Abstract
Simple SummarySoils with inadequate levels of selenium are widespread in the northwest, northeast, and southeast USA. Therefore, dietary supplementation of forage-grazing beef cattle with additional selenium is recommended in these regions for optimal growth, immune function, and fertility. We have reported that the form of selenium provided to Angus-cross cows can affect circulating concentrations of progesterone on day 6 of the estrous cycle, a time when increased progesterone is known to promote fertility. Hence, we sought to confirm this initial finding, determine the effect of the form of selenium on peripheral concentrations of progesterone during gestation, and determine the effect of the form of selenium on circulating concentrations of prolactin during lactation. Cows were supplemented with equimolar amounts of either an inorganic form, or a 1:1 mixture of inorganic and organic forms of selenium throughout this study. We confirmed our original finding that the mixed (1:1 inorganic to organic selenium) supplement increased systemic progesterone in the early luteal phase of the estrous cycle, and determined that cows maintained on this same supplement had elevated concentrations of progesterone throughout gestation. Interestingly, these same cows revealed a treatment-induced decrease in systemic prolactin during late lactation. The form of selenium provided to cows can be manipulated to affect reproductive responses and offers a viable management tool to improve fertility in cows in regions with selenium-deficient soils.Soils with marginal to deficient levels of selenium (Se) are widespread in the northwest, northeast, and southeast US. Supplementation to the diet of forage-grazing beef cattle with a vitamin-mineral mix containing additional Se is recommended in these geographic regions. We have reported that the form of supplemental Se provided to Angus-cross beef cows can affect circulating levels of progesterone (P4) on day 6 of the estrous cycle, a time when increased P4 is known to promote fertility. The objectives of this study were to (1) confirm and expand upon our initial report that the form of Se provided to cows affects early luteal-phase concentrations of systemic P4, (2) determine the effects of the form of Se on concentrations of P4 during gestation, and (3) determine the effects of the form of Se on concentrations of prolactin (PRL) during lactation. Throughout this study, Angus-cross beef cows had ad libitum access to a vitamin-mineral mix containing 35 ppm of Se in either an inorganic form (ISe) or a 1:1 mix of inorganic and organic forms (MIX). We observed a MIX-induced increase (p = 0.006) in systemic concentrations of P4 on day 7 but not on days 4 or 10 of the estrous cycle, consistent with our earlier report. We observed a MIX-induced increase (p = 0.02) in the systemic concentration of P4 at months 1, 3, 5, and 7 of gestation, and a MIX-induced decrease (p < 0.05) in systemic concentrations of PRL at months 5 and 6 of lactation. In summary, the form of Se provided to cows can be manipulated to affect the early luteal phase and gestational concentrations of P4, and postpartum concentrations of PRL.
Highlights
Dietary selenium (Se) is required for the synthesis of selenoproteins, including glutathione peroxidases and thioredoxin reductases, which catalyze the breakdown of hydrogen peroxide and lipid hydroperoxides, protecting extracellular and intracellular cell membranes [1,2,3,4]
We previously demonstrated that the consumption of equimolar amounts of Se in organic (OSe), inorganic (ISe), or mixed (MIX, 1:1 OSe:inorganic Se (ISe)) forms by beef cows throughout pregnancy resulted in distinct transcriptome profiles in the testes collected from their newborn bull calves, including the differential expression of mRNAs known to regulate gonadal steroidogenesis [15], and that cows consuming mix of inorganic and organic forms (MIX) versus ISe had an increased concentration of systemic progesterone (P4) on day 6 of the estrous cycle [16]
Cows maintained on the MIX treatment group versus ISe had a greater concentration of systemic P4 on day 7 (p = 0.006) but not on days 4 or 10 (p > 0.05) post-estrus (Table 1)
Summary
Dietary selenium (Se) is required for the synthesis of selenoproteins, including glutathione peroxidases and thioredoxin reductases, which catalyze the breakdown of hydrogen peroxide and lipid hydroperoxides, protecting extracellular and intracellular cell membranes [1,2,3,4]. A deficiency in Se has been shown to reduce rates of growth [5], alter immune responses [6,7], and reduce indicators of fertility [8], including an increased rate of abortion and perinatal mortality [9]. Because the content of Se in forages is dependent upon the content of Se in the soil, supplementation to the diet of forage-grazing beef cattle with a vitamin-mineral mix containing Se is recommended in these areas. Free-choice vitamin-mineral mixes containing Se have been formulated with an inorganic form of Se, sodium selenate or sodium selenite. The form of Se available to an animal affects the bioavailability of Se in blood and tissues, and the bioactivity of
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