Abstract
Urine patches from ruminant livestock are risk areas for soil nitrogen (N) loss from grazed pastures. Urine volume and N concentration at any given urine event influences the relative N loading onto the soil. Forages such as chicory (Cichorus intybus L.) and plantain (Plantago lanceolate L.) with high water and mineral content present an opportunity to modulate urination behaviour and urinary nitrogen (UN) excreted into the environment. This study compares urination patterns, milk production and N use efficiency, of cows grazing chicory, plantain, or ryegrass (Lolium perenne L.) with 13% white clover (Trifolium repens L.; RGWC) herbage. Fifty-four Friesian x Jersey cows in late lactation were blocked into replicated groups of six cows, and offered one of three pasture types. Automated urine sensors measuring urine volume and timing were affixed to approximately 10 random cows per treatment for 24 h. Milk yield was similar for all treatments (19.1 +/- 0.52 kg/cow.day), but milk solids production (protein + fat) were greater from cows grazing chicory than RGWC (1.86 vs 1.72 kg MS/cow.day, P < 0.01) while plantain was intermediate (1.76 kg MS/cow.day). There was large variation in urine event volume (0.13-11.6 1 per event), though mean urine volume per event was similar for each treatment (3.01 +/- 0.3 1 per event; P = 0.24). Water, sodium and potassium intakes from herbage was greatest for chicory compared with plantain or RGWC. Frequency of urination increased with increasing water, sodium and potassium intakes and cows grazing chicory and plantain urinated more often (28.6 and 21.2 events/cow.day, respectively) than those grazing RGWC (13.9 events/cow.day, P < 0.05). Consequently, cows grazing chicory excreted 1.5 and 2.4 times more urine per day (P < 0.01) than cows grazing plantain and RGWC, respectively. Apparent N intake was similar between cows grazing chicory and RGWC, but greater than cows grazing plantain. However, UN concentrations from cows grazing chicory and plantain were similar (P > 0.05), but substantially lower than RGWC (1.3 vs 4.8 g/kg; P < 001). The reduction in UN in cows grazing herbs is mainly attributed to increased number of urination, which resulted in urine dilution. The combination of similar urine volume per event in all three forages, frequent urinations and substantially lower UN concentration in cows grazing the forage herbs indicate a benefit from forage herbs to reduce N load onto pasture.