Heat stress has a dramatic impact on feed consumption and milk production in dairy cows. It is responsible for large economic losses in the livestock industry. Documented evidence has proven that selenium can effectively alleviate heat stress in dairy cows.
Heat stress in all animals evokes a physiological response and the result is an elevated internal temperature. In attempt to get back to homeostasis, dairy cows will increase respiration rate, panting and sweating which will lead to energy expenditure taken away from milk yield and reproductive performance. Meanwhile dry matter (DM) intake is reduced. Animals in this status are more prone to secondary bacterial infections that can also attribute to poor performance. Cows are especially at-risk around parturition, specifically week-1 to peak lactation. Strategies to reduce oxidative and metabolic stress associated to inflammation are necessary. Along with management solutions to alleviate heat stress such as installing sprinklers, adding an adequate source of selenium that can change the immunological and physiological status is an option to combat heat stress. Excential Selenium 4000, a pure L-selenomethionine dust-free feed preparation, is a readily available form which provides the highest selenium deposition, while reducing oxidative stress by decreasing free radicals and inflammatory response sustaining performance under stress conditions.
Excential Selenium 4000 (Se4000) has documented evidence that it increases the deposition of selenium in livestock including equine, swine, broilers, layers, and dairy relative to both selenite and selenised yeast. As seen in Figure 1, a total of 24 Holstein Friesian cows, originally on a low Se diet were placed on one of the 4 following treatments:
The inclusion of Se4000 resulted in the highest deposition in milk, 61% increase relative to selenite and outperforming selenised yeast. This also translates in improved Se deposition in colostrum which can lead to improved passive immunity. This is because L-selenomethionine, can be stored into the body in replacement of methionine. As a result, selenium in the form of L-selenomethionine is incorporated and stored into muscle, milk, and blood in view of being transformed into selenide to de novo selenocysteine in the liver and subsequent selenoprotein synthesis. Although selenised yeast has some L-selenomethionine and other organic selenium derivatives, those other derivates cannot be incorporated into animal proteins the same way; less selenomethionine means less deposition and storage reserves.
The more readily available L-selenomethionine (Se4000) allows for improved immune status. In mammals, it was discovered that providing L-selenomethionine significantly lowered expression of Cyclooxygenase-2 (Cox2) and interferon gamma (Ifnγ) relative to selenite, numerically lower than selenised yeast during normal production. These genes are involved in inflammation when elevated. In the same study during a pathogen (lipopolysaccharide) challenge, mammals that were given selenite as their selenium source had a gene profile that indicated oxidative stress (elevated up-regulation of Txnrd1, Cat, selenogenes SelS, SelN1, before challenge and an immediate downregulation 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 challenge, redirecting energy costs away from an inflammatory response to a response important to the producers, performance.
Improving immunity during times of stress can reduce secondary pathogen overgrowth and infections. Proper selenium supplementation can improve the efficiency of leucocytes and antioxidants such as glutathione peroxidase. Without proper antioxidant defence mechanism, cows can become susceptible to immunosuppression. One study investigated the effect of dietary selenium supplementation on milk composition. Somatic cell counts were significantly lowered by 26% in dairy that were given L-selenomethionine for 63 days compared to selenite. Somatic cell counts in the L-selenomethionine 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-selenomethionine treatment including an increase in conjugated linoleic acid (CLA), rumenic acid. Mammary function can be improved with elevated CLA’s 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 reduced lipid oxidation in caciocavallo cheese.
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; non-lactating and lactating cows as low as 10-16%. In ruminants, it is especially crucial to provide a selenium source that is readily available.
Heat stress is associated with decreased milk production, increased disease incidence and impaired reproduction. In a commercial dairy study, cows were deficient of selenium (below 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 significantly improved and was no longer deficient (67 µg Se/L). At 8 weeks, Se in the blood continued improving (76 µg Se/L) despite elevated ambient temperatures (average 71.6oF).
High ambient temperature during late gestation can also influence the transfer of passive immunity to calves. This can lead to a poor start to these calves. In a commercial trial with 2 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, calves in the L-selenomethionine group had significantly improved selenium content in the milk by 85% and the 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.
Heat stress can elicit a number of physiological responses, causing inflammation and imbalance to the immune system in dairy 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 are better equipped to regulate homeostasis through regulating oxidative and metabolic stress and to have the reserves available when needed.
Author: Kim Wilson (Ph.D.), Technical Commercial Manager
References are available on request