Passage of stable isotope-labeled grass silage fiber and fiber-bound protein through the gastrointestinal tract of dairy cows

Fractional passage rates are required to predict nutrient absorption in ruminants but data on nutrient-specific passage kinetics are largely lacking. With the use of the stable isotope ratio (δ) as an internal marker, we assessed passage kinetics of fiber and fiber-bound nitrogen (N) of intrinsically labeled grass silage from fecal and omasal excretion patterns of δ¹³C and δ¹⁵N. In a 6 × 6 Latin square, lactating dairy cows received grass silages [455 g/kg of total diet dry matter (DM) ] in a 2 × 3 factorial arrangement from ryegrass swards fertilized at low (45 kg of N/ha) or high (90 kg of N/ha) levels of N and harvested at 3 maturity stages. Feed intake (16.7 ± 0.48 kg of DM/d; mean ± standard error of the mean) and milk yield (26.7 ± 0.92 kg/d) increased at the high level of N fertilization and at decreasing maturity. Nutrient digestibility decreased with increasing plant maturity, particularly at the high level of N fertilization, essentially reflecting dietary treatment effects on the nutritional composition of the grass silage. Fractional rumen passage rates (K₁) were highest and total mean retention time in the gastrointestinal tract (TMRT) was lowest when based on the external marker chromium mordanted fiber (Cr-NDF; 0.047/h and 38.0 h, respectively). Fecal δ¹³C in the acid detergent fiber fraction (¹³CADF) provided the lowest K₁ (0.023/h) and the highest TMRT (61.1 h) and highest peak concentration time (PCT; 24.3 h) among markers. In comparison, fecal fiber-bound N (¹⁵NADF) had a considerably higher K₁ (0.032/h) and lower TMRT (46.4 h) than ¹³CADF. Total N (measured with ¹⁵NDM) had a comparable K₁ (0.034/h) to that of ¹⁵NADF but provided the highest fractional passage rates from the proximal colon-cecum (K₂; 0.37/h) and lowest PCT (17.4 h) among markers. A literature review indicated unclear effects of grass silage maturity on K₁ and unknown effects of N fertilization on K₁. Our study indicated no effect of advancing maturity on fecal K₁ and a trend for K₁ to increase with the high level of N fertilization. Parameter K₂ increased, whereas PCT and TMRT generally decreased with the high level of N fertilization. Omasal digesta sampling largely confirmed results based on fecal sampling. Results indicate that the use of δ¹³C and δ¹⁵N can describe fiber-specific passage kinetics of forage.     

Passage kinetics of C-labeled corn silage components through the gastrointestinal tract of dairy cows

Fractional passage rates form a fundamental element within modern feed evaluation systems for ruminants but knowledge on feed type and feed component specific passage rates are largely lacking. This study describes the use of carbon stable isotopes (¹³C) to assess component-specific passage kinetics of 6 intrinsically ¹³C-labeled corn silages varying in quality (2 cultivars × 3 maturity stages) in a 6 × 6 Latin square design using 6 rumen-fistulated lactating dairy cows. An increase in maturity increased starch and decreased neutral detergent fiber and acid detergent fiber contents of corn silages. Passage kinetics were assessed for an external (chromium mordanted fiber; Cr-NDF) and an internal marker (¹³C isotopes) collected in feces and omasal digesta. The best fit was obtained with a deterministic multicompartmental model compared with stochastic Gn and GnG1 models with increasing order of age dependency (n = 1 to 5) for both sampling sites. The Cr-NDF marker yielded higher rumen fractional passage rates (K₁) than did ¹³C in the dry matter (¹³CDM) in feces (0.042/h vs. 0.023/h). Omasal marker excretion patterns support the conclusions based on conventional fecal marker excretions. Component-specific passage was assessed for acid detergent fiber (¹³CADF) in feces and for starch (¹³CST) in omasal digesta. The fractional passage rate based on fecal ¹³CDM and ¹³CADF did not differ. Omasal ¹³CST provided higher K₁ values (0.042/h) than omasal ¹³CDM (0.034/h) but lower values than omasal Cr-NDF (0.051/h). Fractional passage rates from the proximal colon-cecum (K₂) based on fecal marker concentrations showed trends similar to K₁, with Cr-NDF providing a value (0.425/h) more than twice as high as that of ¹³CDM (0.179/h) and ¹³CADF (0.128/h). Total mean retention time in the gastrointestinal tract was approximately double for ¹³CDM (64.1 h) and ¹³CADF (77.6 h) compared with Cr-NDF (36.4 h). Corn silage quality did not affect any of the estimated passage kinetic parameters. In situ fractional degradation rates did not differ among corn silages, except for a decreased fractional degradation rate of starch with advancing maturity. Results indicate that isotope labeling allows assessment of component-specific passage kinetics of carbohydrate fractions in corn silage.     

Performance of several Cr and Yb analytical techniques applied to samples of different biological origin (digesta or faeces)

This paper compares the performance, in terms of Cr (liquid phase marker) and Yb (solid phase marker) recovery from spiked samples, of five mineralization procedures applied to faeces, whole duodenal digesta, particulate and liquid phases of duodenal digesta, whole ruminal digesta and ruminal fluid from cattle. Two Holstein–Friesian heifers, fitted with permanent ruminal and duodenal cannulae, and fed twice daily on barley straw and a concentrate (15:85), were used as sample donors. Cr and Yb were added to the samples at 5, 25, 125 and 625 µg g^?1 dry matter, and analyzed by atomic absorption spectrometry. There were differences in marker recovery (p = 0.0481) depending on the mineralization procedure utilized but their performance was not affected by marker type (p = 0.6143). The interaction between type of sample and digestion procedure was statistically significant (p = 0.0290) and the results showed that homogeneous samples (whole duodenal digesta, the particulate phase of duodenal digesta and faeces) allowed the more even distribution of the marker and an easier and more complete mineralization. In contrast, heterogeneous samples (whole rumen digesta and rumen fluid) resulted in either a lesser attachment of markers to the particles and/or incomplete mineralization of the samples, which resulted in a higher variability between procedures. The interaction between type of sample and marker was also significant (p = 0.0426), with Cr recovery being more affected by type of sample than Yb. Copyright © 2004 Society of Chemical Industry     

The diurnal pattern of ileal dry matter and endogenous ileal nitrogen flows in the growing pig

The aim was to examine the diurnal pattern of endogenous nitrogen flow at the terminal ileum of the pig. Seven entire male pigs with a mean body weight of 58 kg had post‐valve T‐caecum (PVTC) cannulae surgically implanted for the collection of ileal digesta. The pigs were fed equal‐sized meals (10% of metabolic body weight, W^0.75, per day) twice daily at 08:00 and 17:00. The semi‐synthetic diet included enzyme‐hydrolysed casein (<5000 Da, 100 g kg^?1 diet) as the sole source of nitrogen (N). The diet also contained chromic oxide (6 g kg^?1) as an indigestible marker. The pigs received the diet for an 8 day period, and digesta were continuously collected for 24 h periods (commencing at 08:00) on the fifth and eighth days. Digesta were analysed for dry matter (DM) and chromium (Cr), and endogenous N was determined in the precipitate + retentate fraction of the digesta following centrifugation and ultrafiltration (10 000 Da molecular weight cut‐off). The concentration of Cr expressed on a digesta DM basis and the ratio of endogenous N to Cr in the digesta were relatively constant over the 24 h digesta collection periods, with no statistically significant (P > 0.05) differences found for the latter measure in the digesta collected between 12:00 and 08:00. The endogenous N flow through the terminal ileum is the net effect of the secretion and reabsorption of endogenous N that occurs throughout the digestive tract. The net result of the latter two processes in the small intestine of the pig leads to a relatively constant endogenous N flow over time post‐feeding. © 2002 Society of Chemical Industry     

Comparison of four markers for quantifying microbial protein flow from the rumen of lactating dairy cows

Eight ruminally cannulated lactating cows from a study on the effects of dietary rumen degraded protein (RDP) on production and N metabolism were used to compare ¹⁵N, total purines, amino acid (AA) profiles, and urinary excretion of purine derivatives (PD) as microbial markers for quantifying the flow of microbial protein at the omasal canal. Dietary RDP was gradually decreased by replacing solvent soybean meal and urea with lignosulfonate-treated soybean meal. The purine metabolites xanthine and hypoxanthine were present in digesta and microbial samples and were assumed to be of microbial origin. The sum of the purines and their metabolites (adenine, guanine, xanthine, and hypoxanthine) were defined as total purines (TP) and used as a microbial marker. Decreasing dietary RDP from 13.2 to 10.6% of dry matter (DM) reduced microbial nonammonia N (NAN) flows estimated using TP (from 415 to 369 g/d), ¹⁵N (from 470 to 384 g/d), AA profiles (from 392 to 311 g/d), and PD (from 436 to 271 g/d). Averaged across diets, microbial NAN flows were highest when estimated using TP and ¹⁵N (398 and 429 g/d), lowest when using PD (305 g/d), and intermediate when using AA profiles (360 g/d) as microbial markers. Correlation coefficients between ¹⁵N and TP for fluid-associated bacteria, particle-associated bacteria, and total microbial NAN flows were 0.38, 0.85, and 0.69, respectively. When TP was used as the microbial marker, ruminal escape of dietary NAN was not affected by replacing solvent soybean meal with lignosulfonate-treated soybean meal in the diets. The direction and extent of response of dietary and microbial NAN flow to dietary treatments were similar when estimated using ¹⁵N, AA profiles, and PD, and were in agreement with previously published data and National Research Council predictions. Microbial and dietary NAN flows from the rumen estimated using ¹⁵N appeared to be more accurate and precise than the other markers. Caution is required when interpreting results obtained using TP as the microbial marker.     

Inclusion of psyllium in milk replacer for neonatal calves. 1. Effects on growth, digesta viscosity, rate of passage, nutrient digestibilities, and metabolites in blood

Based on research in other species, inclusion of psyllium in milk replacer might improve nutrient utilization and gastrointestinal function in neonatal calves. Male Holstein calves were fed a milk replacer (22% crude protein, 20% fat) either without or with psyllium (1.1% of dry matter) from 2 d through 28 d of age. Milk replacer was reconstituted to 12.5% dry matter (DM) and fed at 12% of calf body weight (BW), adjusted weekly. Water was offered ad libitum but no starter was fed. Three calves per treatment were harvested weekly to sample digesta from the rumen, abomasum, jejunum, proximal colon, and distal colon. Mean daily intakes of water, DM, crude protein, and metabolizable energy did not differ between treatments. Average daily gain of BW did not differ between treatments. Digesta from the abomasum and colon of calves fed psyllium was more viscous than digesta from control calves. Mean retention time of digesta in the total digestive tract tended to be greater for calves supplemented with psyllium (9.7 vs. 8.4 h). Feces and digesta from the proximal and distal colon of calves fed psyllium had lower DM content than feces and digesta from control calves. Total-tract apparent digestibility of DM (92.8 vs. 94.1%) was lower for psyllium-fed calves, likely as an effect of the addition of the more poorly digestible psyllium; digestibilities of energy and ash also tended to be lower. The prefeeding plasma glucose concentration (10 h after previous feeding) tended to be greater for psyllium-fed calves but concentrations of nonesterified fatty acids, β-hydroxybutyrate, cholesterol, urea N, and total protein did not differ between treatments. Blood components did not differ between treatments at 2 h postfeeding. Inclusion of psyllium in the milk replacer of neonatal calves increased digesta viscosity and slowed passage of digesta through the gastrointestinal tract.     

Nitrogen partitioning and isotopic fractionation in dairy cows consuming diets based on a range of contrasting forages

Nine multiparous Holstein-Friesian cows (initially 97 d in milk), were used in a 3 × 3 lattice square design experiment with 4-wk periods. All cows received 4 kg/d concentrates and dietary treatments were based on silages offered ad libitum: perennial ryegrass (PRG); timothy (TIM); tall fescue (TF); red clover (RC); red clover/corn silage mixture [40/60 on a dry matter (DM) basis; RCC]; red clover/whole-crop oat silage mixture (40/60 on a DM basis; RCO); or red clover/whole-crop oat silage mixture (25/75 on a DM basis; ORC). The remaining treatments were based on RCO with feed intake restricted to the level of PRG (RCOr) or with a low protein concentrate (50/50 mixture of barley and molassed sugar beet pulp; RCOlp). Experiment objectives were to evaluate diet effects on N partitioning and N isotopic fractionation. Yields of milk and milk protein were consistently high for diets RC, RCC, and RCO and low for the diets based on poorly ensiled grass silages. Restriction of intake (RCOr) and inclusion of a higher proportion of whole-crop oat silage (ORC) and the low-protein concentrate (RCOlp) led to some loss of production. Diet had little effect on milk fat, protein, and lactose concentrations: low concentrations of milk protein and lactose reflect the restricted energy intakes for all treatments. The highest diet digestibilities were measured for RC and PRG, whereas increasing inclusion of the whole-crop oat silage (0, 60, and 75% of forage DM) led to a marked decrease in diet digestibility (0.717, 0.624, and 0.574 g/g, respectively). Urinary excretion of purine derivatives, an indicator for rumen microbial protein synthesis, was significantly higher for RCC than for TIM and TF. Nitrogen intake ranged between 359 and 626 g/d (treatment means). Partitioning of N intake to feces and urine was closely related to N intake, although urinary N losses were less than predicted from N intake for the 60/40 mixtures of cereal silage and red clover silage. The ¹⁵N content of milk, urine, and feces were all influenced by diet ¹⁵N content. Isotopic fractionation meant that feces and milk were enriched and urine was depleted in ¹⁵N relative to the diet. Significant relationships were observed between the extent of enrichment of urine, feces, and milk, suggesting some commonality in fractionation pathways. The trend for the lowest ¹⁵N enrichment in milk protein occurring in diets with low N-use efficiency (milk N/feed N) was contrary to expectations, possibly because of endogenous contributions to milk protein or fractionation when dietary ammonia was incorporated into microbial protein.     

Estimation of rumen outflow in dairy cows fed grass silage-based diets by use of reticular sampling as an alternative to sampling from the omasal canal

A study was conducted to compare nutrient flows determined by a reticular sampling technique with those made by sampling digesta from the omasal canal. Six lactating dairy cows fitted with ruminal cannulas were used in a design with a 3 × 2 factorial arrangement of treatments and 4 periods. Treatments were 3 grass silages differing mainly in neutral detergent fiber (NDF) concentrations: 412, 530, or 639 g/kg of dry matter, each combined with 1 of 2 levels of concentrate feed. Digesta was collected from the reticulum and the omasal canal to represent a 24-h feeding cycle. Nutrient flow was calculated using the reconstitution system based on 3 markers (Co, Yb, and indigestible NDF) and using ¹⁵N as a microbial marker. Large and small particles and the fluid phase were recovered from digesta collected at both sampling sites. Bacterial samples from the reticulum and the omasum were separated into liquid- and particle-associated bacteria. Reticular samples were sieved through a 1-mm sieve before isolation of digesta phases and bacteria. Composition of the large particle phase differed mainly in fiber content of the digesta obtained from the 2 sampling sites. Sampling site did not affect marker concentration in any of the phases with which the markers were primarily associated. The ¹⁵N enrichment of bacterial samples did not differ between sampling sites. The reticular and omasal canal sampling techniques gave similar estimates of marker concentrations in reconstituted digesta, estimates of ruminal flow, and ruminal digestibility values for dry matter, organic matter, starch, and N. Sampling site × diet interactions were also not significant. Concentration of NDF was 2.2% higher in reconstituted omasal digesta than in reconstituted reticular digesta. Ruminal NDF digestibility was 2.7% higher when estimated by sampling the reticulum than by sampling the omasal canal. The higher estimate of ruminal NDF digestibility with the reticular sampling technique was due to differences in NDF concentration of reconstituted digesta. This study shows that nutrient and microbial protein outflow from the rumen can be measured using a reticular sampling technique. The reticular sampling technique provides a promising alternative to sampling from the omasal canal because there is less interference with the animal and it does not require advanced sampling equipment.     

Distribution of 15N in amino acids during 15N-leucine infusion: impact on the estimation of endogenous flows in dairy cows

The distribution of ¹⁵N in AA during [¹⁵N]Leu infusion and its impact on the estimation of endogenous nitrogen (EN) flows in dairy cows was evaluated in 4 lactating cows equipped with ruminal, duodenal (n = 4), and ileal (n = 2) cannulae fed a silage-based diet during a 35-d experimental period. To label EN, starting on d 27, an infusion of L-[¹⁵N]Leu (0.45 mmol/h) was performed for 200 h. Samples of feed, duodenal and ileal digesta, feces, blood, urine, and mucosa of the rumen and duodenum were taken at 0900, 1100, 1300, and 1500 h on d 34 and at 0800, 1000, 1200, and 1400 h on d 35. The enrichment and fluxes of total N and individual AA were determined and used to calculate the EN flows at the duodenum, ileum, and in the feces. Based on the concept that EN comprises desquamation and secretions, EN flows were estimated, using as representative of the enrichment of EN only the enrichment of the gut mucosa (upper limit) or the average of the mucosa and the export protein enrichment (assumed to have a similar enrichment to casein; lower limit). Estimations of duodenal and fecal EN flows using the isotope dilution of ¹⁵N-total and ¹⁵N-Leu were not different and EN was an important fraction of duodenal and fecal flows, representing 14 to 30% of the duodenal flow and 18 to 31% of the fecal flow, depending on the dilution method used. The total EN flow at the duodenum is present in approximately equal proportions as either free EN or EN incorporated into bacterial protein. Ileal EN flow was 18% greater than the fecal EN flow. Using the combination of the gut and export protein, the duodenal and fecal EN flows estimated with the isotopic dilution of Leu vs. other labeled AA were less different than when estimated using the enrichment of gut mucosa alone. The current approaches have highlighted that present prediction schemes probably underestimate EN flows at the duodenum and, in consequence, overestimate net protein and AA supply. Refinement of the procedures may allow direct and accurate estimation of metabolic fecal protein, an important component of the so-called maintenance requirement of dairy cows.     

Technical note: A new high-performance liquid chromatography purine assay for quantifying microbial flow

An HPLC method was developed to quantify the purines adenine and guanine and their metabolites xanthine and hypoxanthine in hydrolysates of isolated bacteria and omasal digesta and to assess the effect of using either purines only or purines plus metabolites as microbial markers for estimating microbial flow from the rumen. Individual purines and their metabolites were completely resolved on a C18 column using gradient elution with 2 mobile phases. Intraassay coefficient of variation ranged from 0.6 to 3.1%. Hydrolytic recovery of the 4 purine bases from their corresponding nucleosides averaged 101% (control), 103% (when added to bacterial isolates), and 104% (when added to omasal digesta). Mean concentrations of adenine, guanine, xanthine, and hypoxanthine were, respectively, 53, 58, 2.8, and 3.5 μmol/g of dry matter in omasal bacteria and 10, 12, 7.5, and 7.5 μmol/g of dry matter in omasal digesta, indicating that xanthine plus hypoxanthine represented 5% of total purines in bacterial hydrolysates but 41% of total purines in digesta hydrolysates. A significant negative relationship (R² = 0.53) between the sum of adenine and guanine and the sum of xanthine and hypoxanthine in digesta samples (but not bacterial isolates) indicated that 89% of the adenine and guanine originally present in ruminal microbes were recovered as xanthine and hypoxanthine. These results suggested that, when total purines are used as the microbial marker, both purines and their metabolites should be quantified and used to compute microbial nonammonia N and organic matter flows.     

Influence of detachment procedure and diet on recovery of solid-associated bacteria from sheep ruminal digesta and representativeness of bacterial isolates as assessed by automated ribosomal intergenic spacer analysis-polymerase chain reaction

Six ruminally and duodenally cannulated sheep were used in a partially replicated 4 × 4 Latin square experiment designed to evaluate the efficiency of 3 detachment procedures (DP) to recover solid-associated bacteria (SAB) from ruminal digesta. The 4 experimental diets contained forage to concentrate (F:C) ratios of 70:30 or 30:70 with either alfalfa hay or grass hay as the forage. Bacterial biomass was labeled with ¹⁵NH₄Cl. The DP were 1) MET: digesta was incubated at 38°C for 15 min with saline solution (0.9% NaCl) containing 0.1% methylcellulose under continuous shaking; 2) STO: digesta was mixed with cold saline solution and homogenized with a stomacher for 5 min at 230 rpm; 3) FRE: digesta was immediately frozen at −20°C for 72 h, thawed at 4°C, mixed with saline solution and subjected to STO procedure. Common to all treatments was storing at 4°C for 24 h after the treatment, homogenization, filtration, and resuspension of digesta 2 times in the treatment solutions. The automated ribosomal intergenic spacer analysis of the 16S ribosomal DNA was used to analyze the similarity between bacterial communities attached to the digesta and those in the pellet obtained after each DP. There were no significant F:C × DP or forage × DP interactions for any variable. On average, STO treatment detached 65.8% of SAB from ruminal digesta, about 1.2 and 1.5 times more than FRE and MET treatments, respectively. Total recovery of SAB in STO pellets (48.9%) was greater compared with FRE (31.7%) and MET (33.1%), values being greater for high-forage compared with high-concentrate diets. Similarity index between the bacteria attached to digesta and those in the pellets were lower for FRE (48.2%) compared with MET (54.1%) and STO (54.1%), which suggests that FRE could have destroyed cell integrity of some bacterial species, thus reducing the bacterial diversity present in the pellets. The STO method was the most effective removing SAB from digesta, but only a moderate similarity between the bacterial communities attached to digesta and those recovered in the bacterial pellets was obtained. Values of duodenal microbial flow estimated using SAB as reference bacteria were greater with FRE compared with STO and MET, but all DP detected similar differences between diets, and therefore did not influence the interpretation of results.     

Effect of lauric acid and coconut oil on ruminal fermentation, digestion, ammonia losses from manure, and milk fatty acid composition in lactating cows

This experiment (replicated 3 × 3 Latin square design) was conducted to investigate the effects of lauric acid (LA) or coconut oil (CO) on ruminal fermentation, nutrient digestibility, ammonia losses from manure, and milk fatty acid (FA) composition in lactating cows. Treatments consisted of intraruminal doses of 240 g of stearic acid/d (SA; control), 240 g of LA/d, or 530 g of CO/d administered once daily, before feeding. Between periods, cows were inoculated with ruminal contents from donor cows and allowed a 7-d recovery period. Treatment did not affect dry matter intake, milk yield, or milk composition. Ruminal pH was slightly increased by CO compared with the other treatments, whereas LA and CO decreased ruminal ammonia concentration compared with SA. Both LA and CO decreased protozoal counts by 80% or more compared with SA. Methane production rate in the rumen was reduced by CO compared with LA and SA, with no differences between LA and SA. Treatments had no effect on total tract apparent dry matter, organic matter, N, and neutral detergent fiber digestibility coefficients or on cumulative (15 d) in vitro ammonia losses from manure. Compared with SA, LA and CO increased milk fat 12:0, cis-9 12:1, and trans-9 12:1 content and decreased 6:0, 8:0, 10:0, cis-9 10:1, 16:0, 18:0, cis 18:1, total 18:2, 18:3 n-3 and total polyunsaturated FA concentrations. Administration of LA and 14:0 (as CO) in the rumen were apparently transferred into milk fat with a mean efficiency of 18 and 15%, respectively. In conclusion, current data confirmed that LA and CO exhibit strong antiprotozoal activity when dosed intraruminally, an effect that is accompanied by decreases in ammonia concentration and, for CO, lowered methane production. Administration of LA and CO in the rumen also altered milk FA composition.     

Changes in alveolar and cisternal compartments induced by milking interval in the udder of dairy ewes

The aim of this work was to evaluate the effects of milking interval (4, 8, 12, 16, 20, and 24 h) on cisternal size and milk partitioning (cisternal and alveolar) in the udders of dairy ewes. Twenty-four dairy ewes (Manchega, n = 12; Lacaune, n = 12) were used in a 2-wk experiment during mid-lactation. Cisternal and alveolar milk yields were measured and milk samples from each udder fraction were collected for analysis. Cisternal milk was obtained after i.v. injection of an oxytocin receptor antagonist, and alveolar milk was obtained after i.v. injection of oxytocin. Enlargement of the cisternal compartment due to milking intervals was measured by ultrasonography for each half udder. Volumes of cisternal and alveolar milk differed according to breed, being greater in Lacaune (888 ± 43 and 338 ± 25 mL, respectively) than in Manchega ewes (316 ± 43 and 218 ± 25 mL, respectively). Alveolar milk increased linearly to 16 h in Manchega and 20 h in Lacaune and remained constant thereafter. Cisternal milk accumulated linearly to 24-h milking intervals in both breeds. Cisternal area (values per udder half) increased as milking interval increased, reaching a plateau at 20 h in Manchega (21 ± 1 cm²) and 16 h in Lacaune (37 ± 1 cm²). Correlation between cisternal area and cisternal milk was the greatest at 8 h (Manchega: r = 0.70 and Lacaune: r = 0.56). Cisternal area correlated with total milk (r = 0.80). Milk fat content varied markedly with milking intervals, increasing in alveolar milk (until 12 h in Manchega, 8.90 ± 0.18%; and 20 h in Lacaune, 8.67 ± 0.19%) and decreasing until 24 h in cisternal milk (5.74 ± 0.29% and 4.85 ± 0.29%, respectively). Milk protein content increased in alveolar milk until 24 h (Manchega, 6.46 ± 0.11%; Lacaune, 5.95 ± 0.11%), but did not vary in cisternal milk. Milk lactose content only decreased at the 24-h milking interval in the cisternal milk of Manchega ewes (4.60 ± 0.04%). In conclusion, our results suggest that cisterns play an important role in accommodating secreted milk during extended milking intervals. Thus, long milking intervals could be a recommended strategy for large-cisterned dairy sheep. Evidence indicates that ultrasonography provides accurate estimations of udder cistern size and could be used as an indicator for selecting large-cisterned dairy ewes.     

Using the Small Ruminant Nutrition System to develop and evaluate an alternative approach to estimating the dry matter intake of goats when accounting for ruminal fiber stratification

The first objective of this research was to assess the ability of the Small Ruminant Nutrition System (SRNS) mechanistic model to predict metabolizable energy intake (MEI) and milk yield (MY) when using a heterogeneous fiber pool scenario (GnG1), compared with a traditional, homogeneous scenario (G1). The second objective was to evaluate an alternative approach to estimating the dry matter intake (DMI) of goats to be used in the SRNS model. The GnG1 scenario considers an age-dependent fractional transference rate for fiber particles from the first ruminal fiber pool (raft) to an escapable pool (λ_r), and that this second ruminal fiber pool (i.e., escapable pool) follows an age-independent fractional escape rate for fiber particles (k_e). Scenario G1 adopted only a single fractional passage rate (k_p). All parameters were estimated individually by using equations published in the literature, except for 2 passage rate equations in the G1 scenario: 1 developed with sheep data (G1-S) and another developed with goat data (G1-G). The alternative approach to estimating DMI was based on an optimization process using a series of dietary constraints. The DMI, MEI, and MY estimated for the GnG1 and G1 scenarios were compared with the results of an independent dataset (n = 327) that contained information regarding DMI, MEI, MY, and milk and dietary compositions. The evaluation of the scenarios was performed using the coefficient of determination (R²) between the observed and predicted values, mean bias (MB), bias correction factor (C_b), and concordance correlation coefficient. The MEI estimated by the GnG1 scenario yielded precise and accurate values (R² = 0·82; MB = 0.21 Mcal/d; C_b = 0.98) similar to those of the G1-S (R² = 0.85; MB = 0.10 Mcal/d; C_b = 0.99) and G1-G (R² = 0.84; MB = 0.18 Mcal/d; C_b = 0.98) scenarios. The results were also similar for the MY, but a substantial MB was found as follows: GnG1 (R² = 0.74; MB = 0.70 kg/d; C_b = 0.79), G1-S (R² = 0.71; MB = 0.58 kg/d¹; C_b = 0.85) and G1-G (R² = 0.71; MB = 0.65 kg/d; C_b = 0.82). The alternative approach for DMI prediction provided better results with the G1-G scenario (R² = 0.88; MB = −71.67 g/d; C_b = 0.98). We concluded that the GnG1 scenario is valid within mechanistic models such as the SRNS and that the alternative approach for estimating DMI is reasonable and can be used in diet formulations for goats.     

Comparison of nitrogen-15 and diaminopimelic acid for estimating bacterial protein synthesis of lactating cows fed diets of varying protein degradability

Three lactating Holstein cows fitted with duodenal cannulae were fed diets containing cottonseed meal, corn gluten meal, or blood meal as protein supplements in a 3 c 3 Latin square experiment. Diets averaged 15% CP and were 60% concentrate, 31% corn silage, and 9% alfalfa hay. The flow marker was Cr2O3; the bacterial protein fraction of digesta CP was estimated by 15N (as ammonium sulfate) and diaminopimelic acid. The undegraded fraction of total feed protein entering the duodenum for respective diets was .52, .57, and .69. The 15N method was less variable than diaminopimelic acid. Based on 15N, percentage of bacterial of total protein differed among treatments (61.5, 59.4, and 55.0, respectively). Ten percent more protein entered the duodenum on blood meal than other diets, but differences were not significant. Protein sources were similar in microbial passage, but degraded protein was used most efficiently for microbial synthesis on blood meal. Incorporation of 15N consumed into bacterial protein ranged from 50 to 83% with numerically highest values on blood meal, suggesting greater efficiency of ammonia, capture. Recoveries of 15N for the 72 h as milk, feces and urine ranged from 54 to 78%.     

Changes in chemical composition of Alxa bactrian camel milk during lactation

Changes in chemical composition of Alxa bactrian camels reared in Inner Mongolia (China) during lactation were investigated. Colostrum and milk samples from 10 nomadic female camels in their first season of lactation were collected periodically from parturition until 90 d postpartum (PP). The average contents of gross composition were 14.23% protein, 4.44% lactose, 0.27% fat, 0.77% ash, and 20.16% total solids in colostrum at 2 h PP, and the respective mean values were 3.55, 4.24, 5.65, 0.87, and 14.31% for regular milk on d 90. A 15-fold increase was shown in fat content during the first 24 h, whereas a sharp decrease was shown during the first 12 h of lactation in protein, ash, and total solids contents. Variation in lactose content was small (4.24 to 4.71%) throughout the study period. Total N, nonprotein N, casein N, and whey protein N were found to be 2.23, 0.06, 0.86, and 1.31 g/100 mL for the colostrum at 2 h PP; and 0.56, 0.04, 0.45, and 0.07 g/100 mL for the milk at 90 d PP. Percentages of caseins increased steadily, whereas whey proteins declined gradually until 3 mo of lactation. Gas liquid chromatography analysis of milk fat showed that the content of even-numbered saturated fatty acids (C_12:0-C_18:0) in camel colostrum (2 h to 7 d PP) was lower than that of regular milk (15 to 90 d PP). The predominant saturated fatty acids were C_14:0, C_16:0, and C_18:0, regardless of the stage of lactation. There was a considerable level of polyunsaturated fatty acids (mainly C_18:1) in Alxa camel's milk fat. The levels of Ca, P, Na, K, and Cl were 222.58, 153.74, 65.0, 136.5, and 141.1 mg/100 g, respectively, at 2 h PP; the values of the minerals were 154.57, 116.82, 72.0, 191.0, and 152.0 mg/100 g, respectively, for the regular milk on d 90. The levels of vitamins A, C, E, B₁, B₂, B₆, and D were 0.97, 29.60, 1.45, 0.12, 1.24, 0.54 mg/L, and 640 IU/L, respectively, in Alxa camel milk at 90 d PP. Vitamin A and C contents were higher and vitamins E and B₁ were lower than those in colostrum. Sodium dodecyl sulfate-PAGE and densitometry results demonstrated that Alxa camel colostrum is rich in immunoglobulins, serum albumin, and 2 unknown fractions, which are reduced in amount (%) within 2 d of lactation. It seems that there is lack of β-lactoglobulin in Alxa camel milk, whereas casein and α-lactalbumin start at a low level and increase gradually until they reach their regular levels in the milk.     

Thermal inactivation of lactoperoxidase in goat,sheep and bovine milk – A comparative kinetic and thermodynamic study

Using isothermal heating, inactivation of lactoperoxidase (LPO) in goat, sheep and cow milk was studied in the temperature range of 70–77 °C. Kinetic and thermodynamics studies were carried out at different time–temperature combination in order to evaluate the suitability of LPO as marker for the heat-treatment of milk and dairy products from different species. The thermal inactivation of LPO followed the first-order kinetics. D- and k-values decreased and increased, respectively with increasing temperature, indicating a more rapid LPO inactivation at higher temperatures. The influence of temperature on the inactivation rate constant was quantified using the Arrhenius and thermal death time models. The corresponding z-values were 3.38 ± 0.013, 4.11 ± 0.24 and 3.58 ± 0.004 °C in goat, sheep and cow milk, respectively. Activation energy values varied between milk species with 678.96 ± 21.43 kJ mol⁻¹ in goat milk, 560.87 ± 28.18 kJ mol⁻¹ in sheep milk and 641.56 ± 13.12 kJ mol⁻¹ in cow milk, respectively.     

Interactions between barley grain processing and source of supplemental dietary fat on nitrogen metabolism and urea-nitrogen recycling in dairy cows

The objective of this study was to determine the effects of methods of barley grain processing and source of supplemental fat on urea-N transfer to the gastrointestinal tract (GIT) and the utilization of this recycled urea-N in lactating dairy cows. Four ruminally cannulated Holstein cows (656.3 ± 27.7 kg of BW; 79.8 ± 12.3 d in milk) were used in a 4 × 4 Latin square design with 28-d periods and a 2 × 2 factorial arrangement of dietary treatments. Experimental diets contained dry-rolled barley or pelleted barley in combination with whole canola or whole flaxseed as supplemental fat sources. Nitrogen balance was measured from d 15 to 19, with concurrent measurements of urea-N kinetics using continuous intrajugular infusions of [¹⁵N¹⁵N]-urea. Dry matter intake and N intake were higher in cows fed dry-rolled barley compared with those fed pelleted barley. Nitrogen retention was not affected by diet, but fecal N excretion was higher in cows fed dry-rolled barley than in those fed pelleted barley. Actual and energy-corrected milk yield were not affected by diet. Milk fat content and milk fat yield were higher in cows fed dry-rolled barley compared with those fed pelleted barley. Source of supplemental fat did not affect urea-N kinetics. Urea-N production was higher (442.2 vs. 334.3 g of N/d), and urea-N entering the GIT tended to be higher (272.9 vs. 202.0 g of N/d), in cows fed dry-rolled barley compared with those fed pelleted barley. The amount of urea-N entry into the GIT that was returned to the ornithine cycle was higher (204.1 vs. 159.5 g of N/d) in cows fed dry-rolled barley than in pelleted barley-fed cows. The amount of urea-N recycled to the GIT and used for anabolic purposes, and the amounts lost in the urine or feces were not affected by dietary treatment. Microbial nonammonia N supply, estimated using total urinary excretion of purine derivatives, was not affected by diet. These results show that even though barley grain processing altered urea-N entry into the GIT, the utilization of this recycled urea-N for microbial production was unaffected as the additional urea-N, which entered the GIT was returned to ureagenesis.     

Prediction of ammonia emission from dairy cattle manure based on milk urea nitrogen: Relation of milk urea nitrogen to ammonia emissions

The main objectives of this study were to assess the relationship between ammonia emissions from dairy cattle manure and milk urea N (MUN; mg/dL) and to test whether the relationship was affected by stage of lactation and the dietary crude protein (CP) concentration. Twelve lactating multiparous Holstein cows were randomly selected and blocked into 3 groups of 4 cows intended to represent early [123 ± 26 d in milk (DIM)], mid (175 ± 3 DIM), and late (221 ± 12 DIM) lactation stages. Cows within each stage of lactation were randomly assigned to a treatment sequence within a split-plot Latin square design balanced for carryover effects. Stage of lactation formed the main plots (squares) and dietary CP levels (15, 17, 19, and 21% of diet dry matter) formed the subplots. The experimental periods lasted 7 d, with d 1 to 6 used for adjustment to diets and d 7 used for total collection of feces and urine as well as milk sample collection. The feces and urine from each cow were mixed in the proportions in which they were excreted to make slurry that was used to measure ammonia emissions at 22.5°C over 24 h using flux chambers. Samples of manure slurry were taken before and after ammonia emission measurements. The amount of slurry increased by 22% as dietary CP concentration increased from 15 to 21%, largely because of a greater urine volume (25.3 to 37.1 kg/d). Initial urea N concentration increased linearly with dietary CP from 153.5 to 465.2 mg/dL in manure slurries from cows fed 15 to 21% CP diets. Despite the large initial differences, the final concentration of urea N in manure slurries was less than 10.86 mg/dL for all dietary treatments. The final total ammoniacal N concentration in manure slurries increased linearly from 228.2 to 508.7 mg/dL as dietary CP content increased from 15 to 21%. Ammonia emissions from manure slurries ranged between 57 and 149 g of N/d per cow and increased linearly with dietary CP content, but were unaffected by stage of lactation. Ammonia emission expressed as a proportion of N intake increased with percentage CP in the diet from about 12 to 20%, whereas ammonia emission as a proportion of urinary urea N excretion decreased from 67 to 47%. There was a strong relationship between ammonia emission and MUN [ammonia emission (g/d per cow) = 25.0 (±6.72) + 5.03 (±0.373) × MUN (mg/dL); R² = 0.85], which was not different among lactation stages. Milk urea N concentration is one of several factors that allows prediction of ammonia emissions from dairy cattle manure.     

Dietary starch source and protein degradability in diets containing sucrose: Effects on ruminal measures and proposed mechanism for degradable protein effects

A feeding study was conducted to evaluate ruminal effects of starch source (STA) and rumen-degradable dietary protein (RDP) in diets with added sucrose. The experimental design was an incomplete Latin square with three 21-d periods, 8 ruminally cannulated lactating cows, and a 2 × 2 factorial arrangement of treatments. Treatments were STA (dry ground corn or high-moisture corn) as more slowly and more rapidly fermenting starch sources, respectively, and relative amount of RDP (+RDP: added protein from soybean meal; −RDP: heat-treated expeller soybean product partially substituted for soybean meal). Diets were formulated to be isonitrogenous and similar in starch and neutral detergent fiber concentrations. Dry matter (DM) intake was 1 kg greater with +RDP compared with −RDP diets. For ruminal digesta measures made 2 h postfeeding, weight of digesta DM was unaffected by treatment; total kilograms of wet digesta and kilograms of liquid tended to be greater with +RDP than with −RDP, and no effect was observed of STA × RDP. Digesta DM percentage was greater with −RDP than with +RDP. At 2 h postfeeding, ruminal pool sizes (mol) of lactate and total AA were larger and those of total organic acids (OA) and ammonia tended to be larger with +RDP than with −RDP; no effects of STA or STA × RDP were detected. Rumen-degradable protein effects on lactate and OA pool sizes may be due to a protein-mediated increase in fermentation rate of carbohydrate. Organic acid concentrations at 2 h postfeeding did not show the same response pattern or significance as the pool size data; high-moisture corn tended to be greater than dry ground corn and no effect was observed for RDP or STA × RDP. Concentration and pool size for OA were more weakly correlated [coefficient of determination (R²) = 0.66] than was the case for other ruminal analytes (R² >0.80). Organic acid pool size and kilograms of digesta liquid were strongly correlated (R² = 0.79), whereas concentration and kilograms of liquid were much less so (R² = 0.21). The correlation of OA moles with kilograms of liquid likely relates to the homeostatic mechanism of water flux across the rumen wall to reduce the osmotic gradient with blood as intraruminal moles of solute change. This action compresses the range of ruminal OA concentrations. With kilograms of ruminal liquid differing across individual measurements, the ruminal OA concentration data are not on the equivalent basis required to be reliably useful for assessing the effect of treatments. Further evaluation of protein effects on carbohydrate fermentation and of methods that allow accurate comparison of treatments for their effect on ruminal OA production are warranted.