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2004 Swine Research Review

Herd Health and Management

Weaning Age, Lighting Impact Gains, Immunity

The duration of lighting and the age at which pigs are weaned can influence their immune system and weight gains, according to preliminary studies at the University of Illinois.

In short, pigs that were weaned at 28 days of age and maintained on 16 hours of light from weaning until 10 weeks of age were the heaviest in the study. They gained at least 7.7 lb. more than their counterparts provided only eight hours of light.

For the study, piglets were weaned at either 14, 21 or 28 days of age, and were moved to a standard nursery and kept on either eight or 16 hours of light until 10 weeks of age. Blood samples were drawn and analyzed to assess the impact of weaning age and light exposure on the immune system.

The combined effect of weaning age and light exposure are depicted in Figure 1. Pigs weaned in all three age groups and exposed to 16 hours of light were the heaviest. Pigs weaned at 21 days of age gained the least amount of weight of those groups exposed to 16 hours of light.

Figure 2 shows body weight at 10 weeks of age and exposure to different lighting treatments. Pigs exposed to 16 hours of light gained much more weight during the study regardless of weaning age. Pigs weaned at 14 days of age and exposed to 16 hours of light gained more weight than all of their counterparts exposed to eight hours of light.

The lightest-weight pigs in the study were those weaned at 14 days of age and exposed to only eight hours of light.

Without the controlled lighting experiment, weaning age dictates immunity. Maternal antibodies appear to be higher in 14-day-old vs. 28-day-old weaned pigs. Cell-mediated immune levels independent of maternal antibodies appear to be higher in older-weaned pigs.

The ability of “natural killer cells” to protect against infection is shown (Figure 3) to be much higher in pigs weaned at an older age (21 and 28 days old) compared to those weaned younger (14 days). Natural killer cells are a type of immune cell that eliminates or attacks viruses and cancerous cells.

Weaning age and the amount of lighting that young pigs are exposed to jointly affects immune response up to 10 weeks of age. The ability of B-lymphocytes to increase was most stimulated by eight hours of light in 28-day-old weaned pigs (Figure 4). B-cells are white blood cells that include elements related to immunity.

Also, by eight weeks of age, pigs weaned at 14 days of age and exposed to only eight hours of light had higher B-cell responses than 14-day-old weaned pigs exposed to 16 hours of light.

In contrast, 28-day-old weaned pigs maintained on 16 hours of light recorded higher total lymphocyte numbers than their eight-hour counterparts, despite having lower B-cell proliferation.

From these trials, it becomes apparent that age of weaning and amount of light exposure can influence different aspects of the immune system in different ways.

For instance, it may be possible to use photoperiod to enhance immunity during times of stress and to improve performance at a particular stage of production.

What remains is to determine the impact of photoperiod manipulation for immune stimulation during production challenges.

Researchers: Janeen L. Salak-Johnson and Sherrie Neikamp, University of Illinois. Contact Salak-Johnson by phone (217) 333-0069; fax (217) 333-8286; or e-mail

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