Acetyl-L-methionine

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.

The present study investigated the plasma methionine (Met) and residual potential of N-acetyl-L-Met (NALM) in lactating dairy cows. Six cows (75 ± 20.1 days-in-milk) were used in a replicated 3 × 3 Latin square design. Within each square, cows were randomly assigned to a sequence of three dietary treatments during each of the three 13-day periods (10 days of treatment adaptation and 3 days of data collection and sampling). The three dietary treatments are as follows: basal diet without NALM (control); control diet with 30 g/day of NALM by rumen placement (30NALM), and control diet with 60 g/day of NALM by rumen placement (60NALM). Rumen NALM dosing led to a linear increase in plasma Met concentration. Abomasal infusion with NALM resulted in both linear and quadratic increases in plasma Met concentration. No NALM was detected in milk, liver, plasma, and muscle samples after rumen placement or abomasal infusion. Supplementation of NALM did not affect dry matter intake and milk yield. The absence of plasma NALM and increases in plasma Met concentration for both ruminal and abomasal NALM dosing suggest that NALM supplemented by either rumen placement or abomasal infusion to lactating dairy cows is deacetylated before entering the central circulation.

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.