Nitrogen excretion and utilisation of dairy cows grazing temperate semi-natural grasslands

• Published in: Animal (Cambridge, England) England), 2024-12, Vol.18 (12), p.101358, Article 101358
• Main Authors: Perdana-Decker, S., Velasco, E., Werner, J., Dickhoefer, U.
• Format: Article
• Language: English
• Subjects: Animal Feed - analysis; Animal Nutritional Physiological Phenomena; Animals; barns; Cattle - physiology; Central European region; creatinine; crude protein; Dairy cattle; Dairying; data collection; diet; Diet - veterinary; digestibility; excretion; farms; Feces - chemistry; Female; Fresh forage; Germany; grasses; Grassland; hay; Lactation - physiology; leys; Low-input farming; meadows; milk; Milk - chemistry; Milk - metabolism; milk production; nitrogen; Nitrogen - metabolism; Nitrogen - urine; Nitrogen balance; nutrient use efficiency; nutritive value; Pasture; risk; secretion; standard deviation; titanium dioxide; urine
• ISSN: 1751-7311; 1751-732X; 1751-732X
• DOI: 10.1016/j.animal.2024.101358

•Dairy cattle contribute substantially to nitrogen emissions via their excretions.•The nitrogen use by cows in low-input grazing systems was investigated on-farm.•Large variation in nitrogen use between farms due to diverse grazing management.•Supplementation had the greatest potential for manipulating nitrogen use and excretion.•On-farm study allowed insights into true, interacting effect of grazing management. Diets reliant on grazed, temperate herbage are prone to greater nitrogen (N) losses via urine than balanced stall-fed diets which poses a greater risk for N emissions. Measures for improving the N utilisation in grazing-based dairy cattle systems are predominantly investigated on homogenous clover-ryegrass pastures with high herbage yields and nutritional quality. In contrast, grazing-based systems reliant on less external inputs (e.g., synthetic fertilisers or concentrates) using semi-natural grassland as main feed source, such as in large parts of Central Europe, received less attention. The N utilisation and excretion of grazing cows in low-input dairy farms were, thus, investigated on nine commercial organic dairy farms in South Germany across one to four periods per farm. The dataset captured a diverse set of dairy production systems comprising 323 individual animal observations. A mean (± one SD) milk production, DM intake (DMI), and pasture DMI of 23.9 kg (± 5.35), 21.0 kg (± 3.21), and 11.3 kg/d (± 4.83), respectively, was determined. Feed intake was estimated using titanium dioxide and faecal CP concentration as markers of faecal excretion and diet digestibility, respectively. Milk N use efficiency (MNE; i.e., milk N secretion as share of N intake) averaged 24.7 g/100 g N intake (± 5.91), which is greater than observations in temperate, high-input grazing systems but lower than in cows receiving balanced diets in the barn. The MNE and another seven indicators of N utilisation and excretion displayed a wide range of values. The grazing management factors explaining this variation were, thus, identified via backward elimination. The supplementation strategy had the greatest potential for manipulating N utilisation and excretion of dairy cows. Increasing shares of fresh forages (i.e., meadow grass or clover-grass leys) as well as of hay in supplement DMI increased N utilisation (e.g., MNE) and decreased urinary N excretion (e.g., urinary N to creatinine ratio), while increasing shares of concentrates in supplement DMI are related to lower N l