Dose-response effects of long-acting injectable vitamin B₁₂ plus selenium (Se) on the vitamin B₁₂ and Se status of ewes and their lambs

Abstract

AIM: To determine the effect of increasing doses of long-acting injectable vitamin B₁₂ plus selenium (Se) given pre-mating on the vitamin B₁₂ and Se status of ewes and their lambs from birth to weaning.

METHODS: Four groups of 24 Poll Dorset ewes each were injected 4 weeks pre-mating with different doses of a long-acting vitamin B₁₂ + Se product, containing 3 mg vitamin B₁₂ and 12 mg Se per ml. The treatment groups received 5 ml (15 mg vitamin B₁₂ + 60 mg Se), 4 ml (12 mg vitamin B₁₂ + 48 mg Se), 3 ml (9 mg vitamin B₁₂ + 36 mg Se), or no vitamin B₁₂ or Se (control). Twelve of the twin-bearing ewes per group were selected for the study. Efficacy of the product was evaluated from changes in the concentrations of vitamin B₁₂ in serum and liver, and of Se in blood, liver and milk in the ewes during gestation and lactation, and in their lambs from birth to weaning. Pasture samples in paddocks grazed by the ewes and lambs were collected at about 2-monthly intervals from 200-m transects.

RESULTS: The flock was Se-deficient, as the mean initial concentration of Se in the blood of ewes was 182 (SE 20.3) nmol/L. Compared with untreated controls, all doses significantly (p<0.01) increased concentrations of Se in the blood of ewes for at least 300 days. Selenium concentrations in milk were likewise increased throughout lactation, as were those in the blood and liver of lambs. The mean concentration of vitamin B₁₂ in the serum of ewes was initially > 1,000 pmol/L, but this decreased within 28 days to <460 pmol/L. Treatment with the 5-ml and 4-ml doses raised serum vitamin B₁₂ concentrations of ewes for at least 176 days (p<0.01), while their lambs had significantly greater concentrations of vitamin B₁₂ in serum and liver for less than 37 days after birth. Tissue concentrations and duration of elevation of both vitamin B₁₂ and Se were proportional to the dose administered. The mean concentrations of Se and cobalt (Co) in the pastures were 32 and 74 µg/kg dry matter (DM), respectively.

CONCLUSIONS: Injecting ewes from a Se-deficient flock 4 weeks prior to mating with 48 or 60 mg Se and 12 or 15 mg vitamin B₁₂ increased and maintained the Se status of ewes for at least 300 days, and of their lambs from birth to weaning. The vitamin B₁₂ status of ewes was increased for at least 176 days and that of their lambs for less than 37 days. Due to the proportional nature of the response to increasing dosage, the dose rate of the formulation tested can be adjusted according to the severity of Se and Co deficiency in a flock.

CLINICAL SIGNIFICANCE: A single subcutaneous injection of vitamin B₁₂ + Se administered pre-mating to Se-deficient flocks is likely to prevent Se deficiency in ewes and their lambs until weaning, as well as increase the vitamin B₁₂ status of ewes and their lambs until 5 weeks after lambing.

KEY WORDS:

• Ewes
• lambs
• long-acting
• subcutaneous injection
• selenium
• vitamin B₁₂
• blood
• liver
• milk

Acknowledgements

We are grateful to John Parr, Simon Green, Matthew Deighton, and Peter Schreurs, all of AgResearch Ltd, for their excellent technical assistance.

Notes

¹ R Ellison, Gribbles-Alpha Diagnostic Laboratory, Hamilton, New Zealand