Ársrit Ræktunarfélags Norðurlands - 01.01.1972, Blaðsíða 44

The object o£ this investigation was to determine the necessary level
of potassium in Icelandic hay (the main ruminant feed in Iceland), in
particular for feeding high yielding cows.
Five cows, at the time of their second calving, were used for the
work. Two of them (nrs. 12 and 25) received hay containing a normal
level of potassium (1,66% K in dry matter). The other three (nrs. 11,
32 and 2), received low potassium hay (1,16% K in DM). One of the
latter (nr. 2) was fed supplementary potassium, amounting to about
40 g K per day when it reached its peak milk yield. As well as rec-
ording feed intake and milk yield of the cows, the pH and potassium
and sodium concentration of their urines were determined morning
and evening.
The main results were os follows:
1. Under the condition of the experiment, potassium deficiency was
observed in cows fed 116—134 g K per day and yielding 25—31 kg
of milk per day; but this was not found with those fed 156—211 g K
per day and yielding 21—28 kg milk per day.
2. Those cows receiving only the low potassium diet (nrs. 11 and 32),
lost their appetites 9—13 days after calving. Their hay intakes also
decreased and the milk yields declined considerably.
3. The other cows (nrs. 12, 25 and 2) showed normal lactation curves
and did not lose their appetites.
4. The potassium concentration and pH of the urines from the cows
on the low potassium diet, were considerably depressed on and
around the period of decreased food intake.
5. It proved impossible to recover appetite and yield in those cows on
the low potassium diet, in spite of an oral dose of potassium salt,
until their diet was supplimented with a vitamin mixture and an
intramuscular dose of corticosteroids was administered.
The main conclusions were as follows:
1. The probable minimum requirement of dairy cows is thought to
be 0,8—1,0 % K in DM per day. The feeding of hay and concen-
trates, as commonly practiced in this country, therefore requires at
least 1,0% K in hay (DM) for low yielding cows and 1,5% K for
high yielding cows, assuming that the concentrates contain 0,5—0,6%
K.
2. The higher the milk yield and/or the smaller is the concentration
of hay in the total feed, the greater is the danger in feeding low
potassium hays, assuming that there are no other variables.