Abstract
The objective of this study was to evaluate the potential of an alumninosilicate clay, marketed under the trade name Biotite V, to improve growing-finishing pig performance and to determine its effects on nutrient digestibility and excretion. Sixty crossbred pigs (22.3${\pm}2.7kg$, Camborough 15 Line female${\times}$Canabred sire) were assigned on the basis of sex, weight and litter to one of four dietary treatments in a $2{\times}4$ (two sexes and four treatments) factorial design experiment. The experimental diets were based on barley and soybean meal and contained 0, 0.25, 0.5 or 0.75% biotite during the growing period (22.3-60.5 kg) and 0, 0.5, 1.0 or 1.5% biotite during the finishing period (60.5-110.3 kg). Each pig was allowed access to its own individual feeder for 30 min twice daily (07:00 and 15:00 h). Individual pig body weight, feed consumption and feed conversion were recorded weekly. The pigs were slaughtered at a commercial abattoir when they reached an average weight of 110.3 kg. Carcass weight was recorded and dressing percentage calculated. Carcass fat and lean measurements were obtained with a Destron PG 100 probe between the 3rd and 4th last ribs, 70 mm of the midline. Total tract digestibility coefficients for dry matter, energy, nitrogen and phosphorus were determined using three males and three females per treatment starting at an average weight of $52.2{\pm}3.8kg$. These pigs were housed under identical conditions as those used in the growing stage and were fed the same diets modified only by the addition of 0.5% chromic oxide as a digestibility marker. Over the entire experimental period (22.3-110.3 kg), daily gain was unaffected (p>0.05) by the inclusion of biotite in the diet. There was a cubic response for feed intake (p=0.06) and a quadratic response (p=0.07) for feed conversion due to biotite. Feeding biotite produced no significant (p>0.05) linear or quadratic effects on any of the carcass traits measured. Dry matter digestibility decreased linearly (p=0.02) with increasing levels of biotite in the diet. However, digestibility coefficients for energy, nitrogen and phosphorus were unaffected (p<0.05) by biotite inclusion. Lactobacilli and enterobacteria numbers were unaffected by inclusion of biotite while Salmonella was not detected in any of the fecal samples. The overall results of this experiment indicate that biotite inclusion did not reduce fecal excretion of nitrogen or phosphorus and failed to improve nutrient digestibility. Neither growth rate nor carcass quality was improved while a modest improvement in feed conversion was observed at lower levels of inclusion. Based on the results of this experiment, it would be difficult to justify the routine inclusion of biotite in diets fed to grower-finisher pigs. Whether or not a greater response would have been obtained with pigs of a lower health status is unknown.