Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/23/2009
Publication Date: 5/1/2009
Citation: Puchala, R., Tovar-Luna, I., Sahlu, T., Freetly, H.C., Goetsch, A. 2009. Technical Note: The Relationship between Heart Rate and Energy Expenditure in Growing Crossbred Boer and Spanish Wethers. Journal of Animal Science. 87(5):1714-1721.
Interpretive Summary: Providing the nutrients needed to grazing ruminants requires knowledge of their energy expenditure. Traditional methodologies used to measure energy expenditure require animals to be confined and, subsequently, measures may not reflect energy expenditure of grazing animals. Heart rate is correlated with energy expenditure of an animal and it has been proposed as a measure of energy expenditure of grazing ruminants. Researchers at the E (Kika) de la Garza Institute for Goat Research and the U.S. Meat Animal Research Center have determined factors that influence the use of heart rate as a measure of energy expenditure in goats. Dietary intake and time of day both influence the ratio of energy expenditure to heart rate. The use of heart rate to predict energy expenditure in grazing ruminants is potentially a viable methodology when external factors that affect the relationship are accounted for.
Technical Abstract: Eight Boer (75%) x Spanish (BS) and 8 Spanish (S) wethers (155 +/- 8 d of age and 19.2 +/- 2.3 kg BW, initial) were used in a replicated crossover design with a 2 x 2 factorial arrangement of treatments to determine effects of genotype, diet quality, and time of the day on energy expenditure (EE), respiratory quotient (RQ), heart rate (HR), and EE:HR with ad libitum, near maintenance, and fasting levels of feed intake. Diets were 65% concentrate and coarsely ground alfalfa hay. Energy expenditure ranked (P < 0.05) ad libitum > maintenance > fasting (500, 390, and 270 kJ/kg BW 0.75). The RQ was similar for the ad libitum and maintenance consumption levels (1.045 and 1.042, respectively) and was lowest during fasting (0.837; P < 0.05). Heart rate was similar between genotypes when fasting and with maintenance intake, but was greater (P < 0.05) for S vs BS when intake was ad libitum (BS: 55, 71, and 92; S: 52, 72, and 100 beats/min for fasting, maintenance, and ad libitum, respectively (SE = 2.0)). There was an interaction in EE:HR (P < 0.05) between level of feed intake and genotype (BS: 5.00, 5.59, and 5.31; S: 5.22, 5.57, and 5.07 kJ/kg BW 0.75:beats/min for fasting, maintenance, and ad libitum, respectively (SE = 0.13)), without an effect of diet. The effect of time on EE, RQ, HR, and EE:HR differed among levels of intake (P < 0.05). General patterns of change in EE, RQ, and HR as time advanced were similar, but increases near meals followed by decreases were of slightly greater magnitude for maintenance vs ad libitum intake. The ratio of EE:HR was greater for the maintenance level of feed intake than for ad libitum intake at most times. Magnitudes of differences in EE:HR among hours suggest desirability of determination over an extended period of time, such as 24 h. These results indicate similar potential for use of HR to predict EE of different genotypes of growing meat goats and that establishing EE:HR with different diets may not be crucial.