Energy expenditure of Angora goat does during the late trimester using the doubly-labelled water technique
C. A. Toerien1, T. Sahlu1, and W. W. Wong2
1E (Kika) de la Garza Institute for Goat Research, Langston, OK, and 2USDA/ARS Children's Nutritional Research Center, Houston, TX.
The double-labeled water (DLW) technique was used to compare CO2 production and energy expenditure (EE) of non-pregnant (NP) (31 ± 0.9 kg BW; n = 4) and pregnant (PREG; single fetus) Angora goat does (32 ± 3.1 kg BW; n = 4) for 10 d (130 ± 1 to 140 ± 2 d) in the late trimester of pregnancy. Animals were housed individually in metabolism crates. Diets for PREG and NP were 2.62 and 2.48 Mcal/kg DM of ME and 80.4 and 76.9 g/kg DM of metabolizable protein, respectively; DMI was greater (P < 0.01) for PREG (932 ± 47 g/d) than for NP (564 ± 7 g/d). After determination of baseline plasma isotope levels, does were infused into the jugular vein with 2H218O, providing 200 mg 2H and 250 mg 18O/kg BW for NP and 250 mg 2H and 300 mg 18O/kg BW for PREG. Isotopic estimates were performed at 6 h post-infusion and at 2- to 4-d intervals. The 2H and 18O dilution spaces were calculated using the multi-point model, and isotopic estimates of 2H2O and H218O fluxes were corrected for isotope losses in feces and methane (2H) and products of gestation (2H and 18O). Fiber growth rate (g/d) was determined from a mid-side patch sample extrapolated to whole-body production, and energy expended on mohair production (EEmoh) was calculated as 10.95 kcal ME/(g d-1). In NP, maintenance EE (EEm) was assumed to be total DLW-derived EE (TEE) - EEmoh. Energy expended for pregnancy (EEp) was similarly assumed to be TEE - EEmoh - EEm. Ratios of isotope distribution spaces (ND/NO) for NP (1.043 ± 0.013) and PREG (1.029 ± 0.012) were acceptable, and kid birth weight (3 ± 0.1 kg) was similar to that of the main herd (2.9 ± 0.1 kg; n = 33). The EEm for NP was 98.4 ± 3.8 kcal ME/(kg BW0.75 d-1). Fiber production and diameter were lower (P < 0.05) for PREG (5.5 ± 0.8 g/d and 31.4 ± 1.3 m, respectively) than for NP (11 ± 1.1 g/d and 37.1 ± 1.8 m, respectively). The EEp for PREG was 65.2 ± 13.6 kcal ME/(kg BW0.75 d-1). In conclusion, pregnancy suppressed mohair production and elevated whole-body energy expenditure to approximately 1.67 times that for maintenance.
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