Development of a urine harness to detect variation in urinary behaviour and urine patch coverage of dairy cows on winter crops

Dairy cow urine is the greatest contributor of nitrate leaching on agricultural systems. This is because there is a large discrepancy between the N content of grazed forages, and the N requirements of the animals; N in excess of an animal’s requirement is excreted, primarily in the urine. Wintering dairy cows can contribute between 11 -24% of total farm N leaching losses, despite representing only 4-9% of the farm system. This is because of high stocking densities on winter forage crops, in conjunction with the high drainage and lack of plant uptake that occurs in winter due to high rainfall and low temperatures. While there is significant knowledge about ruminant urinary N concentrations, there is very little information available about the volume, frequency and distribution of dairy cow urine, and there is no data on these variables in winter grazing systems. A urine harness was developed to measure the variability of dairy cow urine frequency and volume. The harness was trialled at Ashley Dene using two different wintering systems for dairy cows – kale fed at an allowance of 14kg DM cow⁻¹ day⁻¹ plus barley straw (3 kg DM cow⁻¹ day⁻¹), and fodder beet fed at an allowance of 8kg DM cow⁻¹ day⁻¹, plus ryegrass baleage (6 kg DM cow⁻¹ day⁻¹). The harnesses were worn for 24 hours, and the trial was repeated three times. Urine patch area was determined by measuring in situ wetted area immediately following a urination event; and by regression following the development of a calibration curve between urine volume and wetted area in situ. Urine harness results showed there was no difference between the two wintering systems on the frequency of urination in 24 hours (10.25 ± 2.25), or the average volume of a urination event (2.39L ± 0.29). Total daily urine volume was greater for kale (29.9L cow⁻¹ day⁻¹) than fodder beet (18.0L cow⁻¹ day⁻¹). The average urine patch area was 1.4 times larger on the kale treatment than on the fodder beet (0.47 vs. 0.25m²). Total leaching losses were calculated as being greater on the fodder beet treatment than the kale (77.8 vs. 53.8kg N ha⁻¹ year⁻¹). This trial developed a satisfactory urine harness, capable of measuring urination volume and frequency, which was able to remain attached to dairy cows that were grazing winter crops in situ for at least 24 hours. The harness was able to show that there was great variability in urinary behaviour of dairy cows. The harness can be used, in combination with urine area to inform models used in the prediction of N losses from agricultural systems.