Biomedical subjects

J L Firkins

Publications and source records attributed to J L Firkins.

At least 19 recordsLinked to original sources

PubMed2006

Integration of ruminal metabolism in dairy cattle.

An important objective is to identify nutrients or dietary factors that are most critical for advancing our knowledge of, and improving our ability to predict, milk protein production. The Dairy NRC (2001) model is sensitive to prediction of microbial protein synthesis, which is among the most important component of models integrating requirement and corresponding supply of metabolizable protein or amino acids. There are a variety of important considerations when assessing appropriate use of microbial marker methodology. Statistical formulas and examples are included to document and explain limitations in using a calibration equation from a source publication to predict duodenal flow of purine bases from measured urinary purine derivatives in a future study, and an improved approach was derived. Sources of specific carbohydrate rumen-degraded protein components probably explain microbial interactions and differences among studies. Changes in microbial populations might explain the variation in ruminal outflow of biohydrogenation intermediates that modify milk fat secretion. Finally, microbial protein synthesis can be better integrated with the production of volatile fatty acids, which do not necessarily reflect volatile fatty acid molar proportions in the rumen. The gut and splanchnic tissues metabolize varying amounts of volatile fatty acids, and propionate has important hormonal responses influencing milk protein percentage. Integration of ruminal metabolism with that in the mammary and peripheral tissues can be improved to increase the efficiency of conversion of dietary nutrients into milk components for more efficient milk production with decreased environmental impact.

Animals↗

PubMed2005

Evaluation of a real-time PCR assay quantifying the ruminal pool size and duodenal flow of protozoal nitrogen.

We have recently developed a real-time polymerase chain reaction (PCR) assay to quantify copies of the genes encoding protozoal 18S rRNA. The assay includes procedures for isolating and concentrating protozoal cells from the rumen for use as a standard to convert 18S rRNA gene copies to a biomass basis. The current objectives were to 1) determine the degree of reduction of bacterial contamination in the protozoal standard, 2) determine if protozoal standards derived from ruminal fluid are appropriate for predicting duodenal flows, and 3) evaluate the assay's determined values for protozoal N in the rumen and flowing to the duodenum compared with independent measurements. Our protozoal collection method reduced non-associated bacterial contamination by 33-fold, the contamination of which could otherwise significantly bias RNA (microbial marker) and N percentages of concentrated protozoal fractions. Based on denaturing gradient gel electrophoresis, the use of protozoal cells isolated from ruminal fluid appears appropriate for use in quantitative assays determining protozoal N flow postruminally. Using real-time PCR, protozoal N was determined to be 4.8 and 12.7% of the rumen microbial N pool and 5.9 and 11.9% of the duodenal flow of microbial N on diets containing low (16%) or high (21%) forage neutral detergent fiber, respectively, which were comparable with independent measures and expectations.

Animals↗

PubMed2005

Processing whole cottonseed moderates fatty acid metabolism and improves performance by dairy cows.

Pelleting cottonseed (CS) improves handling characteristics. Our objectives were to determine whether increasing the particle size of the CS pellet or dilution of a smaller pellet with delinted CS would limit the rate of CS oil release to optimize digestibility of fatty acids (FA) and fiber while maintaining milk fat production. In a 5 x 5 Latin square design with 3-wk periods, 5 rumen-cannulated cows were fed 1) control with CS hulls (CSH) and CS meal plus tallow and Ca soaps of FA, 2) whole CS (WCS), 3) small CS pellets (SP; 0.44-cm die diameter), 4) larger CS pellets (LP; 0.52-cm die diameter), or 5) a blend of 1/2 SP plus 1/2 partially delinted CS (SPD). Diets contained 39.6% concentrate, 14.4% CS, and 46% forage (40:60, alfalfa hay:corn silage) on a DM basis and were balanced to have similar concentrations of CS protein, CS fiber, and total fat. In a production trial, dietary treatments were 1) WCS control, 2) LP, 3) SPD, and 4) SPD fed at 90%. Sixty cows averaging 105 d in milk were fed the WCS diet for 2 wk and then assigned to one of the 4 diets for 12 wk. Total tract digestibility of NDF was unaffected, but N digestibility was lower for SPD than for other treatments. Fatty acid digestibility was higher for SP and LP (82.6 and 82.3%) than for CSH or SPD treatments (78.8 and 75.3%), and WCS was intermediate (81.1%). The trans-11 C18:1 from cows fed SP and LP (6.58 and 6.24% of total milk FA) was greater than that from cows fed CSH, WCS, and SPD (3.23, 3.79, and 3.97%). The trans-10 C18:1 in milk fat from SP and LP (0.508 and 0.511%) was higher than that in WCS and SPD diets (0.316 and 0.295%); CSH was intermediate (0.429%). Using passage rates estimated from the NRC, disappearance of total FA in situ was estimated to be 17.7, 44.2, 46.6, and 35.0% for WCS, SP, LP, and SPD, respectively. In the production trial, a diet x week interaction was explained by a trend for progressively greater milk production for SPD and SPD90 than for WCS or LP. Milk fat was lower for LP (2.74%) and SPD90 (2.85%) than for WCS or SPD (3.07 and 3.08%). The fat yield was lower for LP than for SPD (1.09 and 1.30 kg/d); WCS and SPD90 were intermediate (1.23 and 1.21 kg/d). Although having a lower FA digestibility, SPD appeared to minimize negative effects of free oil from SP in the rumen, explaining higher DMI and milk production compared with WCS or LP.

Animal Nutritional Physiological Phenomena↗

PubMed2004

Effects of substrate, passage rate, and pH in continuous culture on flows of conjugated linoleic acid and trans C18:1.

A dual-flow continuous culture system consisting of 4 fermenters was used in a 4 x4 Latin square design. The objective of the research was to evaluate the effects of solid dilution rate (SDR), pH, and concentration of linoleic acid (LA) in the feed mixture on the production of conjugated linoleic acid (CLA) and trans-C18:1. The 4 treatments were 1) control = pH 6.5, 1% LA, 4%/h SDR; 2) high solid dilution rate (HSDR) = pH 6.5, 1% LA, 8%/h SDR; 3) high linoleic acid (HLA) = pH 6.5, 3% LA, 4%/h SDR; and 4) low pH (LPH) = pH 5.8, 1% LA, 4%/h SDR. Inoculum was collected 6 h after feeding from a cow fed 40% alfalfa hay and 60% grain. Liquid dilution rate was held at 0.12/h. All treatments except HLA contained 2% tallow. The LA was dissolved in buffer and continuously infused into the fermenters. The CLA flows were 16.5, 20.4, 23.2, and 25.2 mg/d for control, HSDR, HLA, and LPH, respectively. Compared with control, LPH increased flows of CLA, cis-C18:1, and C18:2, and decreased flow of C18:0. The neutral detergent fiber (NDF) and acid detergent fiber (ADF) digestibilities were not affected by pH. The HSDR tended to increase CLA flow compared to control, possibly because a shorter solid retention time led to incomplete biohydrogenation (BH). The NDF and ADF digestibilities and bacterial numbers were reduced by HSDR. With more LA available as a substrate for CLA, HLA resulted in a higher flow of CLA than control. The HLA resulted in the highest acid detergent fiber and fatty acid digestibilities, bacterial numbers, and BH. Increasing solids passage rate, reducing pH, and increasing dietary LA appears to increase in vitro CLA production.

Acetates↗

PubMed2004

Effects of dry matter intake, addition of buffer, and source of fat on duodenal flow and concentration of conjugated linoleic acid and trans-11 C18:1 in milk.

The primary objective of the study was to investigate the effects of DM intake, addition of buffer, and fish vs. soybean oil on duodenal flows and milk concentrations of conjugated linoleic acid (CLA) and trans-11 C18:1. Four ruminally and duodenally cannulated multiparous cows averaging 106 +/- 17 d in milk at the start of the trial were used in a 4 x 4 Latin square design with treatments as follows: 1) control=diet contained 2% fish oil and fed ad libitum, 2) buffer addition (BUFF)=control diet with 0.8% of NaHCO3 added, 3) low DM intake (LDMI)=DMI restricted to 80% of the control but concentration of fish oil was increased to 2.5% to provide for similar fatty acids (FA) intake, and 4) soybean oil (SBO)=same as control except 2% soybean oil was substituted for fish oil. The diets consisted of 36.2% forage and 63.8% concentrate. Each period consisted of 18 d, with the last 7 d devoted to data collection and the first 4 d used to determine the appropriate amount of feed to be offered to the cow on LDMI. Duodenal flows of CLA and trans-C18:1 were lower for SBO than for diets with fish oil. Feeding buffer did not affect ruminal pH or duodenal flows of trans-11 C18:1 and CLA. Restriction of DMI decreased duodenal flow of trans-11 C18:1 but did not decrease duodenal flow of CLA compared with control. In milk, CLA concentration was lower for SBO (24.5, 17.9, 18.5, and 10.1 mg/g of FA for control, BUFF, LDMI, and SBO, respectively). Cows fed fish oil had higher duodenal flow and milk concentration of n-3 polyunsaturated fatty acids than the cows fed SBO. Compared with SBO, fish oil is more effective in increasing duodenal flows of CLA and trans-11 C18:1, and thus, concentration of CLA in milk.

Animal Feed↗

PubMed2003

Effects of a beverage containing an enzymatically induced-viscosity dietary fiber, with or without fructose, on the postprandial glycemic response to a high glycemic index food in humans.

OBJECTIVE: Dietary supplementation with guar gum or fructose has been reported to reduce the postprandial glycemic response to an oral glucose challenge. As a result of the poor palatability of most foods containing guar gum, a novel low-viscosity beverage with guar gum was developed that becomes viscous in vivo through an enzymatic induction. The primary study objective was to determine the effect of an amylase-induced viscosity (I-V) product, with or without supplemental fructose, on the postprandial glycemic response to a high glycemic index test meal in healthy nondiabetic subjects. DESIGN: The study was a four-treatment, placebo-controlled, double-blind, randomized block protocol. SETTING: The study was performed at Glycaemic Index Testing, Inc., Toronto, Ontario, Canada. SUBJECTS: A total of 30 healthy nondiabetic volunteers (13 male, 17 female, mean+/-s.e.m. age of 51+/-3 y and body mass index of 24.2+/-0.4 kg/m(2)) participated in the study. INTERVENTION: In the morning after an overnight fast, subjects participated in four 3-h meal glucose tolerance tests on separate occasions. The test meals contained 50 g of available carbohydrate from maltodextrin and white bread (control) or the same meal with either 5 g of guar gum (3.6 g galactomannan), 5 g of fructose, or 5 g of guar gum +5 g of fructose. RESULTS: Treatments containing guar gum had a reduced (P<0.01) baseline-adjusted peak glucose response and incremental area under the glucose curve. In contrast to previous studies, fructose increased (P<0.05) the baseline-adjusted peak glucose concentration. CONCLUSIONS: Guar gum incorporated into an amylase I-V product provided a means to stabilize blood glucose levels by reducing the early phase excursion and then by appropriately maintaining the later phase excursion in healthy nondiabetic humans.

Adolescent↗

PubMed2003

Effects of urea infusion and ruminal degradable protein concentration on microbial growth, digestibility, and fermentation in continuous culture.

The effects of urea and rumen-degradable protein (RDP) on microbial growth, digestibility, and fermentation were examined using dual-flow continuous culture. The experimental design was a 4 x 4 Latin square with a 2 x 2 factorial arrangement of treatments. Factors were urea infusion (0.4 g/L of artificial saliva) and RDP concentration, and the treatments were as follows: 1) low RDP (8% of dietary dry matter) without urea (LDNU), 2) high RDP (11% of dietary dry matter) without urea (HDNU), 3) low RDP (8% of dietary dry matter) with urea (LDU), and 4) high RDP (11% of dietary dry matter) with urea (HDU). The LDNU (i.e., negative control) and HDNU treatments were formulated to be nitrogen limiting. Results indicated that infusion of urea increased all digestibility measurements (P < 0.05), which in turn increased (P < 0.05) volatile fatty acid, NH3 nitrogen, trichloroacetic acid-soluble nitrogen, and soluble protein concentrations. Increasing dietary RDP improved dry matter and organic matter digestibility (P < 0.05) but did not alter acid detergent fiber or nonfiber carbohydrate digestibilities (P > 0.05). Isobutyrate concentration decreased (P = 0.05) with increased RDP. Increased dietary RDP increased crude protein degradation and soluble protein concentration (P < 0.05), but NH3 nitrogen, trichloroacetic acid-soluble nitrogen, and peptide nitrogen were unaffected by changing RDP levels. Microbial growth efficiency was 19.9, 24.9, 28.0, and 32.2 g N/g organic matter truly digested for LDNU, HDNU, LDU, and HDU, respectively, and was significantly improved both by urea infusion (P = 0.002) and increased RDP concentration (P = 0.021). The interactions of urea and RDP (P < 0.05) were explained by the high digestibility of neutral detergent fiber, nonstructural carbohydrate, and especially hemicellulose, with the HDNU treatment. The results of this study indicated that hemicellulose-degrading bacteria were able to effectively compete with nonstructural carbohydrate-degrading bacteria for available peptide and amino acid nitrogen. Further, the extent of protein degradation was dependent on the availability of NH3 nitrogen in the system.

Animals↗

PubMed2003

Technical note: Specific PCR amplification of protozoal 18S rDNA sequences from DNA extracted from ruminal samples of cows.

A protozoa-specific primer (P-SSU-342f) was designed and paired with a eukarya-specific primer to amplify a 1,360-bp fragment of DNA encoding protozoal small subunit (SSU) ribosomal RNA from ruminal fluid of cows fed a mixed forage:grain diet or alfalfa hay. Sequencing of clones showed that P-SSU-342f is specific to ruminal protozoa and, with slight modifications, the primer will be useful for ecological studies of ruminal protozoa.

Animals↗

PubMed2003

Effects of 2-hydroxy-4-(methylthio) butanoic acid (HMB) on microbial growth in continuous culture.

2-Hydroxy-4-(methylthio) butanoic acid (HMB) positively affects milk composition and yield, potentially through ruminal actions. Four continuous culture fermenters were used to determine the optimal concentration of HMB for digestibility of organic matter (OM), neutral detergent fiber (NDF), acid detergent fiber (ADF), and hemicellulose and synthesis of microbial N. A highly degradable mix of hay and grain was used as a basal diet to simulate a typical lactation diet. Three concentrations of HMB (0, 0.055, and 0.110%) and one concentration of dl-Met (0.097%) were infused into the fermenters according to a 4 x 4 Latin square design. Digesta samples were collected during the last 3 d of each of the four 10-d experimental periods. Digestibility of OM, hemicellulose, and NDF was largely insensitive to treatment. Digestibility of ADF showed a quadratic effect to supplementation of HMB, with 0.055% having lower digestibility than 0 or 0.110%. Total production of VFA was not influenced by HMB supplementation, but differences in concentration and production of individual VFA were seen. Isobutyrate increased linearly with increasing HMB supplementation. Propionate concentration decreased linearly with increased HMB supplementation, but propionate production showed a quadratic trend (P = 0.13). A higher concentration of acetate was detected for dl-Met compared with the highest HMB concentration. There were trends (P < 0.15) for dl-Met to decrease the production of isobutyrate and to lower the concentration of butyrate when compared with HMB. Microbial efficiency was not different among treatments. The proportion of bacterial N produced from NH3-N decreased linearly with increasing HMB, and bacteria receiving dl-Met synthesized more N from NH3-N than those receiving HMB. These data suggest that supplementation of HMB may have a sparing effect on branched chain volatile fatty acids because the fatty acids are not needed to provide carbon for synthesis of valine, isoleucine and leucine with ammonia. Comparisons of bacterial community structure in the fermenter effluent samples using PCR amplicons containing the ribosomal intergenic spacer region and its flanking partial 16S ribosomal RNA gene showed no distinct banding patterns, though treatments tended to group together. Both Met and HMB affect the rumen microbial population, but Met supplied as dl-Met does not act identically to that supplied as HMB.

Ammonia↗

PubMed2002

Whole linted cottonseed as a forage substitute fed with ground or steam-flaked corn: digestibility and performance.

Six ruminally and duodenally cannulated Holstein cows were used in a 6 x 6 Latin square design. The objective was to evaluate any potential interactions in site of nutrient digestion when neutral detergent fiber (NDF) from cottonseed was incrementally substituted for forage NDF (FNDF) from alfalfa silage and when starch availability was varied by feeding ground (G) or steam-flaked (SF) corn. Iso-NDF diets were forage control with G corn (21% FNDF), 5% whole cottonseed (WCS) with G or SF corn (18% FNDF), 10% WCS with G or SF corn (15% FNDF), and 15% WCS with G corn (12% FNDF). Ruminal or total tract digestibilities of organic matter (OM) or nonstructural carbohydrate (NSC) were unaffected, but efficiency of microbial protein synthesis decreased as WCS increased. Ruminal NDF digestibility was not affected despite a linear decrease in pH, but postruminal NDF digestibility decreased with increasing WCS. Ruminal digestibilities of OM and NSC were higher for SF than G corn but did not affect efficiency of microbial N synthesis. Dry matter intake increased quadratically with increasing level of WCS but decreased when SF replaced G corn. Milk yield did not differ across treatments. Milk fat percentage was affected quadratically and milk protein increased linearly with increasing WCS. Milk fat percentage decreased but milk protein was not affected when SF replaced G corn. Lack of an interaction between corn source and level of WCS substitution suggests that WCS was equally effective in maintaining ruminal fermentation and digestibility in diets varying in ruminal starch availability.

Ammonia↗

PubMed2002

Whole linted cottonseed as a forage substitute: fiber effectiveness and digestion kinetics.

Six ruminally and duodenally cannulated Holstein cows were used in a 6 x 6 Latin square design to 1) evaluate the potential interaction in effectiveness of neutral detergent fiber (NDF) from whole cottonseed (WCS) when it was substituted for forage NDF (FNDF) and fed with ground (G) or steam-flaked (SF) corn and 2) to determine whether the kinetic properties of NDF digestion further clarify the effectiveness of WCS. The six dietary treatments were: forage control with G corn (21% FNDF), 5% WCS with G or SF corn (18% FNDF), 10% WCS with G or SF corn (15% FNDF), and 15% WCS with G corn (12% FNDF). Based on chewing activity, the NDF from WCS was estimated to be 84% (SE = 36%) as effective as alfalfa silage NDF. Decreasing passage and digestion rates of potentially digestible NDF with increasing WCS increased the evacuated pool size of ruminal DM, apparently explaining the similar ruminal mat consistency among treatments. Measures of effectiveness ofWCS treatments did not interact with corn source. Fluid dilution rate was estimated based on a two-compartment model describing Co dilution, but no treatment differences were detected. There was a strong linear bias for estimates of ruminal NDF digestibility based on a single compartment model using the digestion rate of potentially digestible NDF and the passage rate of either indigestible NDF or digestible NDF when compared with NDF digestibility calculated using duodenal flows. Although further verification is needed, these digestion and passage kinetics help explain why WCS are effective at stimulating chewing during eating and rumination.

Animal Feed↗

PubMed2002

Lactation performance by dairy cows fed wet brewers grains or whole cottonseed to replace forage.

Holstein cows starting at wk 8 of lactation were used to evaluate lactation performance when wet brewers grains, whole linted cottonseed, or starch-coated whole linted cottonseed (Easiflo) were substituted for forage. The wet brewers grains were added to diets to decrease forage neutral detergent fiber from 21% incrementally down to 15% while simultaneously decreasing nonfiber carbohydrate concentration from 40.3% down to about 33.8%. The cottonseed treatments all had similar concentrations of forage neutral detergent fiber (15%) and nonfiber carbohydrates (33.1 and 36.0%). Dry matter intake and milk production were similar across treatments. Milk fat percentage was decreased for Easiflo versus whole linted cottonseeds, but no other responses were detected. The current National Research Council (NRC) energy model was evaluated using individual cow data that were averaged over the entire 16-wk treatment period. For treatment means, the output of energy averaged 99% of the net energy of lactation intake, indicating very good corroboration of the model to account for energy usage for a group of cows. However, the ability to predict energy usage for individual cows was less accurate based on the comparison of residuals of observed and predicted body weight change regressed against predicted body weight change, apparently because of compounding of random errors in this prediction, which was alleviated over a larger number of observations. These results also corroborate current NRC guidelines for minimum forage neutral detergent fiber concentrations for lactating cows past the calving transition period.

Animal Feed↗

PubMed2001

Glycemic response to a food starch esterified by 1-octenyl succinic anhydride in humans.

To evaluate the glycemic response to a food starch esterified by 1-octenyl succinic anhydride (OSA), 30 healthy nondiabetic adult subjects were studied in a double-blind crossover design. After an overnight fast, subjects consumed a product containing either 25 g of glucose or 25 g of OSA-substituted starch. Finger-prick capillary blood was obtained at baseline and 15, 30, 45, 60, 90, and 120 min postprandial for glucose measurement. After OSA treatment, the rise in blood glucose was reduced (P < 0.05) at 15 and 30 min and tended (P < 0.08) to be lower at 45 min. Mean peak rise in glucose was reduced 19% (P < 0.01) by OSA (3.30 +/- 0.19 versus 2.66 +/- 0.16 mmol/L) compared to glucose, but time to peak did not differ between treatments. Net incremental area under the curve was also lower (P < 0.05) on OSA compared to glucose. Minimal effects on gastrointestinal symptoms (intensity and frequency of nausea, cramping, distention, and flatulence) were noted for both products, with no clinically significant difference between products. In conclusion, starch substitution with OSA attenuated the postprandial glycemic excursion compared to an equivalent glucose challenge and was well tolerated by fasting healthy adult subjects.

Adult↗

PubMed2001

Site of nutrient digestion by dairy cows fed corn of different particle sizes or steam-rolled.

Five primiparous Holstein cows were cannulated in the rumen, duodenum, and ileum and were fed diets containing 50% alfalfa silage and 36.6% coarse-, medium-, or fine-ground corn (CGC, MGC, and FGC, respectively, with mean particle sizes of 4.8, 2.6, or 1.2 mm), steam-rolled corn (SRC; density of 0.53 kg/L), or a 50:50 mix of CGC and SRC (SC) to evaluate how corn processing affects site of digestibility of nonstructural carbohydrates (NSC) and neutral detergent fiber (NDF). Decreasing the particle size of corn quadratically affected true ruminal digestibility of NSC (49.8, 46.5, and 87.0%, respectively). Because of compensatory digestion postruminally, a smaller increase (from 91.3 to 98.0%) in total tract digestibility of NSC was noted as particle size decreased. A small but significant linear shift in NDF digestion from the rumen to the large intestine was detected as corn particle size decreased. The addition of SRC to CGC linearly increased true NSC digestibility in the rumen about 20 percentage units but had much smaller effects on total tract digestibility. Despite the large impact of corn processing on NSC digestibility in the rumen, flow of bacterial N to the rumen was not affected by treatment. Reducing the particle size of corn decreased the apparent escape of corn protein, but steam-rolling had no effect. Corn should be finely ground to maximize total tract OM digestibility or steam-processed to densities less than 0.53 kg/L for maximal starch digestibility. However, fine-grinding or steam-processing of corn may have only a modest impact on total tract OM digestibility.

Animals↗

PubMed2000

Effects of degree of fat saturation on fiber digestion and microbial protein synthesis when diets are fed twelve times daily.

Three Holstein heifers and one nonlactating cow, fitted with ruminal and duodenal cannulas, were arranged in a 4 x 4 Latin square design to determine the effects of degree of fat saturation on ruminal neutral detergent fiber digestion and microbial protein synthesis and to determine whether changes in the efficiency of microbial protein synthesis were related to protozoal populations in the rumen. Corn silage-based diets contained no added fat or 4.85% of diet dry matter as partially hydrogenated tallow, tallow, or animal-vegetable fat. Iodine values of fat sources were 12.8, 50.6, and 109.7 for partially hydrogenated tallow, tallow, and animal-vegetable fat, respectively. Cattle were fed every 2 h and consumed 1.5% of body weight as dry matter daily. Ruminal neutral detergent fiber digestibility was decreased by added fat but was not affected by increasing iodine value. Flows of microbial N and non-NH3-nonmicrobial N to the duodenum were not affected by treatment. Ruminal protozoa concentration decreased linearly as the iodine value of fats increased. The efficiency of microbial protein synthesis was increased and protozoa concentrations tended to decrease when fat was fed. Decreased ruminal protozoa concentration may have decreased intraruminal N recycling. Biohydrogenation of added fat may result in a low ruminal concentration of unsaturated fatty acids when cows are fed frequently, reducing the negative effects of unsaturated fat sources on ruminal neutral detergent fiber digestibility. Protozoa were inhibited by unsaturated fat, but it is not clear if biohydrogenation and frequent feeding lessened inhibition.

Animal Feed↗

PubMed2000

Compartmental modeling with nitrogen-15 to determine effects of degree of fat saturation on intraruminal N recycling.

Two- and three-compartment models were developed to describe N kinetics within the rumen using three Holstein heifers and one nonlactating Holstein cow fitted with ruminal and duodenal cannulas. A 4 x 4 Latin square design included a control diet containing no supplemental fat and diets containing 4.85% of diet dry matter as partially hydrogenated tallow (iodine value = 13), tallow (iodine value = 51), or animal-vegetable fat (iodine value = 110). Effects of fat on intraruminal N recycling and relationships between intraruminal N recycling and ruminal protozoa concentration or the efficiency of microbial protein synthesis were determined. A pulse dose of 15(NH4)2SO4 was introduced into the ruminal NH3 N pool, and samples were taken over time from the ruminal NH3 N and nonammonia N pools. For the three-compartment model, precipitates of nonammonia N after trichloroacetic acid and ethanol extraction were defined as slowly turning over nonammonia N; rapidly turning over nonammonia N was determined by difference. Curves of 15N enrichment were fit to models with two (NH3 N and nonammonia N) or three (NH3 N, rapidly turning over nonammonia N, and slowly turning over nonammonia N) compartments using the software SAAM II. Because the three-compartment model did not remove a small systematic bias or improve the fit of the data, the two-compartment model was used to provide measurements of intraruminal N recycling. Intraruminal NH3 N recycling (45% for control) decreased linearly as fat unsaturation increased (50.2, 43.0, and 41.7% for partially hydrogenated tallow, tallow, and animal-vegetable fat, respectively). Intraruminal nitrogen recycling was not correlated with efficiency of microbial protein synthesis or ruminal protozoa counts.

Ammonium Sulfate↗

PubMed2000

Effects of starch source and level of forage neutral detergent fiber on performance by dairy cows.

The effectiveness of neutral detergent fiber (NDF) from soyhulls and whole cottonseed for replacing NDF from forage was evaluated in a lactation trial during wk 10 to 25 of lactation. Forty-eight cows were blocked and randomly assigned within a block to one of four diets: 1) 21% forage NDF with corn 2) 16% forage NDF with corn, 3) 16% forage NDF with corn and wheat (1:1) and, 4) 11% forage NDF with cottonseed and corn. Soybean hulls were added at approximately 23.0% of dry matter (DM) for the 16 and 11% forage NDF diets to replace forage and formulate diets with 35% nonfiber carbohydrates. Actual forage NDF concentration were 17.8, 14.0, 13.9, and 9.4%, respectively. Dry matter intake and milk yield were highest for cows fed 11% forage NDF with cottonseed. Milk fat percentage was higher for cows consuming 21% forage NDF and 16% forage NDF with corn than for cows fed the two other diets. Cows fed 16% forage NDF with corn and wheat experienced milk fat-protein inversion, but ruminal acetate:propionate was lower for cows fed 11% forage NDF than cows fed 16% forage NDF. Body weight (BW) and BW change were not different among treatments. Time spent chewing was similar among all diets. For cows in midlactation, forage NDF may be reduced to 9 to 11% when cottonseed is at 11% of DM and dietary nonstructural carbohydrates are at 30% of DM. Forage NDF may be reduced to 14 to 16% without cottonseed when nonstructural carbohydrates are at 30% of DM.

Animal Feed↗

PubMed1999

Estimation of microbial nitrogen flow to the duodenum of cattle based on dry matter intake and diet composition.

The objectives of this study were: 1) to evaluate the National Research Council equation used to predict microbial N flow to the duodenum in lactating cows, and 2) to determine whether improved equations could be developed by using dietary parameters used in the field. Treatment means from 55 trials with lactating and nonlactating cattle with duodenal cannulas were subjected to the backward elimination procedure of multiple regression. Variation within and among trials was accounted for by weighting the observations and including trial effects in all models. The equations to predict microbial N flow based on net energy for lactation (NEL) intake were different from the equation based on NEL intake used by the dairy National Research Council. Dry matter intake (DMI) estimated microbial N flow as well as did NEL intake, indicating that DMI drives predictions based on NEL intake. When multiple dietary factors [i.e., DMI; dietary percentages of crude protein, forage, and neutral detergent fiber; and all two-way interactions] were included, the resulting equation [microbial N (grams per day) = 16.1 + 22.9 x DMI (kilograms per day) - 0.365 x DMI2 - 1.74 x dietary neutral detergent fiber (percentage of dry matter)] tended to fit the data better than the equations based on NEL intake but not better than the equation based on DMI alone. The multiple-factor equation appeared to be the best overall equation for prediction; in contrast to the equation based on DMI, this equation is sensitive to diet composition. An asymptotic multiple-factor equation was developed, which may be more appropriate when extrapolating beyond the data range.

Animal Feed↗