Do Cows Under Subacute Ruminal Acidosis (SARA) Attempt to Self-Medicate?

Abstract

The objective of this study was to examine feed-sorting behavior of dairy cows in response to a grain challenge that leads to Subacute Ruminal Acidosis (SARA). Sixteen multiparous, rumen-cannulated lactating Holstein cows were used. During the first 49 days of the experiment, all cows received a High-Forage diet (HF; 77:23, F: C; NFC=35). Cows were then transitioned to a High-Grain (HG; 50:50, F: C; NFC=48) diet on days 50 and 51 and remained on the HG until day 72. Feed intake was recorded daily. Particle size distribution of feed and orts were analyzed using the Penn State Particle Separator (PSPS) on days 36 (HF) and 71 (HG). The extent of feed-sorting was evaluated by calculating sorting indices for each PSPS dietary fraction for each given diet. A sorting index of a given fraction of the PSPS was calculated as the actual DMI expressed as a percentage of the predicted DMI of that fraction. Ruminal pH was recorded continuously every minute using an indwelling system on days 36 (HF), 50, 51 (onset of SARA) and day 71 (chronic SARA). Data were analyzed using Proc Mixed of SAS with day as a fixed effect and accounting for repeated measurement. Orthogonal contrasts were utilized to compare days. Ruminal pH on day 36 (16±46 min/d <5.6) indicated healthy rumen conditions. Ruminal pH recorded on days 51 and 71 (551±46 min/d <5.6 and 246±46 min/d <5.6, respectively) indicated an established SARA. Sorting assessment on day 36 showed that cows while on HF diet sorted against large particles (>19 mm, p<0.05) and concurrently sorted for the short and fine particles (<8 mm, p<0.05). Under SARA (HG), the cows showed an altered preference by sorting for (p<0.05) long particles and against (p<0.05) the short and fine particles. The results suggested that cows undergoing SARA may alter their feed-sorting behavior, likely in an attempt to self-medicate their condition, by selecting long particles and avoiding short and fine particles.