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Biomedical subjects

A D Sheppard

Publications and source records attributed to A D Sheppard.

12 recordsLinked to original sources
PubMed1988

The retention and efficacy of soluble-glass boluses for providing selenium, cobalt and copper to sheep.

The efficacy and retention of prototype and commercial (Cosecure) soluble-glass boluses containing selenium, cobalt and copper and having a similar size, density and composition were evaluated in separate 12-month trials with sheep grazing low selenium pastures but with adequate cobalt and copper levels. In both trials, sheep confirmed by X-ray as containing a bolus grew at a significantly greater rate than control sheep. This was attributed to the correction of a selenium deficiency. Although liver copper, and liver and serum vitamin B12 levels were significantly greater in treated sheep than controls on some occasions, the differences were not as great or consistent as with blood selenium levels. The rate of bolus loss was high and in both trials, approximately 40% of the sheep had lost the bolus after 6 months. No prototype boluses were present after 12 months. Intact Cosecure boluses were recovered from 3 sheep out of 30 after 12 months whilst one animal contained a part bolus. The recovered boluses were approximately 45% lighter than when originally administered. Bolus loss did not appear to be due to complete dissolution. In sheep which had lost the bolus, blood selenium levels fell with a half-life of 43 +/- 10 days.

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PubMed1988

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.

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PubMed1983

Failure of orally administered zinc to prevent experimentally induced footrot in sheep.

Two groups of adult Merino sheep, initially grazed on pasture, were dosed daily with zinc sulphate (1 mg Zn/kg LW) or zinc oxide (15 mg Zn/kg LW) for six and seven weeks, respectively. On the 18th day, both groups were transferred to indoor pens together with unmedicated control sheep, and five days later the feet of all animals were infected artificially with a virulent strain of Bacteroides nodosus. By the fourth week after challenge, 85% or more of the feet challenged had developed advanced footrot, and no significant differences in the incidence and severity of lesions between dosed and un-dosed groups were recorded. Plasma zinc concentrations, monitored throughout the experiment, remained at similar levels in sheep receiving the lower dose rate and in the controls. At the higher dose rate, plasma zinc levels increased till Day 23, but thereafter declined to values comparable to those of undosed animals. At post mortem, no evidence of zinc toxicosis was found, and only the kidneys of sheep receiving the higher dosage showed a significant accumulation of zinc compared with the controls.

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PubMed1983

Selenium in New Zealand pastures.

In grasses and clovers the highest concentrations of selenium were found in the leaves. The selenium content of different species in spring pastures on the same soil type did not vary widely although the slower growing and more deeply rooting species contained higher levels. The concentration of selenium in a pasture varied with time of the year, the lower levels being usually associated with conditions that stimulated rapid growth of the herbage, although factors other than growth rate were also involved. Lucerne appeared to be unusual in that in some areas it accumulated much higher levels of selenium than was found in other associated species. A very wide variation in levels of selenium in pastures growing on different soils has been observed 3-1500 ng/g). Selenium-responsive unthriftiness in grazing lambs occurred where the selenium content of spring pastures was <20 ng/g. Pastures containing >30 ng/g were apparently adequate while intermediate levels were probably marginally deficient.

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PubMedDate not supplied

Changes in blood levels of zinc, copper, selenium, glutathione peroxidase, vitamin B12 and total and free thyroxine in sheep removed from pasture and held without food for 50 hours.

Blood was collected from a group of ten sheep immediately after removal from pasture and thereafter at regular intervals for 50 hours whilst maintaining them without food but with adequate water. The samples were analysed for parameters normally examined as an aid to the diagnosis of zinc, copper, selenium, cobalt and iodine status. Serum vitamin B12 levels increased with time. Mean plasma zinc concentrations and mean serum concentrations of both T4 and fT4 followed significant parabolic trends. Maximum mean zinc levels (50 +/- 10% higher than initial values) were recorded after 30 hours. T4 and fT4 levels peaked at approximately 26 hours. Zinc levels at two hours were 20 +/- 5% lower than the initial values. Whole blood copper, selenium and glutathione peroxidase levels did not change significantly with time the largest differences were 11 +/- 6%, 5 +/- 4% and 10 +/- 8% respectively.

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