CHAPTER 108 Noninfectious Causes of Infertility and Abortion
Anatomic abnormalities are present in about 2% of all newborn pigs. Nonlethal anatomic aberrancies may result in infertility and may account for 10% to 20% of cases of reproductive failure in nonbreeding gilts. Most anatomic abnormalities, except those of the external genitalia, are not apparent in live animals. Because of the frequency of occurrence of anatomic abnormalities, gilts that do not cycle within 30 to 60 days after selection or delivery, or those that do not conceive after the second or third mating, should be culled. Generally, diagnostic investigations of individual gilts are not justified; however, if more than 10% of a group of replacement gilts have infertility problems, a diagnostic investigation, including slaughter checks, is indicated.
Cystic ovarian disease is a common cause of reproductive failure in sows. Cystic ovaries may be present in 10% to 25% of infertile sows. Single cysts are an incidental finding at slaughter and do not affect cyclicity or fertility. Multiple cysts, small or large, may be associated with infertility. Multiple small cysts (10 to 15 mm in diameter) secrete estrogen and occasionally may be associated with anestrus. Multiple large cysts (15 mm to 10 cm) secrete progesterone and commonly are associated with anestrus.
Physical problems that potentially interfere with reproduction include injuries of the vulva or vagina, or both; musculoskeletal problems; and diseases of the gastrointestinal and cardiovascular systems.
Trauma to the genital tract may result from vulva-biting by aggressive sows in group housing systems, from farrowing injuries, or from breeding injuries. These types of injuries usually impair reproduction by causing adhesions that occlude the reproductive tract, thereby interfering with coitus or gamete transport. They also predispose the affected animal to the development of chronic vaginitis or endometritis. Animals with severe injuries to the lower genital tract or chronic endometritis as a result of those injuries should be culled.
Lameness due to foot pain, poor conformation, trauma, footrot, or nonseptic laminitis may predispose affected animals to reproductive problems. Gilts may be added to the breeding herd but never mated because they are too lame to mate or because they exhibit weak physical signs of estrus. Pregnant sows may be culled because of foot and leg problems. In some herds, musculoskeletal diseases represent the primary reproductive problems because of their impact on nonproductive sow days, farrowing rate, cull rate, death rate, and, subsequently, overall replacement rate.
Nonseptic laminitis occurs secondary to injury and is characterized by inflammation of the corium, foot pain, and a digital pulse. The front limbs are primarily affected. Damage to the hoof pad or hoof wall may allow penetration by bacteria into the corium, resulting in footrot, subsolar abscesses, or other hoof problems. Traumatic injury to the hooves is more common on the lateral toes, possibly because they bear more weight than the medial toes. Joint or bone infections may occur secondary to trauma as well.
Other musculoskeletal system problems that may interfere with reproduction, especially in gilts, are osteochondrosis and degenerative joint disease. These conditions result from developmental lesions that affect cartilaginous growth plates. Clinical signs range from subtle changes in gait to inability to stand. Such signs usually are noted in the first 4 to 8 months of life. Genetic background, conformation, and floor type are believed to contribute to the condition, although these conditions may develop in any fast-growing animal. Direct correlations between growth and nutrition and osteochondrosis and degenerative joint disease lesions are difficult to establish. The best methods to prevent joint lesions are to provide adequate nutrients, feed intake, and a proper environment and to select breeding stock with good physical conformation from genetic lines with no history of the condition.
Gastrointestinal problems may contribute to reproductive inefficiency either directly, by interfering with exhibition of strong physical signs of estrus, or indirectly, by causing death or disorders leading to culling of pregnant sows. Common gastrointestinal problems include gastric ulcers and gastrointestinal accidents such as gastric dilatation, torsion, or volvulus. Clinical presentation with gastric ulcers is characterized by anemia, sudden death, gastrointestinal pain, vomiting, and bloody or dark feces. The definitive lesion seen at necropsy is ulceration of the pars esophagea. Maintenance of feed particle size at 700 to 800 μm or greater and added fiber in gestation diets may be helpful in preventing gastric ulcers.
Gastrointestinal accidents occur sporadically but may be common in some herds. Sows are predisposed to occurrence of gastrointestinal accidents by irregular feeding times, feeding of gruel or whey, and excessive excitement at feeding time. Establishment of a regular feeding time, addition of fiber to the diet, and use of a drop-feeding system that delivers feed to all sows simultaneously are the best methods for prevention.
Cardiac failure is a commonly diagnosed cause of death in some sow herds. Obesity, parturition, heat stress, copulation, fights, and transport predispose affected animals to cardiac failure. A diagnosis of cardiac failure should be made only after other causes of death in adult sows have been ruled out.