Quantifying short-term foraging behavior of cattle grazing a tall grass: A preliminary study with maize

Abstract

Relatively little information is available on foraging behavior of animals grazing tall grasses (> 1 m tall) despite extensive works on grasses as a sward (< 0.3 m tall). This study investigated short-term foraging behavior of cattle grazing maize ( Zea mays L.) plants to quantify how animals exploit a tall grass in terms of jaw movement and dry matter (DM) intake. In the feeding tests, Japanese Black cows (1 animal in each test) were allowed to graze a maize plant erected at the center of an arena (6 m × 6 m). Each plant was prepared to have 8 leaves of full- or half-size (trimmed to the half-length). The mass of leaves removed by the animals was estimated based on the size (length × width)–weight and defoliation length–weight relationships in individual leaves on the stem. The cows foraged the maize plants at similar rates of jaw movement for the full- and half-size leaves (60.6 vs. 63.2 cycles min − 1 , respectively). The number of jaw movements allotted per leaf was significantly greater for the full-size leaves than for the half-size leaves (9.3 vs. 6.9 cycles leaf − 1 ), reflecting the difference in leaf mass (4.20 vs. 2.76 g DM leaf − 1 ). The cows grazed mainly lower leaves at the initial stage of feeding and progressively shifted to upper leaves. They seized a full-size leaf by the proximal or mid part for ease of prehension, and seized a half-size leaf by the mid or distal part because of higher accessibility. Furthermore, the cows were able to process more than 1 leaf by a single jaw movement. Both intake per jaw movement (0.43 vs. 0.35 g DM cycle − 1 ) and intake rate (26.0 vs. 22.3 g DM min − 1 ) were similar for the full- and half-size leaves, which was attributed to the fact that the half-size leaves were still long (45.9 ± 1.0 cm) and broad (10.2 ± 0.1 cm as the maximal width) enough to ensure bite mass comparable to that from the full-size leaves. The results show that cattle have the ability to forage a tall grass efficiently by controlling the allotment of jaw movements among the leaves on the stem and among the positions within the individual leaves. At the same time, the results suggest that harvesting by cattle of a tall grass is potentially less efficient than that of a tall, dense grass sward.