52. Swine Medicine and Management

CHAPTER 52. Swine Medicine and Management

Roy N. Kirkwood




HERD MANAGEMENT






I. Estrous cycle




A. Pubertal estrus occurs at about 6 months of age and about 100 to 120 kg in gilts


B. Gilt age at pubertal estrus can be reduced by exposure to a boar. To be effective, the gilts should be at least 165 days of age, and the boar must be at least 9 months old


C. Gilts and sows are polyestrous with a cycle duration of 21 days (range 18 to 24 days)


D. The estrous cycle consists of diestrus (luteal phase of about 15 days), proestrus (follicular phase of about 4 days), and estrus (sexual receptive period of about 2 days)


E. The luteinizing hormone (LH) surge controlling time of ovulation occurs at the onset of estrus


F. Ovulation occurs about 40 hours after onset of the LH surge (about 70% of the way through estrus). The process of ovulation takes 2 to 4 hours


G. The follicular remnants luteinize to form corpora lutea that secrete progesterone. The corpora lutea are required for maintenance of pregnancy; loss of the corpora lutea at any time will terminate the pregnancy


H. If the animal is not pregnant, the luteolytic signal (prostaglandin F2α) is secreted from the endometrium during days 12 to 14 of the estrous cycle. The PGF2α enters the uterine vein, moves to the ovarian artery by countercurrent transfer, arrives at the ovary, and induces luteolysis


I. Estrous periods can be synchronized by feeding 15 to 20 mg/day of the progestagen allyl trenbolone


J. Estrus occurs about 5 days after last feeding. If amount fed is less than 13 mg/day, cystic follicles may occur


II. Breeding




A. Most common breeding method is artificial insemination (AI), although pasture breeding is used on many outdoor farms


B. Boars ejaculate about 75 × 10 9 sperm in 250 mL seminal plasma. AI doses contain only 2-4 × 10 9 sperm in 80 to 100 mL of extender. Semen is deposited into the cervix of the sow


C. For optimal fertility, AI should occur during the 24 hours before ovulation. To maximize the likelihood of this, AI is performed at 24-hour intervals while the sow is in estrus


D. Sperm are transported to the oviduct by coordinated uterine contractions, where a sperm reservoir is formed in the first 2 to 4 cm of the isthmus


E. To ensure adequate uterine contractility and good fertility, a boar should be in front of the sow during insemination


F. Toward the end of the estrous period (after ovulation), uterine immunocompetence is reduced because of a shift from estrogen to progesterone dominance. Insemination at the end of the estrous period or early diestrus is a major cause of uterine infections


III. Pregnancy




A. Duration of gestation averages 115 days, normally distributed with a range of 111 to 119 days


B. The signals for maternal recognition of pregnancy are embryonic estrogen secretion. The first signal occurs at about 11 to 12 days after breeding; the second signal is more prolonged and occurs during days 17 to 30 after breeding


C. The effect of the embryonic estrogen is to redirect the luteolytic PGF2α away from the uterine blood supply and into the uterine lumen. The signal also induces production of luteotrophic PGE2


D. To ensure an adequate signal for maternal recognition of pregnancy, there must be at least four embryos in the uterus


E. If bred sows fail to conceive or conceive but have too few embryos to provide an adequate first signal, they exhibit a regular (18 to 24 or 38 to 45 days) return to estrus. Regular returns are considered a failure of conception. If the ratio of 21- to 42-day returns is less than 3:1, a problem with estrus detection is likely


F. If sows conceive and receive the first signal, but not the second signal, for maternal recognition of pregnancy, there is a partial luteotrophic effect and the sows exhibit an irregular (25- to 37-day) return to estrus. Irregular returns are considered a failure of pregnancy. If regular to irregular return ratio is less 3:1, too many pregnancies are being lost


G. If a sow receives both signals for maternal recognition of pregnancy and then loses her litter, she may become pseudopregnant



V. Lactation




A. The most common lactation length is about 21 days. Shorter lactations (12-16 days) may reduce post-weaning fertility


B. If sows do not consume sufficient nutrients during lactation, post-weaning fertility is reduced (longer wean-estrus intervals, reduced pregnancy rates, and smaller subsequent litters)


C. The primary objective in lactation management is maximizing sow feed intake. High ambient temperatures, such as in the summer, reduce sow feed intake and can result in seasonal infertility


D. The first limiting amino acid for swine is lysine. Lactating sows require about 60 g of total lysine per day, and if lactation feed intake is significantly reduced, dietary fortification with lysine is indicated


VI. Wean-to-estrus interval (WEI)




A. Usually, sows exhibit estrus 4 to 5 days after weaning. A WEI of 6 to 12 days is associated with reduced subsequent farrowing rates and litter sizes. A longer WEI is associated with parity 1 sows, short lactations, and low lactation feed intakes


B. Long WEI can be treated with an injection of gonadotrophins at weaning


C. Short WEI (<6 days) results in a longer duration of estrus and, in contrast, a long WEI (>5 days) results in a short duration of estrus


D. Because sows ovulate about 70% of the way through estrus, this means the interval from estrus onset to ovulation is longer in sows having a short WEI than in those having a long WEI. Timing of AI should be modified accordingly


GASTROINTESTINAL DISEASES




Enteric Bacteria






I. Colibacillosis




A. Colibacillosis, caused by the gram-negative flagellated bacillus Escherichia coli (e.g., F4 [K88], F5 [K99]), induces a watery diarrhea at any age, including the first few weeks after weaning. Occasional septicemia may occur during the first 48 hours of life. Edema disease is a unique form of colibacillosis presenting with neurologic signs (see Edema Disease under Neurologic Disease)


B. The pilus (fimbria) mediates adhesion to enterocytes or the overlying mucus. The most common pilus types in neonates are K88, K99, F41, and 987P. Post-weaning, the most common pilus types are K88 and F18


C. Following adhesion, E. coli elaborate enterotoxins that affect ion channels and cause active secretion of chloride, which is followed passively by water. The secretory diarrhea leads to death from dehydration


D. Diagnose colibacillosis on diarrhea with absence of blood, mild or no villus atrophy, and isolation of profuse or pure culture of pathogenic serotype


E. Treat affected suckling pigs with antimicrobial (e.g., gentomycin). If not currently performed, institute sow vaccination against E. coli, and improve farrowing house hygiene. Additional control measures for weaned pigs include 2500 to 3000 ppm zinc oxide in the diet for the first 2 weeks after weaning and, if necessary, antimicrobials in the water supply


II. Clostridial disease




A. Clostridia most commonly affecting pigs are C. perfringens types A and C and also C. difficile


B. Peracute or acute C. perfringens type C affects pigs within hours of birth. The less severe subacute or chronic forms affect pigs from 3 to 21 days


C. The bacterium elaborates β-toxin, causing enterocyte damage followed by bacterial penetration and adherence to the basement membrane


D. In the acute form, the toxin causes severe necrotizing-hemorrhagic enteritis, possibly with gas bubbles evident in the serosa. The pig often dies before any hemorrhagic diarrhea becomes evident


E. In the subacute-chronic form, diffuse fibrinous mucosal necrosis is observed without hemorrhage. The lesion is similar to that observed with coccidiosis


F. Diagnose on evidence of hemorrhagic enteritis in neonatal pigs with variable morbidity but high case mortality. On postmortem, the jejunum will appear bright purplish red


G. Definitive diagnosis requires demonstration of the β-toxin


H. Affected pigs will die, but others in the litter will be protected by oral ampicillin. Long-term control involves improved farrowing house hygiene and sow vaccination


I. C. perfringen type A is less severe, causing nonhemorrhagic diarrhea, usually in pigs less than 3 days old, but it can also occur in weaned pigs. It is characterized by a high morbidity but low mortality


I. Treat with oral penicillin or ampicillin, improved hygiene, and sow vaccination


J. C. difficile causes nonhemorrhagic diarrhea, usually in pigs 1 to 7 days of age with a high morbidity and relatively high (50%) case mortality. May also observe dyspnea



L. Diagnosis is based on clinical signs, postmortem lesions, and bacterial culture


III. Porcine proliferative enteropathy (PPE)




A. PPE is caused by the intracellular bacterium Lawsonia intracellularis. Fecal-oral infection leads to invasion of intestinal crypt cells, particularly in the ileum


B. Cellular infection leads to apoptosis, hyperplasia, and the crypts filling with polymorphonuclear neutrophils


C. Villus apical capillaries may dilate and rupture. Changes may regress, continue and result in benign adenomatosis, or they may become necrotic or potentially hemorrhagic


D. Usually, infection results in a soft stool (oatmeal consistency) seen in grow-finish. However, the hemorrhagic condition is more likely in young adults (e.g., replacement breeding stock)


E. In grow-finish, small intestine (particularly ileum and possibly proximal spiral colon) is thickened and reticulated (looks like the surface of the brain)


F. Diagnose on pig age, clinical signs, histology, polymerase chain reaction (PCR), or serology

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Apr 6, 2017 | Posted by in GENERAL | Comments Off on 52. Swine Medicine and Management

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