Suboptimal mobility in spring calving, pasture-based dairy systems: causes and economic consequences

Suboptimal mobility (any deviation from optimal mobility) is an important area of concern in modern dairy production systems. Up to now, suboptimal mobility in dairy cows managed in spring calving, pasture-based systems have been overlooked. Therefore, the aim of this thesis was to gain a better understanding of the potential causes and impacts of all levels of sub optimal mobility in spring calving, pasture-based dairy cows. First, the associations between claw disorders and mobility scores were investigated. The mobility scoring method utilized in this thesis is a four-point scale from 0, which refers to a cow with optimal mobility, to 3 which refers to a cow with severely impaired mobility. The presence of most types of claw disorders were associated with an increased likelihood of a cow having any level of suboptimal mobility. Therefore, it is implied that mobility scoring of cows should be routinely practiced to identify cows with imperfect mobility at an earlier stage. Second, potential risk factors were identified for suboptimal mobility. Potential cow-level risk factors for suboptimal mobility included body condition score, milk yield, genetics for ‘lameness’, somatic cell score, calving month and cow breed. While, potential herd-level risk factors for suboptimal mobility included the length of time taken to complete the milking process, farm layout factors and foot bathing practices. These factors should be considered by farm advisors when advising and implementing a cow/herd health program for dairy cows in spring calving, pasture-based systems. Third the production and reproductive impacts of specific levels of suboptimal mobility were analysed. Yield losses of up to 4.7% were associated with mobility score 3. Elevated somatic cell count, and longer calving intervals were associated with all levels of suboptimal mobility. Cows with any level of suboptimal mobility were more likely to be culled. This demonstrates associations between specific mobility scores and production and reproductive performance in spring calving, pasture-based dairy cows scored during the summer grazing period. Finally, the economic impact of varying prevalence of suboptimal mobility was determined within typical spring calving, pasture-based dairy herds. A new sub model predicting suboptimal mobility was developed and integrated within the Pastured Based Herd dynamic model. The impact on profitability was simulated based on production and reproductive effects of individual animals as well as the associated treatment costs. For a very poor mobility herd the overall farm net profit was €16,500 less compared to a good mobility herd. The substantial decrease in farm net profit is due to reduced milk yield, increased culling, and treatment costs for mobility issues. Therefore, as the prevalence of cows with suboptimal mobility scores (even mild suboptimal mobility scores) increases within a herd, the overall farm next profit decreases. Based on this thesis it is concluded that although the prevalence of severe suboptimal mobility with spring calving, pasture-based herds is less than that in other types of systems, the potential impact of the less severe states of suboptimal mobility have a substantial effect on production and reproductive performance, and the overall profitability of the farm.