A review of selenium deficiency in grazing ruminants. Part 2: towards a more rational approach to diagnosis and prevention

ESTIMATING SELENIUM STATUS: Although the importance of selenium in ruminants has been recognised for over 30 years, problems associated with selenium deficiency are still frequently identified in grazing livestock operations. There is a growing diversity of tools available for the management of selenium deficiency giving rise to diagnostic and therapeutic dilemmas for the veterinary practitioner. There is no single test for selenium adequacy which can be considered superior in all diagnostic situations because the method of choice depends on the objective of the testing procedure. REFERENCE RANGES: Reviewing the available data, the current New Zealand reference ranges for selenium concentrations in ruminant tissue and feed appear valid. CLINICAL RELEVANCE: Management of selenium deficiency will continue to be important in grazing ruminants. Practising veterinarians should be familiar with the appropriate use of tests for selenium deficiency. Advice should be based on micronutrient analysis of animal tissue, defensible reference ranges backed by production response data, and supplementation programmes which optimise the return on investment.     

Selenised compressed salt blocks for selenium deficient sheep

Salt blocks containing 30 or 120 ppm selenium were tested as the sole supplement for sheep farmed in a selenium-deficient area of New Zealand (Te Anau). Both concentrations were unsatisfactory in preventing selenium deficiency. In five trials using 120 ppm Se salt, the highest percentages of sheep found to be deficient were 31% (lambs) and 32% (ewes). If sheep which were classed as marginally deficient were included these percentages became 63% (lambs) and 56% (ewes). Some instances of selenium-responsive unthriftiness in lambs were encountered, and in one trial there was the possibility of selenium-responsive infertility having contributed to the low lambing performance of the ewes. There was no evidence of white muscle disease. Selenium levels in the liver and kidney were well below the permitted maximum. Because selenised salt failed to eliminate selenium deficiency, its use as a sole supplement for sheep grazing selenium deficient pasture is not recommended.     

Alpha-tocopherol, selenium and polyunsaturated fatty acid concentrations in the serum and feed of spring-calving dairy heifers

The objectives of this study were to provide baseline data for alpha-tocopherol, selenium and polyunsaturated fatty acid concentrations in the serum and feed of New Zealand dairy cattle, and to assess the likelihood that abnormal peroxide metabolism has a role in the impaired lactational and reproductive performance noted in selenium-deficient cattle. Twenty-four Friesian heifers were randomly allocated one of four winter diets consisting of hay with or without selenium supplementation, or pasture and silage with or without selenium supplementation. A winter diet consisting exclusively of hay (alpha-tocopherol concentration 19 mg/kg of dry matter) resulted in a pre-calving serum alpha-tocopherol concentration of 1.2 mg/l compared to 4.5 mg/l for pastured heifers (p<0.01). The pre-calving alpha-tocopherol concentration for the heifers fed hay fell into the range considered deficient (<2.0 mg/l), whereas heifers fed pasture and silage remained in the range considered adequate throughout the study period. Serum fatty acid concentration, and the proportion of fatty acids that were polyunsaturated, were lowest in the hay-fed heifers before calving (1.0 mg/ml, 37.1% respectively), and remained unchanged following re-introduction to pasture after calving in late July and August. Serum fatty acid concentration did not increase following the re-introduction of the heifers to pasture because of the unexpectedly low fatty acid concentration (4.8 g/kg of dry matter) of the mature winter pasture. In October, however, the proportion of fatty acids in serum that were polyunsaturated increased (50%) as did serum cy-tocopherol concentrations (greater than 13 mg/l). Mean serum selenium concentrations in the unsupplemented heifers ranged from 139 to 204 nmol/l, being lowest in October (p<0.01). Supplementation with intraruminal selenium pellets (two pellets delivering about 3 mg of selenium/day) increased serum selenium concentration and glutathione peroxidase activity (p<0.01) whereas the type of winter diet had no effect (p>0.05). These results suggest that dairy cattle wintered on hay can become Vitamin E-depleted, whereas the feeding of pasture and silage should provide adequate Vitamin E. The pasture offered following calving during July and August provided a low dietary polyunsaturated fatty acid challenge, suggesting that abnormal peroxide metabolism is unlikely to be an important mechanism in the impaired performance of selenium-deficient adult cattle which calve at this the of year.     

微量元素硒在公猪营养和繁殖中的生理作用

硒通过参与硒蛋白的合成在猪营养中发挥重要作用。硒蛋白是调节体内抗氧化系统的中心,其中谷胱甘肽过氧化物酶是猪抗氧化功能研究最多的硒蛋白。但其他硒蛋白在公猪精液生产和维持精液质量中也有重要作用。公猪精液的特点是含有大量易氧化的长链多不饱和脂肪酸,需要有效的抗氧化防御。猪对硒的需求因环境和其他条件的不同而不同,同时处于繁殖期的公猪对硒缺乏特别敏感,因此,满足硒的需求具有重要意义。但在许多情况下,原料中硒水平没有精确定量,很难判断基础日粮是否缺乏硒。本文对目前市面上的硒来源及其对公猪营养和繁殖的生理作用进行综述,旨在为生产上有效利用硒提供理论依据。 [关键词]硒;营养;繁殖;公猪;生理作用     

Serum selenium concentrations and glutathione peroxidase activities in cattle grazing forages of various selenium concentrations

In cows from 15 dairy herds (n = 210), serum selenium (Se) concentrations ranged from 0.021 to 0.789 microgram/ml, whereas 0.05 to 0.40 microgram/ml is the reported range for adequate serum Se concentrations in cattle. Serum Se concentrations of dairy cattle appeared to follow a geographic distribution pattern. On the basis of herd mean serum Se concentrations, adequate serum Se concentrations were found in cattle from only 1 of 5 herds grazing forage in the geographic area classified as Se deficient for cattle. Adequate mean serum Se concentrations were found in cattle from 4 of 5 herds located in geographic areas described as having variable forage Se concentrations (Se-marginal areas). Of the 10 herds from these 2 areas, there were only 2 herds in which 95% of the cattle had serum Se concentrations in the Se-adequate range (0.05 to 0.40 microgram/ml). In 2 selected neighboring farms in the Se-deficient area, cattle in 1 herd had adequate serum Se concentrations and cattle in the other herd had less than adequate serum Se concentrations (less than 0.05 microgram/ml). Therefore, more cattle are at risk of developing Se-deficiency disease than is commonly believed and forage of neighboring farms may have different Se concentrations. Serum Se concentrations (up to 0.789 microgram/ml) correlated with glutathione peroxidase enzyme activity; this serum Se concentration (0.789 microgram/ml) is approximately 6.2 times higher than previously reported in dairy cattle. Therefore, RBC glutathione peroxidase activity may be useful in determining the diagnosis of chronic Se toxicosis.     

Blood selenium concentrations of sheep and goats from selected areas of Kenya

A systematic mapping technique based on blood, forage and soil selenium levels was employed to locate areas of selenium deficiency, adequacy or excess in areas of Kenya where grazing of small ruminants predominates. A total of 1,478 blood samples from both sheep and goats, 180 forage samples and 90 soil samples were analysed for selenium levels. During the wet seasons 28% of the sheep and 15% of the goats had marginal to deficient blood selenium concentrations while during the dry season 20% of the sheep and 12% of the goats had marginal to deficient blood selenium concentrations. Forage samples had a range of 0.03 to 0.66 ppm selenium while soil samples had a range of 0.06 to 0.98 ppm selenium. Although many animals had blood selenium levels of less than 0.05 ppm, below which selenium deficiency signs might occur, none of the animals manifested these signs.     

AN EXAMINATION OF THE SELENIUM NUTRITION OF SHEEP IN VICTORIA

The selenium nutrition of sheep throughout Victoria was assessed by a survey of the blood glutathione peroxidase activity in 708 flocks. It was shown that the blood glutathione peroxidase activity in sheep had a seasonal variation with lowest levels in the spring. The enzyme activity was correlated with the blood selenium concentration. Areas where blood selenium was less than 0.03 μg/ml in spring were defined. Sheep with low selenium nutrition were grazing pastures in the high rainfall areas on acid soils, particularly those derived from granite.
Selenium concentrations in pasture samples examined were greater than 0.02 mg/kg, and it was found that superphosphate application had no significant effect on the selenium content of pasture. However, management practices such as high stocking rates and rates of application of superphosphate to pasture were associated with low blood glutathione peroxidase activities in sheep.
It was concluded that the selenium nutrition of most of the sheep flocks in Victoria is adequate, and that the deficient areas are localised. There seems little requirement for supplementation of adult sheep. As the delayed type of white muscle disease in spring lambs appears to be the main selenium-responsive disorder, direct supplementation of lambs in the low selenium areas would be the most effective method of ensuring adequate selenium nutrition.     

Comparison of selenium levels and glutathione peroxidase activity in bovine whole blood.

Blood glutathione peroxidase activity and selenium levels were found to correlate well, indicating that glutathione peroxidase activity can be used to assess blood selenium levels in beef cattle. The glutathione peroxidase activity of blood is less stable than is the selenium concentration but when blood was stored at 4 degrees C, the glutathione peroxidase activity remained constant for seven days.     

Depot injection of barium selenate for long-term prevention of selenium inadequacy in beef cattle

In southern Australia, cattle at risk from selenium (Se) deficiency can be given an oral dose of supplements that are effective in maintaining adequate Se status for between 9 and 12 months. The present study was undertaken to assess the duration of the effect of parenteral barium selenate (BaSe) in raising the Se status of cattle at pasture in an area of marginal Se deficiency. The BaSe was given subcutaneously to Hereford heifers, using an 18-gauge needle. Cattle had regular blood sampling to assay Se, from 8 days before dosing to 1155 days afterwards. Results show that a single injection of BaSe was effective in elevating blood and plasma Se concentrations to normal values for at least 2 to 3 years, when given to beef cattle of low normal Se status. We suggest that a prophylactic dosage of 0.5 mg Se/kg body weight as BaSe should be given every 2 years to prevent Se inadequacy in beef cattle grazing pasture of marginal Se content.     

Seasonal variation in selenium status of different classes of grazing goats in a semi-arid region of Pakistan

The selenium status of three different classes of goats ((i) female lactating, (ii) female non-lactating, and (iii) male goats) grazing semi-arid pasture in the southern part of the Punjab province, Pakistan and that of selenium concentration of soil and dietary sources, ingested by those animals were investigated during two different seasons of the year (winter and summer). Soil, forage, feed, water from the pasture and blood plasma, urine, faeces, and (if applicable) milk from these goats were collected fortnightly. The samples were analyzed for selenium concentrations. Soil selenium showed both seasonal and sampling periods effect on its concentration while forage selenium was affected only by the seasonal changes. No significant effect of seasons or fortnights on feed selenium level was observed. In fecal samples selenium concentration in lactating and non-lactating and plasma of male goats were affected by sampling periods. While fecal selenium in male goats showed significant effect on its concentration both seasonal and within fortnights. Severe deficient level of soil selenium during both seasons and marginal deficient level of forage selenium during summer were observed. Selenium concentrations in feed slightly exceeded the requirements of ruminants in feed during both seasons of the year. Plasma selenium concentrations in all goat classes were higher in winter than that in summer showing no seasonal or fortnight variation and its concentration was slightly lower in lactating goats as compared to other classes. On the bases of these results, it is concluded that overall selenium status of the goats based on plasma selenium concentration may be considered adequate mainly due to the mineral supplement provided all over the year, since soil and forage selenium concentrations were low to deficient.     

The effect of copper on the response of lambs to selenium supplementation when grazing a selenium deficient pasture

Two trials were undertaken with lambs grazing selenium deficient pasture to determine if copper would enhance liveweight and fleece-weight responses to selenium supplementation. In the first trial, lambs given selenium or selenium plus copper gained significantly more weight and had higher fleece-weights after 260 days than did control lambs or lambs given copper alone. Copper given alone or together with selenium had no significant effect on liveweight or fleece-weight when compared with control lambs and lambs that were given selenium alone respectively. This finding was confirmed in a second trial when growth and fleece-weights of selenium and selenium plus copper treated lambs were compared and no significant differences found. In both trials copper significantly raised liver copper levels. In selenium supplemented but not in selenium deficient sheep, copper significantly increased blood selenium levels.     

Absence of a weight gain response to Vitamin B12 supplementation in weaned dairy heifers grazing pastures of marginal cobalt content

AIM: To obtain information on serum and liver vitamin B12 and urinary methylmalonic acid concentrations as diagnostic tests to predict a weight gain response to supplementation with vitamin B12 in young dairy cattle when grazing pasture of low cobalt content. Methodology. Forty dairy cattle (12 Friesian, 14 Friesian x Jersey and 14 Jersey) were allocated to two equal sized groups, treated and untreated, based on liveweight. At monthly intervals for 14 months, all animals were weighed, their serum and urine sampled, their liver biopsied and the pasture sampled from the paddocks they were grazing and going to graze. Serum and liver were assayed for vitamin B12 concentrations. For the first 5 months of the trial, urine was assayed for methylmalonic acid concentrations. Both washed and unwashed pasture samples were assayed for cobalt concentrations. RESULTS: No weight gain response occurred vitamin B12 supplementation in young growing cattle grazing pasture with a cobalt concentration of 0.04-0.06 mg/kg DM. For 5 months of the trial, liver vitamin B12 concentrations from untreated calves were in the range 75-220 nmol/kg and serum vitamin B12 concentrations were as low as 72 pmol/1. There was no associated growth response to supplementation. CONCLUSION: Further trials involving young cattle grazing pastures with cobalt concentrations less than 0.04 mg/kg DM are required to reliably determine liver and serum vitamin B12 concentrations at which growth responses to vitamin B12 or cobalt supplementation are likely under New Zealand pastoral grazing conditions.     

Relation between selenium content and glutathione-peroxidase activity in blood of cattle

To identify a simple method for assessing the selenium demand in cattle, the relationship between selenium content in whole blood and the concentration of the selenium containing enzyme glutathione peroxidase (EC 1.11.1.9; GSH-Px) in red blood cells was studied. On six farms with suspected low soil selenium content, blood samples were collected from groups of calves, yearlings and adults at the end of the housing period and of the grazing period. The data obtained showed a highly significant correlation between the parameters mentioned: GSH-Px (U/g Hb) = 3.261 * Se (micrograms/kg) - 40.553. In growing animals there was a decline in Se supply with age, followed by a gradual recovery in heifers. This was most pronounced on some sandy soils and on peat soil. Seasonal effects could not be demonstrated.     

The biological selenium status of livestock in Britain as indicated by sheep erythrocyte glutathione peroxidase activity.

The reliability of erythrocyte glutathione peroxidase activity as an indicator of selenium status in livestock is discussed. Based on this measurement, a survey is described of the biological selenium status of sheep on each of 329 farms in Britain. Results showed that 47 per cent of these farms were probably unable to provide grazing livestock with sufficient selenium to maintain blood levels greater than 0.075 microgram per ml. Increased selenium deficiency from the increasing use of home grown feeds as a major constituent of livestock rations may be causally related to the increase of white muscle disease and other selenium responsive diseases in Britain.     

The relationship of erythrocyte glutathione peroxidase to blood selenium in swine

The erythrocyte glutathione peroxidase activity and blood selenium have been investigated in swine fed a Se deficient diet with, and without, selenium supplementation. A highly significant correlation (r = 0.90) between erythrocyte glutathione peroxidase and blood selenium was found.     

Serum glutathione peroxidase activity and blood selenium in pigs

Blood serum glutathione peroxidase activity and blood selenium concentration were measured in blood samples from pigs subjected to experimentally induced selenium deficiency and dietary selenium supplementation on graded levels. A highly significant correlation between blood selenium and serum GSH-Px activity in pigs, especially in selenium deficient pigs, was demonstrated. There was also a strong relationship between blood selenium concentration and serum GSH-Px activity in pigs receiving dietary selenium at graded levels. Serum GSH-Px activity exhibited an excellent close-response relationship to dietary selenium. Linear regression analysis showed that the increased serum GSH-Px activity was a function of the dietary selenium concentration. The fitness of serum in monitoring slight changes of the selenium status of pigs with help of the estimation of GSH-Px activity was discussed. The measurement of serum GSH-Px activity seems to provide a useful and rapid means for defining selenium requirements and for identifying selenium deficiency in growing pigs.     

Selenium deficiency of beef cattle in Idaho and Washington and a practical means of prevention

The majority of beef cattle assayed for whole blood glutathione peroxidase (GSH-Px) activity in Idaho and Washington were deficient in selenium. Cattle in the more arid sections of these states tended to have higher selenium levels than those in areas with moderate and high rainfall. Animals pastured on irrigated forages had lower selenium concentrations than those grazed on dry land pasture. Cattle were supplemented by the addition of sodium selenite to a salt-mineral mixture. Ninety mg selenium per kg (ppm) salt-mineral mix fed to cattle significantly (P less than 0.001) elevated selenium (GSH-Px) levels well into normal ranges by 3 months when fed to extremely selenium deficient animals. Thirty ppm selenium was insufficient to raise GSH-Px levels into normal ranges. In addition, 20 ppm selenium was insufficient to sustain blood selenium concentrations of selenium adequate animals. Selenium given in the salt-mineral mix provided an effective, economical, and easily regulated source of dietary selenium. This supplement can be provided the entire year even under range conditions. Calves of cows placed on the 90 ppm selenium supplement had significantly (P less than 0.005) improved weaning weights (10 months) and an indication of a decreased incidence of infectious diseases.     

喀斯特山区草地施肥对放牧乌蒙半细毛羊抗氧化系统功能的影响

为选择草地施肥的肥料种类,减少施肥对乌蒙半细毛羊产业的影响,在威宁县凉水沟种羊场多年生人工草地开展施肥和放牧试验。 结果表明:凉水沟种羊场人工草地牧草铜含量相对较低,但仍高于乌蒙半细毛羊营养需要标准;施肥极显著增加牧草氮含量(P<0.01),各施肥处理之间没有明显差异。硫酸铵施肥显著增加牧草硫和锌含量(P<0.01),显著降低了牧草硒的含量(P<0.01)。放牧试验结束时,施硫酸铵草地的乌蒙半细毛羊血液中铜、铁和硒的含量极显著低于施硝酸铵草地和对照组(P<0.01), 动物血液锌和硫含量极显著高于硝酸铵施肥牧场和对照组(P<0.01)。硫酸铵施肥牧场的乌蒙半细毛羊血红蛋白、红细胞压积容量极显著低于硝酸铵施肥牧场和对照牧场(P<0.01),血清铜蓝蛋白含量、血清超氧化物歧化酶活力、血清谷胱甘肽过氧化物酶活力和血清过氧化氢酶等抗氧化酶的活力极显著低于硝酸铵施肥牧场和对照牧场(P<0.01),丙二醛的含量显著高于硝酸铵施肥牧场和对照牧场(P<0.01)。血液其他矿质元素和血液指标及血清生化值在2个施肥处理和对照之间均差异不显著。 因此得出结论,草地施肥的种类需要根据土壤矿物质分布和含量情况确定,铜含量低的牧场不适合硫酸铵施肥,硫酸铵施肥明显影响了乌蒙半细毛羊机体抗氧化系统功能。     

The efficacy of intraruminal pellets composed of elemental selenium and iron in sheep

Commercial selenium pellets, manufactured after CSIRO workers drew attention to the significance of grain size on the rate of release of selenium, were tested in 27 sheep grazing a low-selenium New Zealand pasture. The pellets were shown by microscopy to contain mainly 10-20 pm particles of selenium, often agglomerated into larger lumps. There was a considerable variation in the length of time pellets maintained blood selenium levels above the deficiency level of 250 nmol/e (20 microg/l). Whereas four animals given pellets had blood levels below 250 nmol/l after only 343 days, two animals had levels of 375 and 400 nmol/l after 651 days when the level in control sheep was 125 +/- 32 nmol/l. The pellets were recovered from all but one animal and had varying degrees of surface coating which was assumed to be mainly calcium phosphate. Two pellets recovered from sheep at 386 and 484 days, when blood selenium levels were 175 and 1813 nmol/l respectively, were sectioned and examined by light and electron microscopy. Both pellets still contained unreacted selenium but differed in the degree of surface coating. The pellet recovered at 386 days had a solid and continuous coating whereas the coating on the pellet recovered at 484 days was not continuous and consisted of an open lattice of interlocking needles. It appears that it is the extent of this coating which limits the effective life of the pellet in sheep.     

微量元素铜在反刍动物生产中的应用研究进展

铜在反刍动物体内有着非常重要的作用,它是维持反刍动物机体正常生理功能、生化代谢及生长发育所必需的微量元素,很多依赖于铜的酶在机体内发挥着重要作用,青藏高原的牧草由于冷季缺乏铜而导致放牧家畜容易出现铜缺乏症状,影响放牧家畜的生长及生产性能的提高,为此需要给放牧家畜补充一定量的铜,但是铜在反刍动物体内的吸收率较低且受到很多因素的影响,可以通过研究这些因素来提高铜的吸收效率,以避免对环境造成污染。铜可以促进瘤胃微生物生长,提高产气量和能量利用效率来提高瘤胃发酵效率和营养物质消化率,还可以提高反刍动物免疫功能和抗氧化性能,最终铜可以提高反刍动物的生产性能,不同反刍动物或者相同反刍动物在不同的生理阶段对铜的需要量不一致,在添加铜时要按照营养需要量结合生产实际添加,以提高铜的添加效率。文章综述了铜吸收及影响因素、铜对反刍动物瘤胃发酵、营养物质消化率、免疫功能、抗氧化性能、生产性能的影响,旨在为铜在反刍动物生产中科学应用提供借鉴和参考。