Survivorship approaches to measuring and comparing cull rates for dairies

Dairy cow mortality. A review

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.

Predicting the probability of abortion in dairy cows: a hierarchical Bayesian logistic-survival model using sequential pregnancy data

Although abortion contributes substantially to poor reproductive health of dairy herds, little is known about the predictability of abortion based on age, previous abortion or gravidity (number of previous pregnancies). A poor understanding of effects of maternal factors on abortion risk exists, in part, because of methodological difficulties related to non-independence of multiple pregnancies of the same cow in analysis of fetal survival data. We prospectively examined sequential pregnancies to investigate relationships between fetal survival and putative dam risk factors for 2991 abortions from 24,706 pregnancies of 13,145 cows in nine California dairy herds. Relative risks and predicted probabilities of abortion (PPA) were estimated using a previously described hierarchical Bayesian logistic-survival model generalized to incorporate longitudinal data of multiple pregnancies from a single cow. The PPA increased with increasing dam age at conception, with increasing number of previous abortions, and if the previous pregnancy was aborted >60 days in gestation. The PPA decreased with increasing gravidity and with increasing number of days open. For cows that aborted, the median time to fetal death decreased slightly as gravidity increased. The study considers several methodological issues faced in epidemiologic investigations of fetal health, including multi-modal hazard functions, extensive censoring and non-independence of multiple pregnancies. The model improves our ability to predict bovine abortion and to characterize fetal survival, which have important applications to herd health management.

Mortality (including euthanasia) among Danish dairy cows (1990–2001)

Mortality among Danish dairy cows was examined using data from the Danish Cattle Database (DCD) and a questionnaire survey. Mortality risk has increased from approximately 2% in 1990 to approximately 3.5% in 1999. The increased mortality was seen for all dairy breeds and all age groups. Mortality among older dairy cows (parity 3 and older) was approximately twice the mortality among younger cows. 30-40% of deaths were during the first 30 days of the lactation. Approximately, 58% of dead dairy cows had been euthanised. Replies from the questionnaire indicate that the proportion of euthanised cows has increased in the past 5 years. In 86% of all deaths (questionnaire survey) a primary reason could be identified; 25% were for locomotor disorders.

Cointegration analysis used in a study of dairy-cow mortality

A competitive environment forces the farmer constantly to adopt new and more-intensive production methods aiming at lowering costs and increasing yields. At debate is whether this intensification of production has an adverse impact on animal health and welfare. We investigated this issue by using cointegration analysis (a new tool used in time series analysis). We introduce cointegration analysis by applying the method in an epidemiological study of dairy-cow mortality. Two long-run epidemiological relations are identified:(i) a physiological relation (where increasing consumption of concentrates corresponded to increasing milk yield and mortality) and (ii) a physical relation (which illustrated that higher mortality was closely related to a higher growth rate of the average herd size, current investments in dairy farming, and higher milk yield). We concluded that a higher level of physiological stress due to higher yield and concentrate consumption has led to increased mortality. Furthermore, changes in the physical environment due to increased mechanisation and larger herd sizes have contributed to less attention per cow and increased mortality.