Highlights
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A dynamic stochastic simulation model was combined with life cycle assessment.
•Foot lesions in dairy cows increase greenhouse gas emissions of milk production.
•Impact on greenhouse gas emissions depends on type of foot lesion.
•Culling of dairy cows is an important contributor to greenhouse gas emissions.
Abstract
The dairy sector is an important contributor to greenhouse gas (GAG) emissions. Foot lesions in dairy cows result in production losses and, therefore, might increase GAG emissions per kg milk. The objective of this study was to estimate the impact of foot lesions in dairy cows on CHG emissions. A dynamic stochastic simulation model was developed to estimate dynamics of digital dermatitis (DD), white line disease (WALD), and sole ulcer (SI), and associated production losses within one lactation. Production losses included were reduced milk production, prolonged calving interval (CI), and culling. Subsequently, a life cycle assessment was performed to estimate the impact of foot lesions on GHG emissions per ton of fat-and-protein-corrected milk (kg CO2e/t FPCM). GHG emissions increased on average by 14 (1.5%) kg CO2e/t FPCM per case of foot lesions (i.e. DD, WLD, and SU combined), ranging from 17 kg CO2e/t FPCM in parity 1, to 7 kg CO2e/t FPCM in parity 5. Emissions of GHGs increased on average by 4 (0.4%) kg CO2e/t FPCM per case of DD, by 39 (4.3%) kg CO2e/t FPCM per case of WLD, and by 33 (3.6%) kg CO2e/t FPCM per case of SU. A prolonged CI explained the majority of the increase in GHG emissions for cows with DD, whereas culling was most important for cows with WLD or SU. DD had the lowest impact on GHG emissions, but the highest prevalence, and, therefore, contributed most to the average impact of foot lesions. This study showed that preventing different types of foot lesions can reduce GHG emissions from the dairy sector. The increasing attention for global warming and possible policies to reduce GHG emissions from agriculture might give dairy farmers another incentive to prevent foot lesions. The impact of foot lesions on GHG emissions, however, can vary among dairy farms, because of differences in prevalence of foot lesions and associated production losses, and in farm management.1. Introduction
Lameness is one of the most important diseases of dairy cows with a prevalence ranging from 0% to 70% (Cramer et al., 2008; Raboisson et al., 2015). Lameness affects the welfare of cows, because it can induce pain (Flower and Weary, 2009). Moreover, lameness reduces milk production by 270–574 kg per cow per lactation, reduces several aspects of reproduction performance (e.g. calving to conception interval, days open, calving interval), and increases the risk of culling (Huxley, 2013).
About 90% of lameness cases are associated with foot lesions (Murray et al., 1996; Somers and O'Grady, 2015). Foot lesions with the highest prevalence on dairy farms are the infectious digital dermatitis (DD), and the non-infectious white line disease (WLD) and sole ulcer (SU) (Amory et al., 2008; Solano et al., 2016), but this varies between countries, regions, and farming system. DD is an infection of the epidermis of the hoof skin, whereas, WLD is a separation of the wall horn (Amory et al., 2008), and SU is an ulcer in the sole, toe or heel (Somers et al., 2003). Both, WLD and SU, are caused by physical or metabolic disturbance (Bruijnis et al., 2010).
Several studies estimated the economic impact of foot lesions (Bruijnis et al., 2010; Cha et al., 2010; Ettema et al., 2010), but the environmental impact of foot lesions has received little attention so far. One of the most urgent environmental issues is global warming, induced by greenhouse gas (GHG) emissions (Steffen et al., 2015). The livestock sector is responsible for around 14.5% of the worldwide GHG emissions, and the dairy sector contributes around 30% of the total (Gerber et al., 2013). Important GHGs in dairy production are carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O), which are mainly emitted during feed production, enteric fermentation, and manure management.
Several feeding, breeding and management strategies exist that reduce the GHG impact of milk production. Examples of such feeding strategies are dietary supplementation of extruded linseed or nitrate, or increasing the share of co-products, such as beet tails in diets of dairy cattle (Van Middelaar et al., 2014b; Van Zanten et al., 2014). Examples of breeding strategies that reduce GHG emissions are increasing the milk yield or longevity of dairy cows (Van Middelaar et al., 2014a). Management strategies that reduce milk production losses, such as reducing the prevalence of foot lesions, might also reduce GHG emissions per kg milk. Chen et al. (2016) estimated that lameness (without indicating the causes of lameness) increased GHG emissions per kg milk for a typical Irish grazed grass dairy farm by 0.7–7.8%. The impact on GHG emissions, however, might be affected by the type of farming system. Moreover, Chen et al. (2016) estimated a general effect of lameness, but did not account for different types of foot lesions and parity of cows. Their study was based on reduced
milk production and weight losses only, while lameness also has an effect on culling and fertility of the cow (Cramer et al., 2009; Huxley, 2013). All these factors (parity, culling, and fertility) have been demonstrated to affect the impact of diseases on GHG emissions (Mostert et al., 2018) and, therefore, should be included when assessing GHG emissions of foot lesions.
The objective of this study was to estimate the impact foot lesions on GHG emissions. In the estimation, we accounted for different types of foot lesions, and the impact of parity, culling, and cow fertility.
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