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Heat production by Alpine, Angora, Boer, and Spanish wether goats consuming different quality diets at a maintenance level of intake

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

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

Six Alpine (AL; 38.4 ± 3.0 kg), Angora (AN; 23.1 ± 2.7 kg), Boer (BO; 40.75 ± 4.5 kg), and Spanish (SP; 33.6 ± 2.16 kg) wethers (1.5 yr of age) were used to determine effects of genotype and diet quality on heat production (HP) when fed near maintenance and fasting. The experiment consisted of four simultaneous crossovers, with 21 d for adaptation before measures. Diets were 60% concentrate (CON: 14% CP and 12.04 MJ ME/kg DM) or ground alfalfa hay (HAY: 18% CP and 10.17 MJ ME/kg DM). Heat production was determined from O2 consumption and production of CO2 and CH4 with a head-box respiration calorimetry system (Sable Systems, Las Vegas, NV), along with urinary N excretion, over 2-d periods in fed and fasting states (4-d fast). Heat production was expressed on the basis of average BW during HP measurement periods. There were no interactions between genotype and diet. Intake of ME was similar among genotypes and between diets. Neither diet (358 and 354 kJ/kg BW0.75 for CON and HAY, respectively; SE = 5.7) nor genotype (359, 361, 346, and 358 kJ/ kg BW0.75 by AL, AN, BO, and SP, respectively; SE = 8.8) influenced fed HP (P > 0.10). Fasting HP was similar between diets but was greatest among genotypes (P < 0.05) for AL (253, 227, 219, and 226 kJ/ kg BW0.75 by AL, AN, BO, and SP, respectively; SE = 7.25), which may have been due to a greater level of activity exhibited by AL than other genotypes during fasting. Efficiency of utilization of ME for maintenance was similar (P > 0.10) between diets (0.68 and 0.67 for CON and HAY, respectively; SE = 0.01). The ME requirement for maintenance, estimated by regressing HP against ME intake, was similar (P > 0.10) between diets (341 and 346 kJ/kg BW0.75 for CON and HAY, respectively; SE = 10.5) and among genotypes (352, 354, 321, and 346 kJ/kg BW0.75 for AL, AN, BO, and SP, respectively; SE = 14.8). In summary, with a level of intake near maintenance, the energy need for maintenance appears similar for AL, AN, BO, and SP 1.5 yr-old wethers goats regardless of diet quality.


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