Effects of dietary forage particle size and concentrate level on fermentation profile, in vitro degradation characteristics and concentration of liquid- or solid-associated bacterial mass in the rumen of dairy cows

This study investigated effects of dietary forage particle size (PS) and concentrate level (CL) on fermentation profiles of particle-associated rumen liquid (PARL) and free rumen liquid (FRL), in vitro degradation characteristics and concentration of bacterial mass attached to the solid or fluid rumen digesta phase in dairy cows. The experiment was a 4 × 4 Latin square design with four late-lactation dairy cows in four 23 day periods. Cows were restrictively fed (17 kg dry matter (DM)/d) one of four diets varying in the theoretical PS (6 and 30 mm) of grass hay and in the levels (approximately 200 and 550 g/kg, DM basis) of a cereal-based concentrate. Proportion of large particles (>6 mm) and the content of structural fibre in the diet increased by reducing dietary CL and, particularly, by increasing hay PS. This effect was not reflected by changes in mean total volatile fatty acid concentration or pH in the rumen. However, cows fed high concentrate diets had pH of 5.28 and 5.37 in PARL at 3 h after the last meal, when fine or long chopped hay was offered. The low pH may indicate a depression of the capacity of PARL to degrade fibre in vitro. Gas production in vitro of concentrate increased with the high concentrate diet at 12 h, suggesting that amylolytic capacity was affected only in early phases of fermentation. In addition, elevating dietary CL appeared to shift ruminal fermentation outputs from propionate to butyrate and valerate. Inclusion of coarsely chopped hay to a high concentrate diet does not appear to bring advantages due to increased structure in restrictively fed dairy cows. In addition, results suggest that the response of pH in PARL is more sensitive to dietary changes (i.e., forage PS and CL) than the response in FRL, and so PARL might be better to evaluate the risk of ruminal disfunction in dairy cows.     

Effect of the proportions of neutral detergent fibre and starch, and their degradation rates, on in vitro ruminal fermentation

Effects of proportions of neutral detergent fibre (aNDFom) and starch, as well as their degradation rates, on rumen fermentation were tested using an in vitro rumen simulation system (SIMCO). The in vitro system was designed to simulate selective particle retention and had an average fluid volume of 1150 ml with a liquid dilution rate of approximately 0.07 h⁻¹. Two types of hay (aNDFom sources) and two types of starch were each included at two different levels in the diet and were examined in an experiment following a 2×2×2 factorial arrangement of treatments (eight diet combinations). The hay was either late-cut timothy (Phleum pretense L.) or early cut meadow grass (Poa pratensis L.), with ruminal in situ aNDFom digestion rates of 0.03–0.04 and 0.07–0.08 h⁻¹, respectively. The two starch types were raw (R) and cooked (C) potato starch with previously determined in vitro ruminal digestion rates of 0.04 and 0.20 h⁻¹, respectively. The starch levels were 300 and 600 g/kg diet dry matter (DM) with the remaining being hay (282–682 g/kg DM) and peptone (14–111 g/kg DM). The aNDFom level varied among the diets with different starch levels and hay types. The peptone acted as a source of peptides and, together with ammonia salts from buffer, was used to balance the N contents of the diets. The feeding level for each of the eight vessels was 28 g DM/d. Two 10-day simulations were made with the system. The average pH was higher (P<0.05) for all treatments with raw potato starch (6.19) versus cooked starch (6.07). Protozoa scores, on a qualitative scale, declined faster at the higher starch level. The aNDFom digestibility was, as expected, higher (P<0.001) for meadow hay (0.57) than timothy (0.32), and was also higher (P<0.001) at the lower starch level (0.54) versus the higher (0.35). Microbial protein production efficiency (mg microbial N/g organic matter truly digested) was higher for the faster degrading aNDFom (P<0.01) and starch (P<0.05) sources, but was not affected by starch level. Cooked starch resulted in a lower acetate proportion (449 mmol/mol versus 591 mmol/mol VFA; P<0.001) but higher proportions of propionate (297 mmol/mol versus 236 mmol/mol VFA; P<0.001), and butyrate (169 mmol/mol versus 127 mmol/mol VFA; P<0.01). Butyrate increased with starch level (127 mmol/mol versus 169 mmol/mol VFA; P<0.01), and was also higher for meadow hay versus timothy (168 mmol/mol versus 128 mmol/mol VFA; P<0.01). Interactions between the treatments demonstrate that the response in VFA pattern to starch level is dependent on starch and aNDFom sources. Substrates such as starch and aNDFom are fermented differently depending on their rates of ruminal degradation.     

Effects of feeding supplemental palmitic acid (C16:0) on performance and milk fatty acid profile of lactating dairy cows under summer heat

The objective was to determine performance and milk fatty acid changes of high producing dairy cows in early lactation, under summer heat, by adding a supplemental rumen inert fat in the form of a saturated free fatty acid (856 g/kg C16:0/kg of total fatty acids) to the total mixed ration (TMR). Early lactation multiparous Holstein cows in two similar pens of 99 and 115 cows were used in a 2 × 2 Latin Square design experiment with 35 d periods during a period when daily high and low temperatures averaged 34.3 and 15.9 °C, the relative humidity averaged 51% and there were no rain events. The TMR was the same for both groups, consisting of approximately 435 g/kg forage and 565 g/kg concentrate, except that the vitamin/mineral premix had no added fat (control, C) or added fat (C16:0) at a level designed to deliver approximately 450 g/cow/d of supplemental fat if cows consumed 26.5 kg/d of dry matter (DM). The two TMR averaged 905 g/kg organic matter (OM), 318 g/kg neutral detergent fiber (aNDF), and 186 g/kg crude protein (CP). The ‘C’ TMR had 58 g/kg total fatty acids with an estimated net energy for lactation (NE_l) of 7.3 MJ/kg (DM), while the C16:0 TMR had 72 g/kg total fatty acids and 7.5 MJ/kg NE_l (DM). Whole tract digestibility of DM, OM, aNDF and CP tended (P<0.10) to increase, and that of fatty acids increased substantially (P<0.01), with C16:0 feeding, whereas, DM intake was not affected. Milk fat content decreased (P<0.01) with C16:0 feeding (37.5 versus 36.0 g/kg), whereas, true protein content tended (P=0.09) to increase. There was a tendency (P=0.07) for increased milk yield (36.69 versus 38.04 kg/d), while milk protein yield increased (P=0.03) with C16:0 supplementation (1.08 versus 1.13 kg/d). Milk fat yield was unaffected by treatment. Concentrations of short and medium chain milk fatty acids (C6:0–C15:0), decreased, or tended to decrease, with C16:0 addition (C13:0 and C15:0, P<0.10; all others, P≤0.05). The concentration of C16:0 increased (P<0.001) in milk triglycerides from cows fed C16:0 (27.10 versus 31.57 g/kg), the longer chain saturated fatty acids C17:0 and C18:0 decreased (P≤0.05) and other long chain unsaturated fatty acids were unaffected. Benefits of C16:0 feeding on cow productivity must be balanced against negative effects on the nutritive value of the milk (i.e., increased C16:0 in milk fatty acids) produced for human consumption. However, relatively low amounts of supplemental C16:0 (27.10 versus 31.57 g/kg in milk triglycerides for C and C16:0 supplemented cows, respectively) were actually secreted in milk, in spite of them being essentially fully digested in the digestive tract. Strategies to divide cows into production groups based on milk yield and/or milk fat proportions could further limit C16:0 secretion in milk. Supplemental dietary C16:0 may have positive effects on milk production that outweigh the negative health effects of the increased C16:0 content in the milk fat.     

Effects of formaldehyde treated mustard cake and molasses supplementation on nutrient utilization, microbial protein supply and feed efficiency in growing kids

Twenty healthy growing male kids (Sannen × Beetal and Alpine × Beetal) of 2–3 months of age, weighing 12 ± 0.61 kg, were randomly assigned to one to four dietary treatments in a 2 × 2 factorial design. Two types of isonitrogenous and isocaloric concentrate mixtures were fed to kids in four treatments being: untreated mustard cake, untreated mustard cake with molasses, formaldehyde treated mustard cake and formaldehyde treated mustard cake with molasses. Both concentrate mixtures were similar in composition with the only difference in RDP and UDP due to replacement of untreated mustard cake by formaldehyde (FA) treated mustard cake. Kids were fed concentrate and forage (berseem hay:wheat straw = 2:1) in a 50:50 ratio. A metabolism experiment of 7 days duration was conducted before the end of the experiment. Kids were housed in individual pens and fed experimental diets for 120 days. No differences occurred in digestibility of DM, OM, CP and NDF_om, but ether extract digestion in kids fed FA treated mustard cake was higher (P<0.05). Supplementation of molasses increased apparent nutrient digestibility, without influencing digestion of CP and NDF_om. Intake of DM, CP and ME did not differ among treatments. The CP content of the diet actually consumed that was supplemented with molasses was lower (P<0.01), with a higher (P<0.01) ME content, without influence of FA treatment on nutritive level of the diet consumed. N balance was higher (P<0.01) in kids fed FA treated MC and supplemental molasses. Microbial protein yield, calculated from purine derivatives excreted in urine, was similar among treatments. The DM intake in the growth experiment was higher by feeding both FA treated MC and molasses. Average daily gain was influenced by feeding FA treated MC, without any effect of supplemental molasses on growth rate of the kids. The higher DM intake and improved growth rate in kids fed FA treated MC resulted better feed efficiency. Higher UDP intake improved growth performance in kids and supplementation of molasses, with or without ruminal escape CP, has no added advantage.     

Effects of Agave salmiana Otto Ex Salm-Dyck silage as forage on ruminal fermentation and growth in goats

Ensiling of Agave salmiana Otto Ex Salm-Dyck, a widespread plant in Mexico, as a viable preservation method to create a potential animal feed resource for ruminants was investigated. Fresh A. salmiana with 205 g dry matter (DM)/kg and wilted alfalfa with 602 g DM/kg were ensiled in combinations (DM:DM) of 1000:0, 500:500 and 350:650, to evaluate feeding value of agave:alfalfa silages on ruminal fermentation and growth of goats. Chemical composition and in situ ruminal disappearance of three total mixed rations (TMRs), which included 240 g/kg DM of each silage (1000:0, 500:500 and 350:650) were determined. The TMR were used to assess ruminal fermentation and growth of 15 goats (20 ± 2.2 kg body weight (BW)). Silage pH (≤4), lactate (>25 g/kg DM) and ammonia (<50 g/kg total N) concentrations indicate that silage quality was good. Lactic acid was the main acid in all silages, acetic acid concentrations were relatively low, and butyrate was only detected in only the 1000:0 agave:alfalfa silage. Potential DM disappearance of the TMR increased quadratically as the amount of alfalfa included in the silage mixture increased. The BW gain and feed efficiency were not changed by treatment, even though DM intake decreased and aNDF intake increased linearly as the amount of alfalfa included in the silage mixture increased. Ruminal pH and butyrate increased, and ammonia N, lactate and propionate decreased linearly as alfalfa proportion of alfalfa in the silage mixture was increased. The TMR ingredient selectivity by the goats may have limited goat performance when alfalfa was included in agave silage mixtures. Because the agave:alfalfa blend improved nutritional quality, ruminal digestibility and intake of agave silage, alfalfa inclusion may improve nutritional characteristics of agave plants silages for ruminants.     

Effect of different drying procedures on the nutritive value of olive (Olea europaea var. europaea) leaves for ruminants

Fresh, freeze-, air- and oven-dried at 60 °C and 100 °C olive leaves (OL) were studied in order to determine the effect of different drying procedures on OL chemical composition, in vitro digestibility, ruminal degradability, and intestinal digestibility. The drying procedure affected all the parameters measured except for gross energy (GE; P=0.194). Protein-bound condensed tannins (CT) decreased (P=0.001) with freeze-, air- and 60 °C drying (from 1.25 up to 0.82 g/kg dry matter, DM). Total CT were only decreased (P=0.001) by drying at 60 °C (from 10.0 to 6.24 g/kg DM). The in vitro crude protein (CP) digestibility increased (P<0.001) with drying except for oven-drying at 100 °C up to 58%. Values for CP digestibility found in freeze- and air-dried OL were not different (P>0.05). No differences (P>0.05) were observed between CP digestibility in air- and oven-dried at 60 °C OL. Effective degradability of DM and CP increased from 0.53 to 0.62 (P=0.005) and from 0.46 to 0.64 (P=0.002), respectively after treatment. The apparent intestinal digestibility of undegraded CP in the rumen was only affected (P=0.046) by oven-drying, which increased it from 0.33 to 0.39. As air-drying did not have detrimental effects on the OL nutritive value it could be an appropriate, simple and low-cost procedure for olive-leaves preservation.     

Effect of roughage level in a total mixed ration on feed intake, ruminal fermentation patterns and chewing activity of early-weaned calves with ad libitum access to grass hay

In this study, two total mixed rations (TMR, based on dry ingredients) consisting (per kg dry matter (DM)) of 300 or 400 g finely chopped hay mixture of grass and alfalfa (H30 versus H40) were compared concerning their effects on dry matter intake (DMI), ruminal fermentation patterns and chewing activity of early-weaned (8 weeks milk-fed) calves. Ten ruminally cannulated male German Holstein calves were randomly assigned to two dietary treatments (n = 5) and observed from an age of 8–15 weeks. One group received the H30 (11.3 MJ metabolizable energy (ME)/kg DM) and the other the H40 (10.7 MJ ME/kg DM) TMR. All calves received grass hay (9.0 MJ ME/kg DM) separately. Water, TMR and hay were offered ad libitum twice daily (08:00 and 16:00 h). Rumen fluid was collected via cannula at an age of 9, 11, 13 and 15 weeks, twice weekly just prior to as well as 1, 3, 5 and 7 h after morning feeding. Chewing activity was recorded by a special head collar. As the calves aged DMI increased rapidly congruent with the recommended range for weaned calves. Because of the differing energy supply, calves receiving the H30 TMR were heavier than calves receiving the H40 TMR (139 kg versus 123 kg, P=0.007). During the trial ruminal pH of all calves were within the target range (6.2 ± 0.5), indicating physiological ruminal fermentation patterns. Daily mean ruminal pH was uninfluenced by treatment, however at an age of 13 and 15 weeks H30 showed a higher short chain fatty acid (SCFA) level than H40 (P=0.098; P=0.036). At an age of 15 weeks H30 showed a critical decrease in ruminal pH (3 h after feeding: 5.7) corresponding to a higher ruminal SCFA concentration (148.2 mmol/L, P=0.007). Chewing activity was well developed at an early age due to an increasing DMI after weaning. At an age of 15 weeks chewing activity (per day: 613–743 min total chewing; 358–418 min rumination) was similar to that of adult cows. In summary, feeding a dry TMR consisting per kg DM of 300–400 g hay to early-weaned calves can be recommended for a successful calf rearing up to an age of 15 weeks.     

Effects of linseed lipids fed as rolled seeds, extruded seeds or oil on organic matter and crude protein digestion in cows

Effects of fatty acids of linseed in different forms, on ruminal fermentation and digestibility were studied in dry cows fitted with ruminal and duodenal cannulas. Four diets based on maize silage, lucerne hay and concentrates (65/10/25 dry matter (DM)) were compared in a 4 × 4 Latin square design experiment where the diets were: control diet (C), diet RL supplied 75 g/kg DM rolled linseeds, diet EL supplied 75 g/kg DM extruded linseeds, and diet LO supplied 26 g/kg DM linseed oil and 49 g/kg DM linseed meal. The diets did not differ in total organic matter (OM) and fibre digestibility, in forestomach and intestinal OM digestibility, and in duodenal N flow. Microbial N duodenal flow tended to be lower for RL versus C diet (P<0.1). Extrusion did not reduce ruminal crude protein (CP) degradation in vivo and in situ. Volatile fatty acid concentration and pattern, and protozoa concentration in the rumen, did not vary among diets. Results confirm the absence of a negative effect of a moderate supply of linseed on rumen function, as well as no effect of extrusion on its ruminal CP degradability.     

Effects of malic acid on rumen fermentation, urinary excretion of purine derivatives and feed digestibility in steers

The objective of this study was to evaluate the effects of malic acid (MA) supplementation on rumen fermentation, urinary excretion of purine derivatives (PDs) and whole gastro-intestinal tract feed digestibility in steers. Eight ruminally cannulated Simmental steers (465 ± 13 kg) were used in a replicated 4 × 4 Latin square design. The treatments were: control (without MA), LMA (MA-low), MMA (MA-medium) and HMA (MA-high) with 0.0, 7.8, 15.6 and 23.4 g MA per kg dry matter (DM), respectively. Diets consisted of corn stover and concentrate (60/40, DM basis). DM intake was approximately 9 kg per day, which was 90% of ad libitum intake including 5.4 kg corn stover and 3.6 kg concentrate. Ruminal pH (range of 6.91 to 6.56), ratio of acetate to propionate (range of 3.88 to 3.25), ammonia N (range of 9.03 to 6.42 mg/100 ml) and lactate (range of 91.25 to 76.31 mg/100 ml) decreased linearly as MA supplementation increased, whereas total volatile fatty acid (VFA) concentration (range of 55.68 to 61.49 mM) linearly (P < 0.05) increased with increase in MA supplementation. In situ ruminal neutral detergent fiber (aNDF) degradation of corn stover was improved but the crude protein (CP) degradability of concentrate mix was decreased with increasing the dose of MA. Urinary excretion of PDs was quadratically (P < 0.01) changed with altering MA supplementation (67.88, 72.74, 75.81 and 73.78 mmol/day for control, LMA, MMA and HMA, respectively). Similarly, digestibilities of DM, organic matter (OM), NDF and acid detergent fiber (ADF) in the total tract were also quadratically increased with increasing MA, and no differences in terms of CP and ether extract digestibility were observed. The results indicate that MA supplementation has the potential to improve rumen fermentation and feed digestion in beef cattle. The MA stimulates the digestive microorganisms or enzymes in a quadratic response. In the experimental conditions of this trial, the optimum MA dose was 15.6 g MA per kg DM.     

Effect of ruminally protected fat on in vitro fermentation and apparent nutrient digestibility in buffaloes (Bubalus bubalis)

Experiments were conducted to evaluate effects of supplementation of calcium salts of long chain fatty acids (Ca-LCFA) as a rumen inert fat (PF) on in vitro fermentation and apparent nutrient digestion in adult buffaloes fed wheat straw based diets. For the in vitro fermentation study, five total mixed rations (TMR) consisting of a concentrate mixture (CM), green Sorghum bicolor, WS and supplemented without (C) or with 30 g/kg dry matter (DM) rice bran fatty acid oil (RBO) (30 RBO) or 20 g/kg RBO + 10 g/kg PF (20 RBO/10 PF) or 10 g/kg RBO + 20 g/kg PF (10 RBO/20 PF) or 30 g/kg PF in the DM in the ratio of 340:50:580:30 were prepared. The in vitro DM degradability (IVDMD), TN, trichloro acetic acid precipitable N (TCA-N), non-protein N (NPN) and ammonia N (NH₃-N) were similar among groups. Within the fat supplemented groups, total volatile fatty acid (TVFA) concentration increased linearly (P=0.025) with PF supplementation. Apparent nutrient digestibility was determined on 20 adult buffaloes divided into five equal groups fed CM supplemented without (C) or with 300 g RBO (30 RBO) or 200 g RBO + 100 g PF (20 RBO/10 PF) or 100 g RBO + 200 g PF (10 RBO/20 PF) or 300 g PF (30 PF) along with limited green S. bicolor and WS maintaining forage: concentrate ratio of 650:350. Fat supplementation had no effect on the DM intake and apparent digestibilities of DM, organic matter (OM), crude protein (CP), total carbohydrate (TCHO) and neutral detergent fiber (aNDF). Within fat supplemented groups, inclusion of PF increased digestibilities of DM, OM, ether extract (EE), TCHO, aNDF and ADF. Supplemental fat also increased the digestible energy (DE) and metabolizable energy (ME) content of the diet, which also increased linearly with PF supplementation. All buffaloes were in positive N, Ca and P balances. We conclude that 200–300 g supplemental PF in the form of Ca-LCFA can be included in straw based diets fed to buffaloes to increase its energy density without adversely affecting DM intake and digestibility.     

Relationships between kernel vitreousness and dry matter degradability for diverse corn germplasm: II. Ruminal and post-ruminal degradabilities

Correlations between kernel vitreousness and ruminal in situ (RDMD) and total tract dry matter (TDMD; sum of ruminal in situ and post-ruminal in vitro measurements) degradabilities were determined for 33 diverse corn germplasm sources. These included a wide range of endosperm characteristics from opaque 2 (o2) types to densely packed flint types, and a number of intermediates. Harvests were done at two growth stages; 1/2 milk-line (ML) and black-layer (BL). Kernels from middle portion of ears were oven dried at 40 °C for 72 h and ground through a Wiley mill (6 mm screen) for measurement of in situ RDMD after 0 and 14 h of incubation using two steers (1.5 g/bag × 8 replicates per time point per steer in 5 cm × 5 cm bags of 50 μm pore size). Residue from the 14 h bags proceeded to an 8 h in vitro enzymatic post-ruminal digestion after which the residue was oven dried at 62 °C for 48 h and dry matter content determined. Inbred by harvest-stage interactions were observed for 0-h disappearance and TDMD. Vitreousness had strong negative correlations with degradability measurements, particularly for more mature (BL) samples (−0.728, −0.770 and −0.603) versus ML (−0.569, −0.541 and −0.338) for 0 h disappearance, RDMD and TDMD, respectively. Vitreousness was highly correlated with corn degradability, especially at a black-layer stage of harvest, in this diverse corn germplasm.     

Effects of glutamate on microbial efficiency and metabolism in continuous culture of ruminal contents and on performance of mid-lactation dairy cows

Three experiments were conducted to determine (1) the dose of glutamate needed to alter fermentation and nitrogen (N) partitioning in a continuous culture system, (2) the effect of supplemental glutamate in diets varying in rumen-undegradable protein on fermentation and N partitioning in a continuous culture system, and (3) the effect of dietary supplemental glutamate on the lactational performance of mid-lactation dairy cows, total tract nutrient digestibility, and ruminal microbial N synthesis. In experiment 1, the equivalent of 0, 40, or 80 g of supplemental glutamate per cow per day was added to a basal diet. The dietary treatments were evaluated in a continuous culture system. Glutamate decreased protein digestion and microbial growth while increasing non-ammonia, non-microbial N. Within the doses tested, the equivalent of 80 g glutamate per cow per day most effectively increased non-ammonia, non-microbial N. In experiment 2, dietary treatments consisted of diets formulated to have low rumen-undegradable protein (LRUP; 62 g/kg DM), low rumen-undegradable protein plus the equivalent of 80 g glutamate per cow per day (LRUP + G), and high rumen-undegradable protein [HRUP; 68 g/kg dry matter (DM)]. The dietary treatments were evaluated in a continuous culture system. When added to a diet low in rumen-undegradable protein, glutamate tended to decrease DM and organic matter (OM) digestibility, decreased total volatile fatty acid (VFA) production, increased fermenter pH, increased feed N converted to microbial N, and had no effect on microbial N production. The LRUP + G diet was similar to the HRUP diet and different from the LRUP diet in feed N converted to microbial N and ammonia N concentration. In experiment 3, 40 Holstein cows were utilized in a crossover study to test the effects of two dietary treatments: 0 or 80 g of supplemental glutamate per cow per day. The addition of glutamate to the diet of lactating dairy cows did not improve lactational performance or nutrient digestibility. Based on the results from these in vitro and in vivo experiments, the addition of glutamate to lactating cow diets is not recommended.     

Diet supplementation with cinnamon oil,cinnamaldehyde, or monensin does not reduce enteric methane production of dairy cows

This study was conducted to evaluate the effect of dietary addition of cinnamon oil (CIN), cinnamaldehyde (CDH), or monensin (MON) on enteric methane (CH₄) emission in dairy cows. Eight multiparous lactating Holstein cows fitted with ruminal cannulas were used in a replicated 4×4 Latin square design (28-day periods). Cows were fed (ad libitum) a total mixed ration ((TMR); 60 : 40 forage : concentrate ratio, on a dry matter (DM) basis) not supplemented (CTL), or supplemented with CIN (50 mg/kg DM intake), CDH (50 mg/kg DM intake), or monensin (24 mg/kg of DM intake). Dry matter intake (DMI), nutrient digestibility, N retention, and milk performance were measured over 6 consecutive days. Ruminal degradability of the basal diet (with no additive) was assessed using in sacco incubations (0, 2, 4, 8, 16, 24, 48, 72 and 96 h). Ruminal fermentation characteristics (pH, volatile fatty acids (VFA), and ammonia (NH₃)) and protozoa were determined over 2 days. Enteric CH₄ emissions were measured over 6 consecutive days using the sulfur hexafluoride (SF₆) tracer gas technique. Adding CIN, CDH or MON to the diet had no effects on DMI, N retention, in sacco ruminal degradation and nutrient digestibility of the diet. Ruminal fermentation characteristics and protozoa numbers were not modified by including the feed additives in the diet. Enteric CH₄ emission and CH₄ energy losses averaged 491 g/day and 6.59% of gross energy intake, respectively, and were not affected by adding CIN, CDH or MON to the diet. Results of this study indicate that CIN, CDH and MON are not viable CH₄ mitigation strategies in dairy cows.     

The effects of and interactions between the maturity of grass silage and concentrate starch source when offered as total mixed rations on the performance of dairy cows

A 2 × 2 factorial feeding experiment was conducted to examine the effects of varying the maturity level of the grass used to prepare silage and the nature of concentrate starch source and their interactions on dry matter intake (DMI), diet digestibility, energy corrected milk (ECM) production and milk composition in dairy cows. Twenty-eight multiparous Swedish Red dairy cows, 133 ± 45 days in milk (DIM), with an average milk yield of 30 ± 4 kg/day and a live weight of 624 ± 69 kg were blocked by DIM and randomly assigned to seven replicated balanced 4 × 4 Latin squares with four 21-day experimental periods. The experimental diets consisted of four total mixed rations (TMR) consisting of early-cut grass silage (EGS) supplemented with either barley- or maize-based concentrate and late-cut grass silage (LGS) supplemented with either barley- or maize-based concentrate. All TMR contained identical proportions of forage (51%) and concentrate (49%). Total tract digestibility was estimated by determining indigestible NDF (iNDF) concentrations in feeds and faeces and using iNDF as an internal marker. The feeds’ ruminal degradation parameters were determined using both in situ (nylon bag) and in vitro (gas production (GP)) techniques. Cows offered diets containing EGS had greater (P < 0.001) daily dry matter (DM) intakes, ECM yields and total tract digestibilities for DM and organic matter (OM), but these were not affected by the nature of the concentrate starch source. No interaction between the maturity of the silage and the nature of the concentrate starch source was observed for DMI, diet digestibility or ECM yield. Both grass silages and concentrates had similar rates of ruminal degradation of NDF when measured in situ. The in situ DM (P < 0.001) and starch (P = 0.001) degradation rates of barley-based concentrate were greater than those for maize-based concentrate. In vitro OM GP rates and extents were similar for both concentrate feeds. The results showed that diets containing EGS offered better animal performance and diet digestibility than diets containing LGS. The concentrate starch source did not affect animal performance, but total NDF digestibility was better with diet containing barley- than maize-based concentrate.     

Effects of exogenous fibrolytic enzymes on in vitro ruminal fermentation of substrates with different forage:concentrate ratios

Batch cultures of mixed rumen micro-organisms were used to study the effects of three fibrolytic enzymes (xylanase from Trichoderma viride (XYL) and fibrolytic enzymes from Aspergillus niger (ASP) and Trichoderma longibrachiatum (TR)) on the fermentation of three substrates composed of grass hay:concentrate in the proportions (dry matter (DM) basis) of 0.7:0.3 (HF), 0.5:0.5 (MF) and 0.3:0.7 (LF). Enzymes were characterized for xylanase, endoglucanase, exoglucanase and amylase activities, and were supplied at rates of 40 and 80 enzymatic units/g substrate DM. In 8 h incubations, all enzymes increased (P=0.048 to P<0.001) the true degradability of substrate DM and the production of acetate, propionate, total volatile fatty acids (VFA) and gas. After 24 h incubation, some of the observed effects disappeared, but all enzymes still increased (P=0.028 to P<0.001) the degradability of substrate acid detergent fibre and the production of acetate, propionate and total VFA. For all enzymes, the effects on ruminal variables were less marked at 24 than at 8 h of incubation. Only few significant (P=0.044 to P=0.001) enzyme × substrate interactions were detected, although the magnitude of the response for each substrate varied with the enzyme. When considering the amount of organic matter apparently fermented (OMAF) and the methane:OMAF ratio as main variables, TR80 produced the greatest increase in OMAF (17.0%) for HF substrate, with ASP80 and TR40 having similar values (11.1 and 12.6%), and XYL and ASP40 showing no effects (P>0.05). A decrease (P<0.05) of methane:OMAF ratio was only found for TR80 at 8 h (17.4%). All enzymes, with the exception of ASP40, increased (P<0.05) OMAF at 8 h for MF substrate (11.3–25.4%), TR80 showing the greatest response. After 24 h of incubation, both doses of XYL and TR increased (P<0.05) OMAF (mean value 8.2%) and decreased methane:OMAF ratio (mean value 9.5%). All enzymes increased significantly OMAF with LF substrate at 8 h (7.5–19.9%), but after 24 h no effect (P>0.05) was detected on OMAF and methane:OMAF ratio. In general, few differences were detected between both doses of enzymes, which indicate than the used enzymes would be effective in enhancing ruminal degradation of substrates at a dose lower than 80 enzymatic units/g substrate DM.     

Prediction of the digestibility of primary growth and regrowth grass silages from chemical composition, pepsin-cellulase solubility and indigestible cell wall content

Prediction of organic matter (OM) digestibility (OMD) of primary growth and regrowth grass silages was studied based on their chemical composition, pepsin-cellulase solubility of OM (OMS) and indigestible neutral detergent fibre (INDF) content. Twenty-five primary and 28 regrowth silages were harvested from mixed timothy (Phleum pratense) meadow fescue (Festuca pratensis) or timothy cocksfoot (Dactylis glomerata) swards by varying the dates of the first and second harvest. In vivo OMD was measured with sheep and indigestible NDF was determined by 12 days ruminal incubation of forage samples in nylon bags using dairy cows fed a forage-based diet. Chemical composition of the silages was significantly correlated with digestibility, but single regression equations led to an unacceptable prediction accuracy of OMD (RMSE>40 g/kg DM). Pepsin-cellulase solubility reliably predicted OMD of primary growth silages (RMSE = 10.8 g/kg DM), but was less accurate for regrowth silages (RMSE = 25.9 g/kg). The prediction accuracy of OMD could be improved by using different equations for the two silage types. Indigestible NDF predicted OMD more accurately than OMS for all silages and especially for the regrowth silages. In contrast to OMS, the relationship between INDF and OMD was similar for both silage types.     

Effect of the level of dry matter and protein and degradation rate of starch on in vitro ruminal fermentation

Effects of starch type, feeding level and level of a mixed N source upon rumen fermentation were examined using an in vitro rumen simulation system (i.e., SIMCO) with a fluid volume of 1100 ml and liquid dilution rate of approximately 0.07/h. Two sources of starch, two feeding levels and two levels of N were examined in an experiment following a 2 × 2 × 2 factorial arrangement of treatments. The starch sources were raw slowly degrading (R), and cooked fast degrading (C), potato starch and constituted 450 g/kg diet dry matter (DM). The remaining was supplied in the form of a grass hay mixture. The feeding levels were 20 (DM20) and 40 (DM40) g DM/d and the diet N level was either low (N1) or high (N2), using peptone and ammonia salt additions in the buffer. Two simulations of 10 days each were completed. The amount of bicarbonate in buffer was varied according to feeding level, and pH (average 6.3) did not differ between treatments. An increased degradation rate of starch (R vs. C) depressed neutral detergent fibre (aNDFom) digestibility (0.46 vs. 0.36) and organic matter true digestibility (OMTD; 0.73 vs. 0.68), but there were no other treatment effects on digestibility. The VFA production efficiency (average 0.47 g VFA/g OMTD) was not affected by the main treatments, although an interaction between starch type and feeding level occurred. A decline in protozoa rating over the 10 day simulations was more apparent at the lower feeding level (DM20), indicating poor growth conditions for protozoa. Higher microbial efficiency (11.0 vs. 8.9 mg microbial N/g OMTD) and a higher proportion of propionate (272 vs. 207 mmol/mol VFA) occurred at DM20 compared to DM40. Increased degradation rate of starch (i.e., R vs. C) resulted in an improved microbial N efficiency (8.8 vs. 11.2 mg/g OMTD) and an increase in the proportion of propionate (226 vs. 253 mmol/mol VFA) at the expense of acetate (610 vs. 591 mmol/mol VFA). Increasing the level of N (i.e., N1 vs. N2) improved the microbial N efficiency (9.2 vs. 10.7 mg/g OMTD) and increased the proportion of propionate (230 vs. 249 mmol/mol VFA) and butyrate (100 vs. 119 mmol/mol VFA) at the expense of acetate (629 vs. 572 mmol/mol VFA). Interactions between starch type and N level upon VFA patterns were apparent. Results support earlier findings in that carbohydrate degradation rate is an important factor determining microbial growth rates and VFA distribution.     

The influence of addition of gallic acid, tannic acid, or quebracho tannins to alfalfa hay on in vitro rumen fermentation and microbial protein synthesis

Tannins may reduce rumen degradability of protein, increase the proportion of feed protein reaching the lower digestive tract for enzymatic digestion and thereby increase the efficiency of protein utilization. The objective was to assess the effects of different types and levels of tannins on rumen in vitro gas production and its kinetics, in vitro true degradability (IVTD) and rumen degradability of protein (IVRDP), and microbial protein synthesis by incubating alfalfa (Medicago sativa L.) hay in buffered rumen fluid. Alfalfa was incubated in buffered rumen fluid with and without the addition of different levels of gallic acid (GA), quebracho tannin (QT), or tannic acid (TA). Tannins at the lower inclusion levels had minimal effects on fermentation products compared to the higher levels. Addition of QT and TA reduced ammonium-N (NH₄⁺-N) concentration. Addition of QT at 20, 40, and 60 g/kg DM decreased NH₄⁺-N by 2, 7, and 12% compared with control whereas addition of TA reduced NH₄⁺-N by 5, 6, and 12% when added at 20, 40 and 60 g/kg DM, respectively. In experiment 2, addition of QT at 50, 100, and 150 g/kg DM, resulted in reduction of NH₄⁺-N by 12, 30, and 51%, respectively, compared with the control. Addition of TA at 50, 100, and 150 g/kd DM reduced NH₄⁺-N by 14, 26, and 47% compared with control. Inclusion of QT at 50, 100, 150 DM reduced IVRDP by 13, 30, and 36% compared with control whereas at these levels of inclusion, TA resulted in reduction of IVRDP by 14, 25, and 48%. Rate of gas production decreased (P<0.001), while asymptotic gas production increased (P<0.0001) with increasing level of GA and TA. Quebracho tannin decreased (P<0.0001) both the rate and asymptotic of gas production. Gallic acid had a positive effect on fermentation as indicated by increased gas production and total short chain fatty acids (SCFA) production. Quebracho tannin decreased 24 h gas production, IVTD, and total SCFA production. Acetate to propionate ratio increased with the addition of GA and but decreased when QT was added. Addition of tannins did not markedly increase total purines but numerical values tended to be higher in the presence of tannins compared with the control. Efficiency of microbial growth was lower in the presence of GA and unaltered by TA, but higher in the presence of QT compared with the control. The effect of tannins on rumen fermentation and protein degradation varied with type and level of tannins. In vivo studies will be conducted to validate the in vitro results.     

Effect of disodium fumarate on ruminal metabolism and rumen bacterial communities as revealed by denaturing gradient gel electrophoresis analysis of 16S ribosomal DNA

The aim of the present study was to examine the effects of feeding diets with addition of disodium fumarate (DF) to goats on ruminal metabolism and changes of rumen bacterial communities. Four cannulated goats were used in a 4 × 4 Latin square design. The results showed that ruminal pH increased linearly (P<0.01)as the amount of DF added increased, while lactate production decreased linearly (P<0.01). DF addition did not affect the production of acetate, propionate, butyrate, TVFA and NH₃-N. The effect of DF on the changes in rumen bacterial-community structure of goats was analyzed using 16S rDNA-based approaches. Amplicons of the V6-V8 variable regions of bacterial 16S rDNA were analyzed by denaturing gradient gel electrophoresis (DGGE), cloning and sequencing. Differences in rumen bacterial community structure were determined based on the Shannon index of diversity for pairwise comparison of the DGGE fingerprints and revealed significant changes in rumen microbiota after DF addition. As compared with those fed with the control diet, goats fed on the diets with DF addition showed a higher bacterial diversity. The sequences of seven amplicons in total 11 clones showed less than 97% similarity with those of previously identified or unidentified bacteria, suggesting that most bacteria in the gastrointestinal tract have not been cultured or identified. Amplicons related to Succinivibrio dextrinosolvens species were found in most DGGE fingerprints derived from goats on the diet containing DF, but not in goats on the control diet. These results demonstrated the ability of DF to improve the metabolism of rumen lactate fermentation and to influence the bacterial composition of the rumen in goats.     

Production of trans C18:1 and conjugated linoleic acid in continuous culture fermenters fed diets containing fish oil and sunflower oil with decreasing levels of forage

Previously, feeding fish oil (FO) and sunflower seeds to dairy cows resulted in the greatest increases in the concentrations of vaccenic acid (VA, t11 C18:1) and conjugated linoleic acid (CLA) in milk fat. The objective of this study was to evaluate the effects of forage level in diets containing FO and sunflower oil (SFO) on the production of trans C18:1 and CLA by mixed ruminal microbes. A dual-flow continuous culture system consisting of three fermenters was used in a 3 × 3 Latin-square design. Treatments consisted of (1) 75:25 forage:concentrate (HF); (2) 50:50 forage:concentrate (MF); and (3) 25:75 forage:concentrate (LF). FO and SFO were added to each diet at 1 and 2 g/100 g dry matter (DM), respectively. The forage source was alfalfa pellets. During 10-day incubations, fermenters were fed treatment diets three times daily (140 g/day, divided equally between three feedings) as TMR diet. Effluents from the last 3 days of incubation were collected and composited for analysis. The concentration of trans C18:1 (17.20, 26.60, and 36.08 mg/g DM overflow for HF, MF, and LF treatments, respectively) increased while CLA (2.53, 2.35, and 0.81 mg/g DM overflow) decreased in a linear manner (P < 0.05) as dietary forage level decreased. As dietary forage levels decreased, the concentrations of t10 C18:1 (0.0, 10.5, 33.5 mg/g DM) in effluent increased ( P < 0.05) and t10c12 CLA (0.08, 0.12, 0.35 mg/g DM) tended to increases (P < 0.09) linearly. The concentrations of VA (14.7, 13.9, 0.0 mg/g DM) and c9t11 CLA (1.78, 1.52, 0.03 mg/g DM) in effluent decreased in a linear manner ( P < 0.05) as dietary forage levels decreased. Decreasing dietary forage levels resulted in t10 C18:1 and t10c12 CLA replacing VA and c9t11 CLA, respectively, in fermenters fed FO and SFO.