David Ll. Thomas

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Repeated records on fertility, litter size, and ovulation rate of Rambouillet ewes and on fertility and litter size of Finnsheep ewes were used to estimate heritabilities and repeatabilities with linear and nonlinear sire and animal models. Linear sire (LSM) and animal models were used with all traits. Nonlinear models were the threshold, Poisson, and(More)
A comparison of linear (LM), threshold (TM), and Poisson (PM) mixed models for genetic analysis of number of lambs born (NLB) from 1-yr-old ewes was conducted using 37,718 and 18,633 records of two Norwegian breeds, Dala and Spaelsau, respectively. Models fitted included flock-year as a fixed effect and the random effect of sire. In the Poisson model, the(More)
The variance and covariance components needed to estimate heritabilities of and genetic correlations among litter size, ovulation rate, scrotal circumference, and BW in a flock of Rambouillet sheep were estimated using REML via an expectation-maximization type algorithm. The heritability estimates from univariate analyses were .14, .21, .25, .36, and .15(More)
The most essential component of precision farming is the yield monitor, a sensor or group of sensors installed on harvesting equipment that dynamically measure spatial yield variability. Yield maps, which are produced using data from yield monitors, are extremely useful in providing the farmer a color-coded visual image clearly showing the variability of(More)
The performance of linear and nonlinear sire and animal models in the analyses of reproductive traits (fertility, litter size, and ovulation rate) in two sheep populations (Rambouillet and Finnsheep) was compared in terms of goodness of fit and predictive ability. Linear sire (LSM) and animal (LAM) models were used with all traits. Nonlinear models were the(More)
A multistate cooperative study was conducted to study the current issue of tail length in docked lambs and its relationship to incidence of rectal prolapse. A total of 1,227 lambs at six locations were randomly allocated to two or three tail dock treatments: 1) short--tail was removed as close to the body as possible, 2) medium--tail was removed at a(More)
Approximate and exact Bayesian analyses of survival from birth to weaning measured as an "all or none" trait were conducted on 2,554 Rambouillet lambs using an asymptotic normal approximation and Monte Carlo numerical integration with importance sampling, respectively. A linear logistic model was used to assess the effects of year, age of dam, sex of lamb,(More)
The variance and covariance components estimated from an experimental flock of Rambouillet sheep were used to predict response in litter size to direct and indirect selection. Indirect traits considered were ovulation rate and scrotal circumference. Ovulation rate was the most useful indirect selection criterion for genetic improvement of litter size.(More)
Commercial milking of sheep is a new agricultural industry in the United States starting approximately 30 yr ago. The industry is still small, but it is growing. The majority of the sheep milk is used in the production of specialty cheeses. The United States is the major importer of sheep milk cheeses with 50 to 60% of annual world exports coming to the(More)
Restoration of degraded land is recognized by the international community as an important way of enhancing both biodiversity and ecosystem services, but more information is needed about its costs and benefits. In Cambridgeshire, U.K., a long-term initiative to convert drained, intensively farmed arable land to a wetland habitat mosaic is driven by a desire(More)