Breeding Management of Pigs

Domesticated sows and gilts are classified as nonseasonal and polyestrous, with the estrous cycle lasting 21 ± 1 days (range: 18–24 days). However, pigs do show seasonal declines in fertility, likely associated with their ancestral relation to the wild pig. Pigs are susceptible to heat stress during summer, and this can impact hormones and follicle development in summer and into autumn. Therefore, more pigs show anestrus, delayed estrus, and conception failures in summer and autumn, which can be explained by the various contributions of heat stress and changing photoperiod.

Sows are behaviorally anestrous during pregnancy, although false pregnancy can sometimes be observed under changing hormones during gestation in group-housed sows. Ovulatory estrus usually does not occur during the first 3 weeks of lactation, except under conditions where cessation of nursing occurred, split or partial weaning removed nursing inhibition on hormones, or in combination with group rearing, high feed levels, and boar contact. Partial weaning or gonadotropin treatment can induce follicle development and estrus during lactation; however, fertility results in the first 3 weeks are inconsistent, poor, and not economical. Normal uterine physiology is reestablished by 21–28 days postpartum. Most sows exhibit estrus 3–7 days after weaning; however, this can depend upon weight loss in lactation, boar exposure, parity, and season of the year.

Estrus in prepubertal gilts and postweaning anestrous sows can be initiated with exogenous hormones such as eCG and hCG in combination. When these animals are inseminated at estrus, good fertility can result, provided that the gilts are of proper age and weight and the weaned sows are in good body condition. This hormone combination can be used to prevent anestrus or delayed estrus in weaned sows at risk for these conditions after weaning and can be effective in parity-1 sows and sows weaned in summer and autumn. However, these hormones do circumvent natural selection for reproductive efficiency, and this should be kept in mind when they are used in breeding management programs.

Exogenous hormones should not be used as a long-term solution to address underlying reproductive problems in a herd; however, some farms use them proactively as part of a planned estrus-management program.

Estrus lasts approximately 36–48 hours (1–2 days) in gilts and ≥ 48–72 hours (2–3 days) in sows. The interval to estrus after weaning affects the duration of estrus in sows and can be influenced by length of lactation, nutrition, body condition, genetics, housing, boar exposure, and other management practices (see table Factors Affecting Ovarian Activity of Pigs).

Sows that return to estrus on day 3 after weaning tend to show longer estrus and can receive three inseminations, while those returning on days 4–5 more often receive two inseminations, and those returning on day 6 might only receive a single service.

In loose-housed females, estrus is often characterized by behaviors that include mounting other females, vocalizing, ears erection, and standing to be mounted (see estrus in weaned sows image). These behaviors can sometimes be observed with physical changes such as vulvar swelling and mucous vaginal discharge. In females confined to stalls, immobility and erect ears in response to fenceline boar exposure can be used to determine estrus, with best results noted when also applying the back-pressure test.

Estrus in weaned sows

Image

A weaned sow showing the standing response to fenceline contact with a mature boar in the alleyway in front of the stall.

Courtesy of Robert Knox, University of Illinois.

Ovulation generally occurs around 70% of the way through the estrus period. During ovulation, approximately 15–24 ova are released over a 1- to 4-hour period. The number of follicles that develop and ovulate is dependent on maturity and increases with number of estrous cycles in gilts and with parity in weaned sows. Ovulation rate increases over the first four parities, so that the fourth to sixth litters tend to be the largest in number.

Ovulation rate can decrease when gilts or sows are undernourished. Most developing gilts in pens are on full feed, thereby avoiding the adverse affects of undernourishment on early reproductive performance. Under circumstances where gilts are not provided access to full feed, increasing energy intake for 10 days before the next expected estrus (ie, “flushing”) can be performed to increase ovulation rate by 2–4 eggs to challenge uterine capacity for increased litter size (1, 2) (see ovaries with large follicles image). To prevent undernourishment in recently weaned sows, an energy-dense diet should be fed until after estrus and breeding (3).

Ovaries with large follicles, pig

Image

An ovary at estrus with large, ovulatory follicles (left), also shown in an ultrasonogram (right).

Courtesy of Robert Knox, University of Illinois.

Behavioral changes of estrus are most pronounced when the sow or gilt is intermittently exposed to a mature boar to allow fenceline or physical contact. This provides an array of stimulation that includes sight, sound, odor, and physical contact to the female's back and flank.

With physical contact, the boar will stimulate the tactile pressure. However, when fenceline boar exposure is used, a human should use hands-on pressure as a critical component to determine estrus. A sow or gilt in standing estrus (heat) normally assumes a rigid, immobile, receptive stance when exposed to a boar. However, this might only become evident when physical stimuli is applied by a human. The ears also can become erect or show a twinge at the base when back-pressure is applied. The estrual female often becomes quiet, with the head in a fixed position. Other physical changes, such as vulvar swelling and discharge, are often unreliable; they do, however, appear to be more marked in young gilts than sows and commonly develop 1–3 days before estrus.

The ultimate criterion of estrus is either standing to the boar or a positive response to the back-pressure test (an attendant applies pressure with the hands in the loin area (see gilt estrus and estrus detection images), with flank or underline stimulation to elicit the standing reaction. This test is very effective when allowing physical contact with a mature, active boar and can also be very effective with fenceline contact when females are in stalls or pens and the boar is in the alleyway or an adjacent pen.

Gilt estrus, pig

Image

An estrus gilt standing to the back-pressure test while exposed to a boar.

Courtesy of Robert Knox, University of Illinois.

Estrus detection, pig

Image

A technician tests for estrus in a stall.

Courtesy of Robert Knox, University of Illinois.

In cases where a boar is not available, less-effective alternatives can include exposing the sow or gilt to a synthetic boar-odor aerosol containing androstenone or to the ejaculate or urine fluids of a boar presented to the female on a boar-taint rag.

Anestrus is a common problem in pre- and postpubertal gilts and weaned sows. Failure to detect estrus must be distinguished from true cases of ovarian inactivity, which is often difficult to confirm. Approaches can involve ultrasonographic assessment of the ovaries, blood sampling for progesterone, slaughter checks, observation of procedures, and detection attempts over an extended period of weeks with records.

First-litter (parity-1) and early-weaned sows are particularly vulnerable to postweaning anestrus. The primiparous sow must support her own growth, as well as maintenance and lactation demands, while her feed intake capacity is not yet fully developed. This can be avoided by breeding only gilts in good condition; not overfeeding during the first gestation; and encouraging energy intake during the first lactation by frequent feeding of high-density diets, wet feeding, and avoiding high temperatures in the farrowing rooms.

Management practices that were once used to prevent disease transmission between the mother and litter, including segregated early weaning, modified medicated early weaning, and medicated early weaning, are not commonly used now because of the detrimental effects on sow fertility. Partial weaning (split weaning) is still used; however, it is important to allow enough pigs to continue nursing so that sows do not begin to develop follicles or ovulate while still lactating (without or with estrus).

Estrus synchronization can be achieved by group weaning lactating sows on a single day, with estrus typically occurring 4–6 days later in > 85% of sows. Administration of a commercially available combination of 400 IU of equine chorionic gonadotropin (eCG) and 200 IU of human chorionic gonadotropin (hCG) per 5 mL dose given as a single IM injection at or within 24 hours after weaning can improve estrus within 7 days after weaning and further tighten the synchronization of estrus (4, 5, 6, 7). This eCG and hCG combination also can induce estrus in gilts with delayed puberty and prevent postweaning anestrus in primiparous sows.

Fixed-time insemination protocols continue to gain interest in the swine industry. Current recommendations call for feeding a synthetic progestagen for 14 days to synchronize the start of the follicle phase in the mature, cycling gilt and then administering the eCG-hCG combination after the last feeding of the progestin, followed by a GnRH analogue (8, 9, 10). With weaned sows, a GnRH analogue is administered 80–96 hours after weaning. Breeding of both gilts and sows is then performed using a single timed artificial insemination (AI) 20–33 hours after GnRH administration (depending on product and route of administration) (11, 12).

Exogenous prostaglandin induces luteolysis of the corpus luteum only after day 12 of the estrous cycle and therefore is not a practical agent for estrous cycle control. However, if this approach is to be used, because prostaglandin is cleared very quickly after injection, administration twice in a PM/AM approach can help induce luteolysis in animals on days 12–15 of the estrous cycle (see ovary with corpora lutea image) (13, 14).

Ovary with corpora lutea, pig

Image

Ovary with corpora lutea (left) and an ultrasonogram of same (right). These structures produce high concentrations of progesterone.

Courtesy of Robert Knox, University of Illinois.

Estrus can also be synchronized by induction of abortion in sows pregnant > 15 days by administration of prostaglandin F2alpha (dinoprost; 15 mg, IM; then 10 mg, IM, 12 hours later) or an equivalent analogue (15).

In the US, estrus can also be synchronized by feeding altrenogest, which is FDA-approved at 15 mg/head, PO, ever y24 hours for 14 days (16) and in other countries approved for use at 20 mg/head, PO, every 24 hours for 18 days (17), with estrus being observed 4–9 days after the last dose with appropriate boar exposure. The designated treatment dose and duration depend upon the approved products and label directions. Combination eCG and hCG can be given on the day of progestagen withdrawal to better synchronize estrus (18).

In modern pig-breeding farms, most females in commercial pork production systems are bred using artificial insemination. AI is routinely performed for breeding weaned sows and replacement gilts. Most semen is supplied to breeding farms from outside genetic suppliers. The semen arrives in a cooled and protected container and is stored in a 16°C (60.8°F) cooler. The semen doses are usually individually packaged, although bulk semen dose packaging is also available from some suppliers.

The semen is typically ordered to arrive just ahead of breeding needs. Many larger farms require multiple semen deliveries to allow for insemination throughout the week. Most boar semen is extended in medium- to long-term extenders that enable sperm to survive in a cooled state for 5–7 days.

Some farms choose to check for estrus and breed at the same time, while others check for estrus and then return in a few hours to inseminate. In either case, boars are present at the time of insemination. When females are detected in estrus, conventional AI involves wiping the vulva clean and then inserting a new disposable foam or spiral catheter using a nonspermicidal lubricant. The catheter should lock in place securely and not cause any discomfort. The semen bottle or bag can then be attached and induced to flow into the female reproductive tract using gravity and negative pressure.

Back, flank, and belly stimulation can induce oxytocin release and uterine contractions to pull semen into the uterus. Gentle pressure can also be applied to help start flow, if needed. It can require up to 5 minutes for the full volume to flow. If leakage occurs, adjust and reposition the catheter to allow proper flow. After insemination is completed, the end of the catheter can be bent and the catheter allowed to remain in the cervix for an additional 5–10 minutes to limit backflow.

A newer insemination technique involves postcervical artificial insemination (PCAI) or intrauterine insemination (IUI). This technology allows for decreased sperm numbers and volume and insemination time compared to the conventional method. In this procedure, females are identified in estrus using a boar and then the boar is removed and not brought back for PCAI, as the presence of the boar induces cervical contractions as a result of oxytocin, which can make insertion of the catheter more difficult.

With PCAI, an outer catheter is inserted into the cervix. Then an inner catheter is passed through the outer catheter and into the uterus. Waiting a few minutes before inserting the inner catheter can help the cervix relax to ease passage. Once the inner catheter is in place, the semen is deposited using mild pressure. The process is very quick, does not require gravity or negative pressure, and avoids most instances of leakage.

Care should be taken when performing PCAI to prevent the inner catheter from damaging the cervix. There should not be blood present upon catheter removal. Insertion of the inner catheter might not be possible in smaller gilts and primiparous sows.

In decades past, natural mating occurred using pen mating with a boar continually housed in the pen with females or using hand mating, which involves supervised natural mating of a boar with a single female. Pen and hand mating are generally only used in smaller operations, and when performed, work best in a pen of pigs in various stages of the estrous cycle.

Pen mating with a group of recently weaned sows is less desirable, because their estrous cycles can occur close together, leading to overuse and depletion of sperm numbers in the boar. Boar rotation will prevent this problem, increasing the number of pigs per litter and pregnancies. However, infertility in one of the boars can be masked, and the sire of the individual pigs within the litter is uncertain. Sperm numbers in the ejaculate can dramatically decrease after just four matings of a single boar within a 1- to 2-day period.

In hand mating, the female is usually mated 2 or 3 times during estrus, with the first service on the first day of standing estrus and subsequent matings at 24-hour intervals. With natural or artificial inseminations, many commercial producers breed the sow or gilt once daily as long as she will accept the boar, which can total 2–3 inseminations. Producers should not breed or inseminate more than 3 times or 3 days for estrous females. Normal estrus durations last 2–3 days.

In AI programs, heat detection is performed either once or twice per day. If heat detection is performed twice per day, gilts and sows should be inseminated 8–12 hours after the onset of standing heat and again 12–16 hours later, and once more if still standing at the next check. If heat detection is performed once per day, gilts and sows should be inseminated within 0–4 hours and again 24 hours later, once more if still in standing heat on the third day.

Timing of AI might need to be modified according to a particular farm’s availability of labor, building design, or herd genetics. Most experienced users of AI obtain the best farrowing rates and litter sizes in gilts and sows when performing two inseminations during an estrus period and ensuring one on each day standing.

With natural mating and artificial insemination, breeding can be performed using semen either from a single sire (meaning sourced from one boar) or from two or more boars. With natural service, different boars can be used to breed for the first and second services to ensure a litter will be produced. However, the sire of the individual pigs in the litter can be uncertain, and lowered fertility in a boar can be masked.

With artificial insemination, most of the females bred for commercial pig production are inseminated with a pool of semen mixed from the ejaculates of 5–6 boars collected around the same time of day. These boars are all of similar genotypes and index value, and knowledge of the paternity of the offspring is not necessary.

With artificial insemination and natural service, single-sire matings are performed when particular genetic (ie, breeding or show animals) offspring are desired, whereas pooled semen is used as a means to produce market hog offspring. Minimum suggested values for extended semen used within 24–120 hours after collection are provided in the table Suggested Values and Protocols for Use of Extended Porcine Semen in an Artificial Insemination (AI) Program. Total sperm numbers in a dose of semen depend on quality and storage time of the semen (19).

Boars should not be overused (see table Suggested Guidelines for Boar Usage According to Breeding Program). This is true even for boars used in an artificial insemination program. Most boars in studs are collected 1–1.2 times per week, with adequate rest days to allow sperm stores to refill. This collection interval can optimize sperm collected and number of doses produced per unit of labor.

For natural mating, if sows are weaned in groups, a boar-to-sow ratio of 1:4 for mature boars and 1:2 for young boars is recommended (20, 21). In hand mating, a mature boar should be used for ≤ 2 breedings per day and not for more than two consecutive days. When using natural service, a boar-to-sow ratio of 1:15–1:25 (average 1:17 or 1:18) is usually needed. When using AI, the boar-to-sow ratio can be increased to 1:150–1:400. However, most commercial breeding operations use AI and purchase semen from outside genetic suppliers, with the boars on the farm used for detection of estrus and not for breeding (19, 22).

Sperm cells reach the oviducts within 30 minutes after breeding and continue to establish the sperm reservoir over the next 2 hours. Sperm establish a functional reservoir in the oviduct that can remain fertile for 24 hours. Fertilization occurs within 2–6 hours after ovulation, provided sperm are already present. The egg typically has a shorter fertile lifespan after ovulation, lasting < 10 hours. Fertilization rates approach 95% in sows; however, embryonic loss of 30–40% is common and accounts for the usual litter size of 12–16 total born pigs (23, 24).

Embryos enter the uterus approximately 48–60 hours after fertilization. Embryos hatch from the zona pellucida and form blastocysts 144 hours after ovulation. Physiological recognition of pregnancy in the dam (embryos secreting estradiol) occurs by day 12–14 of gestation, with intrauterine migration and distribution of embryos. Embryo attachment begins by day 13–14, with attachment complete by day 40; a minimum of four embryos must be present at this time for pregnancy to continue. Skeletal mineralization develops by day 40, with fetuses immunocompetent by day 70–75 (25).

Fetal deaths that occur after day 40 can result in abortion and expulsion of the entire litter. However, if only a few die, they can be retained until birth. Retained dead fetuses in this sterile environment become mummified and are usually expelled at the time of farrowing. If lost earlier in gestation, they can be difficult to see. The average gestation length of the pig has been increasing and now ranges 115–116 ± 1 days from first service, slightly shorter in sows with larger litters.

Embryos are at greatest risk of dying during the first 30 days, and efforts should be directed toward avoiding stresses to the sow (eg, overfeeding, heat stress, regrouping, handling or moving, immunization) during this critical period. Pregnancies of < 16 days are especially susceptible to heat stress. Avoiding exposure to outside animals decreases disease risk.

In litter-bearing species such as the pig, notable decrease in potential liveborn as a result of early embryo loss between days 10 and 30 of gestation is of interest (26). Whether diet affects these losses has been controversial for both full-feeding (> 4–5 lb [> 2 kg]) and limit-feeding of sows and gilts after breeding and through day 30. What might be more critical are dietary provisions to meet the metabolic demands of the pregnant gilt and the young first-parity sow (that are still growing) and the sows still recovering body condition following a 3- to 4-week lactation (27).

Most producers use the first third of gestation to establish the desired body condition of the sow and then maintain until farrowing. It is important to avoid overfeeding and overconditioning sows in late gestation, as this can increase stillborns and decrease feed intake in lactation. Farrowing less than five piglets can be indicative of breeding failures or early embryo death after the time of attachment.

To increase colostral antibodies, the gilt or sow should be immunized during the last 6 weeks of gestation. An immunization program can include vaccination against Escherichia coli, atrophic rhinitis, and erysipelas, as well as provision of any other vaccines appropriate for the disease situation on the individual farm.

Several techniques are available for pregnancy determination (see table Common Tests for Detection of Pregnancy In Pigs). In most larger commercial breeding herds, pregnancy is typically diagnosed using transabdominal real-time ultrasonographic examination. On smaller farms, pregnancy is most commonly determined by noting that the female does not return to estrus 18–24 days after service. However, this method is only 75–85% accurate, as not all nonpregnant females display a regular return to estrus by 21 days (28).

Three types of ultrasonography machines (real-time [B-mode], pulse echo [A-mode], and Doppler) assess for pregnancy in different ways:

• Real-time (B-mode) ultrasonographic examination is the primary type used for commercial pig production. It involves visualization of a 2D image of scanned tissues directly under the transducer (placed in the low flank, aiming at opposite shoulder). The machines are portable and mostly affordable for midsize and larger breeding farms. Their use allows quick diagnosis of pregnant or open sows housed loose in pens or in stalls.

• Pulse-echo (A-mode or amplitude depth) ultrasonographic examination involves ultrasonic waves emitted from a hand-held transducer placed on the skin in the flank area. Reflected waves from a fluid-filled area (ie, developing conceptus or fetus) are picked up by the transducer and converted into either an audible or visual signal.

• Doppler ultrasonographic examination detects changes in sound frequency (fluid movement) using an audible signal; movements indicative of pregnancy include blood flow in middle uterine or umbilical arteries, fetal heartbeat, and fetal movements.

B-mode ultrasonographic techniques are generally used at 26–30 days after breeding to determine pregnancy. Peak fluid within the chorioallantois is reached at day 30 of gestation (29). After this time, the fluid volume-to-fetus ratio begins to decline as the conceptus develops and occupies more space within the membranes.

Although uncommonly used for this purpose, rectal palpation can be performed in larger sows to confirm pregnancy at > 30 days' gestation. When performing rectal palpation, the examiner palpates for fremitus, size, and position of the middle (medial) uterine artery in relation to the external iliac artery. The tone and tension of the cervix and weight and contents of the uterus can also be used to help confirm pregnancy. Other techniques, such as hormonal assays (eg, estrone glucuronide, progesterone, prostaglandin) and vaginal biopsy, are not economically feasible (29, 30).

The appearance of the sow in late gestation changes with approaching birth. The sow develops a swollen abdomen and mammary glands, a swaybacked appearance, and a relaxed vulva. The birth canal is prepared for farrowing as a result of hormone-induced structural changes in the connective tissues of the cervix, pelvis, vagina, and vulva in response to estrogen and relaxin. The preparturient period also involves restlessness and nest building in the last 24 hours before birth. Mammary glands become turgid, and the secretion changes from serous to milk as parturition approaches.

Parturition is initiated by increased cortisol concentration, which also stimulates release of prostaglandin F2alpha (PGF2alpha) from the uterus and changes in placental hormone production. PGF2alpha causes luteolysis of the corpora lutea and further release of relaxin, which causes even further relaxation of the birth canal and cervix. Oxytocin is released from the posterior pituitary gland, which causes uterine contractions and onset of labor.

The coordination of piglet birth is under local and systemic control of placental hormone production and uterine control of the myometrium. Localized actions of prostaglandin, oxytocin, and estrogen control piglet delivery and order. Piglets are usually delivered at frequent intervals (average 10–15 minutes; range 5–45 minutes). Uterine horn evacuation is most often random.

The stillbirth rate usually is 5–10% (23, 24), with intrauterine deaths most often related to extended farrowing duration causing anoxia or because of dystocia related to fetal size or positioning issues; however, they can also result from illness or infection. Anoxia occurs when the umbilical cord ruptures or becomes constricted because of the extreme length of the uterine horn or when there is a delay in transit along the birth canal. Stillborn and weak piglets also can occur in temperature-stressed sows or sows with low Hgb concentration (< 9 g/dL). Any increase in the time interval between piglet births (eg, because of exhaustion, atony of the uterus, or dystocia) increases the chance of injury or death to the piglets still in the uterus.

Litter sizes have continued to increase, and with this, an increase in the incidence of farrowing durations reaching 5 hours. Pigs born last in the litter or after an extended duration are prone to hypoxia, weakness, and lower survival. They can also be at a disadvantage in obtaining the minimal-requirement volume for the highest-quality colostrum. Piglets born last of from prolonged farrowings should receive more attention to help them survive and thrive.

Piglets are born in both cranial (60%) and caudal (40%) presentations (31, 32). Assistance can be provided in the form of oxytocin injections (10–30 IU, IM or SC, repeated as necessary) (33) and manual removal of piglets. Walking the sow for a few moments also can be helpful, if practical. The number of pigs born alive can be increased by approximately one per sow if an attendant is present to assist delivery (see Preweaning Mortality in Pigs). However, this might not always be possible or predictable, as sows have a tendency to farrow overnight. Passage of the fetal membranes should occur within 4 hours after delivering the last piglet, and this is especially important in sows that experienced a long farrowing, as a retained placenta can cause serious health risks to the sow.

Farrowing can be induced by IM injection of 10 mg of natural PGF2alpha (ie, dinoprost) or an equivalent dose of a synthetic analogue (34, 35). Farrowing generally occurs 18–36 hours later (most within 22–32 hours) in 80–90% of sows when PGF2alpha is given after 114–115 days' gestation (34, 35). Some farms use induction to prevent late farrowings for those that have not started by day 116. Induction can be used so that most farrowings occur during normal working hours; however, this can be unpredictable.

Good records are essential, and average days of gestation for the sow herd and individual breeding dates for each sow must be known. PGF2alpha must be used within 72 hours of the expected farrowing date to prevent an increase in stillbirths. The slightly premature piglets require good environmental conditions that would include clean conditions, dry flooring, heat lamps or pads, and protection from drafts, particularly in cold weather. Farrowings can be concentrated into an even shorter period by injecting oxytocin after PGF2alpha injection (36, 37, 38). In this situation, oxytocin shortens the interval to parturition; however, it can increase the likelihood of dystocia. One recommendation is to give oxytocin 15–24 hours after prostaglandin only if milk can be stripped from the teats (37). Successful farrowing can also be induced by giving a single or double vulvomucosal injection of prostaglandin (35).

Incidence of dystocia has typically been low in sows (1–2%). As with all polytocous species, uterine inertia accounts for most dystocia in swine, noticeably in larger litters. Other causes include fetal malposition, obstruction of the birth canal, deviation of the uterus, fetopelvic disproportion, and maternal excitement. Anxious or fearful sows will get up and down more frequently, which can disrupt normal progression of farrowing.

A thorough digital examination of the birth canal is prerequisite to therapeutic intervention. Medical treatment for unobstructive dystocia can include use of an ecbolic (uterine contraction stimulation) agent (oxytocin) (37). Administration of injectable calcium might be warranted if uterine inertia is suspected.

Lactation peaks at 3–4 weeks postpartum, and most sows are weaned at 21–28 days. Poor lactation can result from problems during farrowing, constipation, low feed intake, heat stress, or mastitis. It is an important cause of pigs failing to grow well in the first weeks, and it can result in impaired productivity in weaned pigs.

Supervised farrowing allows for drying of piglets, relocation to a warming area, and assistance in finding a nipple. These can prevent piglet loss as a result of chilling, weakness, crushing, and poor colostrum and energy intake. Early litter management in the first 3 days of birth can help ensure that all pigs access a teat to nurse. Most producers try to process litters and cross-foster within 2–3 days after birth. Early intervention for pigs that are not growing well or appear weak is important to early pig survival.

• Lay Jr DC, Matteri RL, Carroll JA, Fangman TJ, Safranski TJ. Preweaning survival in swine. J Anim Sci. 2002;80(E-Suppl_1):E74-86.

• Kirkwood RN, langendijk P, Carr J. Management strategies for improving survival of piglets from hyperprolific sows. The Thai Journal of Veterinary Medicine. 2021;51(4):629-636.

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