and parity number - Body condition score at weaning, breeding, and mid-gestation - Lactation length for each parity - Weaning-to-estrus interval for each parity - Breeding dates and boar IDs for each service - Pregnancy confirmation date and method - Farrowing date and litter data (total born, born alive, stillborn, mummies) - Health events and treatments with withdrawal dates - Culling date and reason Research on blood composition changes across the porcine breeding cycle suggests that physiological markers may eventually support more precise record keeping and intervention timing [7]. However, current practice relies on observable signs and standardized record systems. ### Common Record-Keeping Failures **Failure 1: Inconsistent Observation Timing** Estrus detection that occurs at irregular intervals or only once daily misses short estrus periods. Sows in standing heat for only 12-18 hours may be missed entirely. Standardize observation times to 12-hour intervals, preferably at the same times each day. **Failure 2: Missing Return-to-Estrus Data** Sows that return to estrus after breeding are often not recorded, leading to inaccurate farrowing rate calculations. Record every return date and possible cause. A return rate above 15% requires investigation of breeding timing, semen quality, or herd health. **Failure 3: Delayed Pregnancy Confirmation** Waiting until day 35 or later to confirm pregnancy wastes feed and housing on non-pregnant sows. Use ultrasound at day 25-30 to identify open sows early. Re-breed or cull open sows promptly to minimize non-productive days. **Failure 4: Incomplete Culling Records** Sows culled for reproductive failure should have a recorded reason such as failure to conceive, abortion, small litter size, or poor maternal behavior. Analyze culling patterns by parity to identify systemic problems. The USDA Agricultural Research Service provides resources on herd management and production efficiency [1]. ### Performance Monitoring and Benchmarking Compare your herd's reproductive performance to established benchmarks using the following metrics: - Farrowing rate: Target 85-90%. Calculate as number of sows farrowed divided by number of sows bred, multiplied by 100. - Non-productive days per sow per year: Target less than 50 days. Calculate as total non-productive days for all sows divided by number of sows in the herd. - Litters per sow per year: Target 2.3-2.5. Calculate as 365 days divided by the average farrowing interval in days. - Sow removal rate: Target 40-50% per year. Calculate as number of sows culled or died divided by average herd size, multiplied by 100. Life-cycle comparisons of pig production models indicate that reproductive efficiency directly affects economic and environmental outcomes [8]. Farms with higher farrowing rates and lower non-productive days achieve better profitability and lower environmental impact per pig produced. ### Professional Escalation Criteria for Record System Issues Consult a veterinarian or swine reproduction specialist when: - Farrowing rate falls below 75% for three consecutive months despite following the intervention framework - Return-to-estrus rate exceeds 20% for more than two months - Average weaning-to-estrus interval exceeds 8 days for more than 60 sows - More than 10% of sows require veterinary intervention for delayed estrus or pregnancy failure - Record analysis shows a pattern of reproductive failure by parity, season, or boar line The USDA Animal and Plant Health Inspection Service provides resources for swine health management and disease surveillance that can support record system improvements [2]. ## Frequently Asked Questions ### What is the average pig gestation period? The pig gestation period averages 114 days, calculated as 3 months, 3 weeks, and 3 days. Most sows farrow between 111 and 117 days after breeding. Gestation length varies by breed, litter size, and parity. ### How long does a sow stay in heat? Estrus in sows lasts 2-3 days, with standing heat lasting 1-2 days. Ovulation occurs approximately 40 hours after the onset of estrus. The standing reflex is the most reliable indicator that a sow is ready for breeding. ### When should I inseminate a sow after detecting heat? Inseminate 12-24 hours after first detection of standing heat. A second insemination 12-24 hours later is recommended if the sow remains in standing heat. This timing ensures sperm are present when ovulation occurs. ### How many times should I inseminate a sow during estrus? Two inseminations during estrus are standard practice. The first insemination occurs 12 hours after detecting standing heat, and the second 12-24 hours later. Some farms use a single insemination with good results if timing is precise. ### What is the normal weaning-to-estrus interval? The normal weaning-to-estrus interval is 4-7 days. Most sows show heat within 5 days of weaning. Factors affecting this interval include lactation length, sow body condition, nutrition, and season. ### How can I improve estrus detection in my herd? Improve estrus detection by observing sows twice daily, using boar exposure for 5-10 minutes, applying the back pressure test, and training staff to recognize all signs of estrus. Consistent timing and record keeping are essential. ### What causes low conception rates in swine? Low conception rates can result from poor estrus detection timing, low semen quality, improper insemination technique, uterine infection, heat stress, or nutritional deficiencies. Review breeding records and consult a veterinarian if rates remain below 80%. ### How do I calculate expected farrowing dates? Calculate expected farrowing dates by adding 114 days to the breeding date. Use a gestation calendar or software to track expected dates. Sows that have not farrowed by day 117 should be examined by a veterinarian. ## Related Farming Guides - [Boar Management And Breeding Soundness](/knowledge/animal-farming/swine/boar-management-and-breeding-soundness) - [Manure Management For Pig Farms](/knowledge/animal-farming/swine/manure-management-for-pig-farms) - [Carp Farming Pond Production Feeding And Harvest Management](/knowledge/animal-farming/aquaculture/carp-farming-pond-production-feeding-and-harvest-management) - [Pig Lameness Monitoring And Flooring Management](/knowledge/animal-farming/swine/pig-lameness-monitoring-and-flooring-management) - [Swine Mortality Management And Deadstock Planning](/knowledge/animal-farming/swine/swine-mortality-management-and-deadstock-planning) ## Related Clinical & Scientific Guides * [Pig Enrichment Programs and Behavior Monitoring](/knowledge/animal-farming/swine/pig-enrichment-programs-and-behavior-monitoring) * [Swine Handling Facility Design for Safe Pig Movement](/knowledge/animal-farming/swine/swine-handling-facility-design-safe-pig-movement) * [Swine Feeding Management for Grow-Finish Pigs](/knowledge/animal-farming/swine/swine-feeding-management-for-grow-finish-pigs) ## References and Further Reading - [www.ars.usda.gov](https://www.ars.usda.gov/animal-production-and-protection) - [www.aphis.usda.gov](https://www.aphis.usda.gov/livestock-poultry-disease/swine) - [www.merckvetmanual.com](https://www.merckvetmanual.com/management-and-nutrition) - [WNT5B regulates myogenesis and fiber type conversion by affecting mRNA stability.](https://pubmed.ncbi.nlm.nih.gov/40612684). International journal of biological sciences, 2025. - [Gut microbiota-derived short-chain fatty acids promote follicular maturation via gWAT-ovary axis in mammals.](https://pubmed.ncbi.nlm.nih.gov/41163076). Microbiome, 2025. - [DYRK1A is a multifunctional host factor that regulates coronavirus replication in a kinase-independent manner.](https://pubmed.ncbi.nlm.nih.gov/38099687). Journal of virology, 2024. - [Analysis of blood composition by porcine breeding cycle.](https://pubmed.ncbi.nlm.nih.gov/38358072). [Veterinary medicine](/blog/careers/veterinary-medicine-careers-from-clinical-practice-to-public-health) and science, 2024. - [Life-cycle comparisons of economic and environmental consequences for pig production with four different models in China.](https://pubmed.ncbi.nlm.nih.gov/38393572). Environmental science and pollution research international, 2024. - [Perinatal dysfunction of innate immunity in cystic fibrosis.](https://pubmed.ncbi.nlm.nih.gov/39841805). Science translational medicine, 2025. - [Molecular breeding of pigs in the genome editing era](https://doi.org/10.1186/s12711-025-00961-7). Genetics Selection Evolution, 2025. - [Analysis on effects of African swine fever on China's pig market and industry development](https://doi.org/10.11975/j.issn.1002-6819.2019.18.025). Nongye Gongcheng Xuebao Transactions of the Chinese Society of Agricultural Engineering, 2019. - [Pig](https://doi.org/10.1016/B978-0-12-809633-8.20520-7). Encyclopedia of Reproduction, 2018. - [Effect of vaccination with a bacterin containing Leptospira interrogans serovar bratislava on the breeding performance of swine herds.](https://api.elsevier.com/content/abstract/scopus_id/0024697246). American Journal of Veterinary Research, 1989. > This article is educational and is not a substitute for veterinary diagnosis, treatment, public-health guidance, or regulatory reporting.