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Immunology and Management: When Should Pigs Be Weaned?

Livestock Update, December 2002

Amy Hensley and C. M. Wood, Virginia Tech

Weanling pigs are vulnerable to disease because their immune systems are not fully functional. The challenge is to protect these baby pigs against antigens in the environment and to determine the best time to wean them. T lymphocytes are often used to measure strength of immunity, as are the many kinds of blood mononuclear cells such as CD2, CD4, and CD8 cells.

One study (Brown et al., 2002) was designed to determine the effects on T lymphocytes of weaning piglets into on-site and off-site nurseries. After weaning (~ 19 days of age), one pig from each group was sacrificed on day 1, 3, 11, and 24 post-weaning. In both facilities, the T lymphocytes were greatest on day 24 post-weaning, the number of CD4+ cells was highest on day 1 post-weaning, and the numbers of CD4+CD8+ cells were lowest on day 3 post-weaning. On all other days, the numbers fluctuated for each facility. This study suggests that different environments in nursery facilities could alter T cell subpopulations and impact when to wean.

An experiment by Vega-Lopez et al. (1995) used weaned and suckling piglets to compare changes in the piglets' immunity. Half of the pigs were weaned at 21 days and put on a soya-containing diet. The other piglets were kept on the sow's milk and not given solid feed. All piglets were sacrificed at 25 days of age. Immune cells in the pigs weaned at 21days of age were higher in concentration than immune cells of the suckling pigs. These results confirm that piglets weaned at a younger age are exposed to environmental antigens sooner than piglets weaned later and therefore produce more immune cells against these antigens.

Another study (Yoo et al., 1997) looked at how a nutrient supplement affected the immune cell population of piglets infected with E. coli. Twenty piglets from two litters were weaned at 21 days of age and assigned to two treatments. The diet of one group of piglets was supplemented with glutamine; the other group was supplemented with nonessential amino acids. Five piglets from each group were infected with E. coli at 26 days of age. All infected pigs had higher levels of leukocytes and blood lymphocytes than controls. However, in the pigs supplemented with glutamine, white blood cell counts were greater than in the unsupplemented pigs

These studies indicate that the concentration of immune cells has a direct effect on the ability of pigs to produce an immune response when exposed to environmental antigens. This information could help producers determine the best time to wean piglets to maximize immunity. These studies also help determine what type of supplementation could help the immune systems to become stronger faster after weaning.

Brown D.C., C.V. Maxwell, M.E. Davis, G.F. Erf, and S. Singh. 2002. Effects of segregated early weaning on systemic and enteric T lymphocyte subpopulations in pigs. J. Anim. Sci. 80(Suppl. 1):30-31.

Vega-Lopez, M.A., M. Bailey, E. Telemo, and C.R. Stokes. 1995. Effect of early weaning on the development of immune cells in the pig small intestine. Vet. Immun. and Immunopath. 44:319-327.

Yoo, S. S., C. J. Field, and M. I. McBurney. 1997. Glutamine supplementation maintains intramuscular glutamine concentrations and normalizes lymphocyte function in infected early weaned pigs. J. Nutr. 127:2253-2259.

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