Factors influencing urea space estimates in goats

A. Asmare¹, L. J. Dawson², R. Puchala¹, T. A. Gipson¹, M. Villaquiran¹, I. Tovar-Luna¹, G. Animut¹, T. Ngwa¹, R. C. Merkel¹, and A. L. Goetsch¹

¹E (Kika) de la Garza American Institute for Goat Research, Langston University, Langston, OK, ² College of Veterinary Medicine, Oklahoma State University, Stillwater

Female Alpine goats, 18 approximately 17 mo of age (yearling) and 18 5-mo-old (growing), were used to determine effects of animal age, urea dose (100, 130, and 160 mg/kg BW), and time without feed and water (shrink; 0, 16, and 24 h) on urea space estimates. A 20% (wt/vol) urea solution was infused into a jugular vein, with blood sampled before infusion and every 3 min to 21. BW was 49.8, 47.4, and 47.0 kg for yearlings and 26.1, 24.6, and 23.9 kg for growing animals after 0, 16, and 24 h shrinks, respectively (SE = 0.80). Time of urea equilibration with body water, determined by a grafted polynomial quadratic-linear model, was affected by a dose x age x shrink interaction (P < 0.05); yearling means did not differ (ranging from 7.3 to 10.8 min), although those for growing animals were greater (P < 0.05) for 0 h-130 mg (13.0 min) and 24 h-130 mg (13.2 min) compared with 24 h-100 mg (7.6 min) and 16 h-130 mg (7.1 min). Based on these times, 12-min samples were used to determine urea space. Urea space was influenced by an age x shrink interaction (P < 0.05), being similar among shrinks for yearlings (17.8, 18.8, and 18.9 kg) and greater (P < 0.05) for growing animals after 0 than 24 h shrink (12.9, 11.3, and 10.0 kg for 0, 16, and 24 h, respectively). Hemoglobin concentration in plasma, as an index of hemolysis, was greater (P < 0.05) for growing than for yearling animals (1.16 vs 1.86%), lowest among doses (P < 0.05) for 100 mg (1.05, 1.74, and 1.75% for 100, 130, and 160 mg, respectively), and highest among shrinks (P < 0.05) for 24 h (1.46, 1.42, and 1.61% for 0, 16, and 24 h, respectively). In conclusion, 13 min after infusion appears a reasonable sampling time for determining urea space in goats. Shrink time may have greater effect on urea space with growing vs older goats, and 24 h of shrink or at least 16 seem desirable before estimating urea space. Urea space estimates were similar with urea doses of 130 and 160 mg, and a lower dose such as 100 mg, though lessening hemolysis, can allow relatively greater effect of shrink time on urea space.