333. Associations Between Rumination Behavior, Liquid Passage Kinetics, and Dry Matter Intake in Finishing Beef Steers.

Abstract Rumination behavior is commonly used as an indicator of rumen function and saliva production in cattle, but its relationship with liquid passage kinetics is not well defined. Understanding relationships between rumination behavior and liquid passage characteristics may provide insight into digestive processes. The objectives of this study were to evaluate the effects of forage particle size, dry matter intake (DMI), and rumination behavior on liquid passage rate and to characterize relationships between rumination time and liquid passage characteristics in finishing beef steers. Twenty-four crossbred beef steers (initial BW = 386 ± 38.8 kg) were blocked by BW, and pens were randomly assigned to one of two dietary treatments (n = 6 pens per treatment; 2 steers per pen). Finishing diets were dry-rolled corn-based and differed only in forage particle size (NEm= 1.90 Mcal/kg). Prairie hay (8% diet DM) was processed using either a 17.8-cm or 10.2-cm screen to achieve respective particle sizes. Rumination behavior was measured continuously throughout the finishing period using ear-tag accelerometers (CowManager SensOor, Agis Automatisering, Netherlands). Steers received a Co-EDTA bolus at the midpoint of the feeding period, followed by serial fecal collections to assess liquid passage rate. Linear mixed models were used to evaluate the effects of diet, DMI, and rumination on liquid passage rate, and effects of diet, DMI, and liquid passage rate on rumination, at the pen level (n = 12 pens). Relationships between rumination and liquid passage variables were assessed using Pearson correlation coefficients on an individual animal basis (n = 24). Dry matter intake was positively associated with liquid passage rate (P = 0.034), whereas dietary treatment and rumination time were not significantly associated with liquid passage rate (P ≥ 0.65). Rumination time was not associated with DMI, treatment, or liquid passage rate (P ≥ 0.14). Additionally, rumination was not correlated with liquid passage characteristics (r = -0.26 to 0.22; P ≥ 0.23). While questions remain regarding the accuracy of ear tag sensor measurements of rumination on cattle fed a finishing diet, these results indicate that rumination behavior was not associated with forage particle size and may have limited value as a proxy for liquid passage kinetics measured using fecal analysis in finishing beef steers.