Title: Forage consumption by cattle in kikuyu grass pastures under intermittent stocking.

 

Abstract: Herbivores exhibit a complex pattern of interaction with the pastoral environment, making plant-animal interface a cause-and-consequence event between pasture structure and ingestive behavior. In this way, grazing management generates different structures before and throughout stocking, so that different grazing patters can be observed, affecting the daily intake level. The aim of this work was to investigate the relationships between forage canopy structure generated by grazing management strategies and foraging parameters by cattle. Two complementary experiments were conducted between December 2012 and June 2014 in kikuyu grass pastures. An initial trial (experiment I) was performed to evaluate daily forage intake by cattle grazing pastures at different pre-grazing heights (10, 15, 20 and 25 cm) provided the same level of defoliation (removal of 50% of pre-grazing height). Once defined the pre-grazing height which supposedly would not limit intake (25 cm), a second test (experiment II) was performed to evaluate the effect of different levels of defoliation (40, 50, 60 e 70%) provided the same pregrazing height. The experimental design was a complete randomized blocks with 4 treatments and 3 repetitions, totalizing 12 experimental units of approximately 1500 m² each one. The grazing heights were monitored by sward stick at 50 random points per evaluation. The following variables were analyzed: i) morphological composition, forage mass and bulk density (stratified during pre-grazing evaluations according to treatments); ii) daily forage intake (determined during experiment I by n-alkanes technique and by disappearance in experiment II); iii) grazing behavior (grazing, rumination, and idling times; number, bites, and time per feeding station; steps between feeding stations; biting rate; being evaluated only during experiment II). The data were submitted to analysis of variance and the linear, quadratic, and cubic trend were analyzed by polynomial orthogonal contrasts (except daily dry matter intake data from experiment I, which was compared by Tukey test). A significance level of 5% was adopted to all evaluations. In a general way, daily forage intake was reduced according to pregrazing height reductions (experiment I; P = 0,032) or level of defoliation increments (experiment II; linear effect; P = 0,02). These responses were attributed to structures generated before and throughout the grazing period, and an apparent unwillingness of animals to accommodate grazing restrictions by behavioral adjustments. Inferences were discussed taking in account grazing management flexibilities in intermittent stocking management.

 

Keywords: Pennisetum clandestinum; pre-grazing height; level of defoliation; displacement pattern; grazing behavior.

 

Author: Daniel Schmitt

Leader: André Fischer Sbrissia

Thesis (Doctors in Animal Science)