Íslenskar landbúnaðarrannsóknir - 01.09.1969, Síða 87

TILRAUNIR MEÐ MJÓLKURKÝR 85
S U M M A R Y
GRAZING EXPERIMENTS WITH DAIRY COWS
IN LAUGARDÆLIR 1958-1961
Kristinn Jónsson and Stefán Aðalsteinsson
Agricultural Research Institute, Reykjavik, Iceland
In the years 1958—1961 eight grazing experiments with dairy cows were carried
out at Laugardælir in Iceland.
In 5 experiments the effect of feeding concentrates to cows on cultivated
pasture on their yield and live weight was investigated. In 3 experiments the
effect of protection coats to the cows was studied, in 2 experiments the effect
of hay versus marrow stem kale as supplement to autumn pasture was studied,
in one experiment cultivated pasture was compared with uncultivated pasture,
in one experiment marrow stem kale grazing was compared witli grazing on
cultivated grassland, and in one experiment the effect of different mineral
supplement mixtures and of feeding concentrates to cows on uncultivated pasture
was studied.
Chemical analyses were carried out on a large number of grass samples from
cultivated and uncultivated pasture.
Feeding concentrates to cows on cultivated pasture produced in no instance
any significant increase in milk yield or live-weight. Concentrate supplement
to uncultivated pasture significantly increased yield in one experiment.
Protective coats showed either no advantage or proved deleterious to milk
yield, and had no effect on live weight.
Marrow stem kale proved to he a better supplementary feed than hay to cows
on cultivated autumn pasture. In the first experiment the advantage was 0.82
kg milk per day (P > 0.05) and in the second year 1.20 kg (P < 0.05). This diff'er-
ence can be ascribed to greater feed unit intake in the marrow stem kale group.
Uncultivatecl pasture gave significantly lower daily yielcl than cultivated
pasture in one trial. Concentrate supplement seemed beneficial on uncultivated
pasture.
Grazing of a marrow stem kale field in addition to cultivated pasture gave
a significantly higher daily milk yield and higher live-weight gain than either
cultivated pasture alone or cultivated pasture plus concentrate supplement.
The state of health of the cows in these experiments was generally poor. No
direct connection could be demonstrated between the health of the cows and
the various mineral supplement mixtures.
The crude protein content of the grass from the cultivated pasture was high,
the calcium content increased slightly, and the phosphorus content fell during
the grazing period. This led to an increase in the Ca/P-ratio.
NCU-N only occasionally rose to a dangerous level in the grass from the
cultivated pasture.
The crude protein content of the grass frorn the uncultivated pasture fell