Effect of potassium/sodium ratio in the pasture on ingestive behaviour of dairy cows

Abstract

The aim of this study was to determine the effect of changing the potassium/sodium ratio in a Lolium perenne L. sward on ingestive behaviour of lactating dairy cows. The experiment considered 5 K/Na ratios that were organised in 10x20 m plots arranged in three randomized complete blocks. To generate the different K/Na ratios, 0 kg K2 O-0 kg Na (control), 50 kg Na ha-1, 100 kg Na ha-1, 400 kg K2 O ha-1 and 800 kg K2 O ha-1 were applied to the different treatments. Plots were grazed by lactating dairy cows, which were offered an herbage mass of 6 kg DM cow-1 (above 5 cms ground level) during a 6 h grazing event. Nutritional composition, K and Na concentration in the pasture, pasture height and herbage mass, as well as pasture removal and grazing behaviour were assesed. Evaluations were conducted at three different seasons (May, September and October). Data were subjected to anova using the proc MIXED of SAS, with the different K/Na ratios as a fixed effect and grazing season as a repeated measure. Fertiliser levels modified K and Na concentrations in the pasture, generating K/Na ratios that ranged between 3 and 48 for 100 kg Na ha-1 y 800 kg K2 O ha-1 respectively (P<0,05). Nevertheless, the K/Na ratio in the pasture had no effect on ingestive behaviour, herbage mass and chemical composition of the pasture. It is concluded that under the conditions of this experiment, K/Na ratio in the pasture has no effect on grazing behaviour of lactanting dairy cows.