Relative bioavailability of 3 rumen-undegradable methionine sources in dairy cows using the area under the curve technique

Bioavailability of rumen-protected histidine, lysine, and methionine assessed using different in vivo methods

The objective of this experiment was to estimate the bioavailability (BA) of rumen-protected (RP) His, RPLys, and 2 RPMet products using 3 in vivo methods: area under the curve (AUC), plasma dose-response (PDR), and fecal free AA (FFAA) methods. We used 8 rumen-cannulated cows in a replicated 4 × 4 Latin square experiment with 16-d periods. Treatments were (1) abomasal infusion of water (control), (2) abomasal infusion of free His, Lys, and Met (FAA), (3) administration of RPHis + RPLys + RPMet1 (rumen-protected methionine protected with ethyl cellulose; RPAA1), and (4) administration of RPHis + RPLys + RPMet2 (rumen-protected methionine protected with a pH-sensitive polymer; RPAA2). On d 7 of each experimental period, a pulse-dose of water (control) or FAA were infused into the abomasum of the cows, or RPAA were placed directly in the rumen, and blood samples were taken from the jugular vein through a catheter 11 times over a 24-h period for the AUC method. Following the AA pulse-dose, infusion lines were installed into the abomasum for continuous infusion of FAA for the PDR method, or RPAA were fed from d 12 to d 16 and cows were fitted with urinary catheters for total collection of feces for the FFAA method. Fecal collection and blood sampling were conducted from d 14 to 16. Due to technical issues likely leading to unrealistic BA estimates, data for the PDR method are reported in the supplemental material. Relative BA based on the AUC method (computed as AUC of RPAA treatment plasma AA concentration divided by AUC of FAA treatment plasma AA concentration) was lower for RPMet1 compared with RPMet2 (43% vs. 61%) and was 45% (SEM = 3.35) and 72% (SEM = 5.99), for RPHis and RPLys, respectively. Rumen escape fractions of RPAA, estimated in a previous study using an in situ method, and digestibility data from the current study were used for calculations of BA for the FFAA method. Bioavailability based on the FFAA method was lower for RPMet1 (67%) compared with RPMet2 (91%) and was 87% (SEM = 0.71) and 75% (SEM = 2.75) for RPHis and RPLys, respectively. The relative differences in estimated BA based on both the AUC and FFAA methods between the RPMet products were as expected, based on literature, and data for all 4 RPAA products corresponded well with previously estimated BA using the FFAA method. The unrealistic data for the PDR method were likely caused by technical deviations from the original method (e.g., once-daily dosing of RPAA and inability to capture representative plasma concentration data with the sampling time points). Therefore, comparison of the PDR method with the AUC and FFAA methods were not possible in this study. Further comparisons are needed without deviations from the original PDR method. Variability in BA data and differences in estimated BA between the in vivo methods highlight the current challenges for accurate measurements of relative in vivo BA of RPAA products. Different protection technologies may call for different methodology to be used for BA estimations. Further research and standardization of in vivo BA methods are warranted.

Assessment of blood sampling time points to determine the relative bioavailability of ruminally protected methionine supplements using the plasma free amino acid dose-response technique

The calculation of the relative bioavailability (RBV) of rumen-protected AA supplements using the plasma free AA dose-response technique currently relies on blood samples obtained 2, 4, 6, and 8 h after the 0500 h feeding during the last 3 d of each period in Latin square experiments with cows fed every 8 h (0500, 1300, and 2100 h). The objective of this study was to determine if this current blood sampling protocol captures the changes that may occur in plasma Met concentrations within a 24-h day to adequately determine the RBV of Met from Smartamine M (SM). Five multiparous lactating Holstein cows were used in a 5 × 5 Latin square design with 7-d periods. Treatments were (1) control (abomasal infusion of tap water), (2) 12 g/d of abomasally infused dl-Met, (3) 24 g/d of abomasally infused dl-Met, (4) 15 g/d of fed Met (20 g/d of SM), and (5) 30 g/d of fed Met (40 g/d of SM). Blood samples were collected via jugular catheters every 2 h after the 0500 h feeding starting on d 5 and ending on d 7 of each period. Plasma Met analysis was conducted using gas chromatography after chloroformate derivatization. Plasma Met concentration was averaged across days for 2-8 h after the 0500 h feeding, 2-8 h after the 1300 h feeding, 2-8 h after the 2100 h feeding, and 2-24 h after the 0500 h feeding. In addition, plasma Met concentration was regressed on 0, 12, and 24 g of infused dl-Met and 0, 15, and 30 g of fed Met. The calculated RBV of Met from SM averaged 83.8%, 83.6%, 87.4%, and 83.0% for the 2-8 h, 10-16 h, 18-24 h, and 2-24 h sampling periods, respectively. The similarity in the estimations of RBV for the 2-8 h and 2-24 h sampling periods indicates that our original blood sampling protocol seems reliable for determining the RBV of ruminally protected Met products.

Differential responses of rumen and fecal fermentation and microbiota of Liaoning cashmere goats after 2-hydroxy-4-(methylthio) butanoic acid isopropyl ester supplementation

The 2-hydroxy-4-(methylthio) butanoic acid isopropyl ester (HMBi), a rumen protective methionine, has been extensively studied in dairy cows and beef cattle and has been shown to regulate gastrointestinal microbiota and improve production performance. However, knowledge of the application of HMBi on cashmere goats and the simultaneous study of rumen and hindgut microbiota is still limited. In this study, HMBi supplementation increased the concentration of total serum protein, the production of microbial protein in the rumen and feces, as well as butyrate production in the feces. The results of PCoA and PERMANOVA showed no significant difference between the rumen microbiota, but there was a dramatic difference between the fecal microbiota of the two groups of Cashmere goats after the HMBi supplementation. Specifically, in the rumen, HMBi significantly increased the relative abundance of some fiber-degrading bacteria (such as Fibrobacter) compared with the CON group. In the feces, as well as a similar effect as in the rumen (increasing the relative abundance of some fiber-degrading bacteria, such as Lachnospiraceae FCS020 group and ASV32), HMBi diets also increased the proliferation of butyrate-producing bacteria (including Oscillospiraceae UCG-005 and Christensenellaceae R-7 group). Overall, these results demonstrated that HMBi could regulate the rumen and fecal microbial composition of Liaoning cashmere goats and benefit the host.

Pharmacokinetics and relative bioavailability study of two cefquinome sulfate intramammary infusions in cow milk

In this study, two intramammary infusions of cefquinome sulfate were investigated for pharmacokinetics and bioavailability. Twelve lactating cows for each group were administered an effective dose of 75 mg/gland for cefquinome, with milk samples collected at various time intervals. The concentrations of cefquinome in milk at different times were determined by the UPLC-MS/MS method. Analyses of noncompartmental pharmacokinetics were conducted on the concentration of cefquinome in milk. Mean pharmacokinetic parameters of group A and group B following intramammary administration were as follows: AUClast 300558.57 ± 25052.78 ng/mL and 266551.3 ± 50654.85 ng/mL, Cmax 51786.35 ± 11948.4 ng/mL and 59763.7 ± 8403.2 ng/mL, T1/2 5.69 ± 0.62 h and 5.25 ± 1.62 h, MRT 7.43 ± 0.79 h and 4.8 ± 0.78 h, respectively. Pharmacokinetic experiments showed that the relative bioavailability of group B was 88.69% that of group A. From our findings, group B (3 g: 75 mg) shows a quicker drug elimination process than group A (8 g: 75 mg), which suggests that the withdrawal period for the new formulation may be shorter.

2-Hydroxy-4-(Methylthio) Butanoic Acid Isopropyl Ester Supplementation Altered Ruminal and Cecal Bacterial Composition and Improved Growth Performance of Finishing Beef Cattle

The objective of this study was to evaluate the effects of isopropyl ester of 2-hydroxy-4-(methylthio)-butyrate acid (HMBi) on ruminal and cecal fermentation, microbial composition, nutrient digestibility, plasma biochemical parameters, and growth performance in finishing beef cattle. The experiment was conducted for 120 days by a complete randomized block design. Sixty 24-month-old Angus steers (723.9 ± 11.6 kg) were randomly assigned to one of the flowing three treatments: basal diet (the concentrate: 7.6 kg/head·d-1, the rice straw: ad libitum) supplemented with 0 g/d MetaSmart® (H0), a basal diet supplemented with 15 g/d of MetaSmart® (H15), and a basal diet supplemented with 30 g/d of MetaSmart® (H30). Results showed that the average daily gain (ADG) increased linearly (P = 0.004) and the feed conversion ratio (FCR) decreased linearly (P < 0.01) with the increasing HMBi supplementation. Blood urea nitrogen (BUN) concentration significantly decreased in the H30 group (P < 0.05) compared with H0 or H15. The ruminal pH value tended to increase linearly (P = 0.086) on day 56 with the increased HMBi supplementation. The concentrations of ammonia-nitrogen (NH3-N), propionate, isobutyrate, butyrate, isovalerate, valerate, and total volatile fatty acid (VFA) were linearly decreased in the cecum (P < 0.05). The results of Phylogenetic Investigation of Communities by Reconstruction of Unobserved States (PICRUSt) showed that the abundance of most pathways with a significant difference was higher in the rumen and lower in the cecum in the H30 group compared to the H0 group, and those pathways were mainly related to the metabolism of amino acids, carbohydrates, and lipids. Correlation analysis showed that ADG was positively associated with the ratio of firmicutes/bacteroidetes both in the rumen and cecum. Additionally, the abundance of Lachnospiraceae, Saccharofermentans, Lachnospiraceae_XPB1014_group, and Ruminococcus_1 was positively correlated with ADG and negatively correlated with FCR and BUN in the rumen. In the cecum, ADG was positively correlated with the abundances of Peptostreptococcaceae, Romboutsia, Ruminococcaceae_UCG-013, and Paeniclostridium, and negatively correlated with the abundances of Bacteroidaceae and Bacteroides. Overall, these results indicated that dietary supplementation of HMBi can improve the growth performance and the feed efficiency of finishing beef cattle by potentially changing bacterial community and fermentation patterns of rumen and cecum.

Effect of Diet Supplementation with the Mycotoxin Binder Montmorillonite on the Bioavailability of Vitamins in Dairy Cows

The objective of this study was to determine the effect of the mycotoxin binder montmorillonite (MMT) supplemented in the diet of dairy cows on the bioavailability of vitamins A, D, E, B1 and B6. Six multiparous Holstein-Friesian cows were used in a crossover design with two periods. Treatments were a control diet with or without MMT. Vitamins were infused individually into the abomasum through the ruminal cannula. Blood samples were collected from the jugular vein at 0, 1, 2, 3, 4, 6, 9, 12, 24 and 48 h after the administration of each vitamin. Results showed that vitamin A reached maximal concentration (Tmax) at 5.3 h after dosing, the maximal concentration (Cmax) was 1.2 times higher than the basal concentration (Cbasal), and the area under the curve (AUC) was 739 arbitrary units. Vitamin B6 reached the Tmax at 13 h after dosing, the Cmax was 1.4 times higher than the Cbasal, and the AUC was 222 arbitrary units. No differences were observed in Cbasal, Tmax, Cmax and AUC of vitamin A and B6 between control vs. MMT-supplemented cows. Plasma concentrations of vitamins D, E and B1 had no concentration peaks, and were not affected by MMT addition. The lack of a response suggests that their plasma concentration may be tightly regulated. Results of this study do not show evidence that MMT affects the bioavailability of vitamins A and B6 in vivo.