Peter T. Thomsen

Invited review: A systematic literature review and meta-analysis of mortality and culling in dairy cattle

Dairy industries and individual farmers are concerned about mortality and culling of dairy animals. This is because the timing and fates of animals that exit dairy farms have important animal welfare and economic consequences that reflect the conditions under which they are farmed and the efficiency of their production systems. Reports from a few countries have indicated increased incidence of mortality, and occasionally culling, of dairy animals in recent decades, and these changes have been associated with intensification of production systems. Dairy industries and farmers need benchmarks for culling and mortality against which they can compare themselves, as well as improved understanding of the extent of any change and of any associated factors. We reasoned that a systematic literature review and meta-analysis of scientific articles published between 1989 and 2014 would allow us to determine whether these reports were universal, to quantify any change over time, and to investigate whether production systems or study factors were associated with culling and mortality. From 3,275 articles retrieved from databases and manual searching of cited articles, 118 articles were appraised independently by 2 assessors, and 51 articles representing 54 studies were determined to be eligible for review and meta-analysis. We estimated that both the annual incidence risk (IR) and incidence density of mortality of cows had increased significantly from 0.02 per cow and 2.32 per 100 cow-years, to 0.04 per cow and 3.75 per 100 cow-years, an increase per decade of 0.02 per cow and 1.42 per 100 cow-years, respectively. We also estimated that the annual IR of culling attributed to low production had declined significantly from 0.07 to 0.05 and that the IR of perinatal, but not neonatal, mortality had increased significantly from 0.04 to 0.06 per decade. We found no evidence of change in overall annual IR of culling of cows over time or any association between study design factors and the IR or incidence density of culling or mortality. These findings provide benchmarks for describing culling and mortality, and should encourage farmers and researchers in countries with modern dairy industries to discover and implement management strategies to reduce the animal welfare and economic costs associated with these changes.

Dairy cow mortality. A review

Summary We reviewed the literature to give an overview over the mortality among dairy cows in countries with a relatively intensive dairy production. A total of 19 studies focussing on dairy cow mortality were identified. Information about objectives, measures of mortality, sample sizes, study designs, causes of death and risk factors from these studies is presented and discussed. Additionally, recommendations for future recordings of mortality that will enable better possibilities for comparison of study results, generalization of results from a study population to a larger population and meta‐analysis are given.

Herd-level risk factors associated with cow mortality in Swedish dairy herds

Abstract An increase in on-farm mortality (euthanasia and death) in dairy herds has been reported in several countries in the last decade. This does not only imply possible problems with animal welfare, but it also causes economic losses to the farmer. The objective of this study was to evaluate time trends in on-farm dairy cow mortality in Sweden and identify potential herd-level risk factors. Data were retrieved on all Swedish dairy herds enrolled in the milk recording scheme between 2002 and 2010. Herds with a herd size of <20 cows or a mortality rate (MR) of >40 dead or euthanized cows per 100 cow-years were excluded. Two different models were used: 1 multiple-year analysis, which included 6,898 herds during the period 2002 to 2010 and 1 single-year analysis including 4,252 herds for the year 2010, where other variables that were not present during the entire multiple year study were analyzed. The outcome variable was the number of euthanized and dead cows per year and season. A negative binomial regression model, adjusted for clustering within herd, was applied to both models. Fixed effects in the multiple-year analysis were breed, calving interval, herd size, milk yield, region, season, pasture period, and year. The fixed effects in the single-year analysis were breed, calving interval, conventional versus organic farming, herd size, housing system, milk yield, region, and season. The results demonstrated that MR gradually increased from 5.1 to 6.6 events per 100 cow-years during the study period. Swedish MR are consequently on par with, or even greater than, MR among dairy herds in other comparable countries. Higher mortality was associated with larger herd size, longer calving intervals, and herds that had Swedish Holstein as the predominant breed. Lower mortality was observed in herds with a higher herd average milk yield, during the fall and winter, and in organically managed herds. There were regional differences in mortality. An interaction between herd size and season was found in both models. Also, an interaction between housing system and milk yield was found in the single-year analysis. This first assessment of on-farm mortality in Swedish dairy herds confirmed that the MR has increased over the last few years. The study also identified some herd-level risk factors.

Herd-level risk factors for the mortality of cows in Danish dairy herds

The factors affecting the mortality of cows in Danish dairy herds were investigated by analysing data from 6839 herds. The mean risk of mortality during the first 100 days of lactation was 2·5 per cent. The risk of mortality increased with increasing herd size (odds ratio [OR] 1·05 for an increase in herd size of 50 cows), with the proportion of purchased cows (OR 1·05 for an increase in the proportion of purchased cows of 0·1), and with increases in the somatic cell count (OR 1·16 for an increase in average weighted mean somatic cell count of 100,000 cells/ml). The risk decreased with increasing average milk yield per cow (OR 0·93 for an increase in mean yield per cow-year of 1000 kg). The risk was lower in free-stall barns with deep litter (OR 0·79) than in barns with cubicles (OR 1) or tie-stalls (OR 1·04). Herds with Danish Holstein (OR 1) or Danish Jersey (OR 0·93) cows as the predominant breed had a higher risk of mortality than herds of the Danish red dairy breed (OR 0·67). The risk of mortality was lower in organic herds (OR 1) than in conventional herds (OR 1·17), and lower in herds that grazed pasture during the summer (OR 0·78).

Evaluation of Three Commercial Hoof-Care Products Used in Footbaths in Danish Dairy Herds

Digital dermatitis is a serious problem in dairy production in many countries. Footbaths have been used extensively for the prevention and cure of digital dermatitis. But there is a lack of scientific evidence regarding the effectiveness of hoof-care products used in footbaths. The objective was to evaluate 3 commercial hoof-care products in 12 Danish dairy herds (testing each product in 4 herds) using a controlled clinical trial. One-half of the herds were conventional and the other half was organically managed. The hoof-care products represented the 3 main groups of active compounds currently legal in Denmark [glutaraldehyde (Virocid), organic acids (Kickstart 2), and quaternary ammonium compounds (Hoofcare DA)]. A split footbath was used, with one side of the cow treated and the other side as a negative control. In each herd, 100 cows were selected randomly. All digital dermatitis lesions were recorded during hoof trimming at the start of the study. The mean prevalence of active digital dermatitis lesions on the hind legs was 21.8 and 22.7% for treatment and control sides, respectively. All cows walked through the footbath 2 d/wk for 8 wk. After 8 wk of treatment the cows were examined again and all lesions were recorded. In each herd, the percentage of cows was calculated with active digital dermatitis lesions at the start of the study that were cured during the study period (termed percentage cured) and the percentage of cows with new infections during the study period (termed percentage new infections). Percentage cured ranged from 13.6 to 100, and percentage new infections ranged from 0 to 35.5. For all hoof-care products, the difference between treatment and control sides was not statistically significant. Overall, there was no effect on percentage cured or percentage new infections for any of the tested hoof-care products.

Evaluation of sensitivity and specificity of routine meat inspection of Danish slaughter pigs using Latent Class Analysis

Two groups of observers, regular meat inspectors and two veterinary researchers, respectively, conducted independent veterinary meat inspection of organs of slaughter pigs from organic or conventional production systems slaughtered at one abattoir in April 2005. A total of 3054 pigs (899 organic and 2155 conventional) were examined. The observed pathological disorders were grouped in four categories; respiratory disorders (RESP), parasitic disorders (PAR), intestinal disorders (INT) and heart disorders (HEART). Using a latent class model, the sensitivity (Se) and specificity (Sp) of meat inspectors and researchers were estimated without the assumption of an available gold standard. The Se for the regular meat inspection was found to be 0.92, 0.16, 0.24 and 0.49 for RESP, PAR, INT and HEART, respectively. The Se for the researchers was found to be 0.81, 0.96, 0.91 and 0.68 for RESP, PAR, INT and HEART, respectively. The Sp for the regular meat inspection was found to be between 0.98 and 1.00 for the four categories. The Sp for the researchers was found to be 0.83, 0.94, 0.76 and 0.99 for RESP, PAR, INT and HEART, respectively. The low Se of ordinary meat inspection for parasitic, intestinal and heart disorders will cause a significant underestimation of the prevalence of diseases reported to the pig producers. Based on our results the true prevalence of diseases (conventional vs. organic slaughter pigs) was (in %): 42 vs. 16, 5 vs. 51, 5 vs. 12 and 9 vs. 5 for RESP, PAR, INT and HEART, respectively.

Locomotion scores and lying behaviour are indicators of hoof lesions in dairy cows.

Locomotion scoring, lying behaviour and lesion recording during hoof trimming are all ways of evaluating hoof health in dairy cows. The objective of this study was to evaluate the relationship between these measures in a random sample of 1340 cows from 42 Danish dairy herds. The hypothesis was that locomotion scoring and/or the monitoring of lying behaviour could be used as tools to identify cows with hoof lesions, either of the horn or of the skin. Cows were locomotion scored, lying behaviour recorded and data on hoof lesions seen during hoof trimming collected. The results were analysed using logistic regression with hoof lesion as the outcome and locomotion score (1-5), mean duration of lying bouts, parity and lactation stage as explanatory variables. This analysis was undertaken for all types of lesions, for hoof horn lesions only and for skin lesions only. Odds of all hoof lesions and of skin lesions increased with increasing locomotion score and increasing mean duration of lying bouts. Odds of horn lesions also increased with increasing locomotion score, but there was no significant association between horn lesions and the mean duration of lying bouts. It was concluded that locomotion scoring and duration of lying bouts may be used as tools in the management of hoof health in dairy herds.

The effect of grazing on cow mortality in Danish dairy herds

The effect of summer grazing in large Danish dairy herds and certain management characteristics of grazing were studied for their impact on dairy cow mortality. Mortality data (from the Danish Cattle Database) from 391 Danish dairy herds (>100 cows) were combined with information from a questionnaire survey of grazing procedures on these herds in 2008. In all, 131 of the herds were identified as summer grazing and 260 as zero-grazing herds. The mortality was affected by an interaction of summer grazing and milking system. The risk of a cow dying was reduced to 46% in a grazing compared to a zero-grazing herd having automatic milking system. In traditional milking system, mortality was reduced to 75% in grazing compared to zero-grazing herds. Within the grazing herds, the risk of mortality decreased with increasing number of hours on pasture during the season. Free access between barn and pasture was associated with increased cow mortality.

A study of the dynamics of digital dermatitis in 742 lactating dairy cows

Digital dermatitis (DD) is a contagious disease of cattle affecting the skin of the claw. The disease presents with a range of severities and can be associated with lameness. Information about the disease dynamics of DD is scarce. Parity and lactation stage have been identified as risk factors for DD and studies have also indicated that not all cows are equal regarding their risk of recurrent disease and prospects for cure from DD. The aim of this study was to investigate host heterogeneity to DD and to identify disease patterns of DD and factors associated with the development and resolution of lesions. In three commercial dairy herds, 742 lactating cows were observed for DD lesions weekly for 11 or 12 weeks. The effects of parity, lactation stage and duration of preceding episode on the hazard of transitions between healthy and lesion states were analysed using a multilevel multistate discrete-time model. One or more DD lesions were observed in 460 cows and lesions were observed in 2426 out of 10,585 observations. In total, 1755 uncensored episodes with DD lesions were observed. Early lactation was associated with a reduced risk of developing lesions compared with mid and late lactation. Lesions that developed in late lactation had a greater likelihood of resolution compared with lesions that developed during early lactation. There was a reduced risk of lesions developing in parity 3 compared with parity 1 cows, but an increased risk of lesions developing in parity 2 compared with parity 1 cows. In the present study, the mean duration of uncensored DD episodes was 1.7 weeks indicating that the duration of the majority of DD lesions might be shorter than the 42 days reported previously. The transitions between disease states suggest that DD is a dynamic disease, and that the early stage lesions are more transient than expected from previous studies. We conclude that studies with shorter observation intervals than one week are needed to fully understand and describe the individual and group dynamics of DD.

Effect of grazing on the cow welfare of dairy herds evaluated by a multidimensional welfare index

Structural development in the prime sector has led to increasing herd sizes and new barn systems, followed by less summer grazing for dairy cows in Denmark. Effects of grazing on single welfare measures in dairy cows - for example, the presence of integument alterations or mortality - have been studied under different conditions. However, the effect of grazing on welfare, conceptualised as the multidimensional physical and mental state of the animal, has not yet been studied in contemporary cubicle loose-housing systems. The aim of our study was to investigate, based on a Welfare Quality® inspired multidimensional dairy cow welfare assessment protocol, the within-herd effect of summer grazing compared with winter barn housing in Danish dairy herds with cubicle free-stall systems for the lactating cows. Our hypothesis was that cow welfare in dairy herds was better during summer grazing than during full-time winter housing. Furthermore, we expected improved welfare with an increase in daily summer grazing hours. In total, 41 herds have been visited once in the winter and once in the summer of 2010 to assess their welfare status with 17 different animal- and resource-based welfare measures. A panel of 20 experts on cattle welfare and husbandry evaluated the relative weight of the 17 welfare measures in a multidimensional assessment scheme. They estimated exact weights for a priori constituted severe compared with moderate scores of welfare impairment concerning each measure, as well as relevance of the measures in relation to each other. A welfare index (WI; possible range 0 to 5400) was calculated for each herd and season with a higher index indicating poorer welfare. The within-herd comparison of summer grazing v. winter housing considered all the 17 measures. The mean WI in summer was significantly lower (better) than in winter (mean 2926 v. 3330; paired t-test P = 0.0001) based on a better state of the integument, claw conformation and better access to water and food. Body condition and faeces consistence were worse in summer. Many daily grazing hours (range average above 3 to 9 h) turned out to be more beneficial than few daily grazing hours (range average above 9 to 21 h) for the welfare of the dairy herds. In conclusion, this study reports a positive within-herd effect of summer grazing on dairy cow welfare, where many daily grazing hours were more beneficial than few daily grazing hours.