[Frontiers in Bioscience 2, d471-481, September 15, 1997]|
THE COLOSTRUM-DEPRIVED, ARTIFICIALLY-REARED, NEONATAL PIG AS A MODEL ANIMAL FOR STUDYING ROTAVIRUS GASTROENTERITIS
Department of Animal Science, North Carolina State University, Raleigh, NC 27695-7626 and Center for Gastrointestinal Biology and Diseases, Chapel Hill and Raleigh, NC
Received 9/5/97 Accepted 9/10/97
3. PROCUREMENT OF COLOSTRUM-DEPRIVED NEONATAL PIGS
Although germ-free, gnotobiotic or specific-pathogen free (SPF), pigs have been extensively used as a model animal for rotaviral gastroenteritis research (7 - 16), the required surgical procedures (hysterectomy, hysterotomy or cesarean section) which are performed on or near the 112th day of gestation (27, 28) are expensive because of the specialized equipment, facilities and personnel needed to undertake them. Since facilities to procure SPF pigs are not readily available, we have been using naturally-farrowed, full-term gestation (114 - 115 days), neonatal pigs (18 - 22) which are obtained under conditions that prevent or minimize sow-acquired, particularly rotavirus, infections. Due to the ubiquitous distribution of rotavirus in swine farms, early research in our laboratory has shown that conventionally-farrowed, colostrum-free pigs are infected, at or shortly after birth, with enough rotavirus so as to result in diarrhea, dehydration and death within 5 to 6 days of age (29). This problem is aggravated in neonatal pigs farrowed during fall and winter when the highest natural incidence of rotavirus has been observed (Gomez, personal communication). A similar winter seasonality of rotavirus gastroenteritis has been reported in epidemiological studies with humans (30 -32).
To prevent sow-acquired infections, pregnant sows obtained from the NCSU Swine Farm are transferred to an isolated farrowing facility, 5 days before farrowing, so that neonatal pigs carrying no known or defined pathogens are farrowed in an antiseptically clean stall after repeating bathing and sanitizing of sows with an iodinated detergent (Wescodyne®, American Sterilizer Company, Medical Products Division, Erie, PA) before delivery. In most of our studies, between 40 and 50 newborn pigs farrowed by five sows have been used in each trial. Usually, the estimated and actual farrowing dates of five sows occur within a 1- to 3-day interval. In order to minimize this interval and synchronize farrowings, as soon as presence of milk (indication that farrowing should occur within 24 hours) is detected in the teats of one sow, an intramuscular injection of 1.5 to 2.0 mL (5 mg/mL of dinoprost tromethamine) of prostaglandins F2alpha (Lutalyse®, The Upjohn Co., Kalamazoo, MI) per sow is administered to the remaining sows. Using this procedure, experimental pigs are born on the same day or have a difference in age of 1 day.
Implementation of a high level of sanitation during farrowing is the most critical aspect to obtain "sanitary" or "pathogen free-like" newborn pigs. To achieve this, sows are attendant-farrowed so that pigs are caught as they are being born, the umbilical cord is clamped with a navel cord clamp (NASCO, Fort Atkinson, WI) to help prevent navel infection, and gently detached from the sow. Each pig is immediately moved from the farrowing crate into a clean plastic container, sprayed with a disinfectant solution, freed from adhering membranes and dried with disposable paper towels, and transferred to an isolation room where its umbilical cord is cut at about 10 cm from the body and disinfected with tincture of iodine (2%). We have been using a 70% ethanol solution as a disinfectant solution because rotaviruses have been shown to be easily inactivated with high concentrations (70% to 90%) of ethanol (33, 34). To minimize the exposure of newborn pigs to the sow environment, newborn pigs are moved out of the farrowing room into the isolation room within 1 to 2 minutes after they are born. Pigs are kept warm, with a heating lamp, in either a disinfected cage or cardboard box until the end of farrowing when they are identified by ear notches and weighed. Pigs are then transferred into a separate room containing an automatic feeding device (Autosow). When simultaneous observations of non-infected and rotavirus-infected pigs are needed, two separate Autosows must be used.
Crossbred newborn pigs obtained in our laboratory during the period January 1992 - December 1996 were farrowed by either white line (½ Yorkshire, ½ Landrace) or crossbred (¼ Yorkshire, ¼ Landrace, ¼ Hampshire, ¼ Duroc) sows which were bred by Hampshire or Duroc boars. There was no difference (p > .05) in the average number (10.2 ± 2.7 vs. 11.0 ± 2.3) and weight (1.36 ± .23 vs. 1.38 ± .19 kg) of newborn pigs per litter as well as in the proportion (%) of males and females (51:49 vs. 48:52) farrowed by either white line (n = 96) or crossbred (n = 42) sows. Values are means ± standard deviation. Parity of the sows varied from 1st (12%), 2nd to 4th (58%), and higher than 5th (30%), but the aforementioned parameters were not affected (p > .05) by parity. On the average, 12% of the newborn pigs per litter weighed less than 1.0 kg and in 44% (61/138) of the litters all newborn pigs weighed more than 1 kg. Newborn pigs weighing less than 1.0 kg are seldom used for experimental purposes.