Evaluation of a rapid determination of heat production and respiratory quotient in holstein steers using the washed rumen technique

Authors: KIM, DOHYUNG - University Of Kentucky; MCLEOD, KYLE - University Of Kentucky; Klotz, James; KOONTZ, ANNE - University Of Kentucky; FOOTE, ANDREW - University Of Kentucky; HARMON, DAVID - University Of Kentucky

Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/2/2013
Publication Date: 7/2/2013
Citation: Kim, D., Mcleod, K.R., Klotz, J.L., Koontz, A.F., Foote, A.P., Harmon, D.L. 2013. Evaluation of a rapid determination of heat production and respiratory quotient in holstein steers using the washed rumen technique. Journal of Animal Science. 91:4267-4276.

Interpretive Summary: In preparation for a study to evaluate the basal metabolic rate (done through a measure of fasting heat production and energy loss through urine) of steers suffering from fescue toxicosis, the use of the washed rumen technique was proposed as method to more rapidly achieve a fasted state in a ruminant. This was desirable because it would to minimize the stress associated with fasting an animal for 3 -4 days prior to collection of any metabolic data. Therefore, the objective of this study was to validate use of the washed rumen technique for rapid measurement of fasting heat production and respiratory quotient, and to compare this with heart rate and core temperature. Observations made in this experiment indicate that an accurate measurement of fasting heat production can be obtained using a shorter-term measurement with the washed rumen technique. This approach provides an alternative to the traditional 48 h fasting time, or measurements made during the third and fourth day after starvation.

Technical Abstract: The objective of this study was to validate use of the washed rumen technique for rapid measurement of fasting heat production (FHP) and RQ, and to compare this with heart rate (HR) and core temperature (CT). Eight Holstein steers (322 ± 30 kg) were maintained in a controlled temperature (21°C) environment and treated as follows: 10 d diet adaptation, 1 d measurement of respiratory gases at 1.5 × NEm (unwashed rumen), 1 d measurement of respiratory gases at fasting (washed rumen), and 7 d to ensure re-establishment of intake. Steers were offered alfalfa cubes top-dressed with a mineral pre-mix at 1.5 × NEm. Using an indwelling probe, CT and HR were monitored continuously during the days respiratory gases were measured. For fasting measurements, the reticulorumen was washed and refilled with ruminal buffer (NaCl = 96; NaHCO3 = 24; KHCO3 = 30; K2HPO4 = 2; CaCl2 = 1.5; MgCl2 = 1.5 mmol/kg of buffer) with Cr-EDTA aerated with 75% N2 and 25% CO2 before introduction to the rumen. Mean daily CT, HR, FHP, and RQ were lower for washed rumen than unwashed rumen (P < 0.001). In order to define the plateau of RQ, the dependence of RQ rate and hour on unwashed and washed rumen was fitted by a one-phase decay equation. The plateau of RQ values was 0.87 ± 0.01 and 0.72 ± 0.01 for unwashed and washed rumen, respectively. The RQ decreased to approximately 0.7, 8 h after washing the rumen. Mean RQ after washing rumen were 0.78, 0.74, and 0.73 (SEM = 0.01) for time segments 0 to 8 h, 9 to 16 h, and 17 to 24 h, respectively. Mean FHP after washing rumen was 18.75, 16.84, and 16.72 (SEM = 0.35) kJ(h·kg0.75) for time segments 0 to 8 h, 9 to 16 h, and 17 to 24 h, respectively. There were no significant differences in RQ and FHP (P = 0.225 and P = 0.810, respectively) between the segment of 9 to 16 h and 17 to 24 h. Thus, an accurate measurement of FHP can be obtained using a shorter-term measurement with the washed rumen technique. This approach provides an alternative to the traditional 48 h fasting time, or measurements made during the third and fourth day after starvation.