H. Boer

Absorption of volatile fatty acids from the rumen of lactating dairy cows as influenced by volatile fatty acid concentration, pH and rumen liquid volume

The effect of rumen liquid volume, pH and concentration of volatile fatty acids (VFA) on the rates of absorption of acetic, propionic and butyric acids from the rumen was examined in lactating dairy cows. Experimental solutions introduced into the emptied, washed rumen comprised two different volumes (10 or 30 l), four levels of pH (4.5, 5.4, 6.3, 7.2) and three levels of individual VFA concentrations (20, 50 or 100 mM-acetic, propionic or butyric acid). All solutions contained a total of 170 mM-VFA and an osmotic value of 400 mOsmol/l. Absorption rates were calculated from the disappearance of VFA from the rumen corrected for passage with liquid phase to the omasum. An increase in initial fluid pH caused a reduction in fractional absorption rates of propionic and butyric acids. Increasing the initial pH from 4.5 to 7.2 reduced fractional absorption rates of acetic, propionic and butyric acids from 0.35, 0.67 and 0.85 to 0.21, 0.35 and 0.28/h respectively. The fractional absorption rates of all VFA were reduced (P < 0.05) by an increase in initial rumen volume. The fractional absorption rate of acetic acid was lower (P < 0.05) at an initial concentration of 20 mM than of 50 mM. The fractional absorption rate of propionic acid tended (P < 0.10) to decrease as the level of concentration increased while fractional absorption rate of butyric acid was not affected by butyric acid concentration. These results indicate that relative concentrations of VFA in rumen fluid might not represent relative production rates and that attempts to estimate individual VFA production from substrate digestion must take account of pH and VFA concentration.

Comparison of the fatty acid composition of fresh and ensiled perennial ryegrass (Lolium perenne L.), affected by cultivar and regrowth interval

Two experiments were conducted to evaluate the effects of grass cultivar and regrowth stage on the fatty acid (FA) profile in fresh and ensiled perennial ryegrass (Lolium perenne L.). The Experiment 1 compared the composition of fresh grass with that of pre-wilted ensiled material of six cultivars, harvested after 25 days of regrowth at a dry matter (DM) yield of approximately 2000 kg DM ha(-1). The Experiment 2 compared fresh and ensiled grass of two cultivars, harvested after 23 and 33 days of regrowth. There were genetic differences in fatty acid profiles in fresh grass, but the physiological basis of these differences was not clear as management, growth conditions and leaf blade proportion were similar among cultivars. The concentrations of most FA declined with increasing regrowth stage. In fresh grass, 98% of the fat was present as esterified fatty acids (EFAs) but in silages, 27-73% of the total FA consisted of free fatty acids (FFAs). The largest changes in FA contents took place in the EFA. In pre-wilted ensiled grass, the contents of most FA were lower than in fresh grass, especially of C18:1 and C18:3

Effect of different processing methods on tannin content and in vitro protein digestibility of faba bean (Vicia faba L.)

High-tannin faba beans (cv. ‘Alfred’) were dehulled using manual and abrasive dehulling procedures. Hulls and dehulled beans were analysed for the level of tannin using the Folin Denis (FD) and Vanillin (Vlln) methods of assay. The levels of tannin detected in whole beans were 1.55% (FD) and 0.67% (Vlln). Only small differences were observed for the yield of dehulled beans with the various dehulling procedures. The levels of tannins (FD) in the seed coat varied between 5.8 and 7.6% with subsequent low levels (0.56–0.65%) in the cotyledons. Condensed tannin levels (Vlln) were almost zero in the cotyledons after manual dehulling. The absolute level of assayable tannins depends largely on the chemical assay used to quantify these levels. Thermal processing of faba beans was carried out by reconstitution, extrusion and reconstitution followed by extrusion. All treatments resulted in a decrease of the tannin level (FD) in whole beans of about 50%. Based on the Vlln assay, the reduction was less pronounced compared with the FD assay. Protein digestibility in vitro of the different thermally processed beans differed between the untreated and extrusion related treatments (P < 0.05). For a good prediction of the biological activity of tannins in vivo, additional studies are needed on the effects of the processing of faba beans on, for instance, their ileal digestibility.

Influence of stage of maturity of grass silages on digestion processes in dairy cows. 2. Rumen contents, passage rates, distribution of rumen and faecal particles and mastication activity

Because of the introduction of a milk quota system in 1984 and the subsequent decrease of the number of dairy cows with some 25%, an increasing number of farms in the Netherlands has a surplus of grass and grass silage, which makes it interesting to increase the roughage proportion in the diet. However, roughage intake by dairy cows in early lactation is limited and the mechanisms controlling roughage intake are still insufficiently understood. Factors presumably influencing roughage intake are the volume of the feed, the rate of physical size reduction, degradation rate in the rumen, passage rate of undigested particles from the rumen and the removal of fermentation end products.In literature, the results of various experiments are reported in which one or a few of these factors, though not all together in an integrated system, were studied. Therefore, in the experiments described in this thesis, the effect of stage of maturity of grass silages on intake, digestibility, rumen fermentation pattern, rumination activity, passage rate from the rumen, degradation rate of the potentially degradable fractions and composition of the rumen contents was studied in an integrated approach.Four experiments with lactating dairy cows fed grass silages harvested at different growth stages ad libitum and a fixed amount of concentrates, 1 or 7 kg depending on stage of latation, were performed.When grasses matured, the chemical composition changed, the cell wall content (Neutral Detergent Fibre) of the silages and the lignin content of the cell wall fraction increased while crude protein (CP) content decreased. Together with this change in composition, the degradation characteristics changed. The soluble fraction (f s ,%), which is supposed to be fully and rapidly degraded in the rumen decreased, the rumen undegradable fraction (residue after 336 h nylon bag incubation, f R , % ) increased whereas the rate of degradation of the degradable, non-soluble fraction (kd, %h-1) decreased. This resulted in a decrease in digestibility of the silages (Chapter II) . Of the CP fraction of the silages, f s as well as f R increased with an increase in cell wall content of the silages. The soluble fraction of the CP was more closely related to the DM content than to the NDF content of the silages. The f s -CP decreased with an increase in DM content of the silage. Rate of degradation of the CP decreased, as for the other components, with an increase in cell wall content. Thus, the fraction of dietary protein escaping rumen fermentation increased with an increase in cell wall content, mainly because of the higher undegradable fraction. The latter fraction, however, is also not digestible in the intestines. Thus, the fraction of dietary protein escaping rumen fermentation and digestible in the intestines was presumably higher for the low cell wall silages (Chapter V).Milk production (g Fat Corrected Milk/kg Metabolic Body Weight) and the amount of concentrates consumed (g/kg BW) together explained 64% of the variation in silage dry matter (DM) intake. Silage DM intake decreased with an increase in concentrate intake. A significant contribution to the explanation of variation in intake was given by the N/OM ratio in the silage and the f R . The addition of these factors increased the percentage of the variation in silage DM intake explained to 68% (Chapter II).The pH in the rumen declined with an increase in concentrate intake, whereas VFA concentrations increased. Diurnal variations in ammonia concentrations were higer for the high concentrate level, but the average ammonia concentrations were lower for the high concentrate level (Chapter IV).Chewing and rumination time were recorded for six 24 h periods per cow. When rumination time (RT) exceeded 9 h a day, an increase in cell wall content of the silages did not result in a further increase in RT, but in a decrease in intake. RT per kg silage DM ingested increased with an increase in NDF content of the silages, whereas RT per kg silage NDF tended to decrease. Average size of particles in the rumen increased with maturity of the silages, resulting in an increased faecal particle size (Chapter IV).Total rumen contents (kg) and rumen DM contents (kg) increased when the proportion of concentrates in the diet increased, but no significant relation with cell wall content of the silages was found. Passage rate of the fluid from the rumen was not affected by diet composition. Rate of passage of undigested particles from the rumen, calculated from the logarithmic decline in faecal marker excretion, increased with an increase in NDF content of the silages and with an increase in intake level (Chapter III). In these experiments, it was concluded that the marker used to measure particle passage rate, Cr mordanted NDF, was not representative for total rumen contents. Cr-NDF particles with a size of 0.2-1mm do not have to be reduced in size, but it was calculated that not even they could be representative for particles with a size able to leave the rumen. Therefore an experiment was conducted in which three different particle sizes of Cr-NDF (<0.3 mm, 0.6-1.0 mm and 15-25 mm) were used to determine particle passage rate. In this experiment, 3 lactating and 3 non-lactating dairy cows were fed grass silage ad libitum, with 7 or 1 kg of concentrates, respectively. No significant differences between lactating and non-lactating cows were found, but rate of passage decreased with an increase in Cr-NDF particle size. Passage rate of the smallest particles (<0.3 mm) was considerably lower than passage rate of the fluid phase. The size of the particulate marker has a great influence on the calculated passage rates (Chapter IV).Kinetics of rumen particles are considered to be important in intake regulation, but the rate limiting step in reduction in rumen fill was still not identified. In an experiment with four dry rumen regulated cows, rumen contents and rates of disappearance of different morainal fractions were determined (Chapter VII) . The cows were fed ad libitum grass silages, differing in cell wall content. morainal passage rates were calculated from the logarithmic decline in rumen Cr pool, as well as by dividing the intake of undegradable organic matter (iOM) or indigestible acid detergent fibre (iADF) by the mean rumen pool of these fractions. The thus calculated passage rates using the pools of iOM or iADF were much lower than using the Cr-NDF (particle size 0.2-1 mm), but the differences between silages were comparable.Particle size distributions of rumen contents, collected at different times after feeding were determined. The iADF content of particles passing a 1.25 mm, but retained on a 0.071 mm sieve was determined. From the results of this experiment it was concluded that clearance rate of particles with a size between 1.25 mm and 0.071 mm is the rate limiting step in reduction in rumen f ill, which in turn seems to depend on the degree of digestion.In the General Discussion (Chapter VIII) , the results from these experiments were combined with literature data on rumen fill and clearance rate from the rumen. Multiple regression analysis showed that milk yield and concentrate proportion of the diet explained 77% of the variation in rumen fill. Roughage characteristics did not have a significant influence on rumen DM fill. Rate of clearance, however, significantly decreased with an increase in roughage NDF content. Rumen fill and rate of clearance were not significantly correlated.From this study it may be concluded that important factors such as intake, digestibility and milk production all three were negatively influenced by an increase in silage cell wall content. When intake is not limited by the capacity of the rumen, as for the dry cows in the experiment described in chapter VII, intake increases with an increase in silage cell wall content.

Effect of infrared irradiation or extrusion processing of maize on its digestibility in piglets

Maize was extruded or irradiated with infrared radiation at various temperatures and moisture contents, to examine the effect of processing conditions on the availability of the starch to young pigs. A digestibility trial with early weaned piglets was conducted with 4 diets. These diets contained 60% untreated, extruded, irradiated or a combination of untreated and extruded maize, respectively. A total of 31 piglets in 2 groups were used with initial body weights of 5.8 and 7.2 kg, respectively. After extrusion at die temperatures of 190 or 210°C, starch availability in vitro (amyloglucosidase-test) was at least 94%. Infrared irradiation of maize followed by flaking resulted in a starch availability of about 30%. Apparent faecal digestibility coefficients of organic matter, crude protein, crude fat, crude fiber, N-free extract and energy in the diets with 60% of maize were not significantly influenced by extrusion or irradiation of the maize component. For piglets of 7.2 kg the apparent digestibility of energy, organic matter and crude protein was higher than for piglets of 5.8 kg (P < 0.05). A second digestibility trial showed no significant effects of diets containing 60% untreated, extruded, irradiated or pressure-cooked maize on digestive coefficients, except for coefficients of NFE. The diet based on pressure-cooked maize had a significantly higher apparent digestibility coefficient for NFE. It is concluded that extrusion or infrared irradiation of maize does not affect apparent digestibility coefficients when the maize forms 60% of diets for healthy piglets with a live weight of about 6 kg. It is also concluded that age and weight of young early weaned pigs are important factors influencing digestibility.

Effects of extrusion on the dye-binding, fluorodinitrobenzene-reactive and total lysine content of soyabean meal and peas

Commercial soyabean meal (hexane extracted and toasted) and peas were processed with a single- and twin-screw extruder, respectively, to test the effects of initial moisture level and die product temperature on the reactive lysine contents. For soyabean meal, extrusion temperatures ranged from 90 to 140°C with moisture levels of 25–40%. Extrusion of peas was carried out at temperatures ranging from 105 to 140°C at moisture levels of 15–30%. Extruded and non-extruded samples were analysed for total lysine, and for reactive lysine, determined by the fluorodinitrobenzene (FDNB) method and the dye-binding lysine (DBL) method. Extrusion of soyabean meal at moderate temperatures (140°C) and high moisture levels (27–40%) resulted in a reduction in FDNB-reactive lysine ranging from 10 to 14%. Increased moisture levels in the soyabean meal resulted in slightly lower FDNB-reactive lysine values; the major decrease was caused by the processing temperature. Extrusion of peas gave a 16% reduction in FDNB-reactive lysine only when the temperature was 140°C and the moisture level was low (15%). Although ther was a marked reduction in reactive lysine units, caused by the heat treatment, this was not detected by total lysine analysis, while DBL analysis gave a significant correlation (r = 0.97; P < 0.001) with the FDNB-reactive lysine procedure for the extruded soyabean meal but not for the extruded peas. For unextruded samples there was close agreement between the total and FDNB-reactive lysine content. Overall, and based on the present findings, it is concluded that the FDNB method is useful for measuring the reduction in nutritional value after extrusion of soyabean meal and peas whereas the rapid DBL procedure gives inconsistent results. The extrusion of soyabean meal and peas at moderate temperatures can lead to loss of reactive lysine units.

A comparison of ten rice-straw varieties grown at two different altitudes during a wet and a dry season, using the in vitro cumulative gas production technique

In vitro cumulative gas production was used to evaluate a series of rice straws for their fermentability. The straws comprised ten different varieties which had been grown at two locations (higher and lower altitudes), during two seasons (wet and dry). Curves were fitted, and the resulting parameters, DM loss and gas yield, were tested for significant differences by an analysis of variance using the Tukey test. Significant differences between the parameters of the fitted curves were found between the offered and refused straw, the material grown at different altitudes, the material from the wet and dry seasons, and between varieties. Significant interactions were found between the environmental factors and cultivar, for the offered and refused feeds.

Effects of ageing on the in vitro fermentation of cell walls and cell contents of entire, fractionated and composite leaves of Italian ryegrass

Changes in fermentability of cell walls and cell contents of Italian ryegrass leaves at two stages of maturity were measured to explain the generally observed decline in herbage quality with ageing. A herbage fractionation method was developed to separate cell contents and cell walls. Cell walls were either untreated or protease-treated. Fermentation characteristics of all cell wall and cell contents fractions, as well as whole and recombined leaves, were measured using cumulative gas and volatile fatty acid (VFA) production. The gas production profiles of all substrates contained two significant phases. After fractionation, addition of the profiles from separated cell contents and untreated cell walls resulted in the same profile as for the recombined leaf. The strongest reduction in gas and VFA production due to leaf ageing was observed for cell contents. The increased ratio between branched and straight chain VFAs suggested that there had been an increase in the protein fermentation. Treatment of cell walls may have removed some easily fermentable cell wall components, as seen in the small differences in gas and VFA production between whole and recombined leaves. It has been concluded that the phases of gas production, separable in kinetic fermentability studies of complex animal feeds, need to be interpreted with caution. The large reduction in fermentability of cell contents with plant maturity, compared with the cell walls, indicated the importance of determining the role of cell contents in herbage quality studies, as the cell contents clearly do not remain uniform.

The Effect of Extrusion Conditions on the Fermentability of Wheat Straw and Corn Silage

Wheat (Triticum aestivum L) straw and corn (Zea mays L) silage were extruded under variable conditions of temperature and screw speed. The resulting extrudates were then tested for their fermentability according to cumulative production of gas, and compared with each other and with the untreated material. VFA analysis was carried out at the end of fermentation, to assess the pattern of fermentation. Analysis of the cumulative gas curves showed significant differences between substrates. Extrusion treatment also led to significant differences, though the effect of screw speed and temperature were not always consistent. However, most differences in cumulative gas production were negative, particularly for wheat straw, which suggests that, under the conditions used, extrusion actually reduced the fermentability of the fibres.

Evaluation of techniques to determine the protein digestibility of heat processed beans for pigs

Studies were made to evaluate the mobile nylon bag technique (MNBT) and two in vitro methods for determining and predicting the apparent ileal dry matter (DM) and nitrogen (N) digestibility of a variety of heat treated bean samples (Phaseolus vulgaris L.) for pigs. For MNBT estimates, 1 g samples of beans, steam heated under different time/temperature conditions were enclosed in nylon bags. After predigestion (pepsin-HCl) and in vivo digestion (duodenum to terminal ileum), the undigested contents of ten bags per bean treatment were analyzed. The disappearance of DM and N of samples as well as the effect of two basal diets was examined using four barrows (30–45 kg liveweight). In addition, the effect of two weight classes was investigated by determining the digestibility in older barrows (liveweight 70–80 kg). In vitro values of digestibility were determined using a multi-enzyme pH-stat assay or a multi-enzyme N-digestibility assay. With the MNBT, the digestibility of DM or N did not differ between weight classes of pigs. Also, no differences were observed between the basal diets. The apparent ileal digestibility values in unprocessed beans were high, ∼ 78% (DM) and ∼ 92% (N). The MNBT showed no accurate prediction of absolute values of apparent ileal digestibility of DM and N, which are known to be considerably lower. However, MNBT shows a good discriminating ability in relation to the test samples. With simple regression analysis correlations of 0.88 (P < 0.05) and 0.96 (P < 0.01) were established for DM and N, respectively, between MNBT ileal digestibility and ileal digestibility determined by total collection. The in vitro enzymatic procedures tested showed no acceptable estimates for absolute values or ranking of N and DM digestibility.