Sward quality affected by different grazing pressures on dairy systems

Abstract

The objective of the experiment was to examine the effects of different stocking densities (3.7, 4.6, and 5.5 cows ha- l) on tiller density, botanical 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 parameters. Percentages of sown [perennial ryegrass (Lolium perenne L. cv ‘Brigantia’) and white clover (Trifolium repens L. cv ‘Huia’)] and volunteer species were not significantly affected by stocking density, although as stocking density increased, tiller density also increased. This effect was more pronounced for volunteer species than sown species. Density was significantly higher before flowering than after flowering or autumn. Stocking density affected the chemical quality of herbage with ADF, CP, P, K, and Mg higher at high stocking density. The Ca/P relationship was lower at high stocking density, but the K/(Ca+Mg) relationship was not significantly affected by stocking density. Chemical quality of the pasture was higher before flowering than after flowering or autumn. The Ca/P ratio exceeded the upper limit recommended for dairy cows, but no osteomalacia was found in the presen texperiment. 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.