before challenge and an immediate down-regulation of Gpx1). Those given an organic source (selenised yeast and Se4000) did not have the same profile. Specifically, Se4000 had an up-regulation of regulatory cytokine interleukin 10 (IL10) which depresses inflammation during times of chal- lenge, redirecting energy away from an inflammatory re- sponse to a response important to the producers: perfor- mance.
Reducing secondary pathogens Improving immunity during times of stress can reduce sec- ondary pathogen overgrowth and infections. Proper seleni- um supplementation can improve the efficiency of leucocytes and antioxidants such as glutathione peroxidase. Without a proper antioxidant defence mechanism, cows can become susceptible to immunosuppression. One study investigated the effect of dietary selenium supplementation on milk com- position. Somatic cell counts were significantly lowered by 26% in dairy cows that were given L-selenomethionine for 63 days compared to selenite. Somatic cell counts in the L-se- lenomethionine treatment were all below 200,000 cells/mL, which is the sensitivity threshold for detection of mastitis. In the same study, free fatty acids were altered in the L-sele no- methionine treatment including an increase in conjugated linoleic acid (CLA), rumenic acid. Mammary function can be improved with elevated CLAs by protecting bovine mammary epithelial cells from lipid peroxidation and reducing the levels of reactive oxygen species. Reducing lipid peroxidation can also be evident in dairy products, where L-selenomethionine was shown to reduce lipid oxidation in caciocavallo cheese.
Selenium in ruminants Selenium absorption tends to be much lower in ruminants relative to non-ruminants due to the ruminal environment creating insoluble forms of selenium. Absorption of inorganic selenium can be as low as 13% in steers and as low as 10–16% in non-lactating and lactating cows. In ruminants, it is especially crucial to provide a selenium source that is readily available. Heat stress is associated with decreased milk production, in- creased disease incidence and impaired reproduction. In a commercial dairy study, cows were deficient in selenium (be- low 65 µg Se/L blood). A total of 30 Friesian cows had diets that included 0.2 ppm Se from selenised yeast replaced by 0.2 ppm Se from Se4000. In two weeks, Se in the blood signif- icantly improved and was no longer deficient (67 µg Se/L). At eight weeks, Se in the blood continued improving (76 µg Se/L) despite elevated ambient temperatures (average 71.6ºF [22ºC]). High ambient temperature during late gestation can also influence the transfer of passive immunity to calves. This can lead to a poor start for these calves. In a commercial trial with two equal groups of 48 cows, selenised yeast (0.15 ppm Se
prior to calving) and sodium selenite (0.15 ppm Se prior to calving and 0.45 ppm Se after calving) were replaced by 0.20 ppm Se from L-selenomethionine as Se4000 prior to calving and after calving in the trial group. One month after calving, suckler cows in the L-selenomethionine group had significantly improved selenium content in the milk by 85%, and their calves had adequate levels of Se in the blood (67 µg Se/L). In addition, the proportion of cows that received more than one artificial insemination reduced by 13% in those given Se4000.
Priming the immune system with selenium Heat stress can elicit a number of physiological responses, causing inflammation and imbalance to the immune system in dairy cows that can affect performance and overall well-being. By priming the immune system with adequate levels of readily available trace minerals such as selenium in the form of L-selenomethionine (Se4000), dairy cows are bet- ter equipped to regulate homeostasis through regulating oxi- dative and metabolic stress and to have the reserves available when needed.
References are available on request ▶DAIRY GLOBAL | Volume 7, No. 3, 2020 35
Heat stress can elicit a number of physiological responses, caus- ing inflamma- tion and imbal- ance to the immune system in dairy cows that can affect performance and overall well-being.
PHOTO: ORFFA
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