Young horses require specific levels of amino acids, vitamins, and minerals for proper development, and researchers know that zinc, in particular, is vital for growing horses' enzyme and immune function. However, there's been little research done in horses evaluating the relationship between zinc and the equine immune system. So researchers from Argentina's Buenos Aires University set out to evaluate zinc levels and serum protein profiles in foals of different ages.

Veterinarians know that zinc deficiencies can result in decreased cell-mediated and humoral (an antibody response to an antigen by the immune system) immune responses, by causing a reduction in monocyte (a type of white blood cell that converts into infection-fighting macrophages), cytokine (inflammation mediators), and leukocyte (another type of white blood cell that fights infection and is involved in inflammation) function.

To learn more, Emilio Adrián De Simone, DVM, PhD, and colleagues employed 304 race-type horses—70 weanlings aged 8-10 months, 125 yearlings aged 12-18 months, and 109 2-year-olds aged 20-24 months—at different farms in Buenos Aires and La Pampa, Argentina. All foals grazed pasture ad libitum and consumed appropriate amounts of a commercial feed containing 40 ppm (parts per million) zinc sulphate, as recommended by the National Research Council in 2007, to meet their individual nutritional needs.

Researchers collected blood samples from all the foals and analyzed zinc, protein, and albumin concentrations in the serum. Then, based on serum zinc concentration, the team classified the foals as either low zinc (less than 100µg/dL [micrograms per deciliter]) or normal zinc levels (100-160µg/dL). The team also randomly selected 78 samples—41 from the low zinc group and 37 from the normal group—and analyzed them for γ-globulin concentration; γ-globulin is an indicator of immunoglobulins, or antibodies, in the blood.

Key study findings included:

  • When compared statistically, weanlings and 2-year-olds had, on average, higher serum zinc concentrations than yearlings;
  • The average serum zinc values for the normal foals were 137µg/dL while the low Zn group averaged 78µg/dL;
  • All foals' serum protein and albumin levels were within the range considered normal (normal protein in horses averages 5.9µg/dL and normal albumin averages 38.405µg/dL); however, when analyzed as a ratio, the albumin/globulin ratio was significantly greater in foals from the low zinc group compared to the normal zinc group (the normal group's ratio was 1.28 +/- 0.294 whereas the low group's was 2.185 +/- 0.818);
  • Yearlings and 2-year-olds in the low zinc group had a significantly lower amount of serum γ-globulins compared to horses with normal zinc levels; no differences were noted in the weaned group; and
  • Researchers saw reduced γ-globulins in all animals with low zinc and a high albumin/globulin ratio; the concentrations ranged from 6.7-14%, a reduction from normal γ-globulins of around 24%. This could signify decreased antibody numbers and possibly a decreased ability to fight off infection or disease.

Maternal zinc status plays an important role in young foals' zinc status. A few months after weaning, however, foals' Zn status becomes dependent on nutritional and genetic factors. The authors believe the aforementioned results indicate that yearlings could be at a higher risk of zinc deficiency than other young horses.

Take-Home Message

Based on their findings, the team concluded that zinc requirements for adequate immune function are not being met by current recommended levels or by the source of zinc used in this study. In this trial, immune function seemed to be impaired, specifically in yearlings and 2-year-olds. Therefore, yearlings and 2-year-olds might be more susceptible to health problems, even when Zn requirements are being met in the diet.

The study, "Association Between Low Serum Zinc Concentration and Hypogammaglobulinemia in Foals of Different Age Categories," appeared in June in the Journal of Equine Veterinary Science

Disclaimer: Seek the advice of a qualified veterinarian before proceeding with any diagnosis, treatment, or therapy.

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