Supplementation of rumen-protected forms of methionine, betaine, and choline to early lactation Holstein cows

Methionine (Met) is frequently the first limiting amino acid or co-limiting with lysine in dairy rations, and Met metabolism is closely linked to that of betaine and choline. Methionine, betaine, and choline are all degraded by microbes in the rumen, so rumen-protected (RP) forms were used to perform two experiments. The objective of these experiments was to investigate the impact of supplementing RP forms of methionine, betaine, and choline to a Met-limited total mixed ration (TMR) on performance, metabolism and ruminal fermentation in early lactation Holstein cows.; Experiment 1 utilized 80 lactating Holstein cows from 21 to 91 days in milk (DIM) that were fed a corn silage-based TMR formulated to meet National Research Council (2001) recommendations, except the Met content was limited (42 g/d). One of four supplements was blended into the TMR to produce four dietary treatments: (1) control, (2) 20 g/d RP-Met, (3) 45 g/d RP-betaine, and (4) 40 g/d RP-choline. The RP-Met supplement was protected by encapsulation. Calcium salts of fatty acids were used to protect the RP-betaine and RP-choline supplements; therefore the same Ca salts of fatty acids were added to the control and RP-Met supplements in order to supply equal amounts of fat to all treatments. Dry matter (DM) intake, body weight, and body condition score were not significantly different among treatments (P > 0.2). Feeding RP-choline to MP cows that received a Met-limited diet improved milk yield and increased milk CP yield, but not in primiparous cows. In this study, supplementing RP-betaine was not beneficial. Cows fed RP-Met or RP-choline had higher milk crude protein yield than cows fed control or RP-betaine (P = 0.02). However, there were no differences in milk fat yield or milk urea nitrogen (P > 0.2).; Experiment 2 utilized 4 dual-flow continuous culture fermentors (700 ml) to determine the effects of supplementation of rumen-protected forms of methionine, betaine, and choline to a Met-limited corn silage-based TMR on microbial metabolism by mixed ruminal cultures. Fermentors were inoculated with rumen fluid and allowed to stabilize for 2 days. Treatments were added for 5 days of adaptation followed by 3 days of sample collection. One of 4 supplements was blended into the TMR to produce 4 dietary treatments with a composition that was similar to those used in Experiment 1. Here, treatments are described as a percent of dietary DM: (1) control, (2) RP-Met (0.09% of DM as Met), (3) RP-betaine (0.20% of DM as betaine), or (4) RP-choline (0.18% of DM as choline). Fat was added to all treatments as in Experiment 1. Four replicates were performed with each fermentor receiving each of the 4 treatments for one replicate. Total volatile fatty acids (VFA) and individual VFA concentrations were not affected by dietary treatment, except for propionate and isobutyrate concentration. Propionate production was significantly lower in RP-choline than in control fermentors ( P = 0.05). Methane production and pH were similar across treatments (P > 0.2). Ruminal ammonia concentration was lower for fermentors receiving RP-choline than those receiving control (P = 0.04). There were no significant differences in microbial N%, flow, or efficiency between treatments (P > 0.2).