Low release of selenium from recovered ruminal pellets

4.3 Oral Treatment of Trace Element Deficiencies in Ruminant Livestock

Oral treatment of trace element deficiencies of livestock has a long although not always distinguished history. It has generally been the method first employed following the discovery of a trace element deficiency. Thus, Robert Fraser (1794) used oral dosing with soil to counteract the effects of cobalt (Co) deficiency in sheep; Hunter, Eden and Green (1945) dosed ewes with copper (Cu) for the control of swayback; McLean, Thomson and Claxton (1959) obtained significant growth responses following selenium (Se) supplementation of unthrifty lambs and Dynna and Havre (1963) used oral dosing with zinc (Zn) as part of the treatment of cattle suffering from a combined Zn-Cu deficiency in Northern Norway.

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.

The influences of dietary intakes and supplementation with selenium and vitamin E on reproduction diseases and reproductive efficiency in cattle and sheep

Retained placenta, endometritis, cystic ovaries and low conception rates are often considered as interconnected conditions in cattle. Wide ranges in amounts of selenium and vitamin E supplements have been advised in late-pregnancy diets and, frequently, they can be synergistically beneficial. Animals at grass or with other green foods should be of adequate vitamin E status, but dietary selenium deficiencies are both more frequent and severe. Selenium status is important for super-ovulation in cattle and multiple births in ewes because of its importance in sperm transport and establishment of ova. However, the potential toxicity of selenium-enriched feed supplements restricts their use on a free-access basis. Giving sodium selenite or selenate by injection provides only a short-term response in the plasma. Barium selenate given in oil by injection provides a more durable response but has potential tissue residue problems. Compressed metallic selenium powder with iron powder in high-density reticulo-ruminal pellets gives sustained release, but uncertainties regarding possible surface coating and the variable effects of selenium particle size may require additional grinders to ensure prolonged release. Neither reticulo-ruminal pellets of such composition nor barium selenate by injection may be used worldwide because only sodium selenite and selenate have general regulatory approval. A sustained-release multi-trace element/vitamin rumen bolus system effective for several months has increased lambing percentages in ewes, and increased herd conception rates and reduced the spread of calving for herds of beef cattle.

Long-acting selenium treatments for sheep

An intraruminal selenium (Se) pellet and a subcutaneous depot of barium selenate, equivalent to 1.6 mg Se/kg body weight, were each effective in maintaining increased blood Se concentrations for at least 200 weeks in ewes at pasture. These treatments given to the ewes 23 to 26 weeks before lambing increased the Se status of their lambs for 4 to 6 months.

Intraruminal selenium pellet for control of nutritional muscular dystrophy in cattle

Administration of an intraruminal selenium pellet to a herd of pregnant crossbred cows was evaluated for controlling nutritional muscular dystrophy in an area of northern Ontario with numerous losses of calves. Cows were winter-fed grass silage. Each spring cows and calves went to pasture. A single dose of intraruminal selenium pellet was given to 80 cows during last 3 mo of pregnancy the 1st yr only while the remaining 80 were controls. During 3 consecutive years, efficacy of intraruminal selenium pellet was evaluated by selenium status of recipient cows and their offspring as well by the incidence of nutritional muscular dystrophy. Selenium in plasma, as well as glutathione peroxidase in whole blood, in the cows administered intraruminal selenium pellet, were higher than in the deficient controls. Ten months after intraruminal selenium pellet treatment, selenium in tissues was higher in treated than in untreated cows but within normal ranges. Before cows were turned out to pasture the 1st yr, milk selenium of intraruminal selenium pellet cows were higher than controls. This technique of selenium dosing was effective in raising the selenium status of the progeny. There was no evidence of nutritional muscular dystrophy in calves from selenium-dosed cows, while 15 calves born of the untreated cows showed clinical symptoms of nutritional muscular dystrophy.