Postruminal Digestion Research Articles

Avoparcin and Monensin Effects on Digestive Function in Cows Fed a High Forage Diet

Three non-lactating cows with ruminal, duodenal, and ileal cannulas were used in a 3×3 Latin square design to evaluate the effect of oral avoparcin and monensin on fibre, starch, and nitrogen (N) digestion. Cows were fed three high forage diets; the control diet had no additive, and the others contained 33 mg kg−1 DM of either avoparcin or monensin. Neither additive affected apparent total tract digestibilities of organic matter, fibre, starch or N. Avoparcin and monensin reduced the ruminal breakdown of fibre, starch and dietary N. Efficiency of bacterial N synthesis was unchanged, and passage of bacterial N to the small intestine was not modified. Compared with the control, additives caused a greater proportion of feed starch, N, and total amino acid to be digested in the small intestine than in the rumen. Diets containing avoparcin or monensin increased availability of total essential amino acid in the small intestine compared with that of control diets. Post-ruminal digestion of fibre was greater for diets supplemented with antibiotics, because the cows compensated digestion in the lower forestomach.

Influence of flake density on the feeding value of steam-processed corn in diets for lactating cows.

Four primiparous Holstein cows (112 d in lactation) with cannulas in the rumen and proximal duodenum were used in a 4 x 4 Latin square design. Dry-rolled (DR) corn (density .52 kg/L) was compared with stream-flaked (SF) corn processed to three flake densities: .39, .32, and .26 kg/L. The basal diet contained (DM basis) 43.4% alfalfa hay, 39.5% corn (DR or SF), 2.2% yellow grease, 9.6% cane molasses, .7% sodium bicarbonate, and 4.6% protein-mineral supplement. Steam flaking increased DM intake (P < .01). There were no treatment effects on ruminal pH (P > .10). Ruminal molar ratios of acetate and propionate were lower (P < .01) for SF than for DR corn and declined (linear component, P < .01) as flake density decreased. Ruminal digestibility of OM was not affected (P > .10) by corn processing. Ruminal starch digestibility increased (linear component, P < .05) as flake density decreased. Ruminal ADF digestibility was decreased by SF (P < .01); this effect was exacerbated by degree of processing (linear component, P < .05). Ruminal N efficiency (duodenal nonammonia N/N intake) was greater (P < .10) for SF than for DR corn because of an improved (P < .10) microbial efficiency. Steam flaking at all densities increased postruminal digestibility of OM (42.4%, P < .01), starch (84.9%, P < .01) N (13.6%, P < .01), and lipid (11.8%, P < .05). Total-tract digestibilities of OM, N, starch, DE and ME were greater (15.2, 11.5, 25.2, 14.9, and 20.0%, respectively, P < .01) for SF (mean of the three densities) than for DR corn. Total-tract digestibility of starch increased (linear component, P < .10) with degree of processing. However, this effect was offset by decreased (linear and quadratic components, P < .05) ADF digestibility. Steam flaking improved the feeding value of corn for lactating cows by improving diet acceptability and digestibility of lipid, starch, and N. Steam flaking increased the estimated NEl of corn by 33%. Optimal flake density probably is between .32 and .39 kg/L.

Prediction of rumen undegradable amino acids that are digested post-ruminally

Data for in situ disappearance of DM, nitrogen (N) and amino acids in canola meal (CM) were used to determine degradation parameters required to estimate effective degradabilities of these nutrients. The non-digestible fraction of DM, N and amino acids in CM was determined using mobile bags after ruminal incubation for 12 h. Linear relationships were determined between dependent variables, ruminal disappearance (DIS) or effective degradability (EDEG) of amino acids and independent variables, DIS or EDEG of DM or N. Use of EDEG vs. EDEG relationships, (r2 greater than 0.87 for amino acids other than methionine and cystine) with the effective degradability of DM, as the independent variable, was the most effective approach over a wide range of rumen outflow rates (k) for prediction of amino acids that escaped ruminal degradation. Use of DIS vs. DIS (an estimate for EDEG of DM served as a value for the independent variable), or EDEG vs. DIS (disappearance of DM at incubation time equal to k−1 was the independent variable) relationships was not as effective. Post-ruminal digestion was predicted as the difference between ruminal escape (based on estimates of effective degradability) and that nutrient present in the residual DM in mobile bags recovered at the terminal ileum. Use of linear EDEG vs. EDEG equations, in association with a mobile bag technique, allowed for prediction of both ruminal escape and post-ruminal digestion of N and amino acids in CM over a range of outflow rates for feed particles from the rumen. Key words: Amino acids, canola meal, ruminal escape, post-ruminal digestion

Avoparcin and monensin effects on the digestion of nutrients in dairy cows fed a mixed diet

An in vivo study was carried out to evaluate the effect of avoparcin on fiber, starch and nitrogen (N) digestion compared with monensin. Three dairy lactating cows with ruminal, duodenal and ileal cannulas were used in a 3 × 3 Latin square design. Cows were fed three diets; the control diet had no additive, and the others contained 33 ppm of either avoparcin or monensin-sodium. There were no treatment effects on ruminal pH and total volatile fatty acid levels; molar proportion of propionate tended to be higher (27.9–29.9 vs. 23.7%) and of butyrate tended to be lower (9.9–12.9 vs. 15.4%) for the antibiotic-supplemented diets. Also, both additives decreased ruminal ammonia N concentration (77.2–105.6 vs. 164.1 mg L−1). The supply of avoparcin or monensin reduced the ruminal breakdown of fiber (36.1 and 37.1 vs. 45.9%) starch (57.4 and 54.7 vs. 63.6%), and dietary N (59.5 and 53.6 vs. 67.3%); efficiency of bacterial protein synthesis was unchanged. Passage of bacterial N to the small intestine was not modified; flows of fiber, starch, nonammonia N and dietary N were improved by the both additives. In comparison with the control, monensin caused a greater quantity of glucose (2100 vs. 1500 g d−1) and total amino acids (AA) (1381 vs. 1047 g d−1) to be digested in the small intestine; avoparcin had a less pronounced effect on the intestinal absorption of glucose (1700 g d−1) and AA (1152 g d−1). Only monensin increased the plasma glucose levels (3.6 vs. 3.1 mM). Both additives did not affect total tract digestibilities of organic matter, fiber, starch, and N. Postruminal digestion of fiber was greater (16.0 vs. 7.3%) for antibiotic-supplemented diets, compensating for the lower forestomach digestion. In comparison with monensin dietary avoparcin had a less pronounced effect on the alteration of nutrient digestion. Key words: Avoparcin, monensin, rumen, intestines, amino acids, digestion, cattle

Intestinal nitrogen digestibility of heat-moisture treated rapeseed meals as assessed by the mobile-bag method in cows

An experiment was designed to study the effects of commercial heat-moisture (HM) treatment (Öpex®) and a rapeseed (Brassica campestris) cultivar on intestinal N and amino acid (AA) digestion values of rapeseed meal (RSM) estimated by the mobile-bag method. Experimental feeds were either untreated or HM-treated rapeseed meals (RSM1, RSM2, RSM3 and RSM4), and soya bean meal (SBM) as a control. RSM1 (untreated) and RSM2 (HM treated) originated from black-seeded single and double zero varieties, respectively, and RSM3 (untreated) and RSM4 (HM treated) from yellowish-seeded double zero varieties. The effect of pepsin-acid incubation of experimental feeds on intestinal digestion values obtained by the mobile-bag method was also investigated. Four ruminally cannulated bulls were used to study N degradability of experimental feeds in the rumen by nylon-bag technique, and four duodenally cannulated non-lactating cows to study post-ruminal digestion values of nitrogenous compounds by the mobile-bag method. HM treatment effectively increased the proportion of rumen-undegradable N in RSM without adverse effects on the subsequent disappearance of N from mobile bags within the intestine. Generally, HM treatment had a similar effect on the disappearance of individual AAs from bags in the intestine as on that of total N. However, the disappearance of amino acid N or individual AAs of RSMs from the mobile bags was clearly greater than that of total N. Rapeseed variety had only a minor impact on the intestinal digestion values of nitrogenous compounds. The digestion values for N were clearly lower for RSMs than for SBM, probably owing to the greater proportion of totally unavailable feed N in RSMs. Pepsin-acid incubation prior to the mobile-bag measurement did not affect the intestinal N digestion values obtained for the rumen-undegradable feeds. Thus pepsin-acid treatment is not necessary in mobile-bag procedure which includes pre-incubation of feeds in the rumen.

Intestinal nitrogen digestibility of heat-moisture treated rapeseed meals as assessed by the mobile-bag method in cows

An experiment was designed to study the effects of commercial heat-moisture (HM) treatment (Öpex®) and a rapeseed ( Brassica campestris) cultivar on intestinal N and amino acid (AA) digestion values of rapeseed meal (RSM) estimated by the mobile-bag method. Experimental feeds were either untreated or HM-treated rapeseed meals (RSM1, RSM2, RSM3 and RSM4), and soya bean meal (SBM) as a control. RSM1 (untreated) and RSM2 (HM treated) originated from black-seeded single and double zero varieties, respectively, and RSM3 (untreated) and RSM4 (HM treated) from yellowish-seeded double zero varieties. The effect of pepsin-acid incubation of experimental feeds on intestinal digestion values obtained by the mobile-bag method was also investigated. Four ruminally cannulated bulls were used to study N degradability of experimental feeds in the rumen by nylon-bag technique, and four duodenally cannulated non-lactating cows to study post-ruminal digestion values of nitrogenous compounds by the mobile-bag method. HM treatment effectively increased the proportion of rumen-undegradable N in RSM without adverse effects on the subsequent disappearance of N from mobile bags within the intestine. Generally, HM treatment had a similar effect on the disappearance of individual AAs from bags in the intestine as on that of total N. However, the disappearance of amino acid N or individual AAs of RSMs from the mobile bags was clearly greater than that of total N. Rapeseed variety had only a minor impact on the intestinal digestion values of nitrogenous compounds. The digestion values for N were clearly lower for RSMs than for SBM, probably owing to the greater proportion of totally unavailable feed N in RSMs. Pepsin-acid incubation prior to the mobile-bag measurement did not affect the intestinal N digestion values obtained for the rumen-undegradable feeds. Thus pepsin-acid treatment is not necessary in mobile-bag procedure which includes pre-incubation of feeds in the rumen.

Effects of forage level and canola seed supplementation on site and extent of digestion of organic matter, carbohydrates, and energy by steers.

The objective of this study was to determine the effects of fat supplementation from canola seed (CS) on ruminal fermentation and postruminal digestion of OM, carbohydrates, and energy of diets containing different levels of forage. Six ruminally and duodenally cannulated beef steers (354 kg +/- 18) were given ad libitum access to six isonitrogenous diets that were offered twice daily in a 6 x 6 Latin square design. Treatments were arranged as a 2 x 3 factorial with two forage levels (70 vs 30% of dietary DM as corn silage) and three forms of CS supplementation including no CS or CS added at 10% of dietary DM as whole CS treated with alkaline hydrogen peroxide or untreated crushed CS. Fat from CS provided 5% of dietary DM. The remaining dietary ingredients were corn, canola meal, molasses, and urea. No interactions (P > .05) between dietary forage level and CS supplementation were observed for ruminal characteristics or digestion of OM, carbohydrates, and energy in the rumen, postruminally, or in the total tract. Fat supplementation from CS did not affect (P > .05) DMI. With few exceptions, fat supplementation did not affect (P > .05) ruminal, postruminal, or total tract digestibilities of OM, structural and nonstructural carbohydrates, and GE. Ruminal disappearance of GE was decreased (P < .05) when diets were supplemented with fat from whole treated CS, and total tract digestibilities of OM and GE were decreased (P < .05) when diets were supplemented with fat from CS in either form. Ruminal pH, concentrations of NH3 N and total VFA, and molar proportions of acetate, propionate, and butyrate were not affected (P > .05) by fat supplementation. Results suggest that fat supplementation from CS (at 5% of dietary DM) as whole treated or untreated crushed had no negative effects on ruminal fermentation of OM, carbohydrates, or energy when steers were given ad libitum access to diets containing high or low forage.

Characteristics of digestion of linted and lint-free cottonseed in diets for feedlot cattle.

Eight Holstein steers (439 kg) with "T" cannulas in the rumen and proximal duodenum were used to evaluate the characteristics of digestion of Pima cottonseed. Treatments consisted of a basal growing-finishing diet containing (DM basis) 1) 15% tapioca, 2) 15% whole linted cottonseed (Delta Pine 61, DP); 3) 15% whole lint-free cottonseed (Pima, PW), and 4) 15% ground Pima cottonseed (PG). Substitution of tapioca with cottonseed decreased (P < .05) ruminal and total tract digestion of OM (10.8 and 3.5%, respectively). Net ruminal microbial N synthesis was also lower (20.5%, P < .10) with cottonseed supplementation. The greater reductions occurred with DP and PG. Characteristics of ruminal and total tract digestion of OM and N were similar for DP and PG. Grinding Pima cottonseed increased ruminal digestion of OM (13%; P < .05) and feed N (18.1%; P < .10). Ruminal digestibility of N in DP, PW, and PG averaged 50.0, 49.4, and 59.3%, respectively. Postruminal digestion of lipid was similar (P > .10) across cottonseed treatments, averaging 76.9%. The comparative DE value of DP, PW, and PG were 4.13, 3.20, and 3.80 Mcal/kg, respectively. It is concluded that the energy value of lint-free Pima cottonseed is similar to that of linted varieties provided that it is ground before feeding. However, grinding will increase ruminal N degradability 20%. Furthermore, depending on the level of incorporation in the diet, grinding Pima cottonseed may decrease ruminal microbial growth and net ruminal protein efficiency.

The role of the large intestine in post-ruminal digestion of feeds as measured by the mobile-bag method in cattle.

To study the importance of site of recovery and other factors related to mobile-bag (MB) digestion values, two consecutive experiments in which diets were applied in a 3 x 3 Latin square design, were carried out with cannulated growing heifers. In Expt 1, several types of experimental feed were exposed to intestinal digestion in mobile bags made of two cloth types and filled with intact or rumen-undegradable (RUD) feed material to be recovered either from the ileum (IB) or faeces (FB). In Expt 2, mean retention time (MRT) of Yb-labelled digesta particles within the intestine and in vivo digestibility of diets were measured. With vegetable concentrates, FB resulted generally in slight overestimation of small-intestinal dry matter and N digestion, while with meat-and-bone meal no difference between FB and IB was found. The respective N digestibility of RUD late-cut silage was clearly underestimated as measured from FB. The disappearance of neutral-detergent fibre (NDF) of all feeds under test was higher from FB than from IB. It was not possible to isolate the influence of the large intestine on the MB values by changing bag cloth type. Irrespective of the longer retention time of bags and longer MRT of Yb in the intestine on a low as compared with a high level of feeding, only NDF disappearance of feeds increased due to lower feeding level. Altering the diet type to increase large-intestinal fermentation, as indicated in vivo, usually had no effect on the MB values. It is concluded that the site of collection of bags does not practically affect small-intestinal digestion values of feed N, unless the feed is rich in fibre.

Ruminal and post-ruminal digestion and nitrogen balance in early weaned calves fed soybean meal and heated soybean meal

Ruminal and post-ruminal digestion and nitrogen balance in early weaned calves fed soybean meal and heated soybean meal

Rumen degradation and post-ruminal digestion of palm kernel by-products in dairy cows

Rumen degradation characteristics and digestion post-rumen were measured in seven (five expellers and two meals) samples of palm kernel by-products using four cannulated (rumen and distal duodenum) dairy cows and nylon bag techniques. The by-products were selected to provide variation in chemical composition and in vitro digestibility. All samples contained high levels of cell wall constituents (70–80% of the fat-free organic matter) and 16–22% protein. The rumen undegradable fraction of neutral detergent fibre (NDF) varied between 23 and 37%; degradation of the NDF fraction was preceded by a lag phase, which was longest in the meals. Rumen degradation of the protein fraction was slow, especially for two Nigerian samples. The meals displayed larger fractions of rumen undegradable protein than the expellers. This fraction was satisfactorily predicted by a univariate relationship with in vitro digestion of protein (pepsin). Variation in protein degradation could not be satisfactorily accounted for by laboratory analyses using fungal proteolytic enzymes alone. The estimated high level of rumen escape protein may be partly attributable to microbial contamination. Post-ruminal digestion of the escape protein varied between 83 and 92% and correlated strongly with in vitro (pepsin) protein digestibility. Calculations suggest a slow rate of outflow from the rumen of both cell wall and protein constituents in palm kernel by-products.

Influence of crambe meal as a protein source on intake, site of digestion, ruminal fermentation, and microbial efficiency in beef steers fed grass hay.

Four ruminally and duodenally cannulated beef steers (558 +/- 37 kg) were arranged in a 4 x 4 Latin square to evaluate the influence of crambe meal as a protein source on intake, digestion, and microbial efficiency. Steers were offered chopped (10.2 cm) brome hay (6.2% CP) for ad libitum consumption and one of four supplements. Protein sources used were soybean and crambe meals (CM). Protein sources were blended to provide four levels of supplemental CM protein (0, 33, 67, and 100%). Protein supplements were fed to provide similar amounts of protein and energy. Amounts of supplements fed were 831, 885, 950, and 996 g of DM/steer daily for 0, 33, 67, and 100% CM treatments, respectively. Crambe meal represented 0, 2.00, 3.83, and 5.88% of the DM intake for respective treatments. Steers were allowed a 21-d adaptation to diets before each collection period. Supplements were offered at 0800 and forage at 0830. Crambe meal had no influence (P > .10) on forage and total DM intake (grams/kilogram of BW). Apparent total tract, ruminal, and postruminal digestion of OM, NDF, ADF, and N were unaffected (P > .10) by CM supplementation.(ABSTRACT TRUNCATED AT 250 WORDS)

The post-ruminal digestion of dry matter, nitrogen and amino acids in wheat-based distillers' dried grains and canola meal

The degradation of dry matter (DM), nitrogen (N) and amino acids (AA) by ruminal microorganisms (ruminal disappearance) in distillers' dried grains with solubles (DDG), groups DG1, DG2 and DG3, prepared from 70%, 75% and 100% wheat grain, respectively, and the remainder maize grain, plus a sample of canola meal (CM) was determined by incubating sample-filled Dacron bags for 12 h in sacco. The total digestion of nutrients was determined using a sequence of in sacco ruminal incubation for 12 h, in vitro digestion in acid-pepsin and with Dacron bags as mobile bags post-abomasally. A collection of mobile bags, via a cannula at the terminal ileum provided an estimate of ileal disappearance, which was a sum of digestion in the rumen, abomasum and small intestine. Recovery of mobile bags in feces provided an estimate of total tract digestion, defined as fecal disappearance, which was ileal disappearance plus the effects of the passage of sample-filled Dacron bags through the large intestine. Acid detergent insoluble N (ADIN) was 16.7%, 8.9% and 9.7% of total N in DG1, DG2 and DG3, respectively. ADIN was 5.7% of total N in CM. Both ADIN, with DG1 lower than DG2, and the composition of fermentative substrate, with DG3 lower than DG2, influenced the ruminal disappearance of DM, N and amino acids in DDG. The ruminal disappearance of DM, N and AA was higher for CM than all three groups of DDG. The ileal disappearance of N and AA was lower with DG1 than DG3 and was the result of a combined effect of ADIN and the composition of fermentative substrate, while there were no consistent differences between CM and DDG. Ileal estimates of disappearance were more sensitive than fecal-based data in identifying differences for total tract digestion among groups of DDG. Except for lysine, whose concentration in DDG was 40% that in CM, the estimated mean weight of AA digested post-ruminally (ileal disappearance minus ruminal disappearance) ranged from +9% to +133% higher for DDG than CM.

Recent advances in understanding of microbial transformation in ruminants

In this review some recent advances in understanding of microbial transformations of nutrients in ruminants is discussed. It is argued that a greater understanding of the importance of an optimal rumen environment for cellulolysis has been achieved in recent years. It is recognised that not only deficient nutrients e.g. N and S, and low pH can limit degradation rate but also that the number of microbes in solution can be a limiting factor particularly for very poor quality roughages. The general conclusion that microbial biomass is a constant relative to fermented carbohydrate is now challenged largely due to development of a new non-invasive technique of estimating microbial protein by urinary purine derivative. Turnover rate of microbes within the rumen and rate of outflow has been identified as a very important factor affecting the ratio of volatile fatty acids to microbial biomass. While the proportion of volatile fatty acids has generally no effect on their utilization, a high propionic acid proportion can adversely affect milk production. High propionic acid proportion is generally associated with production of large amounts of B 12 analogues which can compete with true B 12 for transport systems and thus indirectly cause B 12 deficiency in sheep. It is concluded that optimal feed utilization and health of the animals can be achieved by ensuring optimal condition for cellulolysis in the rumen and that except for protein and fat there is little or no advantage in encouragement of postruminal digestion of carbohydrates.

Effects of Excessive Supplemental Fat on Feedlot Cattle Growth Performance and Digestive Function

Ninety medium-framed crossbred steers (245kg) were used in a 205-d feeding trial to evaluate the influence of 4, 8, and 12% supplemental fat (tallow soap stock) on feedlot growth performance. Increasing level of fat supplementation depressed ADG (P<.01), DM conversion (P<.01), and dietary NE (P<.05). Depressions in DM conversion and dietary NE were more marked at the 12% level of fat supplementation. There was a quadratic effect (P<.01) of level of fat supplementation on DM intake, with intake being higher for 12% supplemental fat than for 8% supplemental fat. Observed:expected diet NEm was 1.00 with 4% supplemental fat and declined (P<.01) to .86 with 12% supplemental fat. The NEm of tallow soap stock declined in a near rectilinear fashion from 5.65 Mcal/kg at the 4% level of supplementation to 2.85 Mcal/kg at the 12% level of supplementation. Six Holstein steers (296kg) with T cannulas in the rumen and proximal duodenum were used to evaluate treatment effects on digestive function. Ruminal digestion of OM (P<.01), feed N (P<.01), and ADF (P<.05) decreased linearly with increasing level of fat supplementation. Most (55%) of the decline in ruminal OM digestion could be directly attributed to ruminal indigestibility of dietary fat. Increasing level of fat supplementation did not influence (P>.10) postruminal digestion of OM, ADF, starch, and N. Postruminal digestion of lipid decreased (P<.01) with increasing level of fat supplementation. Total lipid intake was a better predictor of postruminal lipid digestibility than percentage supplemental fat. True digestibility of supplemental tallow soap stock at the 8 and 12% levels of supplementation averaged 63 and 40%, respectively. Total tract OM digestion declined linearly (P<.01) with increasing level of supplemental fat. This decline was due to differences in lipid digestion. There were no associative effects of supplemental fat on total tract digestion of ADF, starch, and N. It is concluded that optimal growth performance response to supplemental fat will be obtained when levels of total lipid intake are less than 1.6g/kg body weight. Detrimental effects of excessive supplemental fat are primarily associated with depressed intestinal lipid digestibility.

Amino Acid Profile and Intestinal Digestibility in Dairy Cows of Rumen-Undegradable Protein from Various Feedstuffs

Three lactating cows fitted with rumen cannulas and three cows fitted with proximal duodenal cannulas were used to determine the effect of in situ rumen degradation on the AA profile of rumen-undegraded protein of 12 feedstuffs. Intestinal digestibility of rumen-undegraded protein was determined using the mobile bag technique. The absorbable AA profile of rumen-undegraded protein for each feedstuff was compared with profiles of the original feedstuff and the rumen-exposed undegraded protein. Branched-chain AA in particular seemed to be rather resistant to degradation in the rumen, as was Phe. Lysine concentrations decreased in the undegraded protein fraction in 9 of 12 feedstuffs; the degradation of Met depended on the feedstuff. The absorbable AA profiles of undegraded protein, in general, closely reflected the AA profiles of the rumen-exposed residues, which suggests that rumen degradation had a greater influence than postruminal digestion on the postruminal provision of specific absorbable AA. Intestinal digestibility of undegraded protein varied from 37.8% for Eragrostis curvula hay to 98% for soybean meal; the constant digestibility factor used by most protein systems should be reconsidered.

Influence of flake thickness on the feeding value of steam-rolled wheat for feedlot cattle

Seventy-two medium-framed, crossbred steers (348 kg) were used in a randomized complete block design performance trial. Experimental diets contained (DM basis) 6% alfalfa hay, 6% sudangrass hay, 79% wheat, 2% yellow grease, 4% cane molasses, and 3% supplement. Treatments were 1) dry-rolled wheat (DRW, density = .52 kg/L); 2) steam-rolled wheat, coarse flake (SRW-C, density = .39 kg/L); and 3) steam-rolled wheat, thin flake (SRW-T density = .30 kg/L). Steam processing increased amyloglucosidase reactivity of wheat starch by 238 and 287% for SRW-C and SRW-T, respectively. Cattle performance was similar (P > .10) for SRW-C and SRW-T. Steam processing wheat increased ADG (13.5%, P < .10) and decreased DM intake/gain (8.8%, P < .05). Diet NE was precisely as expected for DRW, confirming the applicability of tabular NE values. Diet NEm was 3.7% lower (P < .05) for DRW than for SRW. The NEm and NEg of SRW were 2.28 and 1.59 Mcal/kg, respectively. Twelve Holstein steers (266 kg) were "T" cannulas in the rumen and proximal duodenum were used in a completely random design experiment to evaluate treatment effects on characteristics of ruminal and total tract digestion. Ruminal digestibilities of OM and starch were similar (P > .10) for DRW and SRW. Postruminal and total tract digestibility of OM (P < .10) and starch (P < .01) were increased with SRW. Dietary DE and ME values were greater (6.1 and 6.6%, respectively; P < .10) for SRW than for DRW.(ABSTRACT TRUNCATED AT 250 WORDS)

Influence of Amount and Degradability of Dietary Protein on Nitrogen Utilization by Dairy Cows

Four Holstein cows fitted with ruminal and T-type duodenal cannulas were utilized in a 4 × 4 Latin square design with a 2 × 2 factorial arrangement of treatments. The TMR contained 25% alfalfa haylage, 25% corn silage, and 50% concentrate and provided either 16.4 or 19.6% CP, with ruminal degradability calculated to be 30 or 45%. Intakes of DM, OM, ADF, NDF, and N were not altered by either amount or degradability of CP. Intake and ruminal and postruminal digestibility of starch were greater when cows were fed diets high in undegradable CP but was not altered by amount of CP. Apparent total tract digestibilities for DM, OM, starch, ADF, and NDF were similar among treatments. Apparent total tract digestibility of N was 4.7 percentage units greater for diets low in ruminally degradable CP. Apparent digestibility of OM, ADF, and NDF and true digestibility of OM in the rumen were not altered by amount of CP or undegradable CP. Increasing the CP content of the diet and the proportion of undegradable CP in the diet increased NAN flow to the duodenum. Except for Met, flows of all AA to the duodenum were increased when CP was increased. Flow of Met to the duodenum was not altered by undegradable CP content of the diet. Production of milk, 4% FCM, and milk CP was not altered by amount of CP or undegradable CP. Milk fat content and yield were increased when diets high in undegradable CP were fed. Results suggest that all diets supplied adequate amounts of AA for these cows or that Met was deficient for all cows.

Effect of extruding on ruminal disappearance and lower gastrointestinal tract digestion of white lupin seeds

The effect of extruding white lupin (Lupinus albus 'Lublanc') seeds (WLS) at 110, 130, 150 or 180 °C on the in vitro solubility of crude protein (CP) and in sacco rumen degradation and intestinal digestion of rumen escape CP and fiber was determined. Rumen degradation was estimated by incubating nylon bags in the rumen of cows for 2, 4, 8, 16, 24 and 48 h. Extruding WLS at 110, 130, 150 and 180 °C reduced the CP-solubility by 32.8, 47.7, 58.4 and 67.5%, respectively. The effective ruminal degradabilities of CP, acid detergent fiber (ADF) and neutral detergent fiber (NDF) were evaluated assuming a ruminal outflow rate of 0.06 h−1. Heating WLS at 110, 130, 150 and 180 °C decreased the ruminal degradability of CP value: 89.8, 79.9, 65.1, 61.8 vs. 93.4% (raw), respectively; the corresponding values for ADF and NDF were: 38.4, 35.3, 34.2, 27.6 vs. 43.6% (raw) and 37.7, 33.1, 32.2, 26.5 vs. 39.4% (raw). Postruminal digestion was estimated using a sequence of ruminal in situ incubation for 4, 8 and 16 h, in vitro incubation in an acid-pepsin bath for 3 h and a mobile nylon bag technique distal to the abomasum. Extrusion of WLS decreased the degradability of CP, ADF and NDF in the rumen with a corresponding increase in the amounts digested in the postruminal sections; the whole-tract digestibility was generally unchanged. Therefore, the processing shifted the digestion of these components from rumen to the lower gastrointestinal tract. Key words: White lupin seed, in vitro solubility, rumen degradability, postruminal digestion, crude protein, detergent fiber

Nutritional Regulation of Postruminal Digestive Enzymes in Ruminants

Nutritional regulation of digestive enzymes has received limited study in ruminants. Comparable studies with non-ruminants report adaptations occurring in pancreatic and mucosal enzyme concentrations and synthesis in response to increased consumption of carbohydrate, lipid, or protein. Adaptations in carbohydrases apparently are mediated through changes in blood glucose and insulin, and changes in lipase are mediated through changes in circulating β-hydroxybutyrate. Increased synthesis and secretion of pancreatic proteases apparently are mediated directly through luminal effects of protein, possibly through a messenger peptide. Available information for ruminants suggests that pancreatic α-amylase concentration increases with increased energy intake, but not with increased carbohydrate intake, independent of energy. This result may indicate an adaptation mechanism similar to that of nonruminants, one that is mediated through increased glucose turnover, not intestinal carbohydrate supply alone. Increased intake of energy or increased intestinal supply of carbohydrates results in little or no increase in mucosal carbohydrases in the ruminant. Comparable data for effects of changing intestinal supply of protein are limited to the developing ruminant. Experiments involving lipid feeding are not available, but duodenal lipid infusion decreases pancreatic lipase secretion. Ruminant data are inadequate to predict accurately an adaptive response to feeding any diet.