Are Beef Cattle Metabolic Rates Correlated with Feeding Level? Dr

Are Beef Cattle Metabolic Rates Correlated with Feeding Level?
Miriah Reynolds and Bret Olson
Department of Animal and Range Sciences - Montana State University, Bozeman
Most beef cattle in Montana are fed hay for 3-5 months each winter
(1). Many ranchers assume that cattle will lose excessive weight if
cattle are not fed hay during winter.
Previous research suggests that
cattle grazing winter range lower
their metabolic rates similar to
wildlife (2), without impacting
reproduction. Heart rate closely
tracks step-wise decreases and
increases in feeding level in
reindeer and red deer (3, 4, figure).
Results and Importance
Our trial was conducted at the Bozeman Agricultural Research and
Teaching (BART) Farm from late February until early April 2015. Six
head of young, non-pregnant, non-lactating Black Angus cattle
were placed in individual pens for 16 days to determine their
desired feeding level (100%). During this initial period, they were
trained to load into our portable metabolic chamber (PMC), an
enclosed horse trailer. During the entire trial, they were fed
chopped hay (7.5% CP). On d 0 of the trial (3/17/15), three cows
were subjected to Moderately Restricted (M; 110% > 55% > 110%)
and three cows were subjected to Restricted (R; 110% > 70% > 35%
> 70% >110%) feeding levels in four day increments:
4.2
O2 consumption (L min-1)
Methods
Background
R1
R2
R3
M1
M2
M3
3.5
R1
R2
R3
M1
M2
M3
R3
R1
R2
M2
M3
R1
R2
R1
2.8
M1
R2
M3
R3
R2
M3
R1
M1
R3
M2
M3
M1
M2
0
4
8
2.1
M2
R3
M3
M1
M2
M1
R2
R1
R3
120
1.4
If metabolic rates of beef cattle track
feeding level, ranchers may be
maintaining elevated metabolic
rates at great expense during winter.
20
1.0
60
-4
0
4
8
12
16
Day
Objective
Our objective was to determine if metabolic rates of beef cattle
track step-wise adjustments in feeding level.
Metabolic rates (based on O2 consumed) of all cows were
measured the morning following each four day feeding increment.
After placing a cow in the portable metabolic chamber, O2
consumed and CO2 respired were measured with a gas analyzer
(Field Metabolic System, Sable Systems, Inc. Las Vegas) for 30-40
minutes.
RQ (CO2 respired/O2 consumed)
Feeding level (%)
80
20
R1
R2
R3
M1
M2
M3
R1
M1
0.8
M2
M3
R2
M2
M1
M3
R3
R3
R1
R1
R2
R3
M1
M2
M3
R2
R1
R2
M2
R3
0.6
M3
M1
R2
R3
R1
M2
M3
M1
M3
12
16
R1
M2
R3
M1
R2
0.4
0
Concepts
4
8
20
Day
RESPIRATION - CHOS + O2 > CO2 + H20 and ENERGY!
Metabolic Rate (MR) is represented as the rate of O2
consumed in L min-1
For most cows, metabolic rates (based on O2 consumed) tracked
feeding levels in a step-wise manner. And as expected, RQs
declined as feeding levels were restricted indicating cattle were
catabolizing fat.
RESPIRATORY QUOTIENT (RQ)
RQ= CO2 respired/O2 consumed
RQs values vary based on diet components, feeding levels
and energy status of the animal.
RQ values
0.7
16
Day
Moderately restricted (M)
Restricted (R)
40
Fat
12
100
Protein
Carbohydrates
1.0
Ambient air was pulled through the chamber at 1,000 L min-1.
Oxygen and CO2 were sampled every second. Chamber measures
were alternated with ambient measures every 3-4 minutes to
determine O2 consumed and CO2 respired.
Overall, these results indicate that cattle entering winter in good
condition that graze rangeland may conserve energy by lowering
their metabolic rates, without impacting reproductive performance,
e.g., at the MAES Red Bluff Research Ranch.
References
1. Olson BE (1991) Winter grazing and feeding practices in Montana. Abstract. Society for
Range Management.
2. Olson BE, Wallander RT, Paterson JA (2000) Do windbreaks minimize stress on cattle
grazing foothill winter range? Can J Anim Sci 80:265-272
3. Meistig K, Tyler NJC, Blix AS (2000) Seasonal changes in heart rate and food intake in
reindeer (Rangifer tarandus tarandus). Acta Physiol Scand 170:145-153
4. Turbill C, Ruf T, Mang T, Arnold W (2011) Regulation of heart rate and rumen temperature
in red deer: effects of season and food intake. J Exp Biol 214:963-970
* Protocol was approved by Montana State University’s Institutional Animal Care and Use Committee (Protocol 2014-AA07).
* We thank A. Hicks-Lynch and V. Wilson for assisting with the study, and the Montana Agricultural Experiment Station and
Montana State University’s Undergraduate Scholars Program for funding.