Effect of varying ruminally degradable to ruminally undegradable protein ratio on nutrient intake, digestibility and N metabolism in Nili Ravi buffalo calves (Bubalus bubalis)

Four Nili-Ravi buffalo calves (100 ± 4 kg) were used in 4 × 4 Latin Square Design to evaluate the influence of varying ruminally degradable protein (RDP) to ruminally undegradable protein (RUP) ratio on dry matter intake (DMI), digestibility and nitrogen (N) metabolism. Four experimental diets A, B, C and D were formulated to contain RDP:RUP of 70:30, 65:35, 60:40 and 55:45, respectively. The calves were fed ad libitum. Dry matter intake by calves fed C diet was higher (P < 0.05) than those fed D diet and lower (P < 0.05) than calves fed A diet, however, it was similar to those fed B diet. There was a linear decrease (P < 0.01) in DMI with decreasing the RDP to RUP ratio. Similar trend was noticed in crude protein (CP) intake. Neutral detergent fiber (NDF) intake was significantly different across all treatment. The decrease in CP and NDF intake was due to decreasing trend of DMI. Dry matter (DM) digestibility in calves fed A and B diets was higher (P < 0.05) than those fed C and D diets. A linear decrease (P < 0.01) in DM digestibility was observed with decreasing the RDP to RUP ratio. Crude protein digestibility remained unaltered across all treatments. Neutral detergent fiber digestibility was higher in calves fed A and B diets than those fed C and D diets. Higher NDF digestibility in calves fed A and B diets was due to higher level of dietary RDP that might resulted in higher ruminal ammonia concentration which stimulate activity of cellulytic bacteria and ultimately increased NDF digestibility. The N retention (g/d) was similar among the calves fed B, C and D diets, however, it was higher (P < 0.05) than those fed A diet. Decreasing the RDP to RUP ratio resulted in linear increase (P < 0.01) in N retention. The N retention, as percent of N intake was significantly different across all treatments. Decreasing RDP to RUP ratio resulted in linear increase (P < 0.01) in N retention, as percent of N intake. A similar trend was noticed in N retention, as percentage of N digestion. Blood urea nitrogen (BUN) concentration in calves fed B diet was higher (P < 0.05) than those fed D diet and was lower (P < 0.05) than those fed A diet, however, it was not different from calves fed C diet. Decreasing dietary RDP to RUP ratio resulted in linear decrease (P < 0.05) in BUN concentrations. The decrease in BUN concentration was because of decreasing level of dietary RDP. The N retention can be increased by decreasing RDP to RUP ratio in the diet of growing buffalo calves and diet containing RDP to RUP ratio 55:45 is considered optimum regarding N retention in buffalo calves.     

Effect of dietary crude protein level and degradability on ruminal fermentation and nitrogen utilization in lactating dairy cows

The objectives of this experiment were to investigate the effects of two ruminally degradable protein (RDP) levels in diets containing similar ruminally undegradable protein (RUP) and metabolizable protein (MP) concentrations on ruminal fermentation, digestibility, and transfer of ruminal ammonia N into milk protein in dairy cows. Four ruminally and duodenally cannulated Holstein cows were allocated to two dietary treatments in a crossover design. The diets (adequate RDP [ARDP] and high RDP [HRDP]), had similar concentrations of RUP and MP, but differed in CP/RDP content. Ruminal ammonia was labeled with 15N and secretion of tracer in milk protein was determined for a period of 120 h. Ammonia concentration in the rumen tended to be greater (P = 0.06) with HRDP than with ARDP. Microbial N flow to the duodenum, ruminal digestibility of dietary nutrients, DMI, milk yield, fat content, and protein content and yield were not statistically different between diets. There was a tendency (P = 0.07) for increased urinary N excretion, and blood plasma and milk urea N concentrations were greater (P = 0.002 and P = 0.01, respectively) with HRDP compared with ARDP. Milk N efficiency was decreased (P = 0.01) by the HRDP diet. The cumulative secretion of ammonia 15N into milk protein, as a proportion of 15N dosed intraruminally, was greater (P = 0.003) with ARDP than with HRDP. The proportions of bacterial protein originating from ammonia N and milk protein originating from bacterial or ammonia N averaged 43, 61, and 26% and were not affected by diet. This experiment indicated that excess RDP in the diet of lactating dairy cows could not be efficiently utilized for microbial protein synthesis and was largely lost through urinary N excretion. At a similar MP supply, increased CP or RDP concentration of the diet would result in decreased efficiency of conversion of dietary N into milk protein and less efficient use of ruminal ammonia N for milk protein syntheses.     

Influence of varying levels of dietary cation anion difference on ruminal characteristics,nitrogen metabolism and in situ digestion kinetics in buffalo bulls

This study was conducted to examine the influence of varying dietary cation anion difference (DCAD) on nutrient intake, digestibility, ruminal characteristics, blood acid base status and in situ digestion kinetics in Nili Ravi buffalo bulls. Four iso‐nitrogenous and iso‐caloric diets having ?110, +110, +220 and +330 mEq/kg dry matter (DM) DCAD were formulated which were represented by A (anionic), LC (low cationic), MC (medium cationic) and HC (high cationic), respectively. These diets were used in four ruminally cannulated Nili Ravi buffalo bulls in a 4 × 4 Latin Square Design. Improved nutrient intake was recorded at high DCAD levels while digestibility remained unaffected. Ruminal ammonia nitrogen, rumen pH, acetate and acetate : propionate ratio were higher in buffalo bulls fed MC and HC diets than those fed A and LC diets. Blood pH and HCO₃^‐ also tended to increase as DCAD level was increased in the diet. Serum Ca and Cl concentrations were higher in bulls fed A and LC diets whereas serum Mg, P and S remained unaffected. Urine pH increased with increasing DCAD level. Nitrogen intake and blood urea nitrogen concentrations were also higher in bulls fed MC and HC diets. There was a consistent increase in ruminal DM and neutral detergent fiber degradability, rate of disappearance and extent of digestion at high DCAD levels in the diet. However, lag time decreased at high DCAD level. This study indicated that buffalo bulls fed MC and HC diets improved feed intake, ruminal characteristics and digestion kinetics.     

Use of additives to capture nitrogen in ammoniated wheat straw: Intake, ruminal parameters, digestibility and nitrogen utilization in buffaloes

This study examined the influence of urea treated wheat straw (UTWS) ensiled with additives on feed intake, digestibility, ruminal characteristics and N utilization in Nili-Ravi buffalo bulls (Babulus bubalis) fed ad libitum. Wheat straw was treated on large scale with 4% urea at a 50% moisture level. The UTWS was ensiled with 6% CSL, 6% acidified molasses, 2% acetic acid and 2% formic acid on DM basis in four different cemented trench silos for 15 days. Four diets each having 50% dry matter (DM) from UTWS ensiled with acetic acid (AD), formic acid (FD), acidified molasses (MD) or corn steep liquor (CD) and 50% DM from concentrate mixture were fed to ruminally cannulated bulls in a 4 × 4 Latin square design. Ruminal total VFA, acetate, cellulolytic ruminal bacterial count, DM and NDF degradability were significantly higher with MD and CD diets compared with AD and FD diets. Intake of different feed fractions was higher in bulls fed MD and CD diets. Total tract apparent digestibility of nutrients was similar across all treatments. Nitrogen retention was higher in bulls fed MD and CD diets than those fed AD and FD diets. Ensiling UTWS with fermentable carbohydrates sources having low pH compared to organic acids increased the N fixation in the matrix of cell wall fiber thus slowing its release at ruminal level that probably enhanced the N synchronization with carbon skeleton (fiber fermentation) and this consequently improved the N utilization.     

Effects of protein concentration and source on nutrient digestibility by mature steers limit-fed high-concentrate diets.

Five ruminally fistulated 3-yr-old mature Holstein steers (average BW 691+/-23 kg) were used in a 5 x 5 Latin square experiment with a 2 x 2 + 1 fact orial arrangement of treatments. Effects of protein concentration and protein source on nutrient digestibility, excretion of DM and fecal N, ruminal fluid volume and dilution rate, ruminal characteristics, and in situ DM disappearance of whole shelled corn, ground corn, and orchardgrass hay were measured in steers limit-fed high-concentrate diets at 1.5% of BW. A negative control basal diet (NC; 9% CP) was supplemented to achieve either 11 or 14% CP; supplemental CP was either from soybean meal (11 and 14% SBM) or a 50:50 ratio of CP from urea and soybean meal (11 and 14% U). Dry matter and OM digestibilities were 5% greater (P < .07) for steers fed the SBM diets than for those fed the U diets. Starch digestibility did not differ (P > .10) among steers fed any of the diets. Nitrogen source did not affect (P > .10) apparent N digestibility or fecal N excretion; however, steers fed the NC diet had the lowest (P < .10) apparent N digestibility compared with those fed all other diets. Ruminal fluid volume was lower (P < .06) when steers were fed the NC diet compared with all other diets; there were no differences (P > .74) among diets for ruminal fluid dilution rate. In general, ruminal ammonia N and VFA molar proportions were not affected by protein source or concentration. Although CP concentration affected (P < .06) in situ DM disappearance of ground corn, CP concentration did not (P > .48) affect total tract digestion of DM or OM. This indicates that CP concentration may have affected site of digestion, but not extent of digestion. When mature ruminants were limit-fed a corn-based diet to meet primarily a maintenance function, protein source and concentration had little effect on measures of nutrient digestion.     

Effects of dietary nonprotein nitrogen on performance, digestibility, ruminal characteristics, and microbial efficiency in crossbred steers

Two trials were conducted to evaluate the effects of dietary NPN levels on animal performance, diet digestibility, ruminal characteristics, and microbial efficiency. Experiment 1 was conducted with 24 Holstein x Nellore crossbred steers (350 +/- 20 kg of BW) distributed in 6 blocks to evaluate intake and digestibility of nutrients and performance. The diets consisted of 70% corn silage and 30% concentrate (DM basis) and were formulated to contain 12.5% CP (DM basis). Treatments consisted of 0, 15.5, 31, and 46.5% of dietary N as NPN. There were no treatment differences in the daily intakes of DM (P = 0.47), OM (P = 0.60), CP (P = 0.24), nonfiber carbohydrates (NFC; P = 0.74), or TDN (P = 0.63); however, NDF intake decreased linearly as NPN increased (P = 0.02). Additionally, no effects of NPN were observed on apparent total tract digestibility of DM (P = 0.50), OM (P = 0.53), NDF (P = 0.63), or NFC (P = 0.44). The apparent total tract digestibility of CP increased linearly (P = 0.01), but ADG (1.14 kg/d) was not influenced (P = 0.96) as NPN increased. In Exp. 2, 4 ruminally and abomasally cannulated steers (300 +/- 55 kg of BW) were fed the same diet used in Exp. 1 to evaluate the effects of NPN levels on intake and digestibility of nutrients, ruminal characteristics, and microbial efficiency. There were no differences in the daily intakes of DM (P = 0.22), OM (P = 0.17), CP (P = 0.31), NDF (P = 0.29), or TDN (P = 0.49). However, NFC intake increased linearly (P = 0.02), and there was a quadratic effect (P = 0.01) on intake of ether extract as NPN increased. Ruminal digestibility of CP increased linearly (P = 0.01) with the increase of dietary NPN. There were no differences (P >or= 0.28) in microbial protein synthesis and microbial efficiency among the treatments. The results of these trials suggest that dietary NPN levels (up to 46.5% of total N) can be fed to crossbred steers receiving corn silage-based diets without affecting their growth performance or ruminal protein synthesis.     

Effects of supplemental ruminally degradable protein versus increasing amounts of supplemental ruminally undegradable protein on site and extent of digestion and ruminal characteristics in lambs fed low-quality forage

Four ruminally and duodenally cannulated Suffolk wether lambs (34.5 +/- 2 kg initial BW) were used in a 4 x 4 Latin square designed experiment to compare effects of supplemental ruminally degradable protein (RDP) vs. increasing amounts of supplemental ruminally undegradable protein (RUP) on ruminal characteristics and site and extent of digestion in lambs. Lambs were fed a basal diet of crested wheatgrass hay (4.2% CP) for ad libitum consumption, plus 1 of 4 protein supplements: isolated soy protein (RDP source) fed to meet estimated RDP requirements assuming a microbial efficiency of 11% of TDN (CON) or corn gluten meal (RUP source) fed at 50, 100, or 150% of the supplemental N provided by CON (C50, C100, and C150, respectively). Neither NDF nor ADF intake was affected (P >/= 0.18) by protein degradability, but they increased or tended to increase (P /= 0.26) for CON and C100, but increased (P /= 0.33) by protein degradability. However, true ruminal N digestibility was greater (P = 0.03) for CON compared with C100. Ruminal ammonia concentrations were greater (P = 0.002) for CON compared with C100 lambs, and increased (P = 0.001) with increasing RUP. Microbial N flows were not affected (P >/= 0.12) by protein degradability or increasing RUP. Likewise, neither ruminal urease activity (P >/= 0.11) nor microbial efficiency (P >/= 0.50) were affected by protein degradability or level of RUP. Total tract OM, NDF, and ADF digestibility was greater (P 相似文献   

Optimum grape pomace proportion in feedlot cattle diets: ruminal fermentation,total tract nutrient digestibility,nitrogen utilization,and blood metabolites

Because of its high content of polyphenolic compounds, the dietary inclusion of grape pomace (GP) in ruminant diets can reduce reactive nitrogen (N) and methane emissions and enhance the shelf life and beneficial fatty acids (FAs) content of meat. However, the dietary inclusion of GP beyond a threshold that is still to be determined for feedlot cattle can also compromise nutrient supply and, thus, growth performance. This study investigated the optimum proportion of GP in finishing cattle diets. Nutrient intake and apparent total tract digestion, ruminal pH and fermentation, estimated microbial protein synthesis, route of N excretion, and blood metabolites were measured. Six ruminally fistulated crossbred beef heifers (mean initial body weight ± SD: 714 ± 50.7 kg) were used in a replicated 3 × 3 Latin square with 21-d periods. Dietary treatments were 0%, 15%, and 30% of dietary dry matter (DM) as GP, with diets containing 84%, 69%, and 54% dry-rolled barley grain, respectively. There was a linear increase (P = 0.07) in DM intake and quadratic change (P ≤ 0.01) in neutral detergent fiber (NDF) intake. There was a quadratic change (P ≤ 0.04) in apparent total tract DM, NDF, and crude protein digestibility as dietary GP content increased. However, there were no treatment effects (P ≥ 0.18) on total ruminal short-chain FA concentration and duration and area pH < 6.2, 5.8, and 5.5. Although N intake did not differ (269, 262, 253 g/d; P = 0.33) across dietary treatments, feeding GP led to a tendency for a quadratic change (P ≤ 0.07) in ruminal ammonia-N and plasma urea-N concentrations. Total N excretion also changed (quadratic, P = 0.03) because of changes (quadratic, P = 0.02) in fecal N excretion as urinary excretion of N and urea-N did not differ (P ≥ 0.15) across treatments. Feeding GP led to quadratic changes (P ≤ 0.01) in fecal excretion of fiber-bound N. Microbial N flow and apparent N retention also changed (quadratic, P ≤ 0.04) as dietary GP proportion increased. In conclusion, responses to dietary GP proportion were mostly quadratic with indications that nutrient supply as reflected by changes in apparent total tract nutrient digestibility, microbial N supply, and apparent N retention could be compromised beyond a 15% dietary inclusion level.     

Wet corn gluten feed and alfalfa hay combinations in steam-flaked corn finishing cattle diets

One finishing trial and one digestibility trial were used to evaluate wet corn gluten feed (WCGF) and alfalfa hay (AH) combinations in steam-flaked corn (SFC) finishing diets. In Exp. 1, 631 crossbred heifers (initial BW = 284 +/- 7.9 kg) were fed SFC-based diets containing combinations of WCGF (25, 35, or 45% of diet DM) and AH (2 or 6% of dietary DM) in a 2 x 3 factorial arrangement of treatments. No interactions existed between WCGF and AH for heifer performance. Increasing dietary WCGF linearly decreased gain efficiency (P < 0.01), dietary NEg concentration (P < 0.05), and 12th-rib fat thickness (P = 0.10). Cattle fed 35% WCGF had the lowest occurrence of abscessed livers, resulting in a quadratic response (P < 0.05) as dietary WCGF increased. In Exp. 2, 12 ruminally cannulated Jersey steers (585 kg) were fed SFC-based diets containing combinations of WCGF (25 or 45% of diet DM) and AH (0, 2, or 6% of diet DM) in an incomplete Latin square design with a 2 x 3 factorial arrangement of treatments. Starch intake was lower (P < 0.05), but NDF intake was greater (P < 0.05) as AH and WCGF increased in the diet. Ruminal pH was increased by AH (linear, P < 0.05) and tended (P < 0.07) to increase with WCGF. Feeding 2% AH led to the greatest ruminal NH3 but the lowest total VFA and propionate (quadratic, P < 0.05). Addition of AH to diets containing 25% WCGF increased acetate to a greater extent than addition to diets containing 45% WCGF (AH x WCGF interaction, P < 0.05). Feeding 45% WCGF tended to increase passage rate (P = 0.17) and decrease (P < 0.05) total tract OM digestibility but increase (P < 0.05) in situ degradation of DM from AH and WCGF. Interactions between AH and WCGF existed (P < 0.05) for ruminal fluid volume (quadratic effect of AH x WCGF level), in situ SFC degradation (linear effect of AH x WCGF level), and in situ rate of WCGF DM disappearance (quadratic effect of AH x WCGF level). We conclude that AH levels may be decreased when WCGF is added to SFC diets as 25% or more of the dietary DM.     

山羊绒生长缓慢期日粮适宜氮硫比的综合评定

利用9只安装有永久性瘤胃瘘管和十二指肠瘘管的周岁二狼山型白绒山羊 ,于山羊绒生长缓慢期(1～2月)研究日粮不同硫含量((分别为0.15 %、0.23 %、0.27 %)以及氮硫比(分别为11.02 :1、7.40 :1、6.03 :1)对绒山羊氮代谢、硫代谢、营养物质消化率、消化道食糜流通量的影响。试验结果表明 :在山羊绒生长缓慢期 ,由日粮中添加无机硫调控氮硫比 ,氮硫比为7.40 :1组可消化氮、沉积氮、沉积氮/进食氮及氮的消化率均显著高于氮硫比为6.03 :1组(P<0.05),亦高于未添加硫组(N/S=11.02),但差异不显著(P>0.05);而沉积氮/可消化氮显著高于其它两组(P<0.05)。随着硫的添加 ,硫的沉积量显著提高 ,但利用率降低。OM、DM、ADF的消化率以氮硫比7.40 :1组高于另两组 ,6.03 :1组最低。饲喂不同氮硫比日粮 ,瘤胃和十二指肠总氮流量各组间无显著差异 ,总硫流量随硫的添加而提高。在绒生长缓慢期日粮中添加硫使ADF、CP、DM的瘤胃动态降解率降低。根据沉积氮、硫、DM、OM、ADF的消化率与日粮硫水平之间二次曲线关系得到绒生长缓慢期日粮适宜硫水平为0.213 % ,适宜氮硫比为7.80 :1。     

Ruminal peptide concentration required to optimize microbial growth and efficiency

Experimentation, with a single-phase continuous culture system operated at fractional dilution rates of 0.03 and 0.09 per hour and four cannulated crossbred steers (260 +/- 20 kg) used in a 4 x 4 Latin square design, was conducted to determine the level of ruminally degradable protein (RDP) that maximized microbial efficiency (MOEFF), microbial nitrogen flow, and nutrient digestibility in the rumen. Treatments consisted of increasing diet RDP levels (from 3.5 to 17.5% RDP on a DM basis). The basal diet was corn with casein or soybean meal used as the source of RDP in the continuous culture experiment and animal study, respectively. Dietary nonstructural carbohydrate (NSC) ranged from 52 to 75% on a dry matter basis. Urea was added to ensure an adequate ammonia nitrogen source for microbial growth. The RDP levels did not affect true digestibility of dry matter and organic matter, ruminal pH, particulate passage rate, or liquid passage rate in the animal study. As RDP increased, bacterial nitrogen production increased linearly (P < 0.05) only for the 0.09/h dilution rate. Microbial efficiency was not influenced by RDP level. Ruminal peptide and NH3 N concentration increased linearly (P < 0.05) as RDP increased. Based on this experimentation, 1.8 mM peptide maximized MOEFF when ammonia nitrogen was not limiting (> 2 mg/dL). We concluded from this research that the RDP requirement of NSC-fermenting bacteria was lower than that currently fed in many diets.     

Effects of barley grain processing and dietary ruminally degradable protein on urea nitrogen recycling and nitrogen metabolism in growing lambs

The objective of this study was to determine how interactions between dietary ruminally degradable protein (RDP) level and ruminally fermentable carbohydrate (RFC) alter urea N transfer to the gastrointestinal tract (GIT) and the utilization of this recycled urea N in rapidly growing lambs fed high-N diets. Four Suffolk ram lambs (34.8 +/- 0.5 kg of BW) were used in a 4 x 4 Latin square design with 21-d periods and a 2 x 2 factorial arrangement of dietary treatments. The dietary factors studied were 1) dry-rolled vs. pelleted barley as the principal source of RFC and 2) dietary levels of RDP of 60 vs. 70% (% of CP). All diets contained 28.8 g of N/kg of DM. Experimental diets were composed of 80% concentrate mixture and 20% barley silage (DM basis) and were fed twice daily at 0900 and 1700 as total mixed rations. Nitrogen balance was measured from d 15 to 20, and urea N kinetics were measured from d 15 to 19 using intrajugular infusions of [(15)N(15)N]-urea. Nitrogen intake (P = 0.001) and fecal (P = 0.002) and urinary (P = 0.03) N excretion increased as dietary RDP level increased, but the method of barley processing had no effect. Feeding dry-rolled compared with pelleted barley (P = 0.04) as well as feeding 60% RDP compared with 70% RDP (P = 0.04) resulted in a greater N digestibility. Whole-body N retention was unaffected (P >/= 0.74) by dietary treatment. Dietary treatment had no effect on endogenous production of urea N and its recycling to the GIT; however, across dietary treatments, endogenous production of urea N (45.8 to 50.9 g/d) exceeded N intake (42.3 to 47.9 g/d). Across dietary treatments, 30.6 to 38.5 g/d of urea N were recycled to the GIT, representing 0.67 to 0.74 of endogenous urea N production; however, 0.64 to 0.76 of urea N recycled to the GIT was returned to the ornithine cycle. In summary, although dietary treatment did not alter urea N kinetics, substantial amounts of hepatic urea N output were recycled to the GIT under the dietary conditions used in this study, and additional research is required to determine how this recycled urea N can be efficiently captured by bacteria within the GIT.     

Effects of oscillating dietary protein on ruminal fermentation and site and extent of nutrient digestion in sheep

Eight cannulated wethers (BW = 52.5 +/- 5.7 kg) were used in a replicated 4 x 4 Latin square designed experiment to evaluate the effects of oscillating dietary protein concentrations on ruminal fermentation, site and extent of digestion, and serum metabolite concentrations. Four treatments consisted of a 13, 15, or 17% CP diet fed daily or a regimen in which dietary CP was oscillated between 13 and 17% on a 48-h basis (ACP). All diets consisted of 65% bromegrass hay (10.5% CP, 61.9% NDF, 37.2% ADF) plus 35% corn-based supplement and were formulated to contain the same amount of degradable intake protein (9.6% of DM) plus additional undegradable intake protein (SoyPLUS, West Central Cooperative, Ralston, IA) to accomplish CP levels above 13%. Each of four experimental periods were 16 d in duration with 12 d for diet adaptation followed by 4 d for sample collection. All wethers were fed at 3.0% of initial BW (DM basis) throughout the experiment, resulting in an average organic matter intake of 1.39 kg/d across treatments. When compared to the 15% CP daily treatment, feeding ACP had no effect (P > or = 0.10) on ruminal or lower tract N, NDF, ADF, or OM digestion. True ruminal OM digestion responded quadratically (P = 0.07) to increasing dietary CP, reaching a maximum of 52.0% of OM intake with the 15% CP treatment. Sheep fed ACP tended to have lower (P = 0.08) ruminal NH3 N concentrations and an overall higher (P = 0.0001) molar proportion of acetate compared to those fed 15% CP daily. Total VFA concentrations were not affected (P > or = 0.45) by increasing dietary CP. Microbial efficiency did not differ (P > or = 0.55); thus, bacterial N flow at the duodenum responded quadratically (P = 0.04) to increasing dietary CP. Nonbacterial N (P = 0.001) and total N (P = 0.01) flows at the duodenum and total tract N digestibility (P < or = 0.04) increased linearly as dietary CP increased. Wethers fed ACP maintained a lower (P = 0.002) serum glucose and lower (P = 0.0006) serum urea N compared to those fed 15% CP daily. Because the CP content of the diet was increased at the expense of corn, the response to increased CP observed in this experiment is most likely due to negative associative effects of supplemental starch on ruminal fermentation and microbial growth. Oscillating the CP content of the diet on a 48-h basis has little effect on digestion or N utilization in sheep compared with feeding the same quantity of protein on a daily basis.     

Effect of dietary level of barley-based supplements and ruminal buffer on digestion and growth by beef cattle

Six ruminally cannulated beef steers were used in a 6 x 6 Latin square experiment with a 3 x 2 factorial arrangement of treatments to evaluate the effects of barley supplementation (BS; 10, 30 or 50% of diet DM) and ruminal buffer (RB; Na sesquicarbonate at 0 or 4% of BS DM) addition to bromegrass hay-based diets on digestion. When early- (boot) and late- (full maturity) havested bromegrass and wheat straw substrates were incubated in situ, no interactions (P greater than .10) involving substrate with dietary BS or RB were observed, indicating that forages differing in fermentability responded similarly to different ruminal environments. Averaged across substrates, RB had no effect with 10% BS and a positive effect with 30% BS, but a negative effect with 50% BS diets (BS x RB, quadratic; P less than .05) for in situ DM and NDF disappearance for 18 and 24 h of incubation and for rate of disappearance of potentially degraded DM and NDF. Intakes of DM and digested DM were greater (P less than .01) for RB diets; however, RB had no effect (P greater than .10) on total tract DM and NDF digestibility. Intake and digestibility of DM increased linearly (P less than .01), whereas NDF digestibility decreased linearly (P less than .01) as BS percentage was increased in the diet. Sixty beef steers (avg initial wt 302 kg) were fed the same dietary treatments in a growth experiment. A numerical improvement in DM intake (P = .20) and ADG (P = .06) was observed when RB was provided with the 50% BS diet. Results of these experiments indicate that RB may moderate negative effects occurring on ruminal fiber digestion when grains are used to supplement forage-based diets; however, improvements in ruminal digestion were not translated effectively to improved animal productivity.     

Influence of protein type and level on nitrogen and forage use in cows consuming low-quality forage

Minimal quantities of ruminally degradable protein from supplements may improve supplement use efficiency of ruminants grazing dormant forages. In Exp. 1, N retention, ruminal NH(3), serum urea N, and NDF digestibility were evaluated for 12 ruminally cannulated cows (Bos spp.) in an incomplete Latin Square design with 3 periods of 42 d each. Cows were fed weeping lovegrass [Eragrostis curvula (Schrad.) Nees] hay (4.1% CP, 75% NDF, OM basis) at 1.3 % BW/d and offered 1 of 3 sources of CP [urea, cottonseed (Gossypium spp.) meal (CSM); or 50% blood meal and 50% feather meal combination (BFM)] fed to supply 0, 40, 80, or 160 g/d of CP. Beginning on d 22 of supplementation, ruminal contents and serum samples were collected at -2, 0, 3, 6, 9, 12, 18, 24, 30, 36, and 48 h relative to the morning offering of hay. On Day 24, feces and urine were collected for 72 h. In Exp. 2, 4 ruminally cannulated steers were used in a replicated 4 by 4 Latin Square to evaluate use of supplements differing in quantity and ruminal CP degradability. Steers were fed 6.8 kg/d chopped sudangrass [Sorghum bicolor (L.) Moench nothosubsp. drummondii (Steud.) de Wet ex Davidse] hay (3.7% CP, 74% NDF on OM basis) and supplemented with 56 g/d of a salt mineral mix (CON); CON + 28 g/d blood meal + 28 g/d feather meal (BFM); CON + 98 g/d CSM (LCS); or CON + 392 g/d CSM (HCS). Treatments provided 0, 40, 40, or 160 g/d of CP for CON, BFM, LCS, and HCS respectively. In Exp. 1, N use and total tract NDF digestibility were not affected by protein sources or amounts (P ≥ 0.18). Ruminal NH(3) concentrations exhibited a quadratic response over time for UREA (P < 0.05) and was greater with increasing inclusion of urea (P < 0.05); whereas BFM or CSM did not differ (P > 0.05) by amount or across time. In Exp. 2, supplementation had a tendency (P = 0.09) to increase DM disappearance. Supplementation also increased (P < 0.01) serum glucose concentrations; however, no difference (P ≥ 0.28) was found between supplements. Serum urea N and ruminal NH(3) concentrations were increased (P ≤ 0.01) in steers fed HCS. Feeding low quantities of a high-RUP supplement maintained rumen function without negatively affecting DM or NDF digestibility of a low-quality forage diet.     

Effects of restricted and ad libitum intake of diets containing wheat middlings on site and extent of digestion in steers

A 5 x 5 Latin square design was used to determine the effects of restricted and ad libitum intake of diets containing wheat middlings on the site and extent of digestion compared to ad libitum intake of a corn-based diet and ad libitum intake of chopped alfalfa hay. Five ruminally and duodenally cannulated Angus steers (519 +/- 41.5 kg BW) were used to compare five dietary treatments. The five treatments were as follows: ad libitum access to a corn-based finishing diet (control), the control diet with 25 percentage units of the corn and soybean meal replaced with wheat middlings offered ad libitum (WM), the WM diet restricted to 75% of predicted ad libitum intake (RWM), the RWM diet with wheat middlings replaced with ammoniated wheat middlings (RNWM), and ad libitum access to a chopped alfalfa hay diet. Although RWM steers were fed to consume 75% of ad libitum intake, RWM steers consumed 15.5% less DM than WM. Steers fed ad libitum hay consumed 28.6, 31.7, and 37.2% less (P < 0.01) DM, OM, and nitrogen than RWM steers. No differences in apparent or true ruminal digestibility were observed among steers fed the control vs WM, WM vs RWM, RWM vs RNWM, or RWM vs hay diets. However, the steers fed the hay diet had 32.5, 33.4, and 36.9% lower (P < 0.01) apparent total tract digestibilities of DM, OM, and N than those fed the RWM diet. Average ruminal pH was lower (P < 0.01) for control steers than those fed the WM diet and for those fed RWM compared to the hay diet. The acetate:propionate ratio was higher for cattle fed hay vs the RWM diet. Microbial DM and OM flow to the small intestine was higher (P < 0.02) for steers fed the RWM diet than those fed the hay diet. In addition, bacterial N flow to the small intestine was higher (P < 0.01) for cattle receiving the RWM diet than the hay diet. Feeding diets containing 25 percentage units of wheat middlings at 75% ad libitum intake had no effect on ruminal digestibility.     

Characterization of dietary protein in Brassica carinata meal when used as a protein supplement for beef cattle consuming a forage-based diet

As a novel oilseed crop in Florida, Brassica carinata has the capacity of producing high-quality jet biofuel, with a protein-dense meal (~40% crude protein; CP) obtained as a by-product of oil extraction. Characterization of the meal protein is limited, yet necessary for formulation of beef cattle diets; therefore, the objective of this experiment was to determine ruminal and postruminal digestibility of protein from B. carinata. Eight ruminally cannulated Angus crossbred steers (473 ± 119 kg) were used in a duplicated 4 × 4 Latin square design, in which in situ ruminal and postruminal degradability of nutrients were evaluated. The three-step in vitro procedure was used to compare CP and amino acid (AA) degradation in B. carinata meal pellets (BCM) with that of cottonseed meal (CSM), dry distillers grains with solubles (DDGS), and soybean meal (SBM). In situ bags were incubated in the rumen for 0 to 96 hr, with the undegraded supplement remaining after 16 hr subjected to serial in vitro enzymatic solutions. Data were analyzed using the MIXED procedure of SAS. Ruminal rate of degradation of dry matter, organic matter, and CP was greatest (P ˂ 0.01; 10.9, 11.3, and 11.5 %/h, respectively) for SBM. Rumen degradable protein (RDP) content did not differ (P = 0.20; 47.8% and 55.1%, respectively) between CSM and DDGS, but was decreased (P ˂ 0.01) compared with SBM and BCM, which did not differ (P = 0.99; 72.3% and 71.8% RDP, respectively). Compared with DDGS, SBM had greater (P < 0.01) intestinal digestibility of rumen undegradable protein (RUP). Intestinally absorbable digestible protein (IADP) was greatest (P < 0.01) for CSM, with SBM and BCM having the least IADP. Total tract digestibility of CP (TTDP) was greater (P < 0.01) for SBM compared with CSM and DDGS. The contribution of RUP to intestinally absorbable AA was 7.2 and 3.1 g of lysine and methionine per kilogram of CP in BCM, respectively. The evaluation of B. carinata meal as protein supplemented for cattle consuming a forage-based diet resulted in 71.8% RDP and 97.1% TTDP, thus indicating its viability as a high-quality protein supplement for beef cattle.     

Manipulation of nitrogen digestion by sheep using defaunation and various nitrogen supplementation regimens

Five ruminally, duodenally, and ileally cannulated sheep (average BW 62 kg) were fed 65% roughage: 35% concentrate diets (CP = 15%) in a 5 x 5 Latin square design to study the applicability of using a combination of defaunation with N supplements (soybean meal [SBM], corn gluten meal [CGM], blood meal [BM], urea, and casein) with different extents of ruminal degradation to manipulate microbial protein synthesis and amount of ruminal escape protein. Diets were fed twice daily (1,759 g DM/d). Defaunation was accomplished with 30-ml doses of alkanate 3SL3 (active ingredient: sodium lauryl diethoxy sulfate)/sheep daily for 3 d with 2 d of fasting. Treatment 1 (control) involved feeding faunated sheep a diet in which the supplemental N (45% of total dietary N) was 67% SBM N and 33% urea N. Treatment 2 involved feeding defaunated sheep the same diet as the control. Treatments 3, 4, and 5 involved feeding defaunated sheep diets in which the supplemental N source was either 67% CGM-BM (1:1 N ratio) N:33% urea N, or 33% CGM-BM N:67% urea N or 33% CGM-BM N:33% urea N:33% casein N, respectively. Compared with the faunated control, defaunation decreased (P less than .05) ruminal ammonia concentration (19 vs 26 mg/dl) and increased (P less than .05) CP flow to the duodenum (253 vs 214 g/d) due to a trend for increases in both bacterial (BCP) and nonbacterial (NBCP) CP flows.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effect of different methods for conserving rice grain on in situ ruminal degradation and in vivo nutrient digestion and rumen fermentation in steers

We investigated the effects of different rice conservation techniques on in situ ruminal degradation and in vivo nutrient digestibility and rumen fermentation in steers. Raw rice grain was dried before crushing (DRY), ensiled after crushing (ENS‐A), or ensiled before crushing (ENS‐B). Six ruminally cannulated steers were used in a replicated 3 × 3 Latin square design with three dietary treatments: diets containing DRY, ENS‐A, or ENS‐B at 36% of the dietary dry matter. The in situ rapidly degradable fraction and effective ruminal degradability were higher for ensiled rice than for DRY, and higher for ENS‐A than for ENS‐B. The ruminal pH was lower and the lactic acid and total volatile acid concentrations were higher for the steers fed ensiled rice than those fed the DRY diet, but a treatment effect was not observed in the comparison between ENS‐A and ENS‐B. The whole‐tract digestibility of crude protein and ether extract was improved when the rice grain was ensiled, but there were no differences in nutrient digestibility between ensiling methods. These results show that ensiling treatment can be a strategy to improve the nutrient value of rice grain, but the ensiling method has little impact on in vivo digestion.     

Processing index of barley grain and dietary undigested neutral detergent fiber concentration affected chewing behavior,ruminal pH,and total tract nutrient digestibility of heifers fed a high-grain diet

The objective of this study was to investigate the effects of processing index (PI) of barley grain and dietary undigested neutral detergent fiber (uNDF) concentration on dry matter (DM) intake, chewing activity, ruminal pH and fermentation characteristics, total tract digestibility, gastrointestinal barrier function, and blood metabolites of finishing beef heifers. The PI was measured as the density after processing expressed as a percentage of the density before processing, and a smaller PI equates to a more extensively processed. Six ruminally cannulated heifers (average body weight, 715 ± 29 kg) were used in a 6 × 6 Latin square design with three PI (65%, 75%, and 85%) × 2 uNDF concentration (low and high; 4.6% vs. 5.6% of DM) factorial arrangement. The heifers were fed ad libitum a total mixed ration consisting of 10% barley silage (low uNDF), or 5% silage and 5% straw (high uNDF), 87% dry-rolled barley grain, and 3% mineral and vitamin supplements. Interactions (P < 0.01) of PI × uNDF were observed for DM intake, ruminating and total chewing time, and DM digestibility in the total digestive tract. Intake of DM, organic matter (OM), starch, and crude protein (CP) did not differ (P > 0.14) between low and high uNDF diets, but intakes of NDF and acid detergent fiber were greater (P = 0.01) for high uNDF diets regardless of barley PI. Heifers fed high uNDF diets had longer (P = 0.05) eating times (min/d or min/kg DM) and tended (P = 0.10) to have longer total chewing times (min/kg DM) than those fed low uNDF diets. Additionally, heifers sorted (P = 0.01) against long particles (>19 mm) for high uNDF diets but not for low uNDF diets. Altering PI of barley grain did not affect (P > 0.12) total volatile fatty acid (VFA) concentration, molar percentages of individual VFA, or duration of ruminal pH < 5.8 and <5.6. Total VFA concentration was less (P = 0.01), acetate percentage was greater (P = 0.01), and duration of ruminal pH < 5.8 and <5.6 was less (P = 0.05) for high compared with low uNDF diets. Digestibility of DM, OM, and CP was greater (P = 0.02) for low vs. high uNDF diets with PI of 65% and 75%, with no difference between low and high uNDF diets at PI of 85%. Blood metabolites and gastrointestinal tract barrier function were not affected (P ≥ 0.10) by the treatments. These results suggest that increasing dietary uNDF concentration is an effective strategy to improve ruminal pH status in finishing cattle, regardless of the extent of grain processing, whereas manipulating the extent of barley processing did not reduce the risk of ruminal acidosis.