The Effects of Dietary Additives on the Growth Performance and Occurrance of Resistant Bacteria in Weanling Pigs

Three replicate trials, with a total of 36 ileal cannulated pigs, were conducted to determine the effects of including carbadox or mannanoligosaccharides in weanling pig diets. Individual crossbred (Yorkshire X Landrace X Duroc) pigs were used as the experimental units and were weaned at approximately 21 days of age, balanced by gender, genetics and weight, and allotted to pens in groups of three. Pens were randomly assigned to one of four treatments including: AB) 55 mg carbadox/kg, BM) 0.2% phosphorylated mannanoligosaccharide, RT) a rotation of the above two treatments, or CT) NRC based control treatment with no additives. Pigs were allowed ad libitum access to water and the assigned treatment as a single-phase diet for a 35-day period. Ileal digesta were collected on days 14, 21, 28, and 35 of the trial. Pigs were sacrificed on day 35 and digesta and tissue samples were collected from the duodenum, jejunum, ileum, cecum, and spiral colon. Digesta were analyzed for pH, dry matter, total aerobes, total anaerobes, lactobacilli, streptococci, E.coli and VFA including: acetate, propionate, butyrate, valerate, isovalerate, and isobutyrate. Tissue samples were fixed and stained with hematoxylin and eosin and examined for villi height and crypt depth measurements.

Intestinal pH of the BM treatment was more alkaline and the CT treatment was more acidic when treatments were compared (P=0.0017). A site effect (P=0.0001) was also observed where the ileum was more alkaline and the cecum more acidic. Ileal dry matter increased (P=0.0007) for all treatment groups through day 28 postweaning and was lowest in the ileum and highest in the spiral colon (P=0.0001). Lactobacilli concentrations were lowest for the AB treatment and highest for the CT (P=0.0400). Time effects were observed where total anaerobe concentrations decreased (P=0.0034) 28 and 35 postweaning for all treatments and ileal E.coli concentrations decreased (P=0.0004) on day 21 postweaning. A site effect (P=0.0001) was observed for all microbial concentrations. Treatment effects were noted for ileal butyrate (P=0.0070) and acetate (P=0.0174) where acetate and butyrate concentrations were greater in the ileum for the AB and RT treatments compared to the BM and CT treatments. Time affected ileal isovalerate (P=0.0113), butyrate (P=0.0001), and acetate (P=0.0001) concentrations. A site effect (P=0.0001) was observed for all VFA concentrations. Treatment X site interactions were observed (P=0.0297) for valerate concentrations. Villi length was significantly shorter in the ileum and crypt depths were deepest in the cecum and spiral colon (P=0.0001).

In a subsequent study to compare effects of carbadox and mannanoligosaccharides on performance, a total of 48 crossbred (Yorkshire X Landrace X Duroc) pigs were weaned at approximately 21 days of age and balanced by gender, genetics, and weight. Pens were randomly assigned to one of the four previously mentioned treatments with each treatment consisting of 3 pens and 4 pigs per pen. Each group was allowed ad libitum access to water and the assigned treatment as a single-phase diet. Pens were used as the experimental units. Performance parameters, including average daily gain, average feed intake, and feed conversion ratio, were measured for a 28-day period and compared across treatments. Feed intake and feed conversion ratio were measured for individual pens. No treatment effects (P>0.05) were noted for any of the growth parameters measured.

Twelve pigs were sacrificed on day 7 and 28 and digesta and tissue samples were collected from the duodenum, jejunum, ileum, cecum, and spiral colon. Digesta were analyzed for pH, dry matter, lactobacilli, E.coli and VFA. Tissue samples were fixed and stained with hematoxylin and eosin and examined for villi height and crypt depth measurements. Individual pigs were used as the experimental units and data were analyzed over time.

Treatment effects (P=0.0109) were observed on day 28 postweaning where pH was highest for the AB and BM treatments and lowest for the CT. Treatment X site interactions (P=0.0333) were observed for percentage dry matter. Site effects (P=0.0001) were observed for both pH and percentage dry matter. Treatment effects were observed for E.coli concentrations on day 28 (P=0.0063) and over all days (P=0.0282). Concentrations were lowest for the AB and BM treatments and highest for the CT treatment. Treatment X site interactions (P=0.0313) were observed for E.coli concentrations on day 28 postweaning. No treatment or site effects (P>0.05) were observed for E.coli resistance to carbadox. Resistance increased (P=0.0032) from day 7 to 28 postweaning for all treatments and sites. Treatment X site interactions (P=0.0500) were observed for E.coli resistance overall. Site effects (P<0.05) were observed for lactobacilli and E.coli concentrations. Treatment X site interactions were observed on day 28 for isobutyrate (P=0.0200), and on day 28 and overall (P=0.0001) for acetate concentrations. Treatment effects (P<0.05) were observed for valerate concentrations on day 7, 28 and over all days. Treatment effects (P=0.0002) were observed on day 28 for acetate concentrations. Site effects (P<0.05) were observed for isovalerate, valerate, propionate, acetate, and butyrate concentrations. Site effects (P<0.05) were observed for villi height and crypt depth.

Results from this research indicate that the intestinal microbial environment is affected by the inclusion of carbadox or mannanoligosaccharides in weanling pig diets.