Stimulation of calcium absorption and reduction in susceptibility to fasting-induced hypocalcaemia in pregnant ewes fed vegetable oil

Abstract

AIM: To test the hypothesis that susceptibility to fasting-induced hypocalcaemia could be reduced by prior stimulation of the ability of late-pregnant ewes to absorb calcium (Ca) from the gastrointestinal tract (GIT) by feeding a vegetable oil supplement. The supplement was expected to decrease the availability of the Ca supplied from a pasture diet, and stimulate the animals' homeostatic system.

METHODS: Mature ewes pregnant with twins (n=28) and grazing at pasture, were randomly allocated to Treated or Control groups, 6 weeks prior to their expected date of parturition (Day 0). Treated ewes (n=14) were drenched with 25 ml soya bean oil twice daily for 3 weeks. Plasma Ca concentrations were determined on Days 0, 8, and immediately before and after a 20-hour fast that began on Day 21, which was intended to simulate the reduced feed intakes that occur on the day of parturition. An index of the ewes' ability to absorb Ca from the GIT was obtained using orally dosed strontium (Sr) as a tracer and the extent of Ca mobilisation from bone was assessed by measuring hydroxyproline concentrations in plasma before fasting on Day 21.

RESULTS: Plasma Ca concentrations were significantly higher in Treated than Control ewes after fasting (p<0.001). The Ca absorption index was also higher in Treated than Control ewes at the end of the 3-week treatment period (p=0.014), but degree of bone mobilisation assessed by concentration of hydroxyproline in plasma did not differ significantly between groups.

CONCLUSION: Susceptibility of late-pregnant ewes to fasting-induced hypocalcaemia was reduced using a soya bean oil supplement. The inclusion of one or more dietary ingredients capable of binding or forming complexes specifically with Ca in the diet of late pregnant ruminants may provide a novel, practical method of reducing periparturient hypocalcaemia.

KEY WORDS:

• Hypocalcaemia
• milk fever
• dairy cow nutrition