Nitrogen balance and blood metabolites of alpaca (Lamapacos) fed three forages of different protein content

Sixteen intact male alpaca consisting of four age groups (AG1, 16 ± 4.4 months, 44.3 ± 9.2 kg; AG2, 25 ± 1.8 months, 51.7 ± 2.3 kg; AG3, 35 ± 1.1 months, 64.7 ± 15.6 kg; and AG4, 60 ± 12.0 months, 67.0 ± 8.2 kg) were housed in metabolism crates (20 °C with 12:12 h on:off light cycle). Three forages, straw (ST), grass hay (GH) and alfalfa (ALF) were fed to each alpaca in random order. The forages were fed at 12 h intervals with water provided ad libitum. Treatment periods were 14 days, with blood samples collected over a 24 h period on day 14 to determine temporal patterns of plasma metabolite and electrolytes. Dry matter intake was lower (P < 0.002) for ST at 212 g/day, while GH and ALF were 678 and 715 g/day, respectively. Nitrogen intake was 2.2, 14.7 and 23.9 g/day (P < 0.002), respectively. Fecal N was 1.5 for ST, 4.8 for GH, and 5.1 g/day for ALF (P < 0.002). Urine N excretion was 6.3 and 6.2 g/day for ST and GH, increasing to 13.6 g/day for ALF (P < 0.02). Nitrogen retained was −5.4, 3.7 and 5.2 g/day for ST, GH and ALF, respectively, with an age and diet × age response (P < 0.01 and 0.05, respectively). Plasma glucose was not different for forage or age, averaging 7.6 mmol/L. Lactate was lowest for GH (0.70 mmol/L), with ST and ALF having similar concentrations (0.87 and 0.96 mmol/L; P < 0.07). NEFA concentrations were highest for ST (398 μmol/L) and similar for GH and ALF (204 and 201 μmol/L; P < 0.003). Plasma urea N concentrations were similar for ST and GH (4.3 and 4.9 mmol/L) increasing to 8.1 mmol/L for ALF (P < 0.001). Plasma creatinine was higher for ST (250 μmol/L) than GH and ALF (214 and 205 μmol/L; P < 0.0001). Sodium and calcium concentrations were lower for ST than GH and ALF (P < 0.06 and 0.002, respectively), while potassium and chloride were not different across forages. Metabolite temporal patterns fluctuated over the 24 h period with glucose, lactate, and α-amino N increasing and NEFA concentration decreasing postprandially. Crude N maintenance requirement was calculated to be 0.84, 0.63, 0.80 and 0.51 g/W0.75 for AG1, AG2, AG3 and AG4, respectively. Overall N requirement was calculated to be 0.60 g/W0.75. These data demonstrate the effects of feeding forages of varying quality on whole-body N utilization, temporal blood metabolite and electrolyte patterns and a possible age effect on maintenance N requirements.