Urination behaviour of non-lactating dairy cows in late gestation offered fodder beet and kale winter forages

Prediction of nitrogen (N) leaching from urine events using modelling tools such as OVERSEER is important for regulation of dairy farm outputs and practices. Risk of N leaching is greatest during winter, particularly in systems which adopt high stocking densities such as those grazing fodder beet and kale crops. However large prediction errors for leaching values from OVERSEER are recognised, highlighting the need for more quantitative information on urination behaviour of dairy cows grazing winter forages. The study was conducted at Ashley Dene research farm (-43.65 º North, 172.33 º East) using 24 high producing Friesian x Jersey dairy cows fed two diets representative of industry practice. Diet treatments were 10 kg DM of fodder beet with 5.6 kg DM of ryegrass baleage (FB) or 16.4 kg DM of kale with 6.4kg of oat straw (KA) . All cows were fitted with a urine harness for 24 to 48 hours which collected data on number, volume, and timing of urine events. Urine patch areas were estimated using the urine harness data and a calibration curve of urine volume and wetted area in the paddocks being grazed. Urine volumes were similar (27.6 L/cow/day, p=0.988) though behaviour was affected by diet whereby FB cows urinated less frequently (8.42 vs 10.1 events/cow/day for FB and KA respectively, p=0.128) but with more volume per event than KA (3.58 vs 2.71 L/cow/day for FB and KA respectively, p=0.04). On their own, similarity in total volumes (FB vs. KA) could not be explained by intake of water (55 vs. 69 L/cow/day, p<0.001), N (237 vs. 472 g N/cow/day, p<0.001), DM (13.4 vs. 17.1 kg cow/day, p<0.001), potassium (2.7 vs. 2.9 g/cow/day, p=0.055) or sodium (0.53 vs. 0.40 g/cow/day, p