Plasma metabolites and nitrogen balance in Lama glama associated with forage quality at altitude

This study evaluated the effects of forage quality on blood metabolites and nitrogen balance in mature, intact male llamas (n = 4, 36 ± 4.4 months, 87 ± 17 kg) at high altitude (4267 m Letanias, Bolivia). Llamas were randomly fed barley hay (B), 80% barley/20% alfalfa hay (BA) and fresh cut grass pasture (P). Animals were housed in metabolism crates and diets were fed for a 7-day adjustment period followed by a 5-day collection period. Feed, feed refusal, feces and urine were collected, dried and N content determined by combustion analysis. Venous blood samples were collected on day 12 at 30 min intervals over a 6 h period. Plasma was harvested and analyzed for electrolytes (Na, K, Cl, Ca, Ca2+, P, Mg) and metabolites (glucose, NEFA, urea N, creatinine, albumin, total protein (TPP), osmolality (Osm)). Plasma electrolytes (Na, K, Mg, P, Cl) and metabolites (glucose, Osm, albumin, creatinine, TPP) were unaffected by forage treatment. Dry matter digestibility was greater for the B and BA than P forage, and N digestibility was significantly higher for BA than either the B or P forages. Nitrogen balance varied significantly between diets. N intake was significantly different between each diet (P < 0.0001), with B having the least N (7.1 g/day), followed by P (14.4 g/day) and BA (19.0 g/day), which provided the most N. Urine N excretion was similar between P (7.7 g/day) and BA (10.6 g/day), similar between P (7.7 g/day) and B (6.2 g/day), but was different (P < 0.04) between B (6.2 g/day) and BA (10.6 g/day). Fecal N excretion was similar between BA (7.4 g/day) and P (8.9 g/day). Both of these treatments produced significantly higher quantities of fecal N than B (4.1 g/day; P < 0.0004). Nitrogen excretion followed the same trend as N intake. Total N excretion was highest in BA followed by P and B forages. Llamas were in negative N balance on the B and P diets. Llamas had an estimated daily maintenance requirement value of 0.58 g crude N/W0.75 and a daily maintenance requirement of 106.2 g CP/day. Mineral intake varied significantly between diets. Overall, pasture provided higher amounts of minerals than the barley forages, except for copper, phosphorus and zinc. These data demonstrate the effects of feeding forages of varying quality on whole-body N utilization, and trends in blood metabolite and electrolyte patterns in llamas at altitude.