Ecological implications of bush encroachment on foraging behavior of dairy cows and goats at SUA farm, Morogoro, Tanzania

Ismail S Selemani

doi:10.17138/tgft(6)169-176

Abstract

The study was carried out at SUA Magadu Farm to investigate the influence of bush encroachment in a native rangeland on foraging behavior and grazing distribution of dairy cows and goats. Characterization of bush in terms of woody density was done using the PCQ method. A mixture of animals (150 cows and 60 goats) were rotationally grazed on areas with 3 different levels of bush encroachment (dense - 60%; moderate - 35%; and open grassland - ≤5%) and grazing behavior of 3 cows and 3 goats was monitored. Six trained observers recorded behavior of these animals for 2 hours in the morning and 2 hours in the afternoon for 9 days on a rotational basis. There were significant interactions between animal species in terms of grazing behavior and level of bush encroachment. Both species spent similar amounts of time grazing on open grassland (>75% of total feeding time) but on treatments with moderate and dense bush encroachment levels goats spent at least 70% of their time browsing, while grazing time of cows did not change. Goats took many more bites than cows on all treatments and as a result spent more time walking than cows. The implications of these findings for management of bush encroachment are discussed. Further studies on nutritive values and chemical composition of key forage species in the study area are recommended as well as the changes in behavior with different seasons and the impacts on animal production.

Highlights

Over the past 50 years the semi-arid savanna ecosystems throughout the world have suffered severe bush encroachment (Britz and Ward 2007; Kambatuku et al 2011), which is associated with the reciprocal competitive interaction between trees and grasses (Kambatuku et al 2011)
Range inventory using the Point Centered Quarter (PCQ) method established that the absolute densities of woody plants in thick bush, moderate bush and open grassland were: 608 ± 60.4; 355 ± 60.4; and 50.6 ± 60.4 trees/ha, respectively
Grazing was the major activity for cows in all situations and for goats in open grassland, while browsing was the main activity for goats in moderate bush and less so in thick bush

Summary

Introduction

Over the past 50 years the semi-arid savanna ecosystems throughout the world have suffered severe bush encroachment (Britz and Ward 2007; Kambatuku et al 2011), which is associated with the reciprocal competitive interaction between trees and grasses (Kambatuku et al 2011). Knowledge of the ruminant-woody plant interaction is most important for appropriate management of livestock and vegetation, in semi-arid savanna ecosystems (Thomas and Twyman 2004). Understanding the consequences of increasing bush encroachment on foraging behavior of dairy cows and goats is imperative for determining effective management strategies. To understand the ecological implications of woody encroachment on livestock performance and carrying capacity of rangeland, quantitative data on woody plant density and distribution in relation to how grazing animals respond to bush encroachment are required. There is limited information on foraging behavior of both dairy cows and goats in these situations, how they respond to spatial heterogeneity following bush encroachment

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Discussion

Conclusion