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Effects of genotype, diet, and feed intake on the relationship between energy expenditure and heart rate in goats

R. Puchala , I. Tovar Luna, A. L. Goetsch, and T. Sahlu

E (Kika) de la Garza American Institute for Goat Research, Langston University, Langston, OK

Heart rate (HR) holds promise as an indirect means of estimating energy expenditure (EE) by ruminants. Therefore, an experiment was conducted to determine effects of genotype, diet, and feed intake on the ratio of EE:heart rate in yearling wether goats. Six Alpine (41 ± 6.3 kg), Angora (23 ± 4.0 kg), 7/8 Boer (39 ± 4.4 kg), and Spanish (36 ± 1.3 kg) wethers (1.5 yr of age) were fed chopped alfalfa hay (18% CP and 10.2 MJ ME/kg DM) or a 60% concentrate diet (14% CP and 12.0 MJ ME/kg DM) at a level of intake near maintenance followed by a 4-d fast in a crossover design experiment. Energy expenditure was measured in a head box respiratory calorimetry system (Sable System, Las Vegas, NV) based on O2 consumption and production of CO2 and CH4 with the Brouwer equation in 2-d periods while being fed and at the end of fasting. To monitor HR, stick-on ECG electrodes were attached to the chest just behind and slightly below the left elbow and at the base of the jugular groove on the right side of the neck. The human S610 HR monitor (Polar Electro, Woodbury, NY) was used to record HR at 1- min intervals. Heart rate per minute was affected by level of intake (60.7 and 38.9 for maintenance and fasting, respectively; SE = 0.9; P < 0.05) and a genotype x feed intake interaction (maintenance: 60.8, 63.6, 59.0, and 59.2; fasting: 42.1, 39.6, 38.3, and 35.6 for Alpine, Angora, Boer, and Spanish, respectively; SE = 1.7; P < 0.05). The ratio of daily EE (kJ/kg BW0.75) to average HR per minute was not affected by genotype (6.01, 5.72, 5.87, and 6.24 for Alpine, Angora, Boer, and Spanish, respectively; SE = 0.22), diet (5.96 and 5.96 for hay and concentrate, respectively; SE = 0.13), level of intake (5.90 and 6.01 for maintenance or fasting, respectively; SE = 0.13), or their interactions. The absence of these effects on EE:HR suggest potential use of HR to estimate EE by goats.


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