Do Movement Patterns of GPS-Tracked Cattle on Extensive Rangelands Suggest Independence among Individuals?

Mitchell Stephenson,Derek Bailey

doi:10.3390/agriculture7070058

Mitchell Stephenson, Derek Bailey

Open Access

https://doi.org/10.3390/agriculture7070058

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Abstract

In behavioral studies, cattle within the same pasture are not considered as independent experimental units because of the potential confounding effects of the herd’s social interactions. However, evaluating cattle behavior on extensive rangelands is logistically challenging for researchers, and treating individual animals as independent experimental units may be beneficial for answering specific research questions. The objective of this study was to evaluate the association patterns among global positioning system (GPS)-tracked cattle at six different study sites in the western United States. A Half-Weight Index (HWI) association value was calculated for each pair of GPS-tracked cows (i.e., dyad) to determine the proportion of time that cattle were within 75 m and 500 m of each other. Cattle at two study sites exhibited relatively low mean HWI-association values (i.e., less than 0.23 HWI); whereas, cattle at other study sites tended to have greater mean HWI associations (i.e., greater than 0.35 HWI). Distinguishing features between study sites with low and high association values were the management of cattle prior to the study, herd size, pasture size, and the number of watering points. However, at all ranches except one, at least 75% of all dyadic associations had HWI values of less than 0.5 at 500 m, indicating that most of the GPS-tracked cows were greater than 500 m from each other for over 50% of tracking period. While interactions among cattle in the same pasture are often inevitable, our data suggests that under some situations, movement patterns of a sub-set of individual GPS-tracked cows may have levels of independence that are sufficient for analysis as individual experimental units. Understanding the level of independence among GPS-tracked cattle may provide options for analysis of grazing behavior for individual cattle within the same pasture.

Highlights

The use of Global Positioning System (GPS) collars has allowed us to make great strides in our understanding of livestock behavior and distribution patterns of animals across diverse landscapes [1,2,3,4,5]
Use of individual animals as the experimental unit for statistical inference in GPS-tracking livestock studies depends on the experimental design of the study and the characteristics of the pasture, herd, and previous management of cattle
While interactions among cattle in the same pasture are often inevitable, our data suggests that many dyadic associations within a random or semi-random sub-set of GPS-tracked cattle may be predominantly independent of each other, or it at least can be argued that associations among some dyads would have minimal influence on the behaviors of each other

Summary

Introduction

The use of Global Positioning System (GPS) collars has allowed us to make great strides in our understanding of livestock behavior and distribution patterns of animals across diverse landscapes [1,2,3,4,5]. The ability to collect large amounts of tracking data with the use of GPS collars has often complicated experimental designs and statistical analyses. Two major statistical problems that arise from GPS tracking data are auto-correlation of consecutive positions from an individual animal and failure to achieve independence among multiple GPS-tracked animals within the same pasture or herd [5,6]. Several studies have evaluated the effect of auto-correlated data with the use of GPS- and radio telemetry-tracked livestock and wildlife [7,8,9]. Fewer studies have evaluated factors that may influence the level of independence exhibited among individual GPS-tracked cattle within the same pasture

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