Analysis of the effects of (sub)plant and crop-related differences due to cultivar, stage of growth and season in perennial ryegrass on production, quality, selection, and intake characteristics in grass-fed and grazing dairy cattle
Grass is the basis of dairy husbandry in The Netherlands. Important quality aspects are the characteristics responsible for intake and digestibility. The content of dry matter,sugars and cell walls, cell wall digestibility, the degree of lignification, and the balance between carbohydrates and protein in rumen fermentation and intestinal digestion are important parameters for intake and utilisation. In grazing, bite size, bite rate and grazing time are important as well for selection and intake. The animal response also depends on sward (sward height, tiller density, leaf/stem ratio, leaf area index) and plant characteristics (size and tensile strength of the leaves). This research aims to quantify the influence of cultivar (genotype), management (fertilisation, sward mass) and season on morphological anatomical and chemical sward and plant characteristics of grass. In addition it is aimed to measure the influence of these effects on intake by stall-fed as well as grazing dairy cattle, to study the consequences for milk and manure production and quality, and to develop methods to select desired genotypes with a higher efficiency. This should result in grass cultivars of superior nutritive value and a higher intake, utilisation and milk production by dairy cattle. Optimising the utilisation and milk production from grass will reduce N losses to the environment. The sward, plant and animal characteristics will be used in the development of calibration equations inNear Infrared Reflectance Spectroscopy (NIRS). It is expected that in future NIRS spectra are not only suitable to predict plant and chemical characteristics, but that from such spectra also intake, digestion pattern and milk production can be predicted. During the first two years a stall-feeding experiment will be conducted with 8 grass perennial ryegrass cultivars contrasting in morphological appearance, digestion chracteristics and sugar content. Measurements include intake, intake rate, rumen fermentation, animal production response and distribution of excreted N between faeces, milk and urine. In the first year experiments will be performed at a sword mass of 1900 kg DM/ha; in the second year cuts will be taken at a higher sward mass of 2500 kg DM/ha, to assess the impact of management. During the third and fourth year 4-6 grass cultivars will also be investigated under grazing conditions, to validate the results obtained with stallfeeding. Because of the size, degree of multidisciplinarity and complexity, the realisation of the project requires a minimum of 3 PhD students to analyse the different aspects of the production - consumption chain: PhD-1 tot analyse aspects of plant physiology and sward ecology in relation to intake, PhD-2 to be primarily involved in the aspects of animal (digestive) physiology related to grass intake (particle size reduction and changes in rumen pool size) and PhD-3 who will take care of the utilisation of N (degradation of grass protein, microbial protein synthesis in the rumen and quality aspects of milk, urine and manure), the distribution of excreted N and quality aspects of milk, faeces and urine. It is essential that the 3 PdH's start at the same time and work in the project in an integrated way. The daily supervisors will ensure good integration. The results of the project must give a better insight in the relationships between grass characteristics, ingestibility, digestibility and nutrient utilisation by dairy cattle, including the distribution of N excretion, and hence contribute to more sustainable dairy production systems. This research also aims to develop a NIRS calibration equation to predict feed intake and/or milk yield from fresh grass. This would strongly improve the efficiency of the selection process, resulting in a much faster development of improved grass cultivars.