Estimation of intake and digestibility of forage-based diets in group-fed dairy cows using alkanes as markers

Dry matter intake is one of the major factors limiting milk production in d airy cows, although the quantity of food consumed by an individual cow when housed and fed as part of a group is rarely known. Such information would permit more precise ration formulation, concentrate allocation and selectio n of cows according to efficiency of milk production. Alkanes have been use d with sheep and cattle to estimate feed intake under grazing conditions an d could provide a technique for measuring intake in housed dairy cows. The purpose of this study was to examine alkanes C-32 and C-36, in combination with alkane C-33, as indigestible markers for estimating intake of housed d airy cows fed on different diets under experimental and commercial conditio ns. Three experiments were conducted with hay-based diets (Expt 1), silage only diets (Expt 2) and a diet consisting of a silage-based basal ration pl us concentrates (Expt 3). Animals were dosed once daily with C-32 and C-36, either on filter papers (Expts 1 and 2) or as part of a specially prepared concentrate (Expt 3). Faecal recoveries of alkanes ranged from 0.88 to 0.9 9. Over the range of intakes found in the three experiments (6-24 kg DM/d), the r(2) values for estimated versus actual dry matter intakes ranged from 0.81 to 0.99. It is concluded that alkanes could provide a useful techniqu e for estimating intake in dairy cows housed and fed in groups.