Rumen-protected choline for dairy cows: The in situ evaluation of a commercial source and literature evaluation of effects on performance and interactions between methionine and choline metabolism

Abstract

The interactions were investigated between methionine and choline metabolism due to interchangeable methyl groups. Feeding trials on dairy cows with choline administration were re-evaluated with a focus on methionine balance and the possible effects of supplementary choline on methionine metabolism. In addition, in situ ruminal stability was estimated for a commercial choline supplement. We examined six experiments that included 11 dietary treatments. The Cornell net carbohydrate and protein system was used to estimate nutrient supply and requirements as well as methionine balance; further methionine supply was assessed according to the ideal protein concept. The re-evaluation of feeding trials confirmed the positive effects of supplementary abomasally available choline on milk yield and health of dairy cows. Although these effects were mainly attributed to an elevated export of triglycerides from the liver, beneficial effects may be further caused by an exoneration of methionine metabolism by sparing S-adenosylmethionine. Therefore, the effects on milk yield or other response variables of additional, abomasally available choline could serve as an indicator of methyl group deficiency and thus methionine shortage. Since from theoretical considerations the demand for methyl groups in dairy cows is related to the stage of lactation, requirements for methionine and methyl groups should be taken as separate entities and the latter should be expressed in relation to energy balance or days in milk. Our in situ data indicate that Reashure choline® was effectively protected against ruminal degradation because at least 600 g·kg-1 of choline were in a rumen-protected form. In conclusion, (I) supplementary choline may improve the yield of dairy cows by elevating the export of triglycerides from the liver and by sparing methionine as a methyl donor, and (II) the demand for methyl groups still lacks adequate consideration in the design of diets for dairy cows. © INRA, EDP Sciences, 2006.