[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
5. FEEDING PROGRAMS FOR ARTIFICIAL REARING OF COLOSTRUM-DEPRIVED PIGS
Due to the aforementioned considerations, feeding regimens for artificial rearing of colostrum-deprived pigs are critical for their survival and adequate growth, particularly during their early post-natal period. In our laboratory, pigs are reared with an automatic feeding device and the details of the characteristics and functioning of this device as well as the environmental rearing conditions have been previously reported (46, 47).
To overcome the lack of passive immunity conferred to newborn pigs by sow's colostral immunoglobulins, colostrum-deprived pigs have been fed milk replacers containing porcine (48 - 52), or bovine (51, 52) serum-derived immunoglobulins or fed bovine colostrum (42, 43, 53). Porcine serum-derived immunoglobulins did not provide effective passive immunity when fed to colostrum-deprived pigs for only 1 day post-partum (48, 49). However, when porcine (50 - 52) or bovine (51, 52) serum-derived immunoglobulins were fed for at least a 5- to 10-day period after birth as an integral part of milk replacers, survival was improved. Apparently more passive immunity was conferred to pigs when immunoglobulins were fed for an extended period after birth, probably as a consequence of a delayed closure time resulting from the feeding regimen used. In these studies, colostrum-deprived pigs were reared in non-isolated environments and fed diets fortified with antibiotics.
The results of several studies carried out in our laboratory suggest that porcine serum-derived immunoglobulins or bovine colostrum can be satisfactorily used as immunoglobulin sources to provide sufficient passive immunity to colostrum-deprived pigs which are artificially-reared in an isolated environment, without antibiotic supplementation, so as to support growth comparable to those of pigs nursed by their dams (Gomez, unpublished results). At present, porcine serum-derived immunoglobulins are commercially available (American Protein Corporation, Ames, IA) but they are mainly used in dry diets for early-weaned (10 to 14 days of age) pigs. Unfortunately, the variability in their IgG content as well as their limited solubility are two major current constraints to expand their use in artificial rearing of colostrum-deprived pigs. Henceforth, in order to provide passive immunity to newborn colostrum-deprived pigs we have been using bovine colostrum which is obtained from dairy cattle maintained at the NCSU dairy herd and consists of pools of the first day's secretions from cows. Bovine colostrum contains antibodies to rotavirus (54) and protects neonatal pigs from the clinical effects of porcine rotavirus (55). Bovine milk concentrate prepared from milk of cows hyperimmunized with human rotavirus serotypes has also been used to induce passive immunity to infantile rotavirus gastroenteritis (56, 57). Passive immunity has also been provided to newborn pigs obtained within 12 hours of birth by inclusion of a commercially available bovine IgG product (Colostrum-Plus, LaBelle Associates, Inc., Bellingham, WA) in the formula for the first 72 hours after birth (58). The Colostrum-Plus dry powder containing bovine IgG and supplemented with essential vitamins, minerals and live microbial cultures appears to be a promising replacement of conventional bovine colostrum.
Details of feeding regimens to artificially rear colostrum-free pigs with automatic feeding devices have been previously described (53, 59, 60). Their initial approach was to feed diets in volumes and at frequencies similar to pigs nursing naturally. A semiautomatic feeding system using a gravity-flow enteral feeding bag has been described by McClead et al. (61) to artificially rear pigs that were allowed to nurse for 4 to 10 hours after birth and it has also been used to rear colostrum-deprived neonatal pigs (16). The regimen developed in our laboratory (41) consisted of feeding pigs a daily volume of diet that was ~30% of their body weight; e.g., a 1,200 g pig was fed 360 mL/day and feedings were divided into 24 equal increments. In order to minimize labor expenses, to prevent and correct mechanical problems with the feeding device's functioning, particularly those happening overnight, as well as to supervise every feeding so as to measure and record the actual diet intake, the number of feedings have been reduced from 24 to either 12, 10 or 8 feedings per day with intervals between feedings of 1¼, 1½ or 2 hours, respectively, starting at 0800 h and finishing between 2130 - 2200 h, every day.
High survival rate, adequate growth and absence or low incidence of diarrhea during the first 5 to 7 days after birth are essential to successfully used colostrum-deprived, artificially-reared, neonatal pigs in studies related to gastrointestinal research. The daily volume of diet, the number and frequency of feedings as well as the dry matter (DM) content of the basal liquid diet are factors that affect the survival, performance and health status of neonatal pigs. Table 1 presents data on growth from birth to 5 days of age and incidence of diarrhea from 3 trials in which bovine colostrum (20% or 50% v/v) provided passive immunity to colostrum-deprived pigs when included into liquid diets containing either 20% or 15% DM and fed for 3 consecutive days after birth; thereafter, pigs were fed the liquid diet alone. Pigs were fed at the same daily rate (300 mL/kg body weight) but at different feeding intervals and number of feedings per day. Pigs were weighed at birth, 3rd and 5th day, and volume of diet for each pig was adjusted according to its body weight. At 5 days of age, the average weight and daily gain of pigs fed 50% (v/v) bovine colostrum mixed with a 20% DM liquid diet (trial 2) were higher (p < .05) than those of pigs in trials 1 and 3, but 30% of the pigs in that group had non-pathological diarrhea compared to 43% and 13% of the pigs in trials 1 and 3, respectively. Rectal swabs taken from diarrheic pigs in all 3 trials were negative to hemolytic E. coli and porcine rotavirus. The results of trial 3 further indicate that lowering the DM content of the basal diet and increasing the number of feedings per day, by reducing the interval between feedings, resulted in an appreciable decrease in the incidence of non-pathological diarrhea but also produced the lowest (p < .05) body weight gain during the first 4 days of life (Table 1).
Table 1. Effects of feeding bovine colostrum (BC) to sow's colostrum-deprived, artificially-reared, pigs on body growth and incidence of diarrhea during the first 5 days of life1
1:Pigs were fed the bovine colostrum/basal diet mix for 3 days after birth and switched to basal diet alone thereafter. Number of feedings and feeding intervals were 8 and 2 h, 10 and 1½ h, and 12 and 1¼ h for trials 1, 2 and 3, respectively. 2:Percentage (v/v) of BC in mix; 20 = 20 parts BC + 80 parts diet; 50 = 50 BC/50 diet. 3:Dry matter content in basal liquid diet. 4:Average daily gains during first 4 days of life since pigs were weighed on their 5th day of life before the first feeding. 5:Percentage of pigs having non-pathological diarrhea or liquid feces on 5th day. 6 abc:Values are means ± SD; values in a column with unlike superscripts are significantly different (p < .05) from each other. Avg: Average.
In most of our studies, between 20% and 30% of colostrum-deprived, artificially-reared, neonatal pigs have shown non-pathological or "nutritional" diarrhea around 5 to 7 days of age which subsided or disappeared thereafter. The immunological differences between colostrum-fed and colostrum-deprived neonatal pigs, the differences in composition between sow's colostrum and milk for naturally-reared pigs and the milk replacers used for artificial-reared pigs and the differences in the amount and number of feedings per day for naturally- vs. artificially-reared neonatal pigs are some of the factors which may contribute to the incidence of "nutritional" diarrhea in colostrum-deprived, artificially-reared, neonatal pigs. Mortality due to this problem has been practically nil or very low, unless newborn pigs had pathological diarrhea, particularly caused by rotavirus, which could happen when strict sanitary conditions at birth were not followed. In general, artificially-reared neonatal pigs fed to appetite or overfed are prone to diarrhea and this has been reported with colostrum-deprived pigs (41, 53, 60, 62) as well as with newborn pigs allowed to nurse their dams for their first 2 days of life (62, 63). Therefore, limited or restricted feeding scales and/or a decrease in the DM content of the liquid diet has helped in eliminating or minimizing the magnitude of non-pathological diarrhea, but has also reduced the growth rate of pigs (60; Gomez, unpublished data).