Abstract
Pasture-based dairy systems rely on the accurate allocation of pasture to both meet livestock requirements and maintain the growth of herbage. Currently, physical fences are used to contain livestock however they can be labor-intensive to shift and maintain. Alternatively, virtual fence (VF) systems offer flexibility and real-time control of livestock location. Pre-commercial neckbands (eShepherd®, Agersens, Melbourne, VIC) emit a warning audio tone (AT) when a cow approaches a VF boundary, paired with an electrical pulse (EP) if the cow continues forward into the exclusion zone (EZ). However, the ability of VF technology to control animal location when pasture is restricted to the previous day's residual, remains unknown. Ten non-lactating Holstein-Friesian dairy cows were trained to use a VF system for 6 days before strip grazing a 1.2 ha paddock of annual ryegrass. Over 10 days the cows grazed eight pasture allocations at a pre-grazing pasture mass of 2,324 ± 81 kg DM/ha (mean ± SE) and post-grazing pasture-mass (post-grazing residual) of 1,649 ± 48 kg/DM/ha with a front VF. The allocations had a physical backing fence that included the fresh allocation and a small area of residual to cater for any GPS drift of the front VF. On each day, with the exception of days 5 and 10, the VF was moved forward, and the cows were provided a new pasture allocation. On days 5 and 10, the VF was not shifted, and cows were only offered the previous allocation's residual pasture. The location of each animal (inclusion, buffer, and exclusion zones) and number of stimuli (AT and EP) delivered were recorded. The number of stimuli delivered between the grazing and hold-off days was similar. Cows spent 89% of time within the inclusion zone (IZ), with significant peaks observed on day 5 and 10. Distance that cows traveled into the EZ reduced across time. There was also evidence of individual variation in the number of stimuli and thus time spent in each zone. Overall, the VF system was successful in containing the dairy cows during strip grazing even when only offered the previous days post-grazing residual.
Highlights
Pasture is the main feed source for dairy cattle in pasture-based systems in the southern hemisphere, due to the temperate climate and sufficient rainfall allowing an entirely outdoor, all year-round grazing system (Holmes et al, 2002b)
There was no significant difference in the number of audio tone (AT) delivered on the hold-off days as compared to the grazing days
The standard deviation (StdDev) of the random effect of cow was identified with a confidence interval (CI) 0.60– 1.58 indicating variation between individual cows in the number of electrical pulse (EP) delivered across days
Summary
Pasture is the main feed source for dairy cattle in pasture-based systems in the southern hemisphere, due to the temperate climate and sufficient rainfall allowing an entirely outdoor, all year-round grazing system (Holmes et al, 2002b). On pasture-based dairy farms, the area and timing of pasture allocations differ to those used in beef systems, tending to be more intensive as they rely on the efficient conversion of pasture into milk (Clark et al, 2016) These systems are efficient in maintaining synchrony between feed demand to match the herd’s energy requirements and the level of pasture growth minimizing surplus or deficits (Holmes et al, 2002a). A minimum pre-grazing herbage mass target is required to ensure that the needs of cattle are met and to avoid overgrazing and a post-grazing herbage mass or residual is the target which the pasture will be grazed down to in order to avoid compromising pasture regrowth (Holmes et al, 2002a) Livestock management on this pasture is centered around successful animal containment behind fixed or temporary fences that physically prevent cows from accessing additional pasture
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