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An adequate feed intake is an important prerequisite to realize high milk production in dairy cows, especially during grazing. The analysis of feed intake behaviour can assist in understanding variation in daily intake and in improving its prediction. Indeed, our results indicated that differences in feed intake behaviour were more pronounced when varying the type of roughage than when varying the type of concentrate. Dry matter intake (DMI) was reduced when a ration high in grass silage was fed, but milk production was only numericaly affected. Grazing management might result in increased herbage intake and higher intake of nutrients from herbage by improved nutritional composition of herbage. In the first grazing experiment, herbage DMI was indeed increased when allocating cows daily (1Da) to a new grazing plot compared to every four days (4D) allocation, but only when pasture mass on offer and sward surface height (SSH) were high. Grazing time increased numerically and ruminating time decreased between days in the 4D treatment, coinciding with differences in rumen fermentation characteristics and milk composition. Milk yield was greater in 1Da than in 4D, but milk fatty acid (FA) composition, potentially influencing human health, showed hardly any difference. In a subsequent experiment, herbage DMI was again greater when allocating twice daily (2D) compared to once daily (1Db), especially when SSH was high. Grazing behaviour was more equally distributed in 1Db than in 2D and milk yield was increased in 2D compared to 1Db at high SSH, but as before milk FA composition hardly differed between treatment. The last grazing experiment aimed to take advantage of the higher sugar contents of grass in the afternoon than in the morning. It showed that grazing behaviour and herbage intake were similar between morning (MA) and afternoon allocation (AA), but cows receiving a fresh plot in the afternoon had a longer evening meal than cows receiving a fresh plot in the morning.

Many organizations in Ethiopia have promoted exotic multipurpose fodder tree species particularly Sesbania sesban for livestock feed and soil improvement. Despite the apparent benefits, the number of farmers planting these trees was low. Moreover, some farmers feeding Sesbania sesban reported reproduction problems in sheep. The latter was supported by a few short term reproduction studies conducted in Ethiopia. The present thesis was conducted to assess farmers’ perceptions about multipurpose fodder trees and about constraints to adoption, and to study effects of long-term feeding of Sesbania sesban on sheep performance. The farmers’ perception was studied by a field survey among 235 farm households from three district with different dominant farming systems (wheat, teff or coffee as the major crop) and the sheep performance studies were a series of experiments at the International Livestock Research Centre in Debre Zeit, Ethiopia. Farmers planted exotic multipurpose fodder trees for their feed value. The valuation for other purposes (soil and water conservation, use as fuel wood) depended on cropping system, vegetation cover and availability of alternative local fodder trees. Major constraints to adoption were agronomic problems, low multipurpose value, and land shortage. Farmers’ decision making criteria to adopt multipurpose fodder trees encompassed multiple objectives: farmers preferred local fodder trees to exotics for biomass production, multi-functionality, life span, and compatibility to the cropping system. In terms of feed value, ease of propagation, and growth potential local fodder trees were ranked lower than or comparable to exotics. A significant correlation was observed between farmers’ feed value score of a fodder tree species and the crude protein content assessed in the laboratory. The number of Sesbania sesban trees currently planted on-farm was about 30% of the recommended number for meat or milk production. Despite some farmers (11.8% of users)

Mathematical models are developed to quantity and integrate the various processes involved with rumen fermentation. Three extant mechanistic models of rumen fermentation were studied (Baldwin et al., Danfær and Dijkstra et al.), each with a truly dynamic representation but different conceptual approach. The models were compared on mathematical representation of individual processes and their prediction accuracy was evaluated. Although the models predicted similar rates of substrate degradation and rumen outflow of organic matter, total crude protein and microbial protein, they differed substantially in representation of the underlying microbial mechanisms. The model of Baldwin et al. performed best in prediction of the combination of rumen pool sizes and duodenal flows, whereas the model of Dijkstra et al. was evaluated to deliver the most realistic outflow of rapidly fermentable carbohydrates. Further, it was identified that all models needed improvement with respect to the prediction of amounts and type of volatile fatty acids (VFA) produced. In a subsequent evaluation is was investigated to what extent individual model elements, of a selection of five, could be responsible for inaccurate VFA predictions. The results suggested that inaccuracy of stoichiometric coefficients of VFA yield from fermented substrate (VFA coefficients) and incorrect representations of VFA absorption kinetics are the most likely causes. New values of VFA coefficients were derived by regression of a stoichiometric model of VFA yield against data of VFA molar proportions observed in vivo in rumen fluid of lactating cows. Inputs to the model were observed rates of rumen substrate degradation. Regression against simulated data sets including random error indicated that the accuracy of this method to estimate VFA coefficients is acceptable. Estimates from regressions against in vivo data delivered new sets of VFA coefficients for roughage-rich and concentrate-rich diets. In a follow-up study t

A widely adopted procedure to characterise the degradation in the rumen and its dynamics is the in situ incubation technique that assumes the washable fraction of feeds (W) to be equal to the soluble (S) fraction and that both are rapidly and completely degraded which may not be the case. Because W fraction is washed out of nylon bags, their behaviour cannot directly be measured. This thesis, therefore, aimed to characterise the degradative behaviour of some important unprocessed and processed concentrate (barley, maize, milo, peas, lupins and faba beans) ingredients and their fractions, using a methodology that fractionates feed samples into its inherent constituents (non-washable, NWF; insoluble washable, ISWF and soluble washable fraction, SWF) in combination with an in vitro gas production technique. The results show that the size of the W fraction obtained in nylon bag studies differs from that of the soluble fraction. Except in lupins, ISWF of the concentrate ingredients was very rich in starch. SWF was relatively rich in ash, crude protein, soluble sugars, anda residualfraction(chemically not determined)but contained only a negligible quantity of starch. The degradative behaviour of this difference (ISWF), measured with in vitro gas production,isvery similar to that of the non-washable fraction. The nature of the VFA profile resulting from the fermentation of the different fractions differs between fractions and changes with time of fermentation. Except in lupins, expander processing decreases the contribution of the truly soluble fraction (SWF) in concentrate ingredients. In maize, milo, peas and faba beans, gelatinised starch serves as a binding agent reducing the size of ISWF. However, the pelleting after expander processing disturbs the binding effect of gelatinised starch to some extent, and increases the size of ISWF. In all cereal grains, faba beans and lupins, thermo-mechanical processing (expander processing and ensuing pelleting) shows a tendency to

Historically, veal calves were fed until slaughter weight with only milk replacer and, in absence of solid feed the physiological development of the forestomachs was limited. In 1997, a new EU legislation stipulated that a minimum amount of solid feed (fiber) has to be provided for the welfare of the calves (solid feed supply reduce abnormal oral behaviors in veal calves; Van Putten, 1982; Veissier et al., 1998); however, no specifications were made about the type and source of feed.Rumen development is triggered by the production of VFA resulting from fermentation ofOMin the rumen (Flatt et al., 1958). Butyrate, and to a lesser extent propionate stimulate the development of the rumen mucosa; mostly because of their use as energy sources by the rumen epithelium (Sander et al., 1959; Tamate et al., 1962). In rearing calves, information on rumen fermentation of different sources of dietary carbohydrates is relatively well documented (Davis and Drackley, 1998; Lesmeister and Heinrichs, 2004) but only a few experiments have been conducted in veal calves.Based on earlier research (Blokhuis et al., 2000) it was hypothesized that stimulating early rumen development in veal calves would be beneficial to their subsequent performance and health. Therefore in vivo experiments were designed to establish the effects of stimulating an early rumen development in veal calves, aiming to optimize nutrient utilization from rumen fermentation and to prevent health problems in the lower gastrointestinal tract (e.g. ulcers in abomasum). In addition the potential interactions of feeding solid feed with a milk replacer based diet were investigated. Finally but not least, the development and evaluation (comparison) of techniques for estimating fermentation characteristics of different substrates, to facilitate the choice of feed ingredient for veal calves diets was also carried out. Chapter 2:This study was conducted to evaluate the effects of concentrate intake, differing in carb

Keywords: perennial ryegrass, dairy cows, intake, digestibility milk production, nitrogen utilisation.In the Netherlands, grass is one of the main roughages in the diet of high productive dairy cows. Grass is associated with two main problems: the limited dry matter intake (DMI) and the low N utilisation by dairy cows. Grassland is renovated every 3- 15 years and is usually resown with a mixture of mainly perennial ryegrass cultivars. The aim of the research described in this thesis was to evaluate the effects of perennial ryegrass cultivars on 1) degradation of herbage in the rumen of dairy cows, 2) the DMI, digestibility and milk production by dairy cows, and 3) the N utilisation by dairy cows. These effects were then related to sward characteristics and chemical composition of these cultivars, in order to identify new selection criteria that may be used in grass breeding programmes. Therefore, the effects of eight cultivars in a stall feeding experiment and four cultivars in a grazing experiment on intake, grazing behaviour, digestibility, milk production, milk composition and N utilisation were determined. The perennial ryegrass cultivars consistently differed in their water soluble carbohydrate (WSC) content. Among cultivars, the largest differences were found in WSC content, whereas the differences in crude protein and neutral detergent fibre content were small. An increased WSC content was expected to increase the palatability, and this may increase the intake. However, there was no effect of cultivar on intake in three of the four years of experiments. In one year, the lower intake of two cultivars was associated with a lower WSC content, but also with a severe crown rust infestation. However, the grazing behaviour did not differ among cultivars. The milk production and milk composition were almost not affected by cultivar, with the exception of the year with differences in intake. The cultivars differed only slightly in the degradation characteristics in th

Keywords:Perennial ryegrass, Lolium perenne , sward morphology, sward cutting, n-alkanes, herbage intake, selection, preference.Perennial ryegrass ( Lolium perenne L.) is the most important species for feeding dairy cows. The majority of the farmers in the Netherlands graze their dairy cows during summer. During grazing, the limited herbage intake is the main limitation of the dairy cows' production. This study examined opportunities for grass breeders to influence the quality of perennial ryegrass cultivars to improve the herbage intake of dairy cows.Six cultivars of perennial ryegrass (Abergold, Respect, Agri, Herbie, Barezane,Barnhem) were intensively studied during two years (2000 and 2001) between June and September. There were differences between the cultivars for important characteristics influencing herbage intake, e.g. herbage yield, sward surface height and density. Furthermore, differences between cultivars were found for the proportions and the biomass of leaf, stem and pseudostem in the sward. The sward cutting and the n-alkanes technique, both methods to determine the herbage intake by grazing dairy cows, were compared with an average that was calculated from the milk production and the live weight of the dairy cows. The sward cutting technique gave very variable results that varied largely per cow and year, and did not match with the expected calculated intake. The n-alkanes method gave less variable results that were more related to the expected calculated intake values. Within the n-alkanes method, the ratio C 32 :C 33 gave the best results.The effects of perennial ryegrass cultivars on the intake of grazing dairy cows were examined. In 2002 and 2003, cows grazed each of the four cultivars during four 2-week periods. Herbage intake was estimated using the C 32 :C 33 -alkanes method. In 2002, a clear difference was found between the cultivars, but in the second year no differences were found. A higher herbage intake was related with a higher mass of

Keywords: fractional passage rate, grass, silage, 13 C-isotope, internal markers, dairy cowsThe main aim of this thesis was to acquire knowledge on the feed specific fractional passage rates of feedstuffs and feed components through different compartments of the gastro-intestinal tract of dairy cows. Fractional passage rates form, next to fractional degradation rates, the determining factors to quantify the escape part of feed components from the rumen. Current feed evaluation systems use feed specific fractional degradation rates, but adopt fixed fractional passage rates. It is increasingly realised that also passage rates vary, amongst others with the level of feed intake, diet quality and diet composition. Besides, international developments in feed evaluation move towards so-called "nutrient based" feed evaluation systems that are more dynamic in nature. Knowledge on feed specific fractional passage rates is essential to further develop such dynamic systems. To meet our main aim, several animal trials were conducted in which the passage behaviour of feed particles originating from grass and grass silages were studied and compared with the traditionally used external markers Cr-NDF and Co-EDTA, using rumen and ileum cannulated animals. The roughages were labelled with the stable isotope of carbon ( 13 C), thus allowing to follow the passage behaviour of the dry matter, the cell wall and the non cell wall fractions. In all cases, 13 C gave slower ruminal passage rates compared to the external markers, and with respect to the labelled fractions the 13 C-labelled cell wall fractions gave the slowest fractional passage rates. A reduction in the level of feed intake of 40% gave decreased marker passage rates with the highest impact on the rumen residence times for the cell wall fractions. The effect of roughage quality on ruminal marker passage was more pronounced for the internal markers compared to the external markers. In combination with in situ degradation charac

Keywords: Dairy cows, Perennial ryegrass, Rumen fill, Clearance, Degradation, Grazing behaviour.In temperate environments, perennial ryegrass is the most widely used species for feeding dairy cows. That is because of its high productivity, palatability, digestibility and nutritive value. However, perennial ryegrass suffers from two main disadvantages: firstly, its unbalanced nutrient content in terms of crude protein (CP) and energy availability at rumen level and secondly, its low dry matter intake (DMI) by high producing dairy cows. In ruminant animals, DMI is a function of the balance between eating motivation, which is strongly related to palatability, on one hand and rumen capacity on the other. This thesis was divided into three parts: the first part aimed to investigate the possibility of improving pasture DMI by increasing rumen capacity. Rumen capacity is related to the rate of clearance (Kcl) of material from the rumen, which is the summation of both rates of degradation (kd) and passage (kp). Six varieties of perennial ryegrass were screened for their clearance and degradation rates using in vitro , in vivo and in situ techniques. The results suggested that there is a narrow range for selection with respect to clearance and degradation rate. The second part of this thesis aimed at investigating the possibility of improving pasture DMI by improving its palatability. Palatability is mainly a function of flavour and taste, which arise from certain compounds in the grass, especially water-soluble carbohydrates (WSC). High sugar grass varieties were fed to dairy cows in mid lactation. The results showed that feeding high sugar grass did not lead to an improved DMI and milk yield under both stall-feeding and grazing conditions. Moreover, milk composition in terms of fat, protein and lactose, rumen pH, fibre clearance and degradation rates were not influenced. However, rumen ammonia and milk urea concentrations were significantly reduced when feeding high sugar

The objective of this thesis was to validate and to compare in situ and in vitro techniques with in vivo data. These techniques were also evaluated for future and practical use in feed evaluation for ruminants. The techniques were compared using the digestion data of 98 forages and the energy values: in vivo total tract organic matter digestibility (OMD) and rumen fermentable organic matter (FOM), and the protein values: microbial nitrogen synthesised in the rumen (MNS) and rumen escape N (REN). The in situ nylon bag technique, the pepsin-cellulase technique, the gas production technique (GPT) and the Tilley and Terry technique showed good potency to predict OMD and the in situ technique and GPT gave most accurate FOM predictions. MNS was evaluated using in vivo data from the literature and showed a significant relationship with the content of crude protein in forages. The method of conservation of forages had an extra effect on MNS. REN was determined using in situ and different in vitro techniques, but only ADIN (fibre attached N) had a good relationship with in vivo

Keywords: heat treatment, maize, barley, starch, protein, in sacco, in vivo, dairy, perennial ryegrass, grazing, supplementation, ruminal fermentation, VFA, rumen, degradability, synchrony.In this thesis the effect of different ways of thermal processing (pelleting, expanding, toasting) of barley and maize on the degradative behaviour of their starch and protein in the rumen of lactating dairy cows are described. In situ studies showed that all thermal processing methods increased the ruminal starch and protein availability of maize, while all thermal processing methods decreased ruminal starch availability but only pelleting increased ruminal protein availability of barley. Based on in vivo experiments compared to untreated grains, expander treatment increased the apparent rumen and total tract digestibility of maize starch but did not affect the digestibility of barley starch. Supplementing grazing dairy cows with pelleted and pressure toasted maize and barley slightly (not significantly) decreased the dry matter intake of grass in the first grazing event in the morning after milking, and it decreased ruminal clearence of nitrogen. Supplementing pasture grass with pelleted and pressure toasted cereal grains decreased the pH, the NH 3 -N level in the rumen, the ammonia to total VFA (TVFA) ratio, the isobutyrate proportion, the acetate to propionate ratio and the non-glucogenic to glucogenic ratio in the rumen. Simultaneously it increased TVFA concentrations, propionate, butyrate and valerate proportions as a percentage of the TVFA. All processed grains did affect production responses in dairy cows, by elevating milk protein and decreasing milk fat production, and milk urea nitrogen but no significant differences between these two heat treatments were found. It is concluded that the need of synchrony is specially important with diets based on fresh grass, in which markedly asynchronous rates of release of energy and nitrogen occur in the rumen. It appears that to ge