Abstract
Short-term grazing behavior variables are sensitive to the canopy structure and have an impact on daily forage intake. This study evaluated the effect of pre- and post-grazing canopy heights on the forage harvesting process at a patch scale in a mixture of Brachiaria brizantha (Hochst. ex A. Rich.) Stapf. syn. Urochloa brizantha R.D. Webster cv. Marandu (palisade grass) and Arachis pintoi Krapov. & W.C. Greg. cv. Belomonte (forage peanut). Treatments were allocated to a split-plot arrangement in a completely randomized design. The plots, in their entirety, consisted of two pre-grazing canopy heights: 25 cm (CH25) and 35 cm (CH35); subplots consisted of three levels of defoliation severity: no defoliation (DS0); 20% depletion of pre-grazing canopy height (DS20); and 40% depletion of pre-grazing canopy height (DS40), with eight replications. Heifers were allowed to graze the patches (0.7 × 0.7 m) and their grazing behavior was recorded. Canopy structure measurements were taken both before and after grazing. Patches from CH35 presented greater stem mass for grass (p = 0.001) and legume (p = 0.002) than did patches from CH25. Bite rate, bite mass and instantaneous intake rate were greater for CH25 than for CH35 (p < 0.001, p = 0.068, and p = 0.074), and bite mass and instantaneous intake rate were lower for DS20 compared to DS0 (p = 0.032 and p = 0.016). Greater stem mass in the grazing strata negatively influenced the instantaneous intake rate.
Highlights
The canopy structure is continuously changing as a result of plant growth, defoliation, and senescence (Mezzalira et al, 2014)
Bite mass and instantaneous intake rate were greater for CH25 than for CH35 (p < 0.001, p = 0.068, and p = 0.074), and bite mass and instantaneous intake rate were lower for DS20 compared to DS0 (p = 0.032 and p = 0.016)
Two pre-grazing canopy heights (CH) were studied in the whole plot: 25 (CH25) or 35 cm (CH35). These pregrazing heights were chosen drawing on the results of Gomes et al (2018), in which CH25 corresponded to light interception between 90 and 95 %, and CH35 corresponded to maximum light interception
Summary
The canopy structure is continuously changing as a result of plant growth, defoliation, and senescence (Mezzalira et al, 2014). It modulates forage harvesting during the grazing process (Benvenutti et al, 2016). Ungrazed canopies facilitate forage harvesting; forage prehension by grazing livestock throughout the occupation period mainly in tropical grass gradually becomes increasingly difficult. Short-term grazing behavior variables are sensitive to the canopy structure and have a pronounced impact on daily forage intake (Carvalho et al, 2015). There is a progressive reduction in short-term intake rate and bite volume (Fonseca et al, 2012; Fonseca et al, 2013), which can result in a reduction in daily herbage intake
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