Bite dimensions for cattle grazing herbage at low levels of depletion

Abstract

The processes that occur during the depletion of a single feeding station by grazing cattle are important to our understanding of intake at larger spatial scales. Factorial experiments were conducted in which feeding stations of different sizes were grazed individually by cattle to various levels of depletion, defined as the number of bites removed. Feeding stations in Experiment 1 (alfalfa) measured 0·11, 0·24 and 0·45 m2, and the numbers of bites removed for depletion levels 1–3 were 35, 70 and 104 m−2 respectively. Feeding stations in Experiment 2 (oats) measured 0·11 and 0·24 m2, and the numbers of bites were 45, 95 and 140 m−2 offered. In both experiments a fourth depletion level (not included in the analysis of variance) determined the maximum voluntary depletion, and exceeded 250 bites m−2 offered. Initial sward height was 20 cm. Bite dimensions were derived from the frequency distribution of residual herbage heights. Treatments were replicated over six and four animals of approximately 500 kg live weight in Experiments 1 and 2 respectively. The mean residual herbage height and the frequency distribution of residual heights indicated that bites were removed predominantly from the top grazing horizon at depletion levels 1–3, with a mean effective bite depth of 8·6 cm. Nevertheless, at the same depletion levels, the mean effective bite area declined from 148 to 87 cm2 in Experiment 1 (alfalfa, Medicago sativa L.) and from 86 to 58 cm2 in Experiment 2 (oats, Avena sativa L.). Feeding station size did not significantly affect mean effective bite area in either experiment. Simulation was used to examine the implications of various overlap rules (from completely random to highly systematic) for within‐grazing‐horizon placement of a circular bite of constant potential area. These rules shaped the relationship between mean effective bite area and number of bites removed per unit sward area offered. Bite placement in which permissible overlap became progressively more lenient as the grazing horizon was depleted, and, with acceptable estimates of potential bite area, yielded results that were similar, though not identical, to those measured. These results can help understanding of the factors that determine the intake gain function at a single feeding station.

The horizontal barrier effect of stems on the foraging behaviour of cattle grazing five tropical grasses

“…In vegetative swards, bite area was not related to sward height which disagrees with previous studies where bite area increased with sward height (Cangiano et al, 2002;Flores et al, 1993;Laca et al, 1992;Ungar et al, 2001). In tall swards the animal can fully exploit the benefits of the tongue sweep movements to gather forage and thus the animal can achieve the maximum bite area.…”

“…The lack of response of bite area to sward height in vegetative swards in the current work can be explained in part by the relatively small body mass of the animals used in this experiment, whose bite area is less sensitive to the increase in sward height than that of bigger animals (Gordon 1987), and by the significant correlation between sward height and grazing resistance (r = 0.88, P b 0.001). Therefore, the positive relationship between bite area and sward height (Cangiano et al, 2002;Flores et al, 1993;Laca et al, 1992;Ungar et al, 2001) could have been compensated by the negative relationship between bite area and sward grazing resistance (Illius et al, 1995) resulting in the observed lack of effect of sward height on bite area of the current experiment.…”

Defoliation patterns and their implications for the management of vegetative tropical pastures to control intake and diet quality by cattle

“…Selective grazing occurs where, independently of pasture condition, cattle prefer the more nutritious and easily ingested top stratum of the pasture before consuming the lower strata that impose a greater restriction on bite dimensions, have a lower diet quality and thus lower potential intake rate (Chacon and Stobbs, ; Hendricksen and Minson, ; Ungar and Ravid, ; Ungar et al ., ). We hypothesize that daily forage intake and diet quality would significantly decrease when the top grazing stratum is removed across the entire area of the pasture.…”

“…We hypothesize that daily forage intake and diet quality would significantly decrease when the top grazing stratum is removed across the entire area of the pasture. While some studies have measured the level of depletion of grazing strata at the feeding‐station level (Ungar and Ravid, ; Ungar et al ., ), the extrapolation of the results of these studies to the paddock level is limited by the ability of the animals to compensate for a reduction in instantaneous intake rate by increasing grazing time. Despite previous studies on tropical pastures demonstrating the effect of green leaf herbage mass on forage intake at the paddock level (Chacon and Stobbs, ; Hendricksen and Minson, ), there are no measurements of the level of depletion of the grazing strata.…”

Sward structure management for a maximum short‐term intake rate in annual ryegrass

“…Wade, ; Carrere et al ., ; Cangiano et al ., ; Benvenutti et al ., ; Goncalves et al ., ). The bite area is reduced as the sward is grazed down because of access to parts of the plant with a higher proportion of stems (Ungar et al ., ). Therefore, the bite mass decreases as the sward height is grazed down because of the combination of a smaller bite area (Ungar et al ., ) and reduced absolute bite depth (Laca et al ., ; Benvenutti et al ., ).…”