1847
Contribution of a chelated trace mineral supplement as a methionine source for dairy cows
This experiment sought to determine whether the methionine contained in a trace mineral supplement made a meaningful contribution toward meeting the methionine requirement of the dairy cow. Four multiparous ruminally-cannulated lactating Holstein dairy cows were used in 4 x 4 Latin square design with 7-d periods. Treatments were administered at a rate of 0.08 g of 2-hydroxy-4-methylthio-butanoic acid (HMTBa)/kg of BW on d 0 of each experimental period: 1) HMTBa chelated to Zn, 80% HMTBa, dosed ruminally (MIN; MINTREX® Zn, Novus International, St. Charles, MO, USA), 2) Ca-salt of HMTBa, 84% HMTBa, dosed ruminally (MHA; MHA® feed supplement, Novus International), 3) HMTBa free acid, 88% HMTBa, dosed ruminally (ALR; ALIMET®, Novus International), and 4) HMTBa free acid, 88% HMTBa, dosed post-ruminally (APR; ALIMET®, Novus International). Approximately 5 kg of rumen mat contents from each animal were removed through the cannula, mixed with the appropriate treatment dose, and replaced in the rumen. For post-ruminal treatment, a 50cc syringe was placed in the omasal canal, and contents were expelled into the abomasum; all other animals received a post-ruminal infusion of water. Blood samples were collected regularly through each experimental period. Feed was restricted for 30 minutes prior to treatment administration, following which, animals were fed for ad libitum consumption. Data were analyzed using MIXED procedure of SAS, using averaged pre-infusion measurements as covariates. Plasma concentrations of methionine did not differ between MIN, MHA, and ALR treatments; however, APR resulted in a greater (P<0.001) concentration of plasma methionine compared with other treatments. A treatment x time interaction (P<0.001) was observed for plasma methionine, in which APR increased at 1.5 h after infusion, reaching peak at 3 h (P<0.001), and leveling with other treatments at 12 h (P>0.10). Greater plasma concentrations of HMTBa (P<0.001) were found in APR than in MIN, MHA and ALR; however, these did not differ between each other (P>0.10). There was a treatment x time interaction (P<0.001) for HMTBa; APR peaked at 1.5 h after infusion (P<0.001), declined sharply until 9 h when lower concentrations of HMTBa were observed compared with other treatments (P≤0.05). After 12 h, HMTBa treatments no longer differed (P>0.10). In conclusion, the availability of methionine in plasma did not differ between treatments administered ruminally; however, significant increases were observed when treatments were administered post-ruminally. These results suggest that MIN may be used to contribute toward the methionine requirement for dairy cows.
Keywords: HMTBa, rumen, supplementation