Abstract
The objective of this experiment was to determine the effect of dietary grain on calcium homeostasis. Six rumen-fistulated dairy cows with 3 or more previous lactations and no history of parturient paresis were randomly assigned to a sequence of diets in a crossover study with 4 periods of 10 days each. Dietary treatments were: A control ration consisting of wrap grass silage alone (1), the control ration supplemented with ammonium chloride and ammonium sulphate salt solution (2), control ration following a period with supplementation (3) and control ration supplemented with increasing amounts of barley from 4 to 10 kg/cow per day, expected to produce subclinical rumen acidosis (4). Daily intake of the diets was adjusted to 14 kg DM/cow per day. On day 11, the calcium-regulating mechanisms in cows were challenged until recumbency by a standardized intravenous EDTA infusion and cows were left to recover spontaneously. Anion supplementation and the feeding of highly fermentable carbohydrate lowered urine pH below 7.0 due to subclinical acidosis. During spontaneous recovery from EDTA induced hypocalcaemia, the cows more quickly regained a whole blood free calcium concentration of 1.00 mmol/L if they had most recently been supplemented with either anionic salts or with increasing amounts of barley, as compared to the basic ration. It is concluded that so-called slug-feeding or 'steaming up' with highly fermentable carbohydrates before parturition in milk fever susceptible cows enhanced calcium homeostasis similar to the effect seen in cows on anionic diets.
Highlights
Successful control of milk fever incidence begins with dietary management of the dry cow
The resistance to hypocalcaemia was measured by the dose needed to induce recumbency, and by Calcium Regaining Time (CRT)
Lack of variation among cows in time to involuntary recumbency entails an equal chance for each individual cow to develop hypocalcaemia manifested by paresis and recumbence as long as the EDTA infusion volume and flow rate was maintained to chelate calcium
Summary
Successful control of milk fever incidence begins with dietary management of the dry cow. The possible effect of such SRA derived systemic acidosis on calcium homeostasis at calving has not been reported, previous investigations have focused on grain or sugar feeding in relation to the occurrence of milk fever (Emery et al 1969, Erb & Gröhn 1988). The aim of this investigation was to determine whether systemic acidosis, induced by increasing daily intake of highly fermentable carbohydrate, may have any regulating effect on calcium homeostasis as monitored by an EDTA infusion challenge to acutely bind calcium to mimic the calcium drain produced by the mammary gland at the onset of lactation. The standardized intravenous Na2EDTA infusion test and the judging criteria were adopted from Mellau et al (2001)
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