Introduction
Cu, Fe, Mn and Zn are known to compete for absorption and interact with one another in the body where they are constituents of many vital systems and contribute to immune, reproductive and athletic performance. Analyses of forages and horse feed in RSA show Fe content is high while Zn and Cu content is low. Fe from grass is considered to be poorly available to horses and the provision of supplementary Fe in feeds and supplements occurs, increasing the overall daily intake. The liver is a storage organ for TM’s and can be used to accurately determine body stores and show long-term dietary intake and absorption of TM’s.
Materials and Methods
Liver samples were collected from 34 horses euthenased for mechanical and financial reasons in KZN. Age, breed and management of the horses varied widely. Samples were freeze dried and underwent wet digestion with Perchloric/nitric acid mix before being analysed for TM content via Atomic Absorption Spectrophotometry, all results are reported on a wet matter basis and horse norms of Dierenfeld et.al. (2005) were used as reference levels. Genstat (14thEd.) was used to analyse data.
Results
Mean Znliv of 37,92μg/g was lower than the norm of 40-125μg/g with 22 of 34 horses below normal and 12 within normal range. The mean Feliv was 643μg/g more than double the upper norm of 300μg/g. 10 horses had normal Feliv and 24 horses had excess Feliv. 24 horses had normal Culiv levels of 4-7.5μg/g with a mean of 6.53μg/g, 4 horses had low and 6 high Culiv. Mnliv was adequate with 31 of 34 horses within the normal range of 1-6μg/g.
Feliv significantly (P<0.001) increased with age while the presence of worms significantly (P<0.001) reduced Feliv levels. Horses receiving 20-30% or >80% of the diet as concentrate had significantly (P0.008) higher Feliv levels than horses eating 0% or 50% concentrations.
Culiv, Mnliv and Znliv were not affected by age, diet or worm presence.
Discussion
Results from this study show the Zn in take of horses in KZN needs to be increased. Due to the importance of Zn in immune and antioxidant function, horses with a Zn deficiency are likely to be more susceptible to viruses and bacteria and have reducedanti-oxidant capabilities. Zn is critical to cognitive and emotional function and deficiency has been shown to increase depression and can lead to difficulties in training and learning ability in animals. Skin, hoof and coat health will be affected by low Zn status due to its integral function in the keratin structure and deficiencies can result in skin infection and lesions, weak hoof walls, slow hoof growth, sun-bleaching of coats and poor pigmentation.
The high Fe concentration found in the sampled horses suggest that Fe is absorbed effectively from both forage and concentrate feeds. Efforts need to be made to reduce Fe intake or to provide horses with balanced TM intakes in an attempt to limit uptake through competitive absorption.
Conclusions
As limited changes to forage Fe content is possible, feeds and supplements supplied to horses should be reformulated to contain minimal Fe and higher concentrations of Zn while maintaining the recommended Cu:Zn:Mn ratio of 1:4:4 (NRC2007). The optimal ratio of Fe:Cu:Zn:Mn needs to be investigated in horses and instituted in feed formulations to ensure adequate absorption of all the TM’s in the correct ratios from the total diet. Methods of reducing dietary Fe and its uptake, in equines need to be explored and more understanding of the relative deficiencies of Zn and Cu compared to Fe need to be investigated.
Further research needs to be undertaken to ascertain whether Feliv values found in this study occur through out RSA where feeds and forages contain excess Fe. Histopathological examination of liver samples would allow for better understanding of the nature of Fe in the livers of horses and the possible negative effects of this Fe.
References
Nutrient Requirements of Horses 6th revised ed. National Research Council 2007
Dierenfeld et.al.2005 Mineral concentrations in serum/plasma and liver tissue of captive and free-ranging Rhinoceros species