The role of a cleft upper lip of alpacas in foraging extremely short grasses evaluated by grazing impulse

The role of a cleft upper lip of alpaca (Lama pacos) in foraging short pastures was investigated using biting forces and associated impulses in animal grazing. Three Merino wethers and three castrated alpacas were used. Ten (10L), 20 (20L), 30 (30L), 40 (40L) or 50 (50L) leaves of orchardgrass (Dactylis glomerata) per load cell were offered to animals, and three-directional biting forces were digitally recorded at 5 s−1000. From the total biting force/time curve, grazing impulse was calculated, equivalent to the area surrounded by the curve. The grand mean of the number of grazed leaves per bite was 9.8 ± 0.53 in alpaca and 17.9 ± 1.31 in sheep. Remaining leaf length after grazing trial was significantly lower in alpaca than in sheep (11.9 ± 0.19 mm versus 18.5 ± 0.41 mm). Alpaca grazed leaves with significantly lower mean biting force (7.0 ± 0.69 N versus 20.0 ± 1.80 N) and significantly shorter duration time per one biting force (0.11 ± 0.005 s versus 0.18 ± 0.19 s) than sheep. The grand mean of sum of grazing impulse was lower (P < 0.002) in alpaca (2.8 ± 0.42 N s) than in sheep (9.4 ± 1.95 N s). Grazed DM weight increased with increasing leaf densities, but there was no difference between alpaca and sheep. The ratio of DM intake to grazing impulse was significantly higher in alpaca than in sheep (0.18 ± 0.016 g DM/N s versus 0.08 ± 0.010 g DM/N s). The grazing strategy in alpaca seems to be an adaptation for foraging extremely short grasses. Alpacas may push aside cleft upper lips when trying to grasp short leaves, resulting in keeping incisors at lower insertion position near the ground surface