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 dairy 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 selection of cows according to efficiency of milk production. Alkanes have been used with sheep and cattle to estimate feed intake under grazing conditions and could provide a technique for measuring intake in housed dairy cows. The purpose of this study was to examine alkanes C32 and C36, in combination with alkane C33, as indigestible markers for estimating intake of housed dairy cows fed on different diets under experimental and commercial conditions. 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 plus concentrates (Expt 3). Animals were dosed once daily with C32 and C36, 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 0·99. Over the range of intakes found in the three experiments (6–24 kg DM/d), the r2 values for estimated versus actual dry matter intakes ranged from 0·81 to 0·99. It is concluded that alkanes could provide a useful technique for estimating intake in dairy cows housed and fed in groups.