A mixture model for bovine abortion and foetal survival

The Uterus as an Influencing Factor for Late Embryo/Early Fetal Loss—A Clinical Update

Simple Summary

Pregnancy loss following a positive pregnancy diagnosis in the absence of infectious disease of the reproductive system is a main factor limiting reproductive efficiency in high producing dairy cows. We describe here some circumstances such as the age of the dam, retained placenta and uterine size in which the uterus may be associated with pregnancy loss.

Abstract

Here we revise circumstances of non-infectious causes in which the uterus may be associated with pregnancy loss during the late embryo/early fetal period (following a positive pregnancy diagnosis in lactating dairy cows). As the uterine size increases with parity and pregnant heifers with no detrimental effects of a previous parturition, a primigravid uterus is proposed as a reference for identifying risk factors that negatively influence pregnancy in lactating cows. Cows suffering placenta retention or with a large uterus at insemination were selected as topics for this revision. Retained placenta, that occurs around parturition, has a long-lasting influence on subsequent pregnancy loss. Although retained placenta is a particularly predisposing factor for uterine infection, farm conditions along with cow factors of non-infectious cause and their interactions have been identified as main factors favoring this disorder. A large uterus (cervix and uterine horns lying outside the pelvic cavity) with no detectable abnormalities has been associated with low fertility and with a greater incidence of pregnancy loss. A large reproductive tract may well derive from an inadequate uterine involution. Therefore, peripartum management and strategies to reduce the incidence of uterine disorders should reduce their associated financial losses in the herds.

Meningoencephalitis, Vasculitis, and Abortions Caused by Chlamydia pecorum in a Herd of Cattle

A cow dairy (n = 2000) in close proximity to a sheep flock had third-trimester abortions and fatalities in cows and calves over a 14-month period. Eighteen of 33 aborted fetuses (55%) had multifocal random suppurative or mononuclear meningoencephalitis with vasculitis. Seventeen of these affected fetuses had intracytoplasmic bacteria in endothelial cells, and 1 fetus with pericarditis had similar bacteria within mesothelial cells or macrophages. Immunohistochemistry for Chlamydia spp. or polymerase chain reaction (PCR) for Chlamydia pecorum or both, performed on brain or pooled tissue, were positive in all 14 tested fetuses that had meningoencephalitis and in 4/4 calves and in 3/4 tested cows that had meningoencephalitis and thrombotic vasculitis. In 1 calf and 11/11 fetuses, C. pecorum PCR amplicon sequences were 100% homologous to published C. pecorum sequences. Enzootic chlamydiosis due to C. pecorum was the identified cause of the late term abortions and the vasculitis and meningoencephalitis in fetuses, calves, and cows. C. pecorum, an uncommon bovine abortogenic agent, is a differential diagnosis in late-term aborted fetuses with meningoencephalitis, vasculitis, and polyserositis.

Epidemiological Investigation of Cattle Abortion and Its Association with Brucellosis in Jimma Zone, Ethiopia

Background

The epidemiology of cattle abortion and its association with brucellosis is not well understood in Ethiopia. Therefore, the aim of this study was to determine the magnitude, associated risk factors of abortion, and its association with brucellosis in cattle of Jimma zone, Ethiopia.

Methods

A cross-sectional study was carried out from October 2018 to October 2019 in Jimma zone. A total of 484 pregnant cattle were randomly selected from two districts based on the composition of the cattle population. Besides, blood samples were collected from a total of 484 randomly selected cattle to assess the presence of Brucella antibody. The presence of an antibody against Brucella organism was first tested by the Rose Bengal Plate test, and then positive serum was confirmed using the complement fixation test.

Results

An overall 14.30% cumulative incidence rate of abortion was recorded in study areas. In this study, breed, herd size, method of breeding, previous history of abortion, accessibility of dog to cattle and season were identified as risk factors for the occurrence of cattle abortion. Higher cumulative incidence of abortion (31.82%) was observed in Brucella antibody positive cattle than those of antibody negative cattle (13.42%). However, the difference noted was not statistically significant (P<0.05).

Conclusion

It is important to create awareness about the impact of the abortion on cattle production and the applicable control technique of abortion should be aimed and implemented. Moreover, further investigation should be conducted to identify the specific cause of abortion and the associated loss in the study areas.

A nonparametric maximum likelihood approach for survival data with observed cured subjects, left truncation and right-censoring

We consider observational studies in pregnancy where the outcome of interest is spontaneous abortion (SAB). This at first sight is a binary 'yes' or 'no' variable, albeit there is left truncation as well as right-censoring in the data. Women who do not experience SAB by gestational week 20 are 'cured' from SAB by definition, that is, they are no longer at risk. Our data is different from the common cure data in the literature, where the cured subjects are always right-censored and not actually observed to be cured. We consider a commonly used cure rate model, with the likelihood function tailored specifically to our data. We develop a conditional nonparametric maximum likelihood approach. To tackle the computational challenge we adopt an EM algorithm making use of "ghost copies" of the data, and a closed form variance estimator is derived. Under suitable assumptions, we prove the consistency of the resulting estimator which involves an unbounded cumulative baseline hazard function, as well as the asymptotic normality. Simulation results are carried out to evaluate the finite sample performance. We present the analysis of the motivating SAB study to illustrate the advantages of our model addressing both occurrence and timing of SAB, as compared to existing approaches in practice.

Factors associated with frequency of abortions recorded through Dairy Herd Improvement test plans

Frequency of abortions recorded through Dairy Herd Improvement (DHI) testing was summarized for cows with lactations completed from 2001 through 2009. For 8.5 million DHI lactations of cows that had recorded breeding dates and were >151 d pregnant at lactation termination, the frequency of recorded abortions was 1.31%. Effects of year, herd-year, month, and pregnancy stage at lactation termination; parity; breed; milk yield; herd size; geographic region; and state within region associated with DHI-recorded abortion were examined. Abortions recorded through DHI (minimum gestation of 152 d required) were more frequent during early gestation; least squares means (LSM) were 4.38, 3.27, 1.19, and 0.59% for 152 to 175, 176 to 200, 201 to 225, and 226 to 250 d pregnant, respectively. Frequency of DHI-recorded abortions was 1.40% for parity 1 and 1.01% for parity ≥ 8. Abortion frequency was highest from May through August (1.42 to 1.53%) and lowest from October through February (1.09 to 1.21%). Frequency of DHI-recorded abortions was higher for Holsteins (1.32%) than for Jerseys (1.10%) and other breeds (1.27%). Little relationship was found between DHI-recorded abortions and herd size. Abortion frequencies for effects should be considered to be underestimated because many abortions, especially those caused by genetic recessives, go undetected. Therefore, various nonreturn rates (NRR; 60, 80, …, 200 d) were calculated to document pregnancy loss confirmed by the absence of homozygotes in the population. Breeding records for April 2011 US Department of Agriculture sire conception rate evaluations were analyzed with the model used for official evaluations with the addition of an interaction between carrier status of the service sire (embryo's sire) and cow sire (embryo's maternal grandsire). Over 13 million matings were examined using various NRR for Holstein lethal recessive traits (brachyspina and complex vertebral malformation) and undesirable recessive haplotypes (HH1, HH2, and HH3) as well as >61,000 matings for a Brown Swiss haplotype (BH1), and 670,000 matings for a Jersey haplotype (JH1). Over 80% of fertility loss occurred by 60 d after breeding for BH1, HH3, and JH1, by 80 d for HH2, by 100 d for BY, and by 180 d for HH1. For complex vertebral malformation, fertility loss increased from 40 to 74% across gestation. Association of undesirable recessives with DHI-recorded abortions ranged from 0.0% for Jerseys to 2.4% for Holsteins.

Spatially dependent polya tree modeling for survival data

With the proliferation of spatially oriented time-to-event data, spatial modeling in the survival context has received increased recent attention. A traditional way to capture a spatial pattern is to introduce frailty terms in the linear predictor of a semiparametric model, such as proportional hazards or accelerated failure time. We propose a new methodology to capture the spatial pattern by assuming a prior based on a mixture of spatially dependent Polya trees for the baseline survival in the proportional hazards model. Thanks to modern Markov chain Monte Carlo (MCMC) methods, this approach remains computationally feasible in a fully hierarchical Bayesian framework. We compare the spatially dependent mixture of Polya trees (MPT) approach to the traditional spatial frailty approach, and illustrate the usefulness of this method with an analysis of Iowan breast cancer survival data from the Surveillance, Epidemiology, and End Results (SEER) program of the National Cancer Institute. Our method provides better goodness of fit over the traditional alternatives as measured by log pseudo marginal likelihood (LPML), the deviance information criterion (DIC), and full sample score (FSS) statistics.

Risk factors for abortion in dairy cows from commercial Holstein dairy herds in the Tehran region

In last decade, pregnancy loss in dairy cattle has had an upward trend bringing difficulties for breeders: the annual cost is estimated around 396 billion Rials (i.e. around 40 million US$) for the Iranian dairy industry. The present study was conducted to determine the influence of maternal factors on abortion and to predict the probability of abortion as well as the effect of these factors on the fetal lifetime in Holstein dairy cattle. Data from 44,629 established pregnancies that included 14,226 heifers and 30,403 pregnancies from 12,265 parous cows in nine industrial dairy herds around Tehran were used. Overall, 4871 pregnancies of parous cows resulted in abortion. Prediction of the probability of abortion (PPA) was estimated by a logistic regression model. Survival analysis was performed using an accelerated failure time (AFT) model assuming a multi-modal hazard function. Effective factors included age of dam at conception, gravidity, open days, number of previous abortion(s), abortion before/after 60 days of gestation in previous conception, herd and season of insemination. The PPA decreased with increasing open days, increasing gravidity and no previous abortion. In addition, the PPA was greater for cows which had been inseminated during summer versus winter. However, the difference between autumn and spring was not significant. Overall, 25 sires out of 695 from which sperm was collected for artificial insemination (AI) had significantly higher risk of abortion, with odds ratios ranging between 1.44 and 4.73 compared to the average. The survival probability increased slightly during gestation as gravidity increased for cows that had a previous abortion. Cows that had aborted before 60 days of gestation in previous conception tended to abort later in their next conceptions.

Bayesian statistics in medicine: a 25 year review

This review examines the state of Bayesian thinking as Statistics in Medicine was launched in 1982, reflecting particularly on its applicability and uses in medical research. It then looks at each subsequent five-year epoch, with a focus on papers appearing in Statistics in Medicine, putting these in the context of major developments in Bayesian thinking and computation with reference to important books, landmark meetings and seminal papers. It charts the growth of Bayesian statistics as it is applied to medicine and makes predictions for the future. From sparse beginnings, where Bayesian statistics was barely mentioned, Bayesian statistics has now permeated all the major areas of medical statistics, including clinical trials, epidemiology, meta-analyses and evidence synthesis, spatial modelling, longitudinal modelling, survival modelling, molecular genetics and decision-making in respect of new technologies.

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.