Sward quality affected by different grazing pressures on dairy systems

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.