Digesta characteristics of dorsal,middle and ventral rumen of cows fed with different hay qualities and concentrate levels

The influence of fibre content of hay (H) and concentrate level (C) on local differences in the composition of ruminal digesta (ratio of solid to fluid digesta, DM, NDF, ADF and ADL content), particle size (MPL), specific gravity (SG) and fermentation (pH and concentrations of SCFA and bicarbonate) have been tested on two ruminally cannulated Friesian cows (520?kg BW) which were fed restricted, using individual cows as experimental units. Digesta samples were collected via cannula from three rumen layers: 5 to 10?cm (top) and 25?–?35?cm beneath the top of the particle mat (middle) and 5?–?10?cm above the rumen floor (bottom). For a main plot treatment (H·C), repeated samples were collected at four time intervals (1?h before and 2, 5 and 10?h after morning feeding) on each of two days. From top to bottom rumen the share of solid digesta mass (SM), DM and NDF contents of squeezed digesta fluid (SRF) and concentration of SCFA decreased (P?P?相似文献   

Studies on the biotin flow at the duodenum of dairy cows fed diets with different concentrate levels and types of forages

Abstract

Biotin is involved in many vital metabolic pathways and must be provided for an efficient fermentation in the rumen, as well as for the intermediary metabolism of the host animal. Factors influencing ruminal biotin metabolism and output are widely unknown at present. Therefore, dairy cows fitted with permanent cannulas in the dorsal rumen and in the proximal duodenum were fed differently composed diets, and the biotin flow at the proximal duodenum was measured. The diets (on DM basis) consisted of 8.9 kg grass hay (Diet 1), 8.9 kg corn silage plus 2.0 kg concentrate (Diet 2), or 7.3 and 7.4 kg grass silage plus 10.0 kg concentrate (Diets 3 and 4). The concentrate in Diets 3 and 4 contained 87% wheat and corn grain, respectively. The cows were pre-fed the rations for 21 days. Thereafter duodenal digesta was sampled every two h for 5 days. Cr₂O₃ served as a flow marker and the microbial proportion of total nitrogen at the duodenum was estimated by near infrared spectroscopy (NIRS). The duodenal flow of biotin was not related to biotin intake, but to the amount of fermented organic matter (FOM) and the amount of microbial protein (Biotin [mg/d] = 0.518 · kg FOM?0.300; r = 0.85 and biotin [mg/d] = 0.012 · g microbial protein + 1.478; r = 0.84), irrespective of the composition of the diet fed. Mean daily biotin flow was 0.48 ± 0.11 mg/kg FOM without any systematic effect of diet composition. The ruminal biotin balance, calculated as the difference between biotin flow at the duodenum and biotin intake, was positive (1.4 – 2.0 mg/d) in cows fed the mixed roughage/concentrate diets and negative (?0.71 mg/d) when the pure hay diet was fed.     

Comparative growth rates of various rumen bacteria in clarified rumen fluid from cows and sheep fed different diets.

Pure cultures of strains of different species of rumen bacteria were grown in filter-sterilized rumen fluid supplemented with glucose, bicarbonate, and reducing agent (cysteine and sulfide). Growth rates were determined in a series of experiments. Strains of species most abundant in the rumen grew more rapidly than strains of less abundant bacteria. Ammonia, amino acids, and peptides increased growth rates to some extent, but the greatest stimulatory effect for less abundant bacteria was provided by other factors, present in yeast extract. Factors released from lysates of mixed rumen microbes stimulated growth, but their rate of release was slow. It was concluded that, besides energy and nitrogen sources, growth factors of an as-yet-undetermined nature probably play an important role in determining the predominance of different bacterial species in the rumen.     

Comparative growth rates of various rumen bacteria in clarified rumen fluid from cows and sheep fed different diets.

Pure cultures of strains of different species of rumen bacteria were grown in filter-sterilized rumen fluid supplemented with glucose, bicarbonate, and reducing agent (cysteine and sulfide). Growth rates were determined in a series of experiments. Strains of species most abundant in the rumen grew more rapidly than strains of less abundant bacteria. Ammonia, amino acids, and peptides increased growth rates to some extent, but the greatest stimulatory effect for less abundant bacteria was provided by other factors, present in yeast extract. Factors released from lysates of mixed rumen microbes stimulated growth, but their rate of release was slow. It was concluded that, besides energy and nitrogen sources, growth factors of an as-yet-undetermined nature probably play an important role in determining the predominance of different bacterial species in the rumen.     

Composition, spatial distribution, and diversity of the bacterial communities in the rumen of cows fed different forages

The species composition, distribution, and biodiversity of the bacterial communities in the rumen of cows fed alfalfa or triticale were investigated using 16S rRNA gene clone library analyses. The rumen bacterial community was fractionated and analyzed as three separate fractions: populations in the planktonic, loosely attached to rumen digesta particles, and tightly attached to rumen digesta particles. Six hundred and thirteen operational taxonomic units (OTUs) belonging to 32 genera, 19 families, and nine phyla of the domain Bacteria were identified from 1014 sequenced clones. Four hundred and fifty one of the 613 OTUs were identified as new species. These bacterial sequences were distributed differently among the three fractions in the rumen digesta of cows fed alfalfa or triticale. Chao 1 estimation revealed that, in both communities, the populations tightly attached to particulates were more diverse than the planktonic and those loosely attached to particulates. S-Libshuff detected significant differences in the composition between any two fractions in the rumen of cows with the same diet and between the communities fed alfalfa and triticale diets. The species richness estimated for the communities fed alfalfa and triticale is 1027 and 662, respectively. The diversity of the rumen bacterial community examined in this study is greater than previous studies have demonstrated and the differences in the community composition between two high-fiber diets have implications for sample selection for downstream metagenomics applications.     

Parameters of fermentation and rumen microbiota of Nellore steers fed with different proportions of concentrate in fresh sugarcane containing diets

The objective of this study was to evaluate the effect of a fresh sugarcane-based diet and different roughage-to-concentrate ratios (70:30, 60:40, 40:60 and 20:80) on the rumen microbiota associated with rumen fermentation parameters and the intake and apparent digestibility of nutrients in Nellore steers. Eight rumen-cannulated Nellore steers (331 ± 8 kg BW) were distributed in a double 4 × 4 Latin square design balanced for the control of the residual effect. The ruminal pH decreased (p < 0.01) and the concentrations of N–NH₃, isovaleric and valeric acids increased linearly (p < 0.05) with an increase dietary concentrate level. Furthermore, an increased concentrate proportion reduced the population of Fibrobacter succinogenes and Ruminococus flavefaciens (p < 0.01) and increased the population of Selenomonas ruminantium and Megasphaera elsdenii (p < 0.01). The protozoa count revealed a predominance of the genus Entodinium. The synthesis of microbial N [g/d] and the efficiency of microbial synthesis [g of microbial N/kg of organic matter apparently digested in the rumen] increased as the proportion of concentrate was increased (p < 0.05). Therefore, it can be concluded that an increasing proportion of concentrate in sugarcane-containing diets enhances the synthesis of microbial protein and does not alter the fibre digestibility, although the population of fibre fermenting bacteria was reduced.     

Effects of the replacement of concentrate and fibre-rich hay by high-quality hay on chewing,rumination and nutrient digestibility in non-lactating Holstein cows

The aim of this study was to investigate the effects of high-quality hay with an elevated sugar content alone or with graded amounts of concentrate feed on chewing and ruminating activity, apparent total tract digestibility (ATTD) and ruminal pH at different time points after feeding in the free ruminal liquid (FRL) and the particle-associated ruminal liquid (PARL). Eight rumen cannulated non-lactating Holstein cows were arranged in a Latin square design in four experimental runs lasting 25 d each. The four diets tested were 60NQ (60% normal-quality hay + 40% concentrate), 60HQ (60% high-quality hay + 40% concentrate), 75HQ (75% high-quality hay + 25% concentrate) and 100HQ (100% high-quality hay). Normal and high-quality hays differed in sugar contents (11.3% vs. 18.7% in dry matter [DM]), neutral detergent fibre (NDF; 57.7% vs. 46.3% in DM), acid detergent fibre (ADF, 35.0% vs. 23.5% in DM) and crude protein (CP, 11.3% vs. 23.5% in DM). Data showed that ATTD of DM, CP, NDF and ADF was higher with the high-quality hay diets. Time spent eating was reduced with high-quality hay. However, time spent ruminating was longest in Group 100HQ. In all groups, ruminal pH of FRL and PARL decreased with time after the morning feeding. But 10 h later, pH of Group 100HQ was higher again compared with the other groups. Considering the average pH in FRL over all measured time points, cows in Groups 60NQ and 100HQ had higher pH values of 6.85 and 6.83, respectively. Regarding pH values in PARL, animals of Group 60NQ displayed the highest pH value (6.68), whereas the lowest value of 6.21 was found in Group 60HQ. Overall, results suggest that high-quality hay maintains the diet’s structural effectiveness by stimulating rumination and stabilising ruminal pH while greatly improving ATTD. However, the structural effectiveness of the high-quality hay gets impaired with increasing proportion of concentrate feed in the diet.     

Characterization of rumen bacterial diversity and fermentation parameters in concentrate fed cattle with and without forage

Aims: To determine the effects of the removal of forage in high‐concentrate diets on rumen fermentation conditions and rumen bacterial populations using culture‐independent methods. Methods and Results: Detectable bacteria and fermentation parameters were measured in the solid and liquid fractions of digesta from cattle fed two dietary treatments, high concentrate (HC) and high concentrate without forage (HCNF). Comparison of rumen fermentation conditions showed that duration of time spent below pH 5·2 and rumen osmolality were higher in the HCNF treatment. Simpson’s index of 16S PCR‐DGGE images showed a greater diversity of dominant species in the HCNF treatment. Real‐time qPCR showed populations of Fibrobacter succinogenes (P = 0·01) were lower in HCNF than HC diets. Ruminococcus spp., F. succinogenes and Selenomonas ruminantium were at higher (P ≤ 0·05) concentrations in the solid vs the liquid fraction of digesta regardless of diet. Conclusions: The detectable bacterial community structure in the rumen is highly diverse. Reducing diet complexity by removing forage increased bacterial diversity despite the associated reduction in ruminal pH being less conducive for fibrolytic bacterial populations. Quantitative PCR showed that removal of forage from the diet resulted in a decline in the density of some, but not all fibrolytic bacterial species examined. Significance and Impact of the Study: Molecular techniques such as DGGE and qPCR provide an increased understanding of the impacts of dietary changes on the nature of rumen bacterial populations, and conclusions derived using these techniques may not match those previously derived using traditional laboratory culturing techniques.     

Effect of niacin supplementation on rumen fermentation characteristics and nutrient flow at the duodenum in lactating dairy cows fed a diet with a negative rumen nitrogen balance

The aim of the present experiment was to ascertain if a daily niacin supplementation of 6 g/cow to lactating dairy cow diets can compensate for the decrease in rumen microbial fermentation due to a negative rumen nitrogen balance (RNB). A total of nine ruminally and duodenally fistulated lactating multiparous German Holstein cows was used. The diets consisted of 10 kg dry matter (DM) maize silage and 7 kg DM concentrate and differed as follows: (i) Diet RNB- (n = 6) with energy and utilisable crude protein (CP) at the duodenum (uCP) according to the average requirement of the animals, but with a negative RNB (-0.41 g N/MJ metabolisable energy [ME]); (ii) Diet RNB0 (n = 7) with energy, uCP, and RNB (0.08 g N/MJ ME) according to the average requirement of the animals; and (iii) Diet NA (nicotinic acid; n = 5), which was the same diet as RNB-, but supplemented with 6 g niacin/d. The negative RNB affected the rumen fermentation pattern and reduced ammonia content in rumen fluid and the daily duodenal flows of microbial CP (MP) and uCP. Niacin supplementation increased the apparent ruminal digestibility of neutral detergent fibre. The efficiency of microbial protein synthesis per unit of rumen degradable CP was higher, whereby the amount of MP reaching the duodenum was unaffected by niacin supplementation. The number of protozoa in rumen fluid was higher in NA treatment. The results indicated a more efficient use of rumen degradable N due to changes in the microbial population in the rumen when niacin was supplemented to diets deficient in RNB for lactating dairy cows.     

Effect of different levels of concentrate allowances on rumen fluid pH,nutrient digestion,nitrogen retention and growth performance of weaner lambs

This experiment was conducted for 90 d to assess the effect of feeding graded levels of concentrate allowance on rumen fermentation characteristics, performance and nutrient utilisation of weaner lambs on restricted or high concentrate allowance using 60 weaner lambs of initial average live weight of 13.90 kg BW in a randomized design. The experimental treatments were 15 or 25 g kg⁻¹ BW or ad libitum concentrate allowance. Roughage source which contained Khejri (Prosopis cineratia) and Siris (Albizia lebback) leaves in 50:50 ratio was offered ad libitum to all the animals. Lambs supplemented with 15 g or ad libitum concentrate had similar dry matter intake (4.2 kg/100 kg BW) but significantly (p < 0.01) lower than 25 g concentrate supplemented group (4.9 kg/100 kg BW). Organic matter and CP intakes increased with increasing concentrate supplementation. Apparent digestibilities of dry matter, organic matter, CP, NDF, ADF and cellulose were significantly (p < 0.01) higher in ad libitum concentrate supplemented than 15 and 25 g concentrate supplemented lambs. Daily ME intake was significantly (p < 0.05) higher in 25 g and ad libitum concentrate supplemented lambs while ME intake kg⁻¹ gain was lower in ad libitum concentrate supplemented lambs (57 MJ kg⁻¹ gain) than those supplemented with 15 or 25 g concentrate (91 MJ kg⁻¹ gain). Generally, average daily gain increased with increasing levels of concentrate supplementation. Ad libitum concentrate supplemented lambs had significantly (p < 0.01) higher daily gains (151 g) than 15 and 25 g concentrate supplemented lambs (77 and 98 g, respectively). Feed efficiency was similar for 15 and 25 g concentrate supplemented lambs but significantly (p < 0.01) lower than the ad libitum concentrate supplemented lambs. All animals were in positive N-balance and the N-balance increased with increasing concentrate supplementation. Mean rumen fluid pH was significantly (6.6, p < 0.01) lower in ad libitum concentrate supplemented lambs compared to 15 or 25 g concentrate fed lambs (6.9). Rumen NH₃-N and total-N-concentrations peaked at 3 h post-feeding. Optimum rumen fluid pH, better nutrient digestibilities, higher N-retention improved growth by 49% of ad libitum concentrate fed lambs.     

Effects of feeding high-quality hay with graded amounts of concentrate on feed intake,performance and blood metabolites of cows in early lactation

Dairy cows are commonly fed energy-dense diets with high proportions of concentrate feedstuffs to meet the increased energy needs of early lactation. However, feeding large amounts of concentrates may cause rumen acidosis and impact cow health. The hypothesis tested was that the energy supply and metabolic health of early-lactation Simmental cows can be maintained when high-quality hay rich in water-soluble carbohydrates (WSC) and crude protein (CP) is fed, despite the proportion of concentrates in the diet being reduced or even excluded. Twenty-four Simmental cows were allocated to one of four feeding groups beginning 10 d before the expected calving date, until 28 d thereafter. The feeding groups were 60CH (60% conventional fibre-rich hay plus 40% concentrate feed), 60HQH (60% high-quality hay plus 40% concentrate feed), 75HQH (75% high-quality hay plus 25% concentrate feed) and 100HQH (100% high-quality hay). The fibre-rich hay and high-quality hay differed in WSC content (110 g vs. 198 g of dry matter (DM)), neutral detergent fibre (646 g vs. 423 g of DM) and CP (65 g vs. 223 g of DM). Individual feed intake and milk production were monitored daily, and blood samples were collected weekly. Dry matter intake (DMI) and milk yield increased post partum, but 4 weeks post partum, the DMI of cows fed 100HQH only reached a daily mean DMI of 18.6 kg, whereas the DMI of the other groups averaged 21.9 kg (p < 0.046). The negative energy balance was less pronounced in cows fed 75HQH since they showed similar milk yields to the cows fed 60CH and 100HQH, but their energy intake was higher. Concentrations of milk components were similar across rations 60CH, 60HQH and 75HQH, as were most of blood parameters. Cows fed 100HQH responded to the energy deficit post partum with a higher ratio of non-esterified fatty acids to cholesterol and a higher concentration of ß-hydroxybutyrate (significant in comparison to cows fed 75HQH, p < 0.05). In conclusion, feeding high-quality hay with a WSC content of 20% in DM has the potential to decrease the proportion of concentrates in dairy cow feeding in early lactation, but cannot fully replace their supplementation due to a limited rumen capacity for forage intake.     

Effects of glyphosate residues and different concentrate feed proportions on performance,energy metabolism and health characteristics in lactating dairy cows

The aim of this study was to examine the influence of glyphosate (GL) residues in feedstuffs on performance, energy balance and health-related characteristics of lactating dairy cows fed diets with different concentrate feed proportions. After an adaption period, 64 German Holstein cows (207 ± 49 d in milk; mean ± SD) were assigned to either groups receiving a GL contaminated total mixed ration (TMR) (GL groups) or an uncontaminated TMR (CON groups) during a 16 weeks trial. Contaminated feedstuffs used were legally GL-treated peas and wheat (straw and grain). GL and CON groups were subdivided into a “low concentrate” group (LC) fed on dry matter (DM) basis of 21% maize silage, 42% grass silage, 7% straw and 30% concentrate and a “high concentrate” group (HC) composed of 11% maize silage, 22% grass silage, 7% straw and 60% concentrate for ad libitum consumption. Body condition score, body weight, DM intake and milk performance parameters were recorded. In blood serum, β-hydroxybutyrate (BHB), non-esterified fatty acids (NEFA) and glucose were measured and energy balance was calculated. Milk was analysed for GL residues. At week 0, 7 and 15, general health status was evaluated by a modified clinical score. The average individual GL intake amounted for Groups CON_LC, CON_HC, GL_LC and GL_HC to 0.8, 0.8, 73.8 and 84.5 mg/d, respectively. No GL residues were detected in milk. GL contamination did not affect body condition score, body weight, DM intake, nutrient digestibility, net energy intake, net energy balance or BHB, glucose, NEFA and milk performance parameters; whereas concentrate feed proportion and time did affect most parameters. The clinical examination showed no adverse effect of GL-contaminated feedstuffs on cows’ health condition. In the present study, GL-contaminated feedstuffs showed no influence on performance and energy balance of lactating dairy cows, irrespective of feed concentrate proportion.     

The effect of different levels of molasses on the digestibility,rumen parameters and blood metabolites in sheep fed processed broiler litter

A 28-d experiment was performed to evaluate the influence of replacing dietary corn/barley with molasses at levels of 0 (M0), 50 (M50) and 100 (M100) g/kg dietary dry matter (DM), as energy sources, in the diets containing heat-processed broiler litter (HBL) (240 g/kg DM) in male Moghani sheep. Digestibility, microbial protein supply (MPS), ruminal parameters and blood metabolites were measured. The digestibility of DM and crude protein (CP) in experimental sheep linearly increased (L, P=0.01) as level of molasses enhanced in the diets. Addition of molasses to diet linearly increased MPS (L, P=0.01) compared to sheep fed the control diet. Ruminal pH and ammonia concentrations linearly declined (L, P<0.05) as level of molasses increased in the diet. There was no difference (P>0.05) in ruminal volatile fatty acid concentrations, except a linear increase in the molar proportion of butyrate (L, P=0.02) among the molasses supplemented groups. Blood urea-N linearly decreased (L, P=0.02) in sheep fed molasses compared to the control group. It can be concluded that replacing corn/barley with molasses in sheep diet improved the utilization of the diet containing HBL.     

Milk fatty acid profile of Peruvian Criollo and Brown Swiss cows in response to different diet qualities fed at low and high altitude

Two identical experimental protocols were followed at 200 and 3,600 m above sea level (a.s.l.) determining the changes of the milk fatty acid (FA) profile of Brown Swiss (BS) and indigenous Peruvian Criollo cows (CR) as a response to diets which were designed to cover the variation in feed quality caused by season. At each site (altitude), six BS and six CR cows, adapted to >3,500 m a.s.l., were fed three dietary treatments (DS, dry-season forage; RS rainy-season forage; OC, diet optimised to meet the cow's requirements) in a 2 × 2 × 3-factorial arrangement. Intakes of FA and milk yield increased from diet DS (low quality diet) to RS and OC (high quality diet) for both cow types. Milk fat proportions of conjugated linoleic acid (CLA), C18:3 c9,c12,c15, total n-3 and polyunsaturated FA (PUFA) were highest (p < 0.05) with diet OC and higher in the lowlands than in the highlands. Low intakes of diet DS obviously resulted in a ruminal energy deficiency and body lipid mobilisation. The ruminal energy deficiency with diet DS was especially pronounced in BS, apparently reducing biohydrogenation rate and leading to lower proportions of C18:0 and higher proportions of C18:3 c9,c12,c15 in milk fat (p < 0.05). Especially C18:3 c9,c12,c15 intake did not concur with its proportion in milk fat, suggesting a strong dependence on energy status. Milk yield and FA excretion with milk were higher for BS than for CR (p < 0.05) with all three diets although milk fat content was lower (p < 0.05) for BS than CR. Milk fat of BS was richer in CLA and PUFA than milk fat of CR (p < 0.05). The desaturase indices for 18 FA were also higher for BS than CR (p < 0.05), suggesting a slightly higher Δ9-desaturase activity for BS, especially with diet DS. Milk fat content was generally higher at the high altitude than at the lowland site (p < 0.05), whereas the FA profile was unexpectedly similar across sites. Various interactions were found among diet type, cow type and altitude (site) indicating that a combination of these factors contributes to the characteristic FA profile of the respective milk.     

Effects of isobutyrate on rumen fermentation, lactation performance and plasma characteristics in dairy cows

The objective of this study was to evaluate effects of isobutyrate supplementation on rumen fermentation, lactation performance and plasma characteristics of dairy cows. Twenty multiparous second filial generation (F2) cows of a cross between Chinese Jinnan Yellow and Holstein cows at 148 ± 4.5 days in milk and 22.3 ± 0.81 kg milk production were used in a replicated 4 × 4 Latin square experiment. The treatments were: control (without isobutyrate), low (LIB), medium (MIB) and high (HIB) isobutyrate supplementation of 20, 40 and 60 g per cow per day, respectively. Experimental periods were 30 days with 15 d of adaptation and 15 d of data collection. Dry matter (DM) intake was not affected by increasing isobutyrate supplementation, but milk yields were highest for the 40 g/d isobutyrate supplementation level, where proportion of milk fat, true protein and lactose were minimized. Ruminal pH (6.38–6.24) and ammonia N (13.8–11.1 mg/100 ml) were linearly (P<0.01) decreased, whereas total VFA concentration (124–131 mM) increased at a decreasing rate with increasing isobutyrate supplementation. The ratio of acetate to propionate increased linearly (P<0.01) from 2.77 to 4.43 as isobutyrate supplementation increased due to the increase in acetate production and decrease in propionate production. Digestibilities of OM in the total tract increased linearly (P<0.01) as isobutyrate supplementation increased, digestibilities of DM and EE were highest for the 40 g/d isobutyrate supplementation level, digestibilities of CP, aNDF and ADF increased at a decreasing rate with increasing isobutyrate supplementation. Plasma concentrations of glucose and growth hormone linearly (P<0.03) increased, whereas concentrations of non-esterified fatty acids linearly (P<0.01) decreased. Results indicate that supplementation of this diet with isobutyrate changed the rumen fermentation pattern towards acetate production, improved digestion and modified plasma concentrations of glucose and growth hormone. This suggests that isobutyrate stimulated digestive microorganisms or enzymes in a dose-dependent manner with the optimum isobutyrate dose at about 40 g per cow per day in terms of improved digestion.     

Relationship between rumen methanogens and methane production in dairy cows fed diets supplemented with a feed enzyme additive

Aims: To investigate the relationship between ruminal methanogen community and host enteric methane (CH₄) production in lactating dairy cows fed diets supplemented with an exogenous fibrolytic enzyme additive. Methods and Results: Ecology of ruminal methanogens from dairy cows fed with or without exogenous fibrolytic enzymes was examined using PCR–denaturing gradient gel electrophoresis (PCR–DGGE) analyses and quantitative real‐time PCR (qRT‐PCR). The density of methanogens was not affected by the enzyme additive or sampling times, and no relationship was observed between the total methanogen population and CH₄ yield (as g per head per day or g kg^?1 DMI). The PCR–DGGE profiles consisted of 26 distinctive bands, with two bands similar to Methanogenic archaeon CH1270 negatively correlated, and one band similar to Methanobrevibacter gottschalkii strain HO positively correlated, with CH₄ yield. Three bands similar to Methanogenic archaeon CH1270 or Methanobrevibacter smithii ATCC 35061 appeared after enzyme was added. Conclusions: Supplementing a dairy cow diet with an exogenous fibrolytic enzyme additive increased CH₄ yield and altered the composition of the rumen methanogen community, but not the overall density of methanogens. Significance and Impact of the Study: This is the first study to identify the correlation between methanogen ecology and host CH₄ yield from lactating dairy cows.     

Influence of hay particle size at different concentrate and feeding levels on digestive processes and feed intake in ruminants. 2. passage,digestibility and feed intake

In order to study the main effects of particle size, three ruminally fistulated cows (550 to 580 kg BW) were fed a constant low concentrate level (3.56 kg DM/d, 20% of total DMI) and a fibre‐rich hay (approximately 60% NDF in DM) in long (28.7 mm), chopped (9.2 mm) and fine ground (2.9 mm) form in a 3 x 3 Latin square design. In another three factorial experiment with 8 wethers (4 animals were ruminally fistulated, mean BW = 68 kg) the main effects and interactions of the above mentioned hay particle sizes at two concentrate levels (10.4 to 13.3% and 29.5 to 40.1% of DMI, resp.) and two intake levels (restricted and ad libitum) were investigated. In comparison to long hay (28.7 mm), feeding of chopped hay (9.2 mm) at low concentrate levels, increased not only the hay intake (7% in dairy cows and 13% in sheep) but also the intake of digestible organic matter (12% in dairy cows and 32% in sheep), due to an increase in the apparent digestibility of OM by 3.8% in dairy cows and 8.2% in sheep. Ad libitum feeding of fine ground hay in combination with low concentrate amount in the ration increased the passage rate in the hindgut and consequently the hay intake, but not the intake of DOM, due to a significant depression of digestibility, especially of fibre fractions (4 to 7% in dairy cows and 4.5 to 14% in sheep), in comparison to 28.7 and 9.2 mm hay particle sizes. The digestibility decreased significantly with restricted feeding of fine ground hay in sheep only in comparison to 9.2 mm particle size. A threefold increase of concentrate amount levelled out all effects of the particle size reduction. The effect of particle size was more pronounced in sheep than in dairy cows.