Selectivity of Bromus valdivianus Phil., Lolium perenne L. and Agrostis capillaris L. by grazing dairy cows

Abstract

Grazing animals can select components of the pasture and hence stimulate changes in the proportion and quantity of the species. The objective of this work was to determine whether dairy cows select Lolium perenne L. (Lp) over Bromus valdivianus Phil. (Bv) and Agrostis capillaris L. (Ac) when they grazed a diverse pasture. The pastures that were evaluated were: Improved pasture (MCF), Mixed pasture (PSF) and Naturalised pasture (NCF). Corridors were established perpendicularly to the pasture plots and transects were placed within them. On each transect, 5 individual vegetative tillers of Lp, Bv and Ac were marked every 12 cm. Dairy cows grazed the pastures. The experimental design was a randomised complete block design with factorial arrangement of the treatments: 3 pasture types x 3 species, with 9 blocks. ANOVA and canonical variate analyses (CVA) were applied. Extended tiller height, tiller leaf number and the total sheath length were positively related to defoliation during grazing. Dairy cows modified the grazing selection according to the season due to tiller structural changes and the available herbage mass. Only the CVA showed selective grazing; during spring and autumn in which A. capillaris was negatively discriminated.