Influence of synchronizing protein and starch degradation in the rumen on nutrient utilization and microbial protein synthesis

Effects of corn silage and grain expressing α-amylase on ruminal nutrient digestibility, microbial protein synthesis, and enteric methane emissions in lactating cows

Increasing ruminal starch digestibility has the potential to improve microbial protein synthesis (MPS), milk production, and feed efficiency. Enogen corn (Syngenta Seeds LLC) expresses high α-amylase activity, and we evaluated effects of Enogen corn silage (CS) and grain (CG) on ruminal starch digestibility, MPS, and milk production in lactating dairy cows. Fifteen Holstein cows (6 ruminally cannulated and 9 noncannulated; average ± standard deviation at the beginning of the trial: 170 ± 40 d in milk; milk yield, 37.2 ± 7.73 kg/d; body weight, 714 ± 37 kg) were used in a replicated 3 × 3 Latin square design (28 d per period) with 3 treatments: a diet containing isoline CS and CG (control, CON); a diet with Enogen CS and isoline CG (ECS); and a diet with Enogen CS and CG (ECSCG). Dry matter (DM; 30%), starch (35% of DM), and particle size distribution of the isoline and Enogen CS were similar. However, the mean particle size of Enogen CG was larger (1.05 vs. 0.65 mm) than that of the isoline CG. Cannulated cows were used for digestibility and nutrient flow measurements, noncannulated cows were used for enteric CH₄ measurements, and all cows were used for production evaluation. Dry matter intake (DMI) and milk yield were greater for ECS and ECSCG compared with CON (26.7 and 26.6 vs. 25.1 kg/d and 36.5 and 34.1 vs. 33.1 kg/d, respectively) without a difference between ECS and ECSCG. Milk protein yield was greater (1.27 vs. 1.14 and 1.17 kg/d) for ECS compared with CON and ECSCG. Milk fat content was greater (3.79 vs. 3.32%) for ECSCG compared with ECS. Milk fat yield and energy-corrected milk did not differ among treatments. Ruminal digestibilities of DM, organic matter, starch, and neutral detergent fiber were not different among treatments. However, ruminal digestibility of nonammonia, nonmicrobial N was greater (85 vs. 75%) for ECS compared with ECSCG. Total-tract apparent starch digestibility was lower (97.6 and 97.1 vs. 98.3%) for ECS and ECSCG compared with CON, respectively, and tended to be lower (97.1 vs. 98.3%) for ECSCG compared with ECS. Ruminal outflows of bacterial OM and nonammonia N tended to be greater for ECS than for ECSCG. Efficiency of MPS tended to be greater (34.1 vs. 30.6 g of N/kg of organic matter truly digested) for ECS versus ECSCG. Ruminal pH and total and individual short-chain fatty acid concentrations did not differ among treatments. Concentration of ruminal NH₃ for ECS and ECSCG was lower (10.4 and 12.4 vs. 13.4 mmol/L, respectively) compared with CON. Methane per unit of DMI decreased for ECS and ECSCG compared with CON (11.4 and 12.2 vs. 13.5 g/kg of DMI, respectively) without a difference between ECS and ECSCG. In conclusion, ECS and ECSCG did not increase ruminal or total-tract starch digestibility. However, the positive effects of ECS and ECSCG on milk protein yield, milk yield, and CH₄ per unit of DMI may show potential benefits of feeding Enogen corn. Effects of ECSCG were not apparent when compared with ECS, partly due to larger particle size of Enogen CG compared with its isoline counterpart.

The Effect of Forage Source and Concentrated Liquid Feedstuff Supplementation on Improving the Synchronization of Ruminant Dietary Energy and Nitrogen Release In Vitro

This study aimed to investigate the effect of supplementation with a mixture of molasses and condensed molasses fermentation solubles (M-CMS) in different synchronization diets formulated with different forage sources in an attempt to improve the fermentation efficiency of diets by M-CMS. In the first experiment, three levels of M-CMS (N: 0%; L: 1.75%; and H: 3.50%) were supplied to diets with or without corn silage to evaluate the supplementation effect on the diet with a synchrony index (SI) of 0.80. In the second experiment, diets containing different corn silage levels (60 or 30% of the forage source) were used to evaluate the effects of M-CMS supplementation on higher SI (at 0.88). The in vitro digestibility, fermentation products, microbial crude protein (MCP), and gas kinetic parameters were determined after 48 h of fermentation. The results demonstrated that M-CMS supplementation improved MCP synthesis in both diets with low and high SI, but did not enhance digestibility. M-CMS supplementation was beneficial to the fermentation stability and extent. It also affected the gas kinetic parameters of the fast- and slow-degradation fractions during fermentation. M-CMS supplementation improved MCP synthesis in diets containing less corn silage. The forage source and degradation rate of individual ingredients should be considered simultaneously to enhance the rumen fermentation efficiency. M-CMS provided a practical choice to further improve MCP synthesis and fermentation stability, even in a diet with high SI.

Dietary wheat and reduced methane yield are linked to rumen microbiome changes in dairy cows

Fermentation of pasture grasses and grains in the rumen of dairy cows and other ruminants produces methane as a by-product, wasting energy and contributing to the atmospheric load of greenhouse gasses. Many feeding trials in farmed ruminants have tested the impact of dietary components on feed efficiency, productivity and methane yield (MeY). Such diets remodel the rumen microbiome, altering bacterial, archaeal, fungal and protozoan populations, with an altered fermentation outcome. In dairy cows, some dietary grains can reduce enteric methane production. This is especially true of wheat, in comparison to corn or barley. Using a feeding trial of cows fed rolled wheat, corn or barley grain, in combination with hay and canola, we identified wheat-associated changes in the ruminal microbiome. Ruminal methane production, pH and VFA concentration data together with 16S rRNA gene amplicon sequences were used to compare ruminal bacterial and archaeal populations across diets. Differential abundance analysis of clustered sequences (OTU) identified members of the bacterial families Lachnospiraceae, Acidaminococcaceae, Eubacteriaceae, Prevotellaceae, Selenomonadaceae, Anaerovoracaceae and Fibrobacteraceae having a strong preference for growth in wheat-fed cows. Within the methanogenic archaea, (at >99% 16S rRNA sequence identity) the growth of Methanobrevibacter millerae was favoured by the non-wheat diets, while Methanobrevibacter olleyae was unaffected. From the wheat-preferring bacteria, correlation analysis found OTU strongly linked to reduced MeY, reduced pH and raised propionic acid levels. OTU from the genera Shuttleworthia and Prevotella_7 and especially Selenomonadaceae had high anti-methane correlations. An OTU likely representing (100% sequence identity) the fumarate-reducing, hydrogen-utilising, rumen bacterium Mitsuokella jalaludinii, had an especially high negative correlation coefficient (-0.83) versus MeY and moderate correlation (-0.6) with rumen pH, strongly suggesting much of the MeY suppression is due to reduced hydrogen availablity. Other OTU, representing as yet unknown species from the Selenomonadaceae family and the genera Prevotella_7, Fibrobacter and Syntrophococcus also had high to moderate negative MeY correlations, but low correlation with pH. These latter likely represent bacterial species able to reduce MeY without causing greater ruminal acidity, making them excellent candidates, provided they can be isolated, for development as anti-methane probiotics.

Feeding strategies with total mixed ration and concentrate may improve feed intake and carcass quality of Hanwoo steers

This study examined the impact of using total mixed ration (TMR) and concentrate on feed intake, daily gain, carcass yield grade, and carcass quality grade of Hanwoo steers and its subsequent economic efficiency. Thirty six 7-month-old Hanwoo steers were assigned to one of the four treatment groups, and each group was divided into three repeated pens, with each repeated pen comprising three steers. The treatment groups were: 1) separate feeding with commercial concentrate and forage (namely, SCF) for the entire experimental period; 2) TMR feeding for a growing period followed by SCF for the early and late fattening period (namely, TMRGSCF); 3) TMR feeding for growing and an early fattening period followed by SCF for the late fattening period (namely, TMREFSCF); and 4) TMR feeding for the entire experimental period (namely, TMRW). The results showed that the SCF treatment had significantly (p < 0.05) higher feed intake during the growing period than other treatments. In contrast, the total feed intake had little difference during early and late fattening as well as the whole period regardless of feeding strategies. Daily gain showed no difference during the growing period. However, it was significantly higher in SCF and TMREFSCF treatments for the early and late fattening period, respectively (p < 0.05). The daily gain during the total raising period is in the order of TMREFSCF > TMRGSCF > SCF > TMRW. Carcass characteristics, including carcass weight, loin eye muscle area, and carcass yield grade, did not significantly differ among different treatments. However, TMRW treatment, wherein TMR was fed for a long time, showed that the cold carcass weight was less compared with other treatments, but carcass yield grade was higher with thinner backfat. Backfat thickness was in the order of SCF > TMRGSCF > TMREFSCF > TMRW, showing that the thickness reduced with longer TMR feeding (p < 0.05). TMRGSCF, which numerically had a higher carcass quality grade, showed higher economic efficiency, whereas SCF showed low economic efficiency. In conclusion, it was more feasible to apply TMR strategy in the growing and early fattening period and then SCF for the early or late fattening period to improve carcass yield, quality grade, and economic efficiency.

Effects of barley and corn as sources of silage and grain on dry matter intake, ruminal fermentation, and total-tract digestibility in growing beef heifers

The objective of this study was to evaluate the use of barley (BS) or corn (CS) silage when fed with dry-rolled barley grain (BG), corn grain (CG), or an equal blend (BCG) of BG and CG for backgrounding cattle. Ruminally cannulated heifers (n = 5) were assigned to an incomplete 6 × 6 Latin square design. Treatments contained either BS or CS in combination with BG, CG, or BCG. Samples were collected to determine dry matter intake, ruminal fermentation, total-tract nutrient digestibility, and nitrogen (N) balance. Interactions between cereal silage and cereal grain sources were detected for the molar proportions of propionate and butyrate where the magnitude of change with the type of cereal grain was increased in heifers fed CS relative to BS. Feeding CS increased estimated microbial N production (silage, P = 0.022) and fecal N excretion (silage, P = 0.042) over BS. Diets containing BG had greater dry matter, organic matter, starch, and gross energy digestibility values compared with CG, but values for BCG were not different (grain, P ≤ 0.043). Based on limited silage × grain interactions, use of CS in backgrounding diets may increase microbial N production relative to BS and dry-rolled CG may reduce apparent total-tract nutrient digestibility relative to dry-rolled BG.

Nutrient digestibility and endogenous protein losses in the foregut and small intestine of weaned dairy calves fed calf starters with conventional or enzyme-treated soybean meal

The aims of this experiment were (1) to compare the effects of a soybean meal with an enzymatic treatment (ESBM) to reduce the concentration of antinutritional factors versus a standard soybean meal (SBM) on foregut and small intestine digestion in weaned dairy calves and (2) to estimate the endogenous losses of crude protein (CP) in the small intestine. Our hypothesis was that a diet containing ESBM instead of SBM would improve ruminal and small intestine digestion and absorption of nutrients. A T-cannula was placed in the duodenum, and a second T-cannula was installed in the distal ileum of 12 Holstein calves at approximately 3 wk of age. Calves were weaned on d 42, and on d 50 they were assigned randomly to a quadruplicated 3 × 3 Latin square with 10-d periods. Digesta samples were collected on d 7 and 8 from the ileum and d 9 and 10 from the duodenum. The diets were fed for ad libitum intake and consisted of a calf starter (CS) of 20% CP with SBM as the main source of protein (CTRL), and an isonitrogenous CS with an ESBM instead of SBM (ENZT). A third diet with a low content of CP (10%) and no soy protein was fed to estimate endogenous N losses and digestibilities of test ingredients. Flows and digestibilities of nutrients were compared between CTRL and ENZT and their test ingredients (SBM vs. ESBM, respectively). Duodenal net flows of CP and total AA as well as ruminal microbial protein synthesis per kilogram of digested CP were greater, and flow of nonprotein N and CP true (corrected by endogenous and microbial flows) foregut digestibility were lower with ENZT than CTRL. The apparent small intestine digestibilities of CP and total AA were greater for ESBM than SBM, but there were no differences between the CTRL and ENZT diets. We observed no differences in digestibilities at the duodenum or ileum of starch or NDF, but true small intestine digestibilities of CP and all AA were greater with ENZT than CTRL. Total endogenous protein losses in the small intestine estimated from calves fed the low-CP with no soy protein diet were 37 ± 1.5 g of CP and 29 ± 1.4 g of AA/kg of DMI. These values may be considered the basal endogenous losses as they are similar to values obtained with the regression method, which estimates N losses when dietary N is null. Our results indicated that the inclusion of an ESBM improved the efficiency of ruminal microbial protein synthesis per digested kilogram of organic matter and CP, and increased CP and AA absorption in the small intestine despite a greater proportion of undigested dietary protein entering the duodenum.

A method of assessing essential amino acid availability from microbial and ruminally undegraded protein in lactating dairy cows

The objective of this study was to extend a stable isotope-based assessment of AA absorption from rumen-degradable protein (RDP) sources to include determination of essential AA (EAA) availability from microbial protein (MCP). To demonstrate the technique, a study using a 2 × 2 factorial arrangement of treatments applied in a repeated 4 × 4 Latin square design was undertaken. Factors were high and low rumen-degradable protein and high and low starch. Twelve lactating cows were blocked into 3 groups according to days in milk and randomly assigned to the 4 treatment sequences. Each period was 14 d in length with 10 d of adaption followed by 4 d of ruminal infusions of ¹⁵N-labeled ammonium sulfate. On the last day of each period, a ¹³C-labeled AA mixture was infused into the jugular vein over a 6-h period to assess total AA entry. Rumen, blood, urine, and milk samples were collected during the infusions. Ruminal bacteria and blood samples were assessed for AA enrichment. Total plasma AA absorption rates were derived for 6 EAA from plasma ¹³C AA enrichment. Absorption of 6 EAA from MCP was calculated from total AA absorption based on ¹⁵N enrichment in blood and rumen bacteria. Essential AA absorption rates from total protein, MCP, and rumen-undegradable protein were derived with standard errors of the mean of 6, 14, and 14%, respectively. An average of 45% of absorbed EAA were from MCP, which varied among 6 EAA and was interactively affected by starch and RDP in diets. Microbial AA availability measured by isotope dilution method increased with the high RDP diets and was unaffected by starch level, except for Met, which decreased with high starch. Microbial protein outflow, estimated from urinary purine derivatives, increased with RDP and was not significantly affected by starch. This was consistent with measurements from the isotope dilution method. Total AA absorption rates measured from isotope dilution were similar to estimates from CNCPS (v. 6.55), but a lower proportion of absorbed AA was derived from MCP for the former method. Compared with the isotope and CNCPS estimates, the Fleming model underestimated microbial EAA and total EAA availability. An average of 58% of the absorbed EAA was converted into milk, which varied among individual AA and was interactively affected by starch and RDP in diets. The isotope dilution approach is advantageous because it provides estimates of EAA availability for individual EAA from rumen-undegradable protein and MCP directly with fewer errors of measurement than can be achieved with intestinal disappearance methods.

Effects of a Grain Source (Corn Versus Barley) and Starter Protein Content on Performance, Ruminal Fermentation, and Blood Metabolites in Holstein Dairy Calves

Simple Summary

Dairy calf producers are concerned about feeding barley grain to dairy calves due to its rapid starch fermentation rate in the rumen compared to corn grain. Therefore, corn grain is still the main energy source in starter diets in dairy calves. However, some studies on bull and dairy calves indicated that there are some potentials for including barley grain in their diets with positively influencing the performance and feed efficiency. Optimum protein content in starter diet is an important factor influencing the animal growth response to grain source. This may be due to adequate nitrogen availability rate when starch is rapidly degraded in the rumen. Therefore, we hypothesized that dairy calves may produce different growth response to grain source with various ruminal starch degradation rate (high degradation rate in barley grain vs. low degradation rate in corn grain) when fed with starters with different protein content. Here we show that the average daily gain, feed efficiency, and ruminal fermentation profile were improved in dairy calves fed with barley grain. Furthermore, when dairy calves receive high protein content in their starter diet, barley grain improves growth performance in comparison with corn grain. Our study suggests that barley grain can be included in dairy calf starter diet when a starter with higher protein content is provided.

Abstract

The effects of a grain source (corn grain (CG) vs. barley grain (BG)) and starter protein content (19% vs. 22% CP, dry matter basis) on growth performance, digestibility, ruminal fermentation, and blood metabolites were evaluated in Holstein dairy calves. Forty 3-day-old female calves with a starting body weight of 39.3 kg were subjected to four treatments in a completely randomized design with two by two factorial arrangements. Treatments were: (1) CG + 19% CP (CG-19CP); (2) CG + 22% CP (CG-22CP); (3) BG + 19% CP (BG-19CP); and (4) BG + 22% CP (BG-22CP). All calves were weaned at 59 days of age and remained in the study until 73 days of age. Starter and total DM intake were not affected by grain source and dietary protein content (p > 0.05). The average daily gain and feed efficiency were improved, and ruminal total short-chain fatty acid, propionate, and butyrate concentrations were increased in BG calves compared to CG calves (p < 0.05). The ruminal concentrations of ammonia nitrogen (d 71; p = 0.02) and acetate (d 35; p = 0.02) were increased in CG fed calves compared to BG. The greatest wither height (p = 0.03) and blood insulin concentration (p = 0.03) were seen in BG-22CP treatment. In conclusion, BG has marginal benefit in the height of calves when fed with diet containing 22% CP which may be recommendable in replacement heifer rearing programs.

Effect of soybean meal replacement by slow-release urea on ruminal parameter, blood metabolites, and microbial protein synthesis in Zel ram

The objective of this study was to determine the effect of soybean meal replacement by slow-release urea on feed intake, ruminal parameters, blood metabolites, dry matter, nutrients digestion, and microbial protein synthesis (MPS) in ram. Rams were used for four 21-day periods. The experimental design was a 4×4 Latin square design. The experiment has consisted of the following four rations: 1) basic diet with soybean meal as a protein source, 2) basic diet with soybean meal plus 0.5 % of DM slow-release urea (SRU), 3) basic diet with soybean meal plus 1 % of DM SRU, and 4) basic diet with soybean meal plus 1.5 % of SRU, respectively. Soybean meal replacement by SRU decreased ruminal ammonia and blood urea. SRU increase in diets significantly increased acetic acid 3 hours after morning feeding, blood glucose, total purine, uric acid excretion, microbial nitrogen, and microbial protein. The results showed that soybean meal replacement by SRU sources had no negative effect on rams performance.

Effect of Two Nutritional Strategies to Balance Energy and Protein Supply in Fattening Heifers on Performance, Ruminal Metabolism, and Carcass Characteristics

Latin America is an important contributor to the worldwide beef business, but in general, there are limited studies considering strategies to reduce nitrogen contamination in their production systems. The study's goal was to assess the effect of two nutritional strategies to balance energy and protein supply in fattening heifers on performance, ruminal metabolism, and carcass characteristics. A total of 24 crossbred heifers (initial body weight 'BW 'of 372 ± 36 kg) were used to create two blocks (based on live weight) of two pens each, that were equipped with individual feeders. Within each block, half of the animals were assigned to a diet based on tabular Crude Protein (CP) requirements denominated Crude Protein Diet 'CPD' but without a ruminal degradable protein balance. The other half received a diet denominated Metabolizable Protein Diet 'MPD', formulated with the metabolizable protein system, balanced for the ruminal degradable protein. Both diets had the same ingredients and as well as similar synchrony indexes (0.80 and 0.83, respectively). For nitrogen concentration in feces and urine as well as microbial crude protein synthesis, a total of 12 heifers (three per pen) were randomly selected to collect samples. The dataset was analyzed as a randomized complete block design with a 5% significance. No diet × time interaction was observed for Average Daily Gain 'ADG' (p = 0.89), but there was an effect of the time on ADG (p ≤ 0.001). No differences were observed neither for final weight, dry matter intake 'DMI', and feed conversion rate (p > 0.05). Heifers fed with CPD showed greater cold carcass weight (p = 0.041), but without differences in ribeye area, backfat thickness, pH, dressing %, and marbling (p > 0.05). Differences between diets were observed for the in vitro parameters as well as for the Total Volatile Fatty Acids 'VFA' and NH3 (p < 0.05). Total N concentrations (urine + feces) of heifers fed with MDP was lower than in those fed with the CPD (p < 0.01), but no differences were observed in microbial protein, purine derivatives, and creatinine (p > 0.05). We conclude that the combination of synchrony and the metabolizable protein system achieve greater efficiency in the use of nitrogen, without negatively affecting animals' performance or the quality of the carcass.

Quantifying the ruminal degradation of nutrients in three cultivars of perennial ryegrass (Lolium perenne L.) sampled during early spring and summer

Context The Australian dairy industry is characterised by pasture-based feeding systems, where grazed pasture is commonly supplemented with cereal grain to increase milk production of dairy cows. Perennial ryegrass (PRG; Lolium perenne L.) is the most commonly used pasture species, with a wide range of cultivars available. However, the nutritive characteristics and the degradation of nutrients in individual PRG cultivars grown in different environments in Australia are unknown, and significant variation between cultivars may impact on supplementary nutrient requirements. Aims The objective of this experiment was to quantify the extent of ruminal degradation of nutrients in three contrasting PRG cultivars (Bealey NEA2, Trojan NEA2 and Victorian SE) harvested during early spring and summer from Gippsland, northern Victoria and south-west Victoria in Victoria, Australia. Methods Degradation parameters were determined by in situ incubation in the rumens of non-lactating, rumen-fistulated Holstein–Friesian cows for 72 h using a nylon bag technique. Key results During both seasons, Bealey NEA2 had the greatest effective degradability of crude protein and neutral detergent fibre compared with Trojan NEA2 and Victorian SE. Cultivars harvested during early spring had greater effective degradability of crude protein and neutral detergent fibre, and a greater amount of rumen degradable protein compared with cultivars harvested during summer. Cultivars harvested from Gippsland had greater crude protein and neutral detergent fibre effective degradability, as well as a greater amount of rumen degradable protein, whereas cultivars harvested from northern Victoria had a greater amount of undegraded dietary protein. Conclusions These results demonstrate that the ruminal degradation of PRG cultivars declines with increasing maturity, and that there are differences between cultivars and regions; however, differences between seasons are of a greater magnitude and are more important to consider when formulating optimal supplementary grain rations. Implications This research has positive implications for farmers who will be able to understand the degradation of nutrients in PRG, and the amounts of rumen degradable protein and undegraded dietary protein available from pasture during each season. Farmers will be able to use this information to formulate supplementary grain rations that complement the nutrients from pasture and optimise milk production.

Effects of toasting and decortication of oat on nutrient digestibility in the rumen and small intestine and on amino acid supply in dairy cows

This study examined the potential for decorticating and toasting of oat (Avena sativa) to supply crude protein (CP) and amino acids (AA) in dairy cows. Four lactating Danish Holstein Friesian cows fitted with ruminal, duodenal, and ileal cannulas were assigned to a 4 × 4 Latin square design. Cows were fed experimental diets ad libitum based on grass-clover silage and toasted fava beans, with oat included in different forms arranged in a 2 × 2 factorial: whole oat, decorticated oat, toasted oat, and decorticated toasted oat. In situ rumen degradability of processed oat was also evaluated. Decortication increased starch intake by 0.38 kg/d and reduced NDF intake by 0.91 kg/d. Toasting reduced ruminal AA digestibility and increased duodenal flow of CP by 0.41 kg/d. In situ degradation rate and effective degradability of CP in the rumen were reduced by 0.46 h^-1 and 310 g/kg CP due to toasting. Both decortication and toasting increased microbial synthesis of CP by 0.20 and 0.41 kg/d, respectively. Decortication and toasting did not affect small intestinal AA digestibility, but did increase the total digested amount of AA by 154 and 250 g/d, respectively. Milk production was not affected by treatments. Methane production (L/d) decreased with decortication and toasting. In conclusion, unless an interaction exists between decortication and toasting, the results indicate additive effects of toasting and decorticating oat for increasing the supply of digestible AA to the small intestine of dairy cows.

Synchronous feeding of liquid protein source with different grains on performance, digestibility, ruminal fermentation, blood metabolites, and carcass characters in growing lambs

The effects of feeding corn steep liquor (CSL; 420 g/kg crude protein, DM basis) along with different cereal grains on performance, digestibility, blood metabolites, ruminal fermentation, and carcass characters of growing lambs were evaluated. The constant amount of CSL was included in basal diet (100 g/kg, DM basis) and grain sources as experimental treatments were as follows: (1) corn grain (CG), (2) barley grain (BG), or (3) wheat grain (WG). The eighteen individually fed Farahani lambs averaging body weight 32 kg were allocated in completely randomized design (6 lambs/each) in a 9-week trial. The results showed that the greatest intake and gain were found in lambs fed CG in contrast to others. Nitrogen intake was constant among diets; however, the greatest nitrogen efficiency was found for corn grain-fed animals. Digestibility of nutrients were reduced in WG-fed animals in comparison with other grains. Ruminal proportions of propionate and butyrate were reduce in WG-fed lambs. The CG-fed animals displayed greater blood glucose and lower BUN concentrations compared with others. The greatest aspartate aminotransferase concentration as well as the greatest liver fat deposition suggested a dysfunction in liver performance in WG-fed animals. Except than that of a tendency for increment in dressing percentage in CG-fed lambs, no carcass character was differed among treatments. In conclusion, results revealed that feeding liquid protein source (CSL) is recommendable when it has been fed along with corn grain in comparison with barley or wheat grains in growing lambs.

The assessment of supplementation requirements of grazing ruminants using nutrition models

This paper was aimed to summarize known concepts needed to comprehend the intricate interface between the ruminant animal and the pasture when predicting animal performance, acknowledge current efforts in the mathematical modeling domain of grazing ruminants, and highlight current thinking and technologies that can guide the development of advanced mathematical modeling tools for grazing ruminants. The scientific knowledge of factors that affect intake of ruminants is broad and rich, and decision-support tools (DST) for modeling energy expenditure and feed intake of grazing animals abound in the literature but the adequate predictability of forage intake is still lacking, remaining a major challenge that has been deceiving at times. Despite the mathematical advancements in translating experimental research of grazing ruminants into DST, numerous shortages have been identified in current models designed to predict intake of forages by grazing ruminants. Many of which are mechanistic models that rely heavily on preceding mathematical constructions that were developed to predict energy and nutrient requirements and feed intake of confined animals. The data collection of grazing (forage selection, grazing behavior, pasture growth/regrowth, pasture quality) and animal (nutrient digestion and absorption, volatile fatty acids production and profile, energy requirement) components remains a critical bottleneck for adequate modeling of forage intake by ruminants. An unresolved question that has impeded DST is how to assess the quantity and quality, ideally simultaneously, of pasture forages given that ruminant animals can be selective. The inadequate assessment of quantity and quality has been a hindrance in assessing energy expenditure of grazing animals for physical activities such as walking, grazing, and forage selection of grazing animals. The advancement of sensors might provide some insights that will likely enhance our understanding and assist in determining key variables that control forage intake and animal activity. Sensors might provide additional insights to improve the quantification of individual animal variation as the sensor data are collected on each subject over time. As a group of scientists, however, despite many obstacles in animal and forage science research, we have thrived, and progress has been made. The scientific community may need to change the angle of which the problem has been attacked, and focus more on holistic approaches.

Recent advances to improve nitrogen efficiency of grain-finishing cattle in North American and Australian feedlots

Formulating diets conservatively for minimum crude-protein (CP) requirements and overfeeding nitrogen (N) is commonplace in grain finishing rations in USA, Canada and Australia. Overfeeding N is considered to be a low-cost and low-risk (to cattle production and health) strategy and is becoming more commonplace in the US with the use of high-N ethanol by-products in finishing diets. However, loss of N from feedlot manure in the form of volatilised ammonia and nitrous oxide, and nitrate contamination of water are of significant environmental concern. Thus, there is a need to improve N-use efficiency of beef cattle production and reduce losses of N to the environment. The most effective approach is to lower N intake of animals through precision feeding, and the application of the metabolisable protein system, including its recent updates to estimation of N supply and recycling. Precision feeding of protein needs to account for variations in the production system, e.g. grain type, liveweight, maturity, use of hormonal growth promotants and β agonists. Opportunities to reduce total N fed to finishing cattle include oscillating supply of dietary CP and reducing supply of CP to better meet cattle requirements (phase feeding).

Effect of diet synchrony on rumen fermentation, production performance, immunity status and endocrine in Chinese Holstein cows

In order to maximise utilisation of nutrients for ruminants, researchers directed the supply of nitrogen and organic matter synchronously to the rumen. In the current research, two experiments were conducted, one using the in situ nylon bag technique and the other using in vivo study. In Experiment 1, dynamic degradation rates of organic matter (OM) and nitrogen of each feedstuff were determined using the in situ nylon bag technique. Accordingly, three diets were formulated with the same chemical components, but differing in synchrony index (0.74, 0.85 and 0.97). Experiment 2 was subsequently carried out in vivo to evaluate the influence of diet synchrony on rumen fermentation, productive performance, immunity status and endocrine in Chinese Holstein cows. Rumen degradability of OM and neutral detergent fibre (NDF) and total tract digestibility of OM were linearly increased with the increase of synchrony index, respectively (P &lt; 0.05). Total volatile fatty acids concentration of rumen fluid was increased linearly with the increase of synchrony index (P &lt; 0.05). Meanwhile, rumen ammonia nitrogen concentration and blood urea nitrogen concentration were decreased in cows with the increase of synchrony index, (P &lt; 0.05). Microbial crude protein production, the efficiency of microbial protein synthesis, and milk protein percentage, were linearly increased with the increase of synchrony index (P &lt; 0.05). Serum concentrations of prostaglandin E2 and immunoreactive fibronectin-γ were linearly decreased with the increase of diet synchrony index (P &lt; 0.05). The aforementioned results implicate that an increase of diet synchrony index could improve diet’s nitrogen utilisation, apparent digestibility of OM, and NDF. Additionally, it could promote rumen fermentation capacity, productive performance and immunity status in dairy cows.

Substituting oat hay or maize silage for portion of alfalfa hay affects growth performance, ruminal fermentation, and nutrient digestibility of weaned calves

OBJECTIVE

The impact of forage feeding strategy on growth performance, ruminal fermentation and nutrient digestibility in post-weaning calves was investigated.

METHODS

Forty-five female Holstein calves (body weight [BW] = 79.79±0.38 kg) were enrolled in the 35-d study at one week after weaning and randomly assigned to one of three dietary treatments. All diets were fed as total mixed ration containing 60% (dry matter [DM] basis) of basal starter feed and 40% (DM basis) of forage, but varied in composition of forage source including i) alfalfa (40% DM, AH); ii) alfalfa hay (26.7% DM)+oat hay (13.3% DM; OH); iii) alfalfa hay (26.7% DM)+corn silage (13.3% DM; WS).

RESULTS

Dry matter intake was not different among treatment groups (p>0.05). However, BW (p<0.05) and average daily gain (p<0.05) of calves fed AH and OH were greater than WS-fed calves, whereas heart girth was greater in OH-fed calves than those fed AH and WS (p<0.05). Ruminal fermentation parameters including proportion of butyric acid, acetated-to-propionate ratio, concentration of total volatile fatty acid, protozoal protein, bacterial protein, and microbial protein in rumen were the highest in OH (p<0.05) and the lowest in WS. Compared with the AH and WS, feeding oat hay to postweaning calves increased crude protein digestibility (p<0.05), and decreased duration of diarrhea (p<0.05) and fecal index (p<0.05).

CONCLUSION

Our results suggested that partially replacing alfalfa hay with oat hay improved ruminal fermentation, nitrogen utilization, and reduced incidence of diarrhea in post-weaning dairy calves.

The Contribution of Mathematical Modeling to Understanding Dynamic Aspects of Rumen Metabolism

All mechanistic rumen models cover the main drivers of variation in rumen function, which are feed intake, the differences between feedstuffs and feeds in their intrinsic rumen degradation characteristics, and fractional outflow rate of fluid and particulate matter. Dynamic modeling approaches are best suited to the prediction of more nuanced responses in rumen metabolism, and represent the dynamics of the interactions between substrates and micro-organisms and inter-microbial interactions. The concepts of dynamics are discussed for the case of rumen starch digestion as influenced by starch intake rate and frequency of feed intake, and for the case of fermentation of fiber in the large intestine. Adding representations of new functional classes of micro-organisms (i.e., with new characteristics from the perspective of whole rumen function) in rumen models only delivers new insights if complemented by the dynamics of their interactions with other functional classes. Rumen fermentation conditions have to be represented due to their profound impact on the dynamics of substrate degradation and microbial metabolism. Although the importance of rumen pH is generally acknowledged, more emphasis is needed on predicting its variation as well as variation in the processes that underlie rumen fluid dynamics. The rumen wall has an important role in adapting to rapid changes in the rumen environment, clearing of volatile fatty acids (VFA), and maintaining rumen pH within limits. Dynamics of rumen wall epithelia and their role in VFA absorption needs to be better represented in models that aim to predict rumen responses across nutritional or physiological states. For a detailed prediction of rumen N balance there is merit in a dynamic modeling approach compared to the static approaches adopted in current protein evaluation systems. Improvement is needed on previous attempts to predict rumen VFA profiles, and this should be pursued by introducing factors that relate more to microbial metabolism. For rumen model construction, data on rumen microbiomes are preferably coupled with knowledge consolidated in rumen models instead of relying on correlations with rather general aspects of treatment or animal. This helps to prevent the disregard of basic principles and underlying mechanisms of whole rumen function.

The effects of synchronizing the rate of dietary energy and nitrogen supply to the rumen on the metabolism and growth of ram lambs given food at a restricted level

The effects of diets formulated to have two rates of organic matter (OM) release and to be either synchronous or asynchronous with respect to their hourly release of OM and nitrogen (N) in the rumen on N retention, microbial N production, growth and metabolism of ram lambs offered food at a restricted level was studied in two experiments. Four diets were formulated to differ in their rate and extent of OM and N release in the rumen based on the sum of in situ degradability data of the ingredients. All diets were formulated to have a similar metabolizable energy (10·4 MJ/kg dry matter (DM)), crude protein (140 g/kg DM) and daily ratio of N : OM released (34 g N per kg OM) and were either synchronous or asynchronous with respect to their hourly N : OM release. The four diets were slow energy, synchronous (SS), slow energy asynchronous (SA), fast energy, synchronous (FS) and fast energy asynchronous (FA). In both experiments the diets were offered at a rate of 1·75 maintenance energy requirements as two equal meals at 09:00 and 17:00 h. In experiment 1 there was no significant effect of diet on OM apparent digestibility or N retention. Lambs given diet FS had the highest daily production of allantoin (7·82 mmol per day; P < 0·05) and microbial N (7·80 g/day; P < 0Ό5). Hourly plasma urea and ß-hydroxy butyrate (3-OHB) concentrations exhibited a cyclical trend between meals with maximum concentrations occurring within 3 h of feeding and were higher in lambs given diet FA.

In experiment 2 the four diets were offered to 32 growing ram lambs. Animals given synchronous diets (SS and FS) had a significantly higher live-weight gain than those given asynchronous diets (SA and FA; (132 g/day v. 107 g/day respectively; P < 0·001). Food conversion efficiency (FCE; kg gain per kg DM intake) was improved proportionately by 0·23 in animals offered synchronous diets compared with asynchronous diets (P < 0·001). There was little effect of diet on carcass composition except kidney fat, which was greater in lambs offered the synchronous diets (P < 0·01). Plasma 3-OHB concentrations were higher throughout the growth period in lambs given diet FA whilst plasma urea concentrations were greater in lambs given the diet SS. In conclusion, greater attention to the formulation of diets to be synchronous for their hourly release of N : OM in the rumen can improve the growth rate and FCE of lambs. This effect may be due to an improvement in energy rather than N metabolism.

Suitable strategy to improve nitrogen utilization and reduce the environmental impact of Nellore bulls supplemented on tropical pasture

Expansion of the biodiesel industry has increased the crude glycerin (CG) supply. Crude glycerin has the potential of replacing corn in ruminant diets because the glycerol can be converted to glucose in the liver of ruminants, providing energy for cellular metabolism. The objective was to evaluate the effects of CG with urea, soybean meal, cottonseed meal, and corn gluten feed, respectively, on intake, digestibility, microbial protein yield, and efficiency of N utilization. Five Nellore bulls (initial BW of 448 kg [SD 14]) grazing tropical pasture were used in a 5 × 5 Latin square design. The supplements were control (no supplementation; only free-choice mineral mixture ad libitum), CG with urea (CG-Urea), CG with soybean meal, CG with cottonseed meal, and CG with corn gluten. Crude glycerin was used in all supplements to replace corn (15% of DM supplement). There were differences between CG-Urea and other supplements with regard to intake of DM (% of BW and total; < 0.01), OM ( < 0.01), CP ( < 0.01), and TDN ( < 0.01). The digestibility of CP was greater ( = 0.04) for animals supplemented with CG-Urea than for those fed other supplements. Animals supplemented with CG-Urea showed greater N intake ( < 0.01) and N ammonia ( = 0.04) than those supplemented with other treatments. Nitrogen retained (g/d) was not affected by protein source but was greater for cattle fed a protein supplement compared with cattle fed the control supplement ( < 0.01). Supplementing the animals with protein sources increased ( = 0.02) the daily production of rumen microbial nitrogen (g/d) compared with the control group. Microbial protein (g/d) was lesser for the control than for protein sources ( = 0.02). However, when expressed relative to TDN ( = 0.35) and CP ( = 0.82), there were no differences across treatments. Crude protein intake per digestible OM intake (g CP/kg digestible OM intake) was greater for animals fed protein sources compared with animals fed control supplements ( < 0.01). Based on nutrients intake and microbial protein yield, CG-Urea supplement has a greater feeding value compared with other protein sources. Crude glycerin, when used to replace corn in 15% of DM supplement, may be effective to improved N utilization and microbial protein yield in rumen of Nellore bulls grazing cv. Marandu.

Effects of Supplementation of Mulberry (Morus alba) Foliage and Urea-rice Bran as Fermentable Energy and Protein Sources in Sheep Fed Urea-treated Rice Straw Based Diet

A digestibility study was conducted to evaluate the effects of supplementing mulberry foliage and urea rice-bran as a source of fermentable energy and protein to 12 sheep fed diets based on urea-treated rice straw (TRS). The three dietary treatments were: T1, TRS with mulberry; T2, TRS with 50% mulberry replaced with rice bran and urea; and T3, TRS with rice bran and urea. The study was arranged in a completely randomized design with four replications for each treatment. The sheep were fed one of the three diets and the supplements were offered at 1.2% of the body weight (BW) and the TRS was provided ad libitum. There were no differences (p>0.05) among the three treatment groups with respect to dry matter (DM) intake (76.8±4.2 g/kg BW^0.75) and DM, organic matter (OM), and crude protein (CP) digestibility (55.3±1.22; 69.9±0.85; 46.3±1.65% respectively for DM, OM, and CP). The digestibility of fiber (neutral detergent fiber [NDF] and acid detergent fiber) was significantly lower (p<0.05) for T3 (46.2 and 46.6 respectively) compared to T1 (55.8 and 53.7 respectively) and T2 (54.1 and 52.8 respectively). Nitrogen (N) intake by sheep on diet T3 was significantly (p<0.05) higher than sheep fed diet T1. However, N balance did not differ among the three diets (3.0±0.32 g/d). In contrast, the rumen ammonia (NH₃-N) concentrations in sheep fed T2 and T3 were significantly (p<0.05) higher than in sheep fed T1. The NH₃-N concentrations for all three diets were above the critical value required for optimum rumen microbial growth and synthesis. Total volatile fatty acid concentrations were highest (p<0.05) in T1 (120.3 mM), whilst the molar proportion of propionic acid was highest in T3 (36.9%). However, the microbial N supply in sheep fed T1 and T3 was similar but was significantly (p<0.05) higher than for sheep fed T2. It was concluded that mulberry foliage is a potential supplement of fermentable energy and protein for sheep fed TRS based diet. The suggested level of supplementation is 1.2% of BW or 32% of the total diet since it resulted in similar effects on the intake of DM, OM, and NDF, digestibility of DM, OM, and CP, N utilization and microbial supply when compared to rice bran and urea supplementation.

Effects of the processing methods of corn grain and soybean meal on milk protein expression profiles in dairy cows

A proteomic approach was used to investigate the effects of the processing method of corn grain and soybean meal on the milk protein expression profile in lactating dairy cows. A total of 12 multiparous Holstein dairy cows were used in a 4×4 Latin square design with a 2×2 factorial arrangement. The primary factors examined were corn (finely ground (FGC) v. steam-flaked (SFC)) and soybean meal (solvent-extracted (SSBM) v. heat-treated (HSBM)), which were used to formulate four diets with the same basal ingredient: 27% FGC and 9% SSBM; 27% SFC and 9% SSBM; 27% FGC and 9% HSBM; and 27% SFC and 9% HSBM. Each period lasted for 21 days. Milk samples were collected on days 18, 19 and 20 of each period. Changes in the milk proteins were assessed by two-dimensional (2D) electrophoresis and ImageMaster 2D Platinum 6.0 software. A total of 13 spots displayed variations in protein spot abundance according to the statistical analysis. These spots were identified by a matrix-assisted laser desorption/ionization-time of flight/time of flight MS. According to the gels, the relative abundance of α(s2)-casein (CN) fragments was higher in the cows fed the SFC-HSBM than that for SFC-SSBM, whereas β-CN, α-lactalbumin and zinc-alpha-2-glycoprotein fragments were down-regulated in HSBM-fed cows. The relative decrease of β-CN expression was validated by western blot and agreed with the MS data. These results suggested that the method used to process soybean meal modified the synthesis and secretion of milk proteins in lactating dairy cows' mammary glands.

Nutritional and ecological evaluation of dairy farming systems based on concentrate feeding regimes in semi-arid environments of Jordan

The objective of this study was to evaluate the nutritional and ecological aspects of feeding systems practiced under semi-arid environments in Jordan. Nine dairy farms representing the different dairy farming systems were selected for this study. Feed samples (n = 58), fecal samples (n = 108), and milk samples (n = 78) were collected from the farms and analysed for chemical composition. Feed samples were also analysed for metabolisable energy (ME) contents and in vitro organic matter digestibility according to Hohenheim-Feed-Test. Furthermore, fecal nitrogen concentration was determined to estimate in vivo organic matter digestibility. ME and nutrient intakes were calculated based on the farmer's estimate of dry matter intake and the analysed composition of the feed ingredients. ME and nutrient intakes were compared to recommended standard values for adequate supply of ME, utilizable crude protein, rumen undegradable crude protein (RUCP), phosphorus (P), and calcium (Ca). Technology Impact Policy Impact Calculation model complemented with a partial life cycle assessment model was used to estimate greenhouse gas emissions of milk production at farm gate. The model predicts CH4, N2O and CO2 gases emitted either directly or indirectly. Average daily energy corrected milk yield (ECM) was 19 kg and ranged between 11 and 27 kg. The mean of ME intake of all farms was 184 MJ/d with a range between 115 and 225 MJ/d. Intake of RUCP was lower than the standard requirements in six farms ranging between 19 and 137 g/d, was higher (32 and 93 g/d) in two farms, and matched the requirements in one farm. P intake was higher than the requirements in all farms (mean oversupply = 19 g/d) and ranged between 3 and 30 g/d. Ca intake was significantly below the requirements in small scale farms. Milk nitrogen efficiency N-eff (milk N/intake N) varied between 19% and 28% and was mainly driven by the level of milk yield. Total CO2 equivalent (CO2 equ) emission ranged between 0.90 and 1.88 kg CO2/kg ECM milk, where the enteric and manure CH4 contributed to 52% of the total CO2 equ emissions, followed by the indirect emissions of N2O and the direct emissions of CO2 gases which comprises 17% and 15%, respectively, from total CO2 equ emissions. Emissions per kg of milk were significantly driven by the level of milk production (r (2) = 0.93) and of eDMI (r (2) = 0.88), while the total emissions were not influenced by diet composition. A difference of 16 kg ECM/d in milk yield, 9% in N-eff and of 0.9 kg CO2 equ/kg in ECM milk observed between low and high yielding animals. To improve the nutritional status of the animals, protein requirements have to be met. Furthermore, low price by-products with a low carbon credit should be included in the diets to replace the high proportion of imported concentrate feeds and consequently improve the economic situation of dairy farms and mitigate CO2 equ emissions.

Revised digestive parameter estimates for the Molly cow model

The Molly cow model represents nutrient digestion and metabolism based on a mechanistic representation of the key biological elements. Digestive parameters were derived ad hoc from literature observations or were assumed. Preliminary work determined that several of these parameters did not represent the true relationships. The current work was undertaken to derive ruminal and postruminal digestive parameters and to use a meta-approach to assess the effects of interactions among nutrients and identify areas of model weakness. Model predictions were compared with a database of literature observations containing 233 treatment means. Mean square prediction errors were assessed to characterize model performance. Ruminal pH prediction equations had substantial mean bias, which caused problems in fiber digestion and microbial growth predictions. The pH prediction equation was reparameterized simultaneously with the several ruminal and postruminal digestion parameters, resulting in more realistic parameter estimates for ruminal fiber digestion, and moderate reductions in prediction errors for pH, neutral detergent fiber, acid detergent fiber, and microbial N outflow from the rumen; and postruminal digestion of neutral detergent fiber, acid detergent fiber, and protein. Prediction errors are still large for ruminal ammonia and outflow of starch from the rumen. The gain in microbial efficiency associated with fat feeding was found to be more than twice the original estimate, but in contrast to prior assumptions, fat feeding did not exert negative effects on fiber and protein degradation in the rumen. Microbial responses to ruminal ammonia concentrations were half saturated at 0.2mM versus the original estimate of 1.2mM. Residuals analyses indicated that additional progress could be made in predicting microbial N outflow, volatile fatty acid production and concentrations, and cycling of N between blood and the rumen. These additional corrections should lead to an even more robust representation of the effects of dietary nutrients on ruminal metabolism and nutrient absorption, of animal performance, and the environmental impact of dairy production.

Effects of synchronicity of carbohydrate and protein degradation on rumen fermentation characteristics and microbial protein synthesis

A series of in vitro studies were carried out to determine i) the effects of enzyme and formaldehyde treatment on the degradation characteristics of carbohydrate and protein sources and on the synchronicity of these processes, and ii) the effects of synchronizing carbohydrate and protein supply on rumen fermentation and microbial protein synthesis (MPS) in in vitro experiments. Untreated corn (C) and enzyme-treated corn (EC) were combined with soy bean meal with (ES) and without (S) enzyme treatment or formaldehyde treatment (FS). Six experimental feeds (CS, CES, CFS, ECS, ECES and ECFS) with different synchrony indices were prepared. Highly synchronous diets had the greatest dry matter (DM) digestibility when untreated corn was used. However, the degree of synchronicity did not influence DM digestibility when EC was mixed with various soybean meals. At time points of 12 h and 24 h of incubation, EC-containing diets showed lower ammonia-N concentrations than those of C-containing diets, irrespective of the degree of synchronicity, indicating that more efficient utilization of ammonia-N for MPS was achieved by ruminal microorganisms when EC was offered as a carbohydrate source. Within C-containing treatments, the purine base concentration increased as the diets were more synchronized. This effect was not observed when EC was offered. There were significant effects on VFA concentration of both C and S treatments and their interactions. Similar to purine concentrations, total VFA production and individual VFA concentration in the groups containing EC as an energy source was higher than those of other groups (CS, CES and CFS). The results of the present study suggested that the availability of energy or the protein source are the most limiting factors for rumen fermentation and MPS, rather than the degree of synchronicity.

Effects of dietary ruminally degradable starch and ruminally degradable protein levels on urea recycling, microbial protein production, nitrogen balance, and duodenal nutrient flow in beef heifers fed low crude protein diets

Davies, K. L., McKinnon, J. J. and Mutsvangwa, T. 2013. Effects of dietary ruminally degradable starch and ruminally degradable protein levels on urea recycling, microbial protein production, nitrogen balance, and duodenal nutrient flow in beef heifers fed low crude protein diets. Can. J. Anim. Sci. 93: 123–136. The objective was to determine the effects of ruminally degradable starch (RDS; 28.6 and 69.2% of total starch) and ruminally degradable protein [RDP; 48.0 and 55.0% of crude protein (CP)] content on urea recycling, nitrogen (N) balance, duodenal nutrient flow, and microbial protein production in beef heifers fed low CP (10%) diets. Four ruminally and duodenally cannulated beef heifers (723±57 kg body weight) were used in a 4×4 Latin square design with a 2×2 factorial arrangement of dietary treatments with 23-d periods. Jugular infusions of [15N15N]-urea (220 mg d−1; 98+ atom percent) were conducted for 4 d (days 18–22) to estimate urea kinetics, with total collection of faeces and urine. Proportions of [15N15N]- and [14N15N]-urea in urinary urea, and 15N enrichment in faeces were used to calculate urea kinetics. Ruminal microbial N production was estimated using 15N as a marker. Ruminal ammonia-N concentration was greater (P=0.01) in heifers fed high RDP as compared with those fed low RDP, and it was also greater (P=0.01) in heifers fed low RDS as compared with those fed high RDS. Microbial N flow to the duodenum increased as RDP level increased on the high RDS diet, but was not affected by RDP level on the low RDS diet (interaction; P=0.04). Urea-N entry rate and urea-N transfer to the gastrointestinal tract were similar (P>0.05) across diets. The amount of recycled urea-N incorporated into microbial N increased as RDP level increased on the high RDS diet, but the opposite was observed on the low RDS diet (interaction; P=0.008). These results indicate that at a low CP level (10%), increasing both RDS and RDP levels can increase microbial N flow to the duodenum and improve the efficiency of use of recycled urea-N for microbial N synthesis.

Effects of synchronization of carbohydrate and protein supply in total mixed ration with korean rice wine residue on ruminal fermentation, nitrogen metabolism and microbial protein synthesis in holstein steers

Three Holstein steers in the growing phase, each with a ruminal cannula, were used to test the hypothesis that the synchronization of the hourly rate of carbohydrate and nitrogen (N) released in the rumen would increase the amount of retained nitrogen for growth and thus improve the efficiency of microbial protein synthesis (EMPS). In Experiment 1, in situ degradability coefficients of carbohydrate and N in feeds including Korean rice wine residue (RWR) were determined. In Experiment 2, three total mixed ration (TMR) diets having different rates of carbohydrate and N release in the rumen were formulated using the in situ degradability of the feeds. All diets were made to contain similar contents of crude protein (CP) and neutral detergent fiber (NDF) but varied in their hourly pattern of nutrient release. The synchrony index of the three TMRs was 0.51 (LS), 0.77 (MS) and 0.95 (HS), respectively. The diets were fed at a restricted level (2% of the animal’s body weight) in a 3×3 Latin-square design. Synchronizing the hourly supply of energy and N in the rumen did not significantly alter the digestibility of dry matter, organic matter, crude protein, NDF or acid detergent fiber (ADF) (p>0.05). The ruminal NH₃-N content of the LS group at three hours after feeding was significantly higher (p<0.05) than that of the other groups; however, the mean values of ruminal NH₃-N, pH and VFA concentration among the three groups were not significantly different (p>0.05). In addition, the purine derivative (PD) excretion in urine and microbial-N production (MN) among the three groups were not significantly different (p>0.05). In conclusion, synchronizing dietary energy and N supply to the rumen did not have a major effect on nutrient digestion or microbial protein synthesis (MPS) in Holstein steers.

The effect of energy and nitrogen supply pattern on rumen bacterial growthin vitro

The effect of energy and nitrogen (N) supply pattern on rumen bacterial growth was investigated in vitro. In experiment 1, glucose was was fed to batch cultures of mixed rumen bacteria according to three patterns namely a pulse dose at time zero (P); even increments at 0·5-h intervals (G) or an intermediate pattern (I), whilst N was supplied in excess. In experiment 2, glucose and N (not in excess) were fed to batch cultures according to four patterns namely glucose and N as pulse doses at time zero, (EPNP); glucose as a pulse dose at time zero and N in 24 even increments at 0·5-h intervals (EPNG); glucose in 24 even increments at 0·5-h intervals and N as a pulse dose at time zero (EGNP) or both glucose and N in 24 even increments at 0·5-h intervals (EGNG). Fermentaton was studied over a 12-h period for both experiments.

In experiment 1, bacterial growth efficiency and specific growth rate (39·8,35·5 and 29·9 (g bacterial dry matter (DM) per mol glucose utilized) and 0·33, 0·27 and 0·20 (fraction per h) for treatments P, I, and G respectively) differed significantly between glucose supply patterns. In experiment 2, bacterial growth efficiency and specific growth rate (33·8, 34·7, 25·9 and 22·5 (g baterial DM per mol glucose) and 0·21, 0·18, 0·14 and 0·13 (fraction per h) for treatments EPNP, EPNG, EGNP and EGNG respectively) differed significantly only between glucose supply patterns.

It is concluded that the pattern according to which a given amount of energy becomes available affects bacterial growth efficiency, with the fastest supply rate giving the highest efficiency and that, within accepted levels of N supply, synchronization between energy and N availability may be of less importance to bacterial growth efficiency than the energy supply pattern.