The effect of subclinical selenium toxicosis on pregnant beef cattle

Trace element concentrations in blood samples from dairy cows with uterine torsion and their neonatal calves

Background and Aim

Mineral deficiencies can lead to dystocia and abnormalities in neonates. Stillbirth of neonatal calves in dairy cows due to dystocia has become an economic problem. Uterine torsion (UT) is a common form of dystocia observed in dairy cows. However, to the best of our knowledge, there have been no reports on the characteristics of serum trace element concentrations in dairy cows with UT. This study aimed to comprehensively measure serum trace element concentrations in dairy cows with UT and dystocia.

Materials and Methods

Dairy cows with (n = 15) and without (n = 27) UT and neonates (n = 9 and n = 26, respectively) were included in this study. Blood samples (10 mL) were collected, and serum trace element concentrations were evaluated using inductively coupled plasma mass spectrophotometry.

Results

The mortality rate at birth was significantly higher in calves delivered by cows with UT than those delivered by cows without UT. The odds ratio for mortality rate at birth in dairy cows with UT was 7.85. Serum zinc (Zn) levels were significantly lower in cows with UT than in cows without UT (p = 0.01). The copper: Zn ratio was significantly higher in cows with UT than in cows without torsion (p = 0.05). In contrast, serum Cobalt (Co) concentrations were significantly higher in neonates from cows with UT than in neonates from cows without UT (p = 0.01).

Conclusion

Uterine torsion is associated with a high mortality rate at birth and considerable economic losses. Cows with UT had low serum Zn levels, and neonates born to these cows had high serum Co levels.

Selenosis in Ruminants

Selenium (Se) is a metalloid that exists as a red amorphous powder, reddish crystal, silver-gray crystal, or brown-black solid. Its potency as a nutrient and a toxicant is such that few people have seen the pure element. It is easy to lose sight of the narrow margin between too little and too much. The most common cause of selenosis is accidental or intentional overuse of supplements. Many target organs and effects of Se toxicity are similar to those of Se deficiency, so laboratory confirmation is necessary. Prevention consists of minimizing exposure to seleniferous feedstuffs and optimizing dietary factors that might aggravate selenosis.

Metals and female reproductive toxicity

Research into occupational exposure of metals and consequences of reproductive systems has made imperative scientific offerings in the preceding few decades. Early research works focused on possible effects on the reproductive functions rather than the complete reproductive health of the woman. Later, it was realized that metals, as reproductive toxins, may also induce hormonal changes affecting other facets of reproductive health such as the menstrual cycle, ovulation, and fertility. Concern is now shifting from considerations for the pregnant woman to the entire spectrum of occupational health threats and thus reproductive health among women.

Toxicological study of sodium selenite on fetal development and DNA fragmentation in liver cells of pregnant rats

The present study was carried out to evaluate the effects of sodium selenite on fetal development and DNA in liver of rats. Pregnant rats were divided into three groups: control group, group treated orally with 5 µg Se/kg body wt. and group treated orally with 10 µg Se/kg body wt. Dams were treated orally with sodium selenite from day 7 to 19 of gestation. Sodium selenite treatment revealed decrease in maternal body weight, reduction in fetal weight, length and number of viable fetuses, increased number of resorbed fetuses and post-implantation loss at the two doses tested. Fetal skeleton showed signs of developmental delay in skull and limbs of the treated groups. Sodium selenite treatment revealed significant reduction of placental and liver weights in treated dams. Sodium selenite-induced oxidative stress in liver tissue of rats as evidenced by increase in lipid peroxidation and glutathione peroxidase activity, while catalase was significantly decreased. Also, increase in DNA fragmentation, marked reduction of hepatic DNA content, and many histopathological changes in the liver were recorded. The results demonstrated that treatment of pregnant rats with sodium selenite at the toxic dosages chosen showed maternal and fetal toxicity that may be concerned with hepatic oxidative stress accompanied with DNA fragmentation and depletion of total DNA content.

The role of dietary selenium in bovine mammary gland health and immune function

Mastitis is not only a major cause of economic losses to the dairy industry but also a major problem in ensuring the quality and safety of the milk, associated with high somatic cell counts and residues of antibiotics used for treatment. One innovative approach to protection against mastitis is to stimulate the animal's natural defense mechanisms. Technological advances in immunological research have increased our ability to exploit the immunity of the bovine mammary gland during periods of high susceptibility to disease. The trace element selenium affects the innate and the adaptive immune responses of the mammary gland through cellular and humoral activities. Substantial research has been carried out on the effect of selenium (Se) on the immune function of the mammary gland and subsequent improvement in bovine udder health and mastitis control. Levels higher than current recommendations and Se-yeast can potentially be used to enhance our capacity to modulate the physiological mechanisms of the bovine mammary gland to respond to infection. This article provides an overview of the most recent research in this field.

Selenium in camel--a review

Requirements for trace minerals in camels, particularly selenium, are not well-known. Selenium supplementation using a pharmaceutical form or commercial mineral mixture is common practice in camels to address the cardiomyopathy often attributed to selenium deficiency. This supplementation is often empirical and based on estimated needs for cattle. Nowadays the use of selenium in animal foodstuffs is commonplace and further investigation of its metabolism (ingestion, dynamic of storage-destocking, excretion) in camels is warranted. The present review aimed to synthesize all the experimental research (comparative selenium status in cow and camel, response to different levels of supplementation at different physiological stages, excretion maternal transfer, experimental toxicosis) and field observations (deficiency, supplementation practices) undertaken in camels. The results underline the particularity of the unique metabolic profile of the camel and lead to practical recommendations for supplementation in camels, highlighting its relative sensitivity to excess Se intake at lower levels than in cattle. The maximal tolerable dose is 8 mg and the recommended doses range from 2 to 4 mg.

Inhibitory effect of selenium supplementation on the reproductive performance in synchronized Merino sheep at range conditions in a selenium-deficient area

The effect of selenium (Se) supplementation on the reproductive performance of Merino ewes mated out of the normal breeding season was studied in a 2 (no Se supplementation vs Se supplementation) x 2 (ewes mated at natural oestrus vs synchronized oestrus) factorial design with 50 ewes per treatment combination. Synchronization of oestrus was achieved by intravaginal insertion of 40 mg cronolone sponges for 14 days and administration of 440 IU PMSG at sponge withdrawal. Se supplementation was by the addition to the concentrate with 0.5 mg/kg of Se in the form of selenomethionin, for the 3 months prior to the mating and during gestation. Ewes were kept under range conditions in south-west Spain, and exposed to Merino rams at a female: male ratio of 4 : 1 from 2 days following sponge withdrawal, or the equivalent time, for 21 days. Se supplementation alone did not improve significantly ewe fertility or lamb birth weight, but there was a positive effect of synchronizing ewes mated out of the breeding season as more of these ewes lambed and produced more lambs than those not synchronized. However, a strong interaction was found between synchronization and Se supplementation, causing a deleterious effect on the reproductive performance of ewes. This negative effect, presumably related to high embrionary mortality caused by Se toxicity, should be taken into account for oestrus synchronizing in Se-deficient areas. The supplementation with Se, for the prevention of nutritional myodystrophy degeneration in lambs, should be conducted in a fashion which does not generate high levels of Se in the ewes around the mating period.

Tolerance of ruminant animals to high dose in-feed administration of a selenium-enriched yeast1

The objective of the study was to determine if there were adverse effects on animal health and performance when a range of ruminant animal species were fed at least 10 times the maximum permitted European Union (EU) Se dietary inclusion rate (0.568 mg of Se/kg of DM) in the form of Se-enriched yeast (SY) derived from a specific strain of Saccharomyces cerevisiae, CNCM I-3060. In a series of studies, dairy cows, beef cattle, calves, and lambs were offered a control diet that contained no Se supplement or a treatment diet that contained the same basal feed ingredients plus a SY supplement that increased total dietary Se from 0.15 to 6.25, 0.20 to 6.74, 0.15 to 5.86, and 0.14 to 6.63 mg of Se/kg of DM, respectively. The inclusion of the SY supplement increased (P < 0.001) whole-blood Se concentrations, reaching maximum mean values of 716, 1,505, 1,377, and 724 ng of Se/mL for dairy cattle, beef cattle, calves, and lambs, respectively. Seleno-methionine accounted for 10% of total whole-blood Se in control animals, whereas the proportion in SY animals ranged between 40 and 75%. Glutathione peroxidase (EC 1.11.1.9) activity was greater (P < 0.05) in SY animals compared with controls. A range of other biochemical and hematological parameters were assessed, but few differences of biological significance were established between treatment groups. There were no differences between treatment groups within each species with regard to animal physical performance or overall animal health. It was concluded that there were no adverse effects on animal health, performance, and voluntary feed intake with the administration of at least 10 times the EU maximum, or approximately 20 times the US Food and Drug Administration permitted concentration of dietary Se in the form of SY derived from a specific strain of Saccharomyces cerevisiae CNCM I-3060.

Comparative toxicosis of sodium selenite and selenomethionine in lambs

Excess consumption of selenium (Se) accumulator plants can result in selenium intoxication. The objective of the study reported here was to compare the acute toxicosis caused by organic selenium (selenomethionine) found in plants with that caused by the supplemental, inorganic form of selenium (sodium selenite). Lambs were orally administered a single dose of selenium as either sodium selenite or selenomethionine and were monitored for 7 days, after which they were euthanized and necropsied. Twelve randomly assigned treatment groups consisted of animals given 0, 1, 2, 3, or 4 mg of Se/kg of body weight as sodium selenite, or 0, 1, 2, 3, 4, 6, or 8 mg of Se/kg as selenomethionine. Sodium selenite at dosages of 2, 3, and 4 mg/kg, as well as selenomethionine at dosages of 4, 6, and 8 mg/kg resulted in tachypnea and/or respiratory distress following minimal exercise. Severity and time to recovery varied, and were dose dependent. Major histopathologic findings in animals of the high-dose groups included multifocal myocardial necrosis and pulmonary alveolar vasculitis with pulmonary edema and hemorrhage. Analysis of liver, kidney cortex, heart, blood, and serum revealed linear, dose-dependent increases in selenium concentration. However, tissue selenium concentration in selenomethionine-treated lambs were significantly greater than that in lambs treated with equivalent doses of sodium selenite. To estimate the oxidative effects of these selenium compounds in vivo, liver vitamin E concentration also was measured. Sodium selenite, but not selenomethionine administration resulted in decreased liver vitamin E concentration. Results of this study indicate that the chemical form of the ingested Se must be known to adequately interpret tissue, blood, and serum Se concentrations.

Selenosis

Despite more than six decades of research, some aspects of the natural history of selenosis remain confused in modern texts. The primary targets of acute Se toxicity in food animal species are the cardiovascular, gastrointestinal, and possibly hematopoietic systems. Swine may develop neurologic lesions; however, the signs of poliomyelomalacia are quite distinct from those described as "blind staggers" by early workers. The most characteristic signs of chronic selenosis are hair and hoof loss; however, other, less specific, damage to the immune system and reproduction are economically more important. Given the numerous interactions of chronic Se with other dietary factors, it is very important to examine the whole environment when dealing with a potential selenosis case.