Mammary uptake, portal-drained visceral flux, and hepatic metabolism of free and peptide-bound amino acids in cows fed steam-flaked or dry-rolled sorghum grain diets.

Our objectives were to measure net fluxes of free AA (FAA) and peptide-bound AA (PBAA) across portal-drained viscera, liver, splanchnic tissues, and mammary tissues, and milk AA output of lactating Holstein cows (n = 8, 86 +/- 8 d in milk). Cows were fed an alfalfa-based total mixed ration containing 40% steam-flaked (SFS) or dry-rolled (DRS) sorghum grain. The total mixed rations were offered at 12-h intervals in a crossover design. Blood samples were obtained from indwelling catheters in portal, hepatic, and mammary veins and from mesenteric or costoabdominal arteries every 2 h from each cow and diet. Intake of dry matter was 17.9 and 18.6 kg/d of the SFS and DRS diets, respectively, but dropped to 16.3 kg/d for cows fed the SFS diet in the last 3 experimental days, sampling day included. Milk and milk crude protein yields (kg/12-h sampling) were 13.85 vs. 13.25 and 0.425 vs. 0.396 for cows fed SFS or DRS, respectively, and were not affected by the considerable drop in dry matter intake of cows fed the SFS diet during the last 3 experimental days. The portal-drained visceral flux of total essential FAA was 417 and 442 g/12 h (SEM 63) in cows fed SFS and DRS, respectively. However, the portal-drained visceral flux of 7 essential PBAA out of the 9 determined was numerically greater in cows fed the SFS diet, and total essential PBAA in that treatment was 77.4 +/- 22.2 compared with 35.4 +/- 50.2 g/12 h for cows fed the DRS diet. This phenomenon was again observed in a greater total splanchnic flux (FAA + PBAA) of 462 and 371 g/12 h in SFS- and DRS-fed cows, respectively. Mammary uptake of essential AA from both pools (free and peptide bound), and recovery of essential AA in milk, was again numerically higher in SFS-fed cows. In addition to FAA, quantifying the contribution of PBAA may improve our understanding of tissue use of AA substrates, and this may ultimately lead to improved diet formulations with respect to intestinal absorption and mammary uptake of AA.

Portal drained visceral flux, hepatic metabolism, and mammary uptake of free and peptide-bound amino acids and milk amino acid output in dairy cows fed diets containing corn grain steam flaked at 360 or steam rolled at 490 g/L.

Objectives were to measure net fluxes of free (FAA) and peptide bound amino acids (AA) (PBAA) across portal-drained viscera (PDV), liver, splanchnic, and mammary tissues, and of milk AA output of lactating Holstein cows (n = 6, 109 +/- 9 d in milk) as influenced by flaking density of corn grain. Cows were fed alfalfa-based total mixed ration (TMR) containing 40% steam-flaked (SFC) or steam-rolled corn (SRC) grain. The TMR were offered at 12-h intervals in a crossover design. Six sets of blood samples were obtained from indwelling catheters in portal, hepatic, and mammary veins and mesenteric or costoabdominal arteries every 2 h from each cow and diet. Intake of dry matter (18.4 +/- 0.4 kg/d), N, and net energy for lactation were not altered by corn processing. Milk and milk crude protein yields (kg/12-h sampling) were 14.2 vs. 13.5 and 0.43 vs. 0.39 for cows fed SFC or SRC, respectively. The PDV flux of total essential FAA was greater (571.2 vs. 366.4 g/12 h, SEM 51.4) in cows fed SFC. The PDV flux of total essential PBAA was 69.3 +/- 10.8 and 51.5 +/- 13.2 g/12 h for cows fed SFC and SRC, respectively, and differed from zero, but fluxes of individual PBAA rarely differed between treatments. Liver flux of essential FAA was greater in cows fed SRC, but only the PBAA flux in cows fed SRC differed from zero. Splanchnic flux of FAA and PBAA followed the pattern of PDV flux, but variation was greater. Mammary uptake (g/12 h) of total essential FAA was greater in cows fed SFC than SRC (224.6 vs. 198.3, SEM 7.03). Mammary uptake of essential PBAA was 25.0 vs. 15.1, SEM 5.2, g/12 h for cows fed SFC or SRC, respectively, and differed from zero in half of the PBAA. Milk output of EAA was 187.8 vs 175.4, SEM 4.4 g/12 h in cows fed SFC and SRC, respectively, and output of most essential AA consistently tended to be greater in cows fed SFC. It is apparent that PBAA comprise a portion of total AA flux across PDV and are affected by grain processing. Further, this pool supplies an important component of AA taken up by the mammary gland. Quantifying the contribution of PBAA may improve diet formulation with respect to intestinal absorption and mammary uptake of AA.

Site of protein digestion in steers fed sorghum grain diets. II. Effect of grain processing methods.

Seven crossbred, abomasally fistulated yearling steers (400 kg) were used in two digestion trials (crossover design) to study the effect of processing sorghum grain on the site and extent of feed and microbial protein digestion. Steers were fed an 81.5% sorghum grain diet in which the grain was either dry-rolled (DR; four steers) or steam-processed, flaked (SPF; three steers). At the end of the first trial steers were switched to the opposite treatment. Dysprosium (21 to 23 micrograms/g of feed) was used as a digesta marker. Feed, abomasal contents and fecal grab samples were collected at 12-h intervals during a 6-d total fecal collection period. Organic matter (OM) intake for SPF and DR grain diets averaged 6,426 and 6,787 g/d, respectively. Compared with DR, SPF increased (P less than .05) the apparent total digestibility and ruminal digestibility of OM. Trichloroacetic acid precipitable protein consumed by the steers was lower (P less than .05) for SPF than the DR treatment. Processing method had no effect on ruminal digestion of crude protein (CP), bacterial protein (BP) synthesis, quantity of CP entering the small intestine or on total digestion of feed protein. There was a trend for increased total and post-ruminal digestion of CP with the SPF diet. Post-ruminal digestion of BP was increased (P less than .05) by SPF grain as compared with DR. Percentage of non-BP digested ruminally, post-ruminally or in the total tract was not significantly affected by processing method.(ABSTRACT TRUNCATED AT 250 WORDS)

Site of protein digestion in steers fed sorghum grain diets. I. Effect of level of feed intake.

Two digestion trials were conducted with seven crossbred, abomasally cannulated yearling steers (400 kg) to study the effect of level of feed intake on the site and extent of feed and microbial protein digestion. Steers, in a crossover design experiment, were fed an 81.5% steam-processed flaked (SPF) sorghum grain diet at either 95% (four steers) or 75% (three steers) of their ad libitum intakes. At the end of the first trial, steers were switched to the opposite treatment. Dysprosium (31 to 32 micrograms/g) was used as an external marker. Feed, abomasal contents and fecal grab samples were taken at 12-h intervals advancing by 2 h each day over a 6-d total fecal collection period. Organic matter (OM) intakes were 6,102 and 4,570 g for the two treatments. Higher level of intake increased (P less than .05) quantities of OM, crude protein and trichloroacetic acid precipitable protein entering the small intestine, digested post-ruminally and digested in the total tract. The higher level of intake decreased (P less than .05) the percentage of bacterial protein (BP) present in the abomasum and percent post-ruminal BP digestion; however, the amounts of BP and non-BP entering the small intestine and digested post-ruminally were greater (P less than .05) in steers fed 95% ad libitum. Most of the feed protein was degraded in the rumen with both treatments. Predicted true feed protein digestibilities were 91.1 and 91.7% for 95 and 75% of ad libitum intakes.(ABSTRACT TRUNCATED AT 250 WORDS)

Comparison of various amino acids for estimation of microbial nitrogen in digesta.

Methods of estimating microbial N in digesta were compared, and two simplified methods were described for separation of diaminopimelic acid (DAP) from methionine in acid hydrolysates of biological samples using an automated amino acid analyzer. Recoveries of DAP when added to bacterial, abomasal and feed samples were 92 to 98%. All samples analyzed (bacteria, protozoa and several feedstuffs) contained detectable DAP (or another amino acid with similar elution time). Apparent DAP-N (percentage of total sample N) in feeds ranged from 12 to 78% of bacterial DAP-N concentration. These values are greater than can be accounted for by bacterial contamination. Correction for apparent dietary DAP was appropriate when using this microbial marker. Reasonable estimation of bacterial N was made in abomasal digesta of steers fed high-grain diets using DAP, lysine or combinations of DAP and leucine or lysine and leucine. There was excellent agreement among these marker methods in ranking dietary treatment regimens with respect to bacterial N present in the abomasum. The use of leucine alone, or the combination of DAP and lysine, gave nonrealistic values. Two-amino-ethylphosphonic acid (AEP) was not detected in acid hydrolysates of mixed ruminal protozoa or abomasal digesta. Two other ninhydrin-reactive compounds with elution times close to AEP were detected in all samples analyzed, which may have been identified as AEP in other studies. It was concluded that corrected DAP and lysine were the best estimates of bacterial N and AEP was precluded as a marker of protozoal N.

Effect of monensin on total volatile fatty acid production by steers fed a high grain diet.

Four rumen-fistulated steers, averaging 315 kg during two experimental periods were used in a replicated 2 X 2 Latin square study designed to determine the effects of monensin supplementation on rumen volatile fatty acid (VFA) production, pH and liquid volume. A 72% steam-flaked, sorghum grain diet was fed twice daily at 0700 and 1700 h at 2.0% of live body weight. Production rates were determined at 11 times during a 24-h feeding cycle by short-term in vitro incubations of whole rumen contents. Monensin increased moles/100 mol (P less than .05) and production rate (mumoles X liter-1 X min-1; P greater than .01) of propionate and depressed moles/100 mol (P less than .01) and production rate (P less than .05) of butyrate. Moles of acetate/100 mol were not affected (P greater than .05) by monensin. Daily propionate production (moles) was increased (P less than .01) by 37% by monensin. Monensin increased total production of acetate (11%) and total VFA production (16%), both nonsignificantly. Both rumen pH and liquid volumes were increased nonsignificantly by monensin.

Effects of monensin on site and extent of whole corn digestion and bacterial protein synthesis in beef steers.

Monensin was fed at 0 and 33 ppm in a crossover trial designed to determine the effect of this compound on ruminal and postruminal utilization of a corn-based diet and bacterial protein synthesis in abomasally fistulated steers. Monensin decreased (P greater than .10) ruminal true digestion of organic matter (OMc, corrected for bacterial cell synthesis) and apparent ruminal digestion of starch by 19%, but had not effect on apparent total tract digestion of OM or starch. Apparent ruminal and total tract digestibilities of crude protein (CP) were unchanged. Monensin decreased (P greater than .07) the contribution of bacterial N to total abomasal N (52 vs 58%), and increased (P greater than .06) the contribution of ruminally undegraded feed N (46 vs 40%), but had not effect on total N or amino acids recovered from the abomasum. Efficiency of bacterial protein synthesis (grams bacterial CP/100 g ruminally digested OMc) was unchanged. Monensin decreased (P greater than .05) the fraction of bacterial N to total N digested postruminally (42 vs 50%) and increased (P greater than .05) the contribution of ruminally undegraded feed N digested postruminally (58 vs 50%). Monensin caused a greater proportion of feed N and starch to be digested in the intestines than in the rumen (with possibly greater resultant metabolic efficiency), and this may account for some of the benefits obtained from feeding this compound with high grain diets.

Effect of 2- versus 6-day collections for the determination of ruminal and postruminal digestion in steers.

Abomasally fistulated steers (500 kg) were used to determine the effect of length of collection period (2 vs 6 days) on total, ruminal and postruminal digestibilities of organic matter, starch and protein. Twice daily, four steers were fed steam-processed flaked grain and three steers were fed dry-rolled sorghum grain in an 82% grain diet. Dysprosium was used as an indicator. Abomasal and fecal samples were collected at 12-hr intervals for 6 days or every 4 hr for 2 days, providing 12 samples per collection period. Nutrient contents of feed, abomasal and fecal samples were similar during both collection periods. Except for total digestibility of crude protein in the dry-rolled grain diet, ruminal, postruminal and total digestibilities of organic matter, starch and protein did not differ between the 2- and 6-day collection periods. Standard deviations for nutrient concentration and digestion coefficients were similar for the two collection periods within both the steam-processed flaked and dry-rolled treatments. Results indicate that sampling six times daily for 2 days provided representative samples for partitioning organic matter, starch and protein digestibilities in abomasally fistulated steers that had been adapted to collection procedures.

Effect of monensin on nitrogen utilization and digestibility of concentrate diets by steers.

Monensin was fed at levels of 0 and 33 ppm in a series of digestion and metabolism trials to determine its effect on utilization of high grain diets and on ruminal parameters in yearling steers. Monensin had no effect (P greater than .05) on apparent digestibility of dry matter, gross energy or starch when fed with a 90% corn diet (10.5% crude protein, dry matter basis). Monensin in this corn-based diet tended to increase crude protein digestibility (63.4 vs 61.3%) and decrease ruminal ammonia concentration (2.5 vs 6.5 mg/100 ml) measured 3 hr postprandially (P greater than .05). In metabolism trials with a 76% sorghum grain diet (11.7% crude protein, dry matter basis), monensin improved apparent digestibility of crude protein (P less than .05) but not dry matter or gross energy (P greater than .05). Retention of nitrogen, expressed as a percentage of nitrogen intake, tended to improve (24 vs 20%) in response to monensin addition to the sorghum grain-based diet (P greater than .05); a similar trend was observed (P greater than .05) for nitrogen retention expressed as a percentage of nitrogen absorbed (41 vs 36%). Total ruminal volatile fatty acid (VFA) concentrations measured 3 hr postprandially were not altered by monensin fed with either diet. The proportion of acetic acid d-creased (P less than .05) and that of propionic acid increased (P less than .05) in response to monensin fed with the corn-based diet. Monensin did not appreciably alter proporations of VFA when fed with the sorghum grain-based diet. Results suggest that a possible improvement in N utilization may account for some of the benefits of feeding monensin with high grain diets.