Short communication: Effect of diet changes on sorting behavior of weaned dairy calves

Dairy cows sort mixed rations; in some cases sorting can lead to digestive disorders. How sorting behavior develops in calves is poorly understood. The objective of this observational study was to determine if sorting behavior of total mixed ration (TMR)-fed dairy calves was affected by the removal of supplementary concentrate. Dairy bull calves (n=18) were provided access to both a TMR (49.1% dry matter) and calf starter fed separately during the preweaning period starting at 3 d of age. Sorting of the TMR was assessed after weaning when calves were provided both feeds at 65 d of age, and again at 70 d immediately following the removal of calf starter from the calf pen. Sorting was measured by comparing the particle size composition of the TMR offered with that of the orts following 24h of feed access. Feed particle fractions were measured using the Penn State Particle Separator with 3 screens (19, 8, and 1.18mm) and a bottom pan to separate the TMR into long, medium, short, and fine fractions, respectively. At d 65, calves sorted for long particles (133±9%) and against small particles (92±3%), with no differences for the remaining fractions (99±5% for medium; 107±5% for fine); these preferences were reversed at d 70 when calf starter was no longer available with calves preferentially selecting fine particles (113±4%), but showing no preference for other fractions (101±11% for long; 99±6% for medium; 97±4% for short). These results indicate that young dairy calves are capable of sorting a TMR and they adjust this behavior in response to the availability of grain.