Animal performance and sward characteristics of Mombaça guineagrass pastures subjected to two grazing frequencies

Cristiane A.F Alvarenga,Valéria P.B Euclides,Denise B Montagner,André F Sbrissia,Rodrigo A Barbosa,Alexandre R De Araújo

doi:10.17138/tgft(8)1-10

Abstract

The aim of this work was to compare grazing management practices of Mombaça guineagrass (Megathyrsus maximus syn. Panicum maximum cv. Mombaça) based on the sward incident light interception (LI) concept. We tested, when the regrowth period in rotationally stocked Mombaça guineagrass ended, if LI (90 or 95%) affected forage accumulation, sward characteristics and animal performance. Both treatments had a common post-grazing canopy height of 50 cm and were replicated 4 times in a randomized complete block design. Pastures were sampled pre- and post-grazing to determine forage mass, morphological composition and forage accumulation rate (FAR). Nutritive value (NV) was estimated in pre-grazing samples. Stocking rate was adjusted twice a week, and animals were weighed every 28 days. Pre-grazing conditions of 90 and 95% LI were reached at pasture heights of approximately 80 and 90 cm, respectively. FAR, sward structure and NV were similar for pastures grazed at 90 and 95% LI. Consequently, stocking rate, average daily gain and liveweight gain/ha were similar for both LI treatments. Data suggest that Mombaça guineagrass can be grazed at pre-grazing heights of 80–90 cm (90–95% LI) without compromising pasture structure and animal performance provided moderate defoliation severity is employed. Further testing of this grazing strategy over longer periods should be carried out with this species as well as other tropical grasses.

Highlights

Some studies with tropical grasses under intermittent stocking have shown that the point at which the canopy intercepts 95% of photosynthetically active radiation (PAR) approximates an ideal time period to interrupt regrowth
Pastures grazed at 95% light interception (LI) had longer rest and grazing periods, greater pre-grazing sward heights, forage mass, green stem (GSP) and dead material (DMP) percentages, plus fewer grazing cycles with lower green leaf percentages (GLP) and leaf:stem ratios (LSR) than those managed at 90% LI (Table 1)
LI had no significant effect on forage accumulation rates (FAR; P = 0.248) and leaf accumulation rates (P = 0.085)

Summary

Introduction

Some studies with tropical grasses under intermittent stocking have shown that the point at which the canopy intercepts 95% of photosynthetically active radiation (PAR) approximates an ideal time period to interrupt regrowth After this point, forage accumulation and nutritive value decrease (Carnevalli et al 2006; Barbosa et al 2007; Zanini et al 2012) as proportions of stem and dead material in pregrazing forage mass increase (Silva et al 2009). Parsons et al (1988) demonstrated that, regardless of variation in management, there was a range in level of interception of PAR by the canopy in which forage production remained relatively stable In this context, Barbosa et al (2007) and Zanine et al (2011) found no difference in the accumulation of leaf blades of guineagrass (Megathyrsus maximus) cv. This suggests there could be some flexibility in the definition of pre-grazing targets, i.e. instead of a specific point there could be a range of possible values

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