Browsing by Person "Dickhoefer, Uta"

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Nitrogen excretion and utilisation of dairy cows grazing temperate semi- natural grasslands
(2024) Perdana-Decker, Sari; Velasco, Elizabeth; Werner, Jessica; Dickhoefer, Uta
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 losses via urine. At the same time, increases in total supplement DMI reduced N utilisation and increased urinary N excretion. Hence, full-time grazing combined with supplementation of fresh forage and hay in the barn is a viable option for low-input, grazing-based dairy operations with moderate levels of N losses.
Production and use of forages from permanent pastures in grazing-based dairy cattle systems in Southwest Germany
(2024) Velasco Gutierez, Elizabeth; Dickhoefer, Uta
A steadily growing world population and its rising standard of living are putting pressure on agricultural systems to provide food of good quality while minimizing environmental impacts. As a result, traditional practices such as grazing are becoming more popular in dairy systems. Permanent grasslands cover 34 % of the agricultural area in the European Union (EU). Semi-natural grasslands (SNG) are defined as permanent grasslands formerly used for mowing or grazing that have not been substantially modified by agricultural practices. The federal State of Baden-Wuerttemberg in Germany has a great proportion of SNG compared to other federal States in the country. The use of forage on SNG in grazing-based dairy cattle systems has the potential to produce milk sustainably, by respecting the environment, closing nutrient cycles, and promoting animal welfare, while ensuring high-quality forage production. However, there is limited data on the performance and practical use of SNG in grazing-based dairy cattle systems. This doctoral thesis aims at characterizing, evaluating, and quantifying the forage on SNG in grazing-based dairy cattle systems in Southwest Germany focusing on (1) forage availability, (2) feed energy self-sufficiency, and (3) feed supplementation in on-farm approach To characterize grazing-based dairy cattle systems and evaluate the potential of SNG for grazing and milk production, semi-quantitative interviews were conducted on 27 farms in the summer of 2018. Above-ground forage biomass from pastures was harvested and analyzed for nutrient composition. Farms differed regarding land endowment and use, dairy herd size, and thus stocking rates. Farmers implemented rotational (n = 12), short-grass (n = 10), continuous (n = 3), or strip (n = 2) grazing systems with < 8 h (n = 4), 8-12 h (n = 14), and > 12 h (n = 9) of daily pasture access during the grazing season. During the summer of 2018, available pasture forage (kg dry matter (DM)/ha) ranged from only 122 to 1,208. Crude protein (CP) and metabolizable energy (ME) concentrations varied greatly with 85 to 282 g and 7.9 to 11.0 MJ/kg DM, respectively. Diet digestibility estimated from fecal CP content ranged from 59.2 to 72.2 g/100 g organic matter (OM). Some farms succeeded in maintaining milk yields constant despite the lack of rainfall in that year. To quantify the forage availability of SNG as well as the feed energy self-sufficiency in seven commercial organic dairy cattle farms in Southwest Germany during the grazing season of 2019 and 2020, exclusion cages were set up in dairy cattle paddocks. Pasture samples were collected inside and outside the exclusion cages every 30 to 65 d, and analyzed by near-infrared reflectance spectroscopy for DM, CP, neutral detergent fiber (NDF), acid detergent fiber (ADF), apparent total tract digestibility organic matter (dOM), and ME. The results showed that SNG have the potential to produce a forage biomass up to 10,959 kg DM/ha and a with concentrations of CP, NDF, ADF up to 232 g/kg DM, 395 g/kg DM, and 214 g/kg DM, respectively. The concentrations of dOM and ME were up to 771 g/kg OM and 10.7 MJ/kg DM, respectively. The potential of grazing on SNG for dairy milk production was not fully exploited, although on some farms and at some times during the grazing season, grazing on SNG provided 100 % of the energy requirements of lactating dairy cattle, while on other farms, grazing on SNG provided only 2.8 % of the energy requirements. The differences in milk production from grazing SNG observed between farms were mainly due to management factors such as stocking rate and feed supplementation, while environmental factors played a minor role. To evaluate the effects of feed supplementation in grazing-based dairy cattle systems, three feeding experiments were conducted to compare feed supplementation under grazing conditions of (1) grass hay versus fresh grass-clover mixtures, (2) grass hay before or after grazing, and (3) timing of concentrate supplementation on two organic commercial dairy cattle farms in Southwest Germany in two periods in 2019 and 2020. Experiment 1 showed that the dairy cattle supplemented with fresh grass-clover mixtures had lower fecal nitrogen (N) excretion compared to the dairy cattle supplemented with grass hay. Experiment 2 demonstrated that grass hay supplementation before grazing led to a decrease in pasture organic matter intake (OMI), while grass hay supplementation in the morning (i.e., hay AM) decreased fecal N excretion in dairy cattle. Experiment 3 showed that offering less concentrate to dairy cattle before grazing resulted in higher pasture OMI in period 1, but also higher N intake and, lower fecal N excretion. The results of the feeding experiments demonstrate that simple management practices, such as the timing of feed supplementation can influence individual N utilization. The results of this doctoral thesis demonstrated that forage of SNG has the potential to produce forage biomass, adequate nutrient content, and energy concentration even under dry conditions. To maximize the use of SNG for grazing, the dynamics between forage biomass and supplemented feed should be considered, to maximize the use of SNG. Grazing management decisions play an important role in the use of forage of SNG for grazing in dairy cattle systems. The present thesis provides insights into grazing-based dairy cattle systems and valuable information on on-farm conditions in Central Europe. Future studies should be carried out in other countries and regions to obtain a more comprehensive panorama of the potential of the forage on SNG for milk production.