Swine Reproduction Papers
When do losses of piglets occur and why? The loss of embryos and fetuses during pregnancy, and loss of piglets at birth, has been well documented in swine and in swine production systems. Approximately 40% of potential piglets are lost as embryos and fetuses before day 40 of gestation. The reasons for these high rates of litter reduction may be a natural mechanism to ensure pregnancy can be maintained or some piglets are born to sustain the species, or may result due to defective embryos, unfavorable uterine environments, and fetal competition for space. At a much lower frequency, some fetuses die in the uterus before farrowing. These undergo degeneration and depending upon when they are lost during gestation, may appear as mummified very small or almost normal sized fetuses at birth. Pigs that are fully formed, but fail to survive the birth process are classified as stillborns.
How common are stillborns?
Stillborns average 6 to 7 % and but range anywhere from 5 to 10% across farms. 1999 PigCHAMP summary data indicates the US average is 0.2 mummified fetuses and 0.8 stillborn pigs per litter. It is reported that the USA has a higher stillborn and preweaning mortality rate than other parts of the world. This is thought to be due to the lower number of farrowing personnel to sows, which can often exceed 1:250. It is suggested that a 1:30 ratio could reduce the incidence of stillborn pigs. In herds where stillbirths are higher than 10%, it is suggested that infectious causes should be investigated.
Stillbirths are related to dystocia or difficult birth during farrowing. Stillborn pigs are not identified as the runts in a litter and are observed to occur more frequently in litters with less than 5 pigs and when more than 14 are born in a litter. Stillborns are observed to be low when 8 pigs are born (.04) but this number increases as litter size increases. Stillborns may occur due to premature rupture of the umbilical cord, early detachment of the placenta from the uterus, or restricted blood flow to the piglet during intense uterine muscle contractions, or during passage through the pelvic canal. It is also observed that the umbilical cord can get wrapped around the piglet's body and get pinched or closed off in the pelvis. Stillborns are also observed to increase when farrowing is induced earlier than day 112 of gestation or if gestation is prolonged past day 116.
What is the ultimate cause of piglet loss?
The fetal lungs acquire the ability for gas exchange at birth. Major changes in lung development occur at days 95-100. During the birth process and soon after liquid is removed from the lung. It has been estimated that the physiologic half-life of oxygen is less than 5 minutes and irreversible brain damage occurs within 5 minutes of umbilical rupture or even impeded blood flow through the umbilicus. It is thought that 93% of all intrapartum deaths are due to umbilical rupture since most stillborn pigs have broken umbilical cords. Fetal hypoxia (lack of oxygen) is most related to piglet survival at farrowing and even temporary hypoxia during birth may cause permanent brain damage and reduce liveborn pig survival. Pig fetuses are very susceptible to intrauterine asphyxia. A period of prolonged intrauterine hypoxia caused by uterine hypertension (high pressure due to contractions) could deplete energy stores (glycogen) needed by the piglet after birth to survive. Most of the pig's glycogen is found in skeletal muscle and this is essential both for movement and temperature regulation. In cases of intrauterine asphyxia, inhalation of fetal meconium (feces) is very common, and 87% of stillborn pigs that die by asphyxiation, have meconium in the oral cavity.
The duration of parturition is highly related to stillbirths and therefore short deliveries are considered highly desirable. As duration of farrowing increases from 1 to 8 hours, stillbirths increase from 2.5 to 10.5%. Interestingly, more than 2/3 of all stillbirths occur in farrowings lasting less than 4 hours. Over 80% of stillborn losses occur in the last 1/3 of the litter in sows. Stillbirths in gilts can occur more frequently in the first two pigs born. The stillbirth rate increase as the interval between pigs exceeds 20 minutes. The average birth interval between successive live pigs is 13 to 18 minutes but between a live pig and stillborn pig is 45 to 55 minutes. However, the intervals are longer between the first two and the last two pigs born in a litter.
Generally speaking the last pig born has less than a 50% chance of survival in any litter. Most piglets must leave the space they occupied during pregnancy and enter empty space previously occupied by a delivered pig. From there, they move through the uterine body, the cervix, and the vagina, and finally exit though the vulva. The umbilical cord is 60 to 75 cm long and if the 120-180 cm of the uterus does not shorten sufficiently after emptying, then rupture of the cord is inevitable. Therefore delivery must subsequently occur within 5 minutes of rupture. Umbilical rupture or premature placental detachment is thought to occur in 20% of stillborn pigs from the first third of the litter and involve up to 50% of stillborn pigs in the last 1/3rd of the litter.
It is not known whether prostaglandin administered during farrowing at this stage, could improve the process.
Stresses on the sow and stillbirths
Temperatures above 30 °C in late gestation from days 102 to 110 increase rate of stillbirths and reduce piglet birth weight. The mechanism for this remains unknown however. Lack of feed and absence of nesting material is also suspected of increasing sow stress levels. Stress has been shown to reduce oxytocin levels during parturition, which would tend to prolong delivery. Therefore it is important to provide conditions that will allow the sow to remain calm and comfortable.
How can you tell if pigs were stillborn?
Stillborn pigs appear normal but they can be distinguished from other pigs that were born alive and died later after birth by the lung flotation test. This test requires the lungs to be dissected and placed in water. If the lungs float, the pig had air trapped in its lungs and was born alive and breathed. If the lungs sink, they contained no air and the animal never breathed. Stillborns can also be classified into type I, which are prepartum deaths due to infection, and type II, which are stillborns that occur during parturition, which are usually non-infectious.
Is lack of uterine contractions involved in stillbirths?
Uterine inertia is rare even during prolonged delivery. However, in cases where this was identified, administration 10 I.U. of oxytocin returned the pattern of contractions to normal for ~10 to 15 minutes. However, this induction of massive contractions could potentially disrupt blood flow to the placenta.
Can any treatments reduce stillbirths?
An assistant present at farrowing can reduce the incidence of stillbirths. Obstetrical assistance will minimize stillbirth rates, and inducing farrowing during the normal working hours will improve the frequency of observed farrowings. It has been reported that ~25% all stillborn pigs can be revived by artificial respiration using a small funnel over the snout. In addition, during assisted farrowing, an attendant can successfully remove fluid and mucus that obstructs the pig's airway and facilitate normal breathing. It was observed that 18 hour farrowing supervision through the night and continuing into the daytime, increased the number of pigs saved.
ACTH (25 to 60 I.U.) administered to sows i.m. on day 110 has been shown to reduce duration of parturition and reduce stillbirths by 40-50% (0.2 pigs/litter saved). This thought to be related to increased corticosteroid levels reaching the fetal lungs and gut and facilitating precocious maturation. Estradiol benzoate given to sows also was reported to reduces stillborn rates. It was suspected that estrogen increased muscle gap junctions, increased oxytocin receptors, and relaxin receptors in both myometrium and cervix. This collectively improved the ability to deliver live piglets.
What are the factors involved in live piglet loss?
Mortality of pigs born alive results from a variety of causes. The industry has set a 10% death loss as acceptable and USDA and PigCHAMP figures indicate a 10 to 14% range for pre weaning mortality. Producers in the top 90th percentile in production records have a preweaning mortality of 8.3%. Of pigs that are liveborn and subsequently die, >50% die within 4 d of farrowing. These typically involve weak pigs that are crushed and die of starvation. Mortality in liveborn pigs is also associated with sows that farrow early, especially those that are induced to farrow on d 110 compared to 112. At day 109 of gestation, piglets can be delivered but many pigs do not survive past one day post-partum. Even pigs from days 110-111 have reduced survival.
Colostral Immunity and Milk
Immunity for the piglet is not obtained through placental transfer of antibodies during gestation and therefore it is born with very limited immune protection. Further, the piglet has finite reserves of body energy and may even be energy deficient after a long and stressful delivery process. It then becomes even more critical for the piglet to obtain both antibodies and energy through the colostrum soon after birth. The piglets should begin to suck within 10 to 35 minutes of birth. If they fail to do so, they can be helped to nurse or even given colostrum. Colostrum will serve to protect the piglet against a host of microbes and also allow it to cope and survive in its new environment through the energy expending activities of nursing, seeking warmth, and moving to prevent being crushed by the mother. Nursing soon after birth and nursing as frequently as possible are highly advantageous for piglet survival since the newborn obtains antibodies only through colostrum ingested within the first 24 h after birth. Antibodies in the mother's milk are very high at this time and when ingested, are readily absorbed. The antibodies in the gut also serve to provide protection within the gut of the piglet. After 24 h, gut acids in the piglet begin forming and stomach pH lowers. After this time period, immunoglobulins from the mother's milk cannot pass through the gut wall and are destroyed. Thus, only the antibodies that are obtained in this manner during this short period will serve to protect the piglet over the next few weeks.
What other factors can help reduce preweaning mortality?
Use of heat lamps. Three lamps used strategically have been shown to be beneficial immediately near the time of birth. Lamps placed behind, and on the sides of sows, but which do not place excessive heat on the sows, can improve piglet survival. Keep all three on during farrowing, and then remove the one behind when farrowing is completed. This will keep pigs from getting or staying behind the sow where they are prone to be crushed when the sow sits down. Then remove the second side lamp at 48 h, which will keep the pigs located to only one side for warmth. If open flooring is used in the farrowing crate a floor mat should be used to reduce drafts on the pigs.
What about crushing?
Crushing has been linked to sow behavior, crate style, size of the sow, and weak pigs. Piglets that suffered hypoxia or dystocia will deplete their body stores of oxygen and even energy more quickly. These pigs will be born weak and may therefore be the ones that are too weak to move and are more susceptible to crushing, chilling and starvation. Crates have been shown to reduce crushing by 3% compared to outdoor systems. Crushing remains a serious problem and crate design may be an important aspect. Reports have indicated that free stall crates may crush more pigs than more restrictive crates. Further, more sophisticated crates, that utilize hydraulic cylinders or other mechanisms to slow the sow's when lying down, can reduce pig loss by 0.8/litter. Other methods to reduce crushing have involved the use of raised flooring in the center of the crate to prevent the frequency and ease of pigs being there when the sow lies down.