Salomon E.1 and Spörndly E.2
1JTI – Institute of Agricultural and Environmental Engineering, Uppsala, Sweden. 2Department of Animal Nutrition and Management, Swedish University of Agricultural Sciences, Uppsala;
eva.salomon@jti.se
Abstract
Trampled and muddy surfaces at paddock entrances can create problems with cow traffic and milk quality;
therefore causing problems for many dairy farmers. The aim was to assess the benefits of two ground stabilizing materials, bark chips and armoured mats, when compared to taking no action. The two-year field experiment used a randomized complete block design with three replications of each treatment plot (6×6 m) at the entrance to nine paddocks. Assessment of trampling damage was performed on 5-6 occasions per season. The number and depth of holes were documented and used to calculate a surface index with which to score degree of damage. The number of cow passes and weather were documented continuously. There was no significant effect of the number of cow passes (2,000-7,000) on the surface index. The armoured mats had a significantly lower surface index indicated less damage due to trampling than bark chips. However, the armoured mats had the highest cost and economic benefit is uncertain as their durability is presently unknown. Taking no action resulted in a significantly lower surface index than compared to bark chips, and was deemed a sufficient measure for current dryer weather conditions than normal and rotational grazing system.
Keywords: cow traffic, pasture, trampling, material, walkway
Introduction
A common problem on dairy farms during the grazing period is that surfaces in pasture walkways, entrances to paddocks and around water troughs become trampled and muddy. Problems associated with these damaged surfaces can, for example, cause problems with milk quality and result in non-functioning cow traffic (Lindgren and Benfalk, 2004; Bergsten, 1997). Ground stabilizing materials can be used to avoid problems like these by stabilizing high loaded sub-surfaces and protecting the ground from damage.
The aim of this project was to evaluate and compare the function and cost of two stabilizing materials, bark chips and armoured mats, with each other and with taking no action.
Materials and methods
The field experiment was included in an existing rotational grazing system for a dairy herd of approximately 280 heads at the Swedish livestock research centre east of Uppsala. The field experiment (2013-2014) used a randomized complete block design with three replications of each treatment plot (6×6 m). The three treatments were applied at the entrance to grazing paddocks used by dairy cows, a sub-area that can be representative of high load trampling. The control treatment consisted of a paddock entrance that had not been subjected to any stabilizing measures. The bark chips were placed in a 25-30 cm deep layer on a sheet of geotextile. The armoured mats with geotextile glued underneath were placed on the ground and fixed with a layer of crushed limestone. The surfaces were then evaluated with an index calculated from the number and size of holes in the surface of the treatment plot (Lindgren and Benfalk, 2004; Lindgren and Lindahl, 2007). The number of holes in the depth categories 0.02-0.05 m, 0.05-0.1 m and >0.05-0.1 m were counted in 30 randomly chosen squares of 0.5×0.5 m, representing 25% of the treatment plot. The number of holes in each category was then multiplied by a factor, i.e. 1: 0.02-0.05 m; 2: 0.05-0.10 m; and 3: >0.10 m to create the surface index. A lower index indicated less damage due
to trampling. Visual evaluation was also performed using photos. The documentation was performed once before the grazing season started, three to four times during grazing season (depending on rotation intensity), and once after the grazing season ended. The number of cow passes through the entrances was documented continuously. Temperature and precipitation were documented continuously at the field experiment using a local weather station. Statistical analysis was then performed, where the surface-index was response variable (Y), and treatment and documentation occasion were explanatory variables (X) (SAS, 2008).
Results and discussion
The first grazing season was dryer than normal for the site. The second grazing season had normal precipitation (except for a dryer July), resulting in different conditions between years concerning risk of trampling damage. None of the years or parts of the two seasons could be considered as having wet conditions.
The number of cow passes differed between years and between the three blocks due to location and paddock differences in biomass production, which influenced the rotation intensity (Table 1). In the field trial we focused on achieving similar number of passes within each block. There was no significant correlation between the number of passes and surface index (P<0.05) for either of the two years.
Both years the bark chip bed had more trampling damage and a significantly higher surface index than the armoured mats and the control (Figure 1). In the first year one plot with bark chips lost its bearing capacity (collapsed) due to the highest number of cow passes, i.e. 7,283 passes. During the second year, with normal precipitation, all three plots with bark chips collapsed. The visible evaluation showed that the cows often avoided walking over the bark chip beds and instead chose to walk on a thin passage beside the beds. As this comparison has been performed on clay soil it is, however, possible that bark chips perform better on other soils. The control area where no action was taken had some trampling damage and a low surface index (Figure 1). In this rotational grazing system where biomass had the chance to re-establish between grazing activities in the control area, and in combination with good growing conditions, the measure of taking no action was sufficient to avoid trampling damages under the prevailing dry to normal weather conditions during the two years. In the second year the control area had a similar surface index to the armoured mats (Figure 1).The armoured mats had no visible trampling damages and a low surface index for both experimental years. So far the armoured mats have been able to withstand two grazing periods and is a promising stabilizing material. Investment costs for 100 m2 armoured mat was 21,900 SEK and for 100 m2 bark chip bed was 6,500 SEK (Nilsson, 2013). Including costs for maintenance and calculating with a life span of ten years the armoured mats need to withstand seven years to reach the same cost as the bark chip beds.
The surface index method was not sufficient when comparing degree of trampling damage between the two stabilizing materials (bark chips and armoured mats). The bark chip material is characterized by having an uneven surface, which resulted in a more than five times higher surface index than the armoured mats and control at the first documentation occasion before entrance of the cows. Complementing with
Table 1. Average number of cow passes documented during the grazing season
Year Bark chips Armoured mat Control
1 4,810 5,070 2,500
2 3,780 4,090 3,850
visual evaluation showed clearly the moment when bark chip beds reached a stage with permanently deep holes and when cows avoided to passes over them.
Conclusions
The armoured mats showed the greatest resistance to trampling damages and were hardly affected during two grazing seasons and a winter in between. Calculations showed that the costs of armoured mats can be as low as bark chip beds if they can be used for seven years. The bark chip beds did not withstand trampling under the conditions of this experiment. Despite this, bark chip beds can be a cheap stabilizing material if the farmer has access to bedding material and can replace the bedding surface during the grazing period (Lindgren and Benfalk, 2004). The measure of taking no action on trampled sub areas was sufficient for current dryer weather conditions than normal in this experiment with a rotational grazing system.
Acknowledgements
This study was funded by the Swedish Farmers’ Foundation for Agricultural Research (SLF).
References
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Nilsson H. (2013). Bark och armeringsmatta för att förebygga trampskador på betesytor hårt belastade av mjölkkor – en utvärdering, Examensarbete/SLU Institutionen för husdjurens utfodring och vård 465, Uppsala.
Figure 1. Average surface index with different letters within each year are significant different (P<0.001).