Effect of dietary supplementation with vitamin C or carbadox on weanling pigs subjected to crowding stress.

A 2 X 3 factorial arrangement was used in each of two trials with two levels of floor space allowance (.25, .13 m2/pig) and three dietary treatments (basal, basal + 660 ppm vitamin C, basal + 55 ppm carbadox). The reduction in floor space allowance was achieved in trial 1 by doubling the number of pigs/pen from eight to 16 and in trial 2 by reducing the size of pens by half. An 18% protein starter diet was used as the basal diet. Total numbers of pigs used were 216 in trial 1 and 144 in trial 2. Pigs were weaned between 4 and 5 wk of age (7.5 kg average wt) and fed ad libitum for 28 d. Reducing floor space allowance caused a (P less than .05) reduction in weight gain of weanling pigs in both trials. When the reduction of floor space allowance was done by increasing number of pigs/pen (trial 1), pigs responded with a significantly reduced feed intake with no change in efficiency of feed utilization. However, when floor space allowance was reduced by changing the size of the pen (trial 2), feed intake of pigs was not affected but efficiency of feed utilization was reduced significantly. Neither form of crowding affected vitamin C concentration in adrenal glands and weights of adrenal glands, spleen and thymus. Dietary supplementation of carbadox, but not vitamin C, produced significantly greater weight gain, feed efficiency, and spleen weight of pigs in both trials. Although there was no interaction between crowding and dietary treatment in affecting the performance of pigs, supplemental carbadox improved the performance of crowding-stressed pigs by maintaining an adequate level of feed intake and improving feed efficiency, whether crowding was caused by increased pig density or by reduced pen size. No significant differences in phytohemagglutinin (PHA) skin test response or in the neutrophil-to-lymphocyte ratio (N/L) were observed among treatments in trial 1, while a significantly reduced response to PHA and a higher N/L were detected in crowding-stressed pigs in trial 2.