Abstract
The exchange of calcium and inorganic phosphate between the
blood and the tissues of cattle was briefly reviewed and an
attempt made to state these exchanges in quantitative terms. It
was suggested that the heavily milking cow depends on 2 continuous
absorption of calcium from the alimentary tract and that
interference with calcium absorption of even a few hours duration
might lead to hypocalcaemia. To test this suggestion, the
alimentary activity and milk yield of calving cows were observed
daily and related to changes in the concentrations of calcium and
inorganic phosphate in the serum and blood. Alimentary activity
was assessed by observing feed intake, faecal output, rumen sounds
end rumen movements. Also, cows were injected with sodium oxalate
or hyoscine hydrobromide to study the effect of hypocalcaemia on
alimentary activity or of alimentary stasis on serum calcium and
blood inorganic phosphate ooncentrations.
Old cows at calving were found to give more milk during the
first forty-eight hours of lactation than young cows and at the same
time the food intake of old cows was greatly reduced. This change
in food intake tended to precede any severe change in blood calcium
levels. Artificially induced hypocalcaemia did not appear to affect
alimentary activity but a hyoscine injection produced stasis of the
alimentary tract in an old heavily milking cow, hypocalcaemia,
hypophosphataemia end clinical symptoms resembling those of milk fever.
The changes in glucose :4-1 citric, lactic and pyruvic acids
in the blood of calving caws were also observed, but it was concluded
that these changes wer) not closely related to the changes in the
concentrate of calcium and inorganic phosphate in the serum and
blood. The absorption of calcium, magnesium, inorganic phosphate
and citric acid in conscious sheep, as estimated by a portal veno
arterial technique, were also studied, with a view to developing a method for oetimating the absorption of nutrients in calving cows
on an hourly basis. A method of preventing hypocalcaemia by
injecting secondary calcium phosphate intraperìtoneal].y was tested
in sheep.
In a search for factors which might precipitate low calcium
and inorganic blood of calving cows, cow plasma was transfused into lambs and posterior pituitary hormones
were administered, to cattle and sheep. The plasma phosphate levels
in lambs were depressed twelve to twentyfour hours after transfusing
plasma of low phosphate con.,et taken from cows before or at calving
or from cows with milk fever. Lftiniatering purified oxytocic
principle to sheep sensitised with oestrogen immediately depressed
the arterial blood levels of calcium and inorganic phosphate and produced
evidence of interference with nor-1 absorption processes, as estimated by a hepatic veno.arterial technique.