The effects of minerals on the growth performance and immunity of weaned pigs .1. Copper and zinc

A total of 80, 4-week-old pigs (averaged body weight 7.2 kg), half male and half female, were randomly assigned to 5 different diet groups according to their body weight and sex. The 5 diet groups were (1) basic diet only, (2) basic diet supplemented with 125 ppm copper (Cu)/100 ppm zinc (Zn), (3) basic diet supplemented with 125ppm Cu/200 ppm Zn, (4) basic diet supplemented with 250 ppm Cu/100 ppm Zn, and (5)basic diet supplemented with 250 ppm Cu/200 ppm Zn. The basic diet contained corn and soybean meal, vitamins, and minerals in which the minerals included 33 ppm Cu, 138 ppm Zn, and 157 ppm iron. The optimal dietary supplementation of Cu/Zn and its possible effects on the growth performance and immunity in weaned pigs were evaluated. The study was done in 4 replicates, each containing 4 pigs. The pigs were fed on the designated diet ad libitum until the age of Ii-week-old (average body weight 25 kg) and the daily feed consumption of each group was measured. The pigs were weighed every other week and immunized with sheep erythocytes (SRBC) and a bacterin of Actinobacillus pleuropneumonia (AP) on weeks 2 and 5. Body weight gain and feed efficiency were calculated. Blood samples were taken right before immunization and thereafter weekly for the measurement of serum antibody titers to SRBC and AP. On weeks 2, 4, 6, and 7, peripheral blood lymphocytes were collected and concanavalin A (Con A)-induced blastogenesis and interleukin 2 (IL-2) production were measured. In addition, the pigs received a dose of phytohemagglutinin (PHA) subcutaneously on days 21 and 45 and the size of swelling at each of the injection site was measured. It appeared that the addition of Cu/Zn of various combinations in the ratio could affect the daily weight gain and feed efficiency during the first 4 weeks, and feed intake during the 3rd-4th week period of pigs after weaning, respectively. A significantly increased daily weight gain and a slightly improved, but not statistically significant, feed efficiency were present in the group of 250 ppm Cu/100 ppm Zn; on the contrary, the groups fed on diet containing lower levels of Cu/Zu showed decrease in daily weight gain. Higher mean anti-SRBC antibody titer was seen in the group of 250 ppm Cu/100 ppm Zn at week 7 when compared to the basic diet group. Although no differences were noted in the antibody titers to AP bacterin among all groups at any of the weeks examined, the averaged values of the overall mean anti-AP antibody titers were higher in the groups containing higher levels of Cu/Zu than were in the groups containing lower levels. For the PHA-induced skin swelling, on day 21 the group of 125 ppm Cu/100 ppm Zn had significantly smaller size of swelling than any other groups; however, the differences were not apparent by day 45. As for the Con A-induced lymphoblastogenesis, the groups of 125 ppm Cu/200 ppm Zn and 250 ppm Cu/100 ppm Zn had significantly higher responses than did other groups at week 2; however, no apparent differences were seen in other time periods: No significant effects were observed in the Con A-induced IL-2 production of peripheral blood lymphocytes. Although no consistent results were seen in any of the tested groups throughout the study, the data of growth performance, anti-SRBC antibody titers, and Con A-induced lymphoblastogenesis suggest that the addition of 250 ppm Cu/100 ppm Zn may have the potential to enhance the growth performance and immunity of pigs at the early stage after weaning.