The objective of the experiment was to examine the effects of different sto
cking densities (3.7, 4.6, and 5.5 cows ha(-1)) on tiller density, botanica
l composition, and chemical (crude protein [CP], acid detergent fiber [ADF]
, Ca, P, K, and Mg) quality of pasture and the seasonal (before flowering [
spring], after flowering [summer], and autumn) distribution of these parame
ters. Percentages of sown [perennial ryegrass (Lolium perenne L. cv 'Brigan
tia') and white clover (Trifolium repens L. cv 'Huia')] and volunteer speci
es were not significantly affected by stocking density, although as stockin
g density increased, tiller density also increased. This effect was more pr
onounced for volunteer species than sown species. Density was significantly
higher before flowering than after flowering or autumn. Stocking density a
ffected the chemical quality of herbage with ADF, CP, P, K, and Mg higher a
t high stocking density. The Cam relationship was lower at high stocking de
nsity, but the K/(Ca+Mg) relationship was not significantly affected by sto
cking density. Chemical quality of the pasture was higher before flowering
than after flowering or autumn. The Ca/P ratio exceeded the upper limit rec
ommended for dairy cows, but no osteomalacia was found in the present exper
iment. Low values of the K/(Ca+Mg)ratio were found in the spring. Therefore
, on these pasture types it is advisable to use concentrates high in Mg or
Mg supplements in the spring in order to avoid hypomagnesemia.