Abstract
The efficiency of grazing ruminant production systems is directly associated to the animals' ingestive behavior, and to structural characteristics of the pastures. The objective of this study was to evaluate the ingestive behavior of young lambs grazing three different heights of Capim Aruana (Panicum maximum). The experiment was carried out in two consecutive years, in which 30 tester lambs (4–5 months old) were equally divided into three paddocks (treatments) corresponding to different average sward heights of Aruana grass: (1) Tall-75 cm; (2) Medium-50 cm; and (3) Short-25 cm in a randomized block design. Ingestive behavior assessments were carried out every 28 days through 10-min observations of the main activities of the animals (grazing, ruminating, idling) and biting rate, from sunrise to sunset. In addition, the productive and qualitative characteristics of the pastures were assessed. Despite differences in pasture structure, grazing time (GT) and idling time were similar among treatments (P = 0.4266 and P = 0.2939, respectively). The shortest ruminating time (RT, P = 0.0181) was recorded in the treatment of lowest sward height. Lambs grazing on this treatment also showed 23% more bites per minute (P= < 0.0001) than animals in the Tall and Medium treatments. A Decision Tree analysis was performed for GT, identifying in a hierarchical order that the initial weight of the animals and sward height explained 62% (R2 = 0.621) of the variation, representing the variables with the greatest influence on GT. Initial body weight explained 48% of the model. Thus, our research shows that the different sward heights of Capim Aruana mainly alter the lamb's RT and biting rate, and that the animals' initial body weight is a key factor influencing GT, given that this variable makes lambs more susceptible to changes in sward height.
Highlights
Pasture production systems represent a significant opportunity for increasing the sustainable production of ruminant animals worldwide
There was an interaction between treatment and period (P = 0.0049) in relation to biting rate, in which the Short treatment had
This experiment shows that young lamb grazing an upright tropical grass do not vary their grazing time (GT) due to the different sward heights, contrasting with what was discussed by Hodgson [9]
Summary
Pasture production systems represent a significant opportunity for increasing the sustainable production of ruminant animals worldwide Under this scenario, animal performance depends of sward attributes such the quality and quantity of forage harvested during the grazing process [1]. Sheep are highly selective animals, a trait that differentiates them from other, larger herbivores [2] This characteristic of selectivity inherent to the species is even more important in young lambs, as they progress through complex feeding periods and behavioral transitions. Lambs are positioned at an optimal point on their growth curve, as they display high levels of intake and performance rates during this period [3] Because of these specific characteristics, it is necessary to understand the ingestive behavior of animals during this critical period, as it is one of the aspects that determines performance. According to Silva et al [6] the structural characteristics of forage plants directly interfere with the ingestive behavior and performance of grazing animals, which, in turn alter the morphological (height, mass, and density) and physiological (photosynthetic rate and phenological stage) characteristics of the forage canopy, modifying subsequent animal and plant responses to grazing
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