Employing a Monte Carlo algorithm in expectation maximization restricted maximum likelihood estimation of the linear mixed model

Multiple‐trait and random regression models have multiplied the number of equations needed for the estimation of variance components. To avoid inversion or decomposition of a large coefficient matrix, we propose estimation of variance components by Monte Carlo expectation maximization restricted maximum likelihood (MC EM REML) for multiple‐trait linear mixed models. Implementation is based on full‐model sampling for calculating the prediction error variances required for EM REML. Performance of the analytical and the MC EM REML algorithm was compared using a simulated and a field data set. For field data, results from both algorithms corresponded well even with one MC sample within an MC EM REML round. The magnitude of the standard errors of estimated prediction error variances depended on the formula used to calculate them and on the MC sample size within an MC EM REML round. Sampling variation in MC EM REML did not impair the convergence behaviour of the solutions compared with analytical EM REML analysis. A convergence criterion that takes into account the sampling variation was developed to monitor convergence for the MC EM REML algorithm. For the field data set, MC EM REML proved far superior to analytical EM REML both in computing time and in memory need.     

Successful reduction of a monozygotic equine twin pregnancy via transabdominal ultrasound‐guided cardiac puncture

In horses, twin pregnancy is pathological and represents a potentially life‐threatening condition to the mare and foal. Twinning occurs in approximately 2% of pregnancies. Of these, the majority of cases are dizygotic twins, resulting from 2 ovulations and monozygotic twins are rare. A 12‐year‐old Quarter Horse mare was presented for breeding management with shipped cooled semen and embryo transfer. Seven days post ovulation, a single late morula/early blastocyst was recovered and transferred immediately to a recipient mare. Thirty‐six days after transfer, transrectal ultrasound examination revealed the presence of 2 embryos. A transcutaneous reduction of one of the fetuses was performed successfully at 128 days of gestation. This report is the first to describe a successful reduction of monozygotic twins by transcutaneous ultrasound‐guided cardiac puncture.     

Does Shrub Removal Increase Groundwater Recharge in Southwestern Texas Semiarid Rangelands?

Evapotranspiration (ET) is a key component limiting groundwater recharge past the root zone in semiarid regions. Vegetation management may alter groundwater recharge if ET is altered due to changes in vegetation type or cover. This study quantifies changes in groundwater recharge following vegetation cover change from native woodland to pasture in a semiarid region of southwest Texas. The Carrizo–Wilcox aquifer is a valuable groundwater resource in this area, where overuse by dependent farming practices has lowered aquifer levels significantly in the last 85 yr. Combining data from short-term (30 mo) monitoring of the changes in soil moisture and long-term (5–30 yr) changes in total soil chloride indicated deep drainage increased slightly where land had been cleared of vegetation. Annual recharge rates below rooting depths (standardized to 155 cm) averaged only 0.72 ±  mm · yr^-1 (mean ± SE) in areas not cleared of woody vegetation, as estimated by chloride mass balance. Upon clearing, 72% of the total chloride naturally occurring in the soil profile was flushed away within 30 yr, leading to an estimated 2.59 ±  mm · yr^-1 additional recharge. Deep soil moisture in recently cleared land increased by up to 17% during the growing season of wet years (double the average rainfall) but did not increase in dry or normal precipitation years, providing supporting evidence that more water penetrated below the roots under certain environmental conditions. These results demonstrate that brush management can increase recharge by modest, but measurable, amounts depending on site-specific soil characteristics and degree of reduction in vegetation.     

Recovery threshold of Toxocara canis eggs from soil

The purpose of this study was to evaluate the threshold of Toxocara canis eggs form soil samples through utilisation of a centrifuge-flotation technique (CFT). Aliquots of soil (1 g each) were artificially contaminated with known numbers of T. canis eggs (1, 10, 25, 50, 100, and 200 eggs). The threshold was evaluated based on a CFT using zinc sulphate (Zn₂SO₄) and sodium nitrate (Na₂NO₃) solutions at a specific gravity of 1.20. The number of eggs recovered was directly proportional to the number of eggs employed to seed the soil. Both solutions enabled full recovery of samples containing merely three eggs; only Zn₂SO₄ demonstrated efficiency in soil contaminated with a single egg. A recovery rate of 100% was obtained for all tests with samples containing 10 and 25 eggs for Zn₂SO₄ and Na₂NO₃, respectively_. There was no difference in the mean number of recovered eggs regarding either the efficacy of the solutions or the repetition of evaluations in the same trial (p > 0.05). Therefore, the CFT is efficient for the detection of Toxocara eggs, even in samples containing low egg numbers.