Production effects and bioavailability of N-acetyl-l-methionine in lactating dairy cows.

Two experiments were conducted to investigate the production effects of N-acetyl-l-methionine (NALM; experiment 1) and to estimate its bioavailability (BA) and rumen escape (RE; experiment 2), respectively, in lactating dairy cows. In experiment 1, 18 multiparous Holstein cows were used in a replicated, 3 × 3 Latin square design experiment with three 28-d periods. Treatments were (1) basal diet estimated to supply 45 g/d digestible Met (dMet) or 1.47% of metabolizable protein (MP; control), (2) basal diet top-dressed with 32 g/d of NALM to achieve dMet supply of 2.2% of MP, and (3) basal diet top-dressed with 56 g/d of NALM to achieve dMet supply of 2.6% of MP. The NALM treatments supplied estimated 17 and 29 g/d dMet from NALM, respectively, based on manufacturer's specifications. In experiment 2, 4 rumen-cannulated lactating Holstein cows were used in a 4 × 4 Latin square design experiment with four 12-d periods. A 12-d period for baseline data collection and 4 d for determination of RE of NALM preceded the Latin square experiment. For determination of RE, 30 g of NALM were dosed into the rumen simultaneously with Cr-EDTA (used as a rumen fluid kinetics marker) and samples of ruminal contents were collected at 0 (before dosing), 1, 2, 4, 6, 8, 10, 14, 18, and 24 h after dosing. Rumen escape of NALM was calculated using the estimated passage rate based on the measured Cr rate of disappearance. Bioavailability of abomasally dosed NALM was determined using the area under the curve of plasma Met concentration technique. Two doses of l-Met (providing 7.5 and 15 g of dMet) and 2 doses of NALM (11.2 and 14.4 g of dMet) were separately pulse-dosed into the abomasum of the cows and blood was collected from the jugular vein for Met concentration analysis at 0 (before dosing), 1, 2, 4, 6, 8, 10, 12, 14, 18, and 24 h after dosing. Supplementation of NALM did not affect DMI, milk yield, feed efficiency, or milk protein and lactose concentrations and yields in experiment 1. Milk fat concentration and energy-corrected milk yield decreased linearly with NALM dose. Plasma Met concentration was not affected by NALM dose. The estimated relative BA of abomasally dosed NALM (experiment 2) was 50% when dosed at 14.4 g/cow (11.2 g/d dMet from NALM) and 24% when dosed at 28.8 g/cow (14.4 g/d dMet from NALM). The estimated RE of NALM was 19% based on the measured kp of Cr at 11%/h. The total availability of ingested NALM was estimated at 9.5% for the lower NALM dose when taking into account RE (19%) and bioavailability in the small intestine (50%). Overall, NALM supplementation to mid-lactation dairy cows fed a MP-adequate basal diet below NRC (2001) recommendations (45 g/d or 1.47% Met of MP) decreased milk fat and energy-corrected milk yields but did not affect milk or milk true protein yields. Further evaluation of BA of NALM at different doses is warranted. In addition, intestinal conversion of NALM to Met needs additional investigation to establish a possible saturation of the enzyme aminoacylase I at higher NALM doses.

Lactational performance of dairy cows in response to supplementing N-acetyl-l-methionine as source of rumen-protected methionine.

The objective of this experiment was to evaluate the effects of supplementing a rumen-protected source of Met, N-acetyl-l-methionine (NALM), on lactational performance and nitrogen metabolism in early- to mid-lactation dairy cows. Sixty multiparous Holstein dairy cows in early lactation (27 ± 4.3 d in milk, SD) were assigned to 4 treatments in a randomized complete block design. Cows were blocked by actual milk yield. Treatments were as follows: (1) no NALM (control); (2) 15 g/d of NALM (NALM15); (3) 30 g/d of NALM (NALM30); and (4) 45 g/d of NALM (NALM45). Diets were formulated using a Cornell Net Carbohydrate and Protein System (CNCPS) v.6.5 model software to meet or exceed nutritional requirements of lactating dairy cows producing 42 kg/d of milk and to undersupply metabolizable Met (control) or supply incremental amounts of NALM. The digestible Met (dMet) supply for control, NALM15, NALM30, and NALM45 were 54.7, 59.8, 64.7, and 72.2 g/d, respectively. The supply of dMet was 88, 94, 104, and 115% of dMet requirement for control, NALM15, NALM30, and NALM45, respectively. Milk yield data were collected, dry matter intake (DMI) was measured daily, and milk samples were collected twice per week for 22 wk. Blood, ruminal fluid, urine, and fecal samples were collected during the covariate period and during wk 4, 8, and 16. Data were analyzed using the GLIMMIX procedure of SAS (SAS Institute) using covariates in the model for all variables except body weight. Linear, quadratic, and cubic contrasts were also tested. Treatments did not affect DMI, milk yield, and milk component concentration and yield; however, feed efficiency expressed as milk yield per DMI and 3.5% fat-corrected milk per DMI were quadratically affected, with greater response observed for NALM15 and NALM30 compared with control. Acetate proportion linearly increased, whereas propionate proportion linearly decreased with NALM supplementation. Blood urea nitrogen linearly decreased with NALM supplementation. Total plasma essential AA concentrations were quadratically affected, as greater values were observed for control and NALM45 than other treatments. Plasma Met concentration was quadratically affected as lower levels were observed with NALM15, whereas Met concentrations increased with NALM45 compared with control. Nitrogen utilization efficiency and apparent total-tract nutrient digestibility were not affected by treatment. Supplementation of NALM at 15 or 30 g/head per day resulted in the greatest improvements in feed efficiency without affecting N metabolism of early- to mid-lactation dairy cows.

Influence of supplementing a methionine derivative, N-acetyl-l-methionine, in dairy diets on production and ruminal fermentation by lactating cows during early to mid lactation.

The present study investigated production responses and ruminal fermentation characteristics of lactating dairy cows when supplemented with N-acetyl-l-Met (NALM) as a source of rumen-protected Met in metabolizable protein (MP)-deficient (MPD) or MP-adequate diet (MPA). Eight lactating dairy cows (53 ± 10.4 d in milk, average ± standard deviation) were blocked by parity and days in milk, and the experiment was performed in a replicated 4 × 4 Latin square design. Within each square, cows were randomly assigned to a sequence of 4 diets during each of the four 21-d periods (14 d of treatment adaptation and 7 d of data collection and sampling). A 2 × 2 factorial arrangement was used; MPD or MPA was combined without or with NALM: MPD without NALM, MPD with NALM (MPD+NALM), MPA without NALM, and MPA with NALM (MPA+NALM). A NALM product was supplemented in the MPD+NALM and the MPA+NALM at 30 g/cow per d. Supplementation of NALM did not affect dry matter intake (DMI) and milk yield regardless of MP concentration. In addition, supplementing NALM resulted in a similar milk true protein concentration and yield. In contrast, NALM supplementation increased milk fat concentration and yield and 3.5% fat-corrected milk yield and tended to increase energy-corrected milk yield regardless of MP difference. Additionally, trends were observed for increased 3.5% fat-corrected milk yield/DMI and energy-corrected milk yield/DMI, and the positive effects were greater under the MPA than the MPD diet, resulting in trends toward interactions between MP and NALM. Dietary treatments had similar effects on ruminal fermentation characteristics and microbial protein yield. Plasma concentration of Met increased under the MPD but not the MPA diet, leading to an MP × NALM interaction. Overall results in the current study suggest that NALM exerted a minor influence on ruminal metabolism, but increased milk fat concentration, resulting in increases in milk fat yield and feed efficiency. Yet, potential effects of NALM on intermediary metabolism between the gastrointestinal tract, the liver, and the mammary gland need to be explored to understand utilization efficiency for production of dairy cows.

Hepatoprotective effect of Fe-TPEN on carbon tetrachloride induced liver injury in rats.

Fe(II)-tetrakis-N,N,N',N'(2-pyridylmethyl) ethylenediamine (Fe-TPEN) catalyzes the dismutation of superoxide, and blocks the toxic effect of paraquat on Escherichia coli growth and survival. We examined antioxidative effects of Fe-TPEN on lipid peroxidation and t-butyl hydroperoxide induced cell damage. Fe-TPEN inhibited the FeSO4/H2O2 induced lipid peroxidation in the rat liver homogenates with an IC50 value of 30.2 microM, and protected Ac2F cell damage by t-butyl hydroperoxide in a dose-dependent manner (EC50 value is 2.6 microM). Also, hepatoprotective effect of Fe-TPEN (5 mg/kg, i.p.) was investigated using CCl4 induced liver injury in rats. This complex inhibited the elevation of serum alanine aminotransferase (AST) and aspartate aminotransferase (ALT) levels in CCl4 induced liver injuries, and improved submassive necrosis and fatty degeneration of the hepatocytes. Fe-TPEN also prevented the loss of total and nonprotein SH contents, glutathione peroxidase and glutathione-S-transferase activity in cytosol of rat liver. Although the exact mechanism of action is not clear, antioxidative properties as well as attenuation of hepatocellular defense systems by Fe-TPEN seem to be important on its potent hepatoprotective effect in CCl4-intoxicated rat.

Randomized double-blind trial of high- and low-dose fleroxacin versus norfloxacin for complicated urinary tract infection.

Patients were entered in a double-blind, placebo-controlled, multicenter study to compare low- and high-dose fleroxacin with norfloxacin for the treatment of complicated urinary tract infection (UTI). A total of 296 patients were enrolled; 102, 97, and 97 patients were randomized to receive 200 mg of fleroxacin (low-dose), 400 mg of fleroxacin (high-dose), both once daily, or 400 mg of norfloxacin twice daily, respectively, for 10 days. Of these patients, 101, 94, and 95 were included in the safety analysis, and 71, 61, and 58 in the efficacy analysis. The main reason for exclusion from the efficacy analysis was failure to isolate a pathogen at baseline. The groups were comparable with respect to demographics. In the low-dose fleroxacin group, 68 (96%) of 71 patients had bacteriologic cures (eight with superinfection), compared with 56 (92%) of 61 in the high-dose fleroxacin group (two with superinfection) and 52 (90%) of 58 in the norfloxacin group (four with superinfection). Escherichia coli was the most frequent isolate in all groups. In the low-dose fleroxacin group, clinical cure was recorded in 61 (86%) of 71, improvement in six, and failure in four. In the high-dose group, clinical cure was noted in 58 (95%) of 61 patients, improvement in two, and failure in one. In the norfloxacin group, 50 (86%) of 58 patients were clinically cured, four were improved, and four failed. Clinical adverse events were reported by 22 (22%) of 101, 36 (38%) of 94, and 19 (20%) of 95 patients in the low-dose fleroxacin, high-dose fleroxacin, and norfloxacin groups, respectively. Insomnia and nausea were reported most frequently in the fleroxacin groups, and nausea and headache were most common in the norfloxacin group. The efficacy and safety of low-dose fleroxacin are comparable to those of norfloxacin for treatment of complicated UTI.