Peter Gates

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Retired animal science researcher and bureaucrat

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Papers by Peter Gates

Quasi-REML" correlation estimates between production and health traits in the presence of selection and confounding: a simulation study

Journal of Animal Science, 1999

Performance of the "quasi-REML" method for estimating correlations between a continuous trait and... more Performance of the "quasi-REML" method for estimating correlations between a continuous trait and a categorical trait, and between two categorical traits, was studied with Monte Carlo simulations. Three continuous, correlated traits were simulated for identical populations and three scenarios with either no selection, selection for one moderately heritable trait (Trait 1, h 2 = .25), and selection for the same trait plus confounding between sires and management groups. The "true" environmental correlations between Traits 2 ( h 2 = .10) and 3 (h 2 = .05) were always of the same absolute size (.20), but further data scenarios were generated by setting the sign of environmental correlation to either positive or negative. Observations for Traits 2 and 3 were then reassigned to binomial categories to simulate health or reproductive traits with incidences of 15 and 5%, respectively. Genetic correlations ( r g12 , r g13 , and r g23 ) and environmental correlations ( r e12 , r e13 , and r e23 ) were estimated for the underlying continuous scale (REML) and the visible categorical scales ("quasi-REML") with linear multiple-trait sire and animal models. Contrary to theory, practically all "quasi-REML" genetic correlations were underestimated to some extent with the sire and animal models. Selection inflated this negative bias for sire model estimates, and the sign of r e23 noticeably affected r g23 estimates for the animal model, with greater bias and SD for estimates when the "true" r e23 was positive. Transformed "quasi-REML" environmental correlations between a continuous and a categorical trait were estimated with good efficiency and little bias, and corresponding correlations between two categorical traits were systematically overestimated. Confounding between sires and contemporary groups negatively affected all correlation estimates on the underlying and the visible scales, especially for sire model "quasi-REML" estimates of genetic correlation. Selection, data structure, and the (co)variance structure influences how well correlations involving categorical traits are estimated with "quasi-REML" methods.

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Bayesian analysis of birth weight and litter size in Baluchi sheep using Gibbs sampling

Journal of Animal Science, 1999

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Nongenetic variation in litter size in Swedish sheep

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Effects of Melatonin, Progestagens, and the Ram on Out-of-Season Reproduction in Swedish Landrace Finewool Sheep

Acta Veterinaria Scandinavica, 1998

One hundred twenty-one Swedish Landrace Fmewool ewes were treated with progestagen sponges (P), t... more One hundred twenty-one Swedish Landrace Fmewool ewes were treated with progestagen sponges (P), teaser ram stimulation (R), or melatonm implants plus teaser ram strmulatton (M) m preparation for breedmg with whole rams in August. Blood progesterone analyses from ewes m the R and M groups gave no evidence of luteal activity before the mtroductlon of teaser rams. There were no s1gmficant differences between treatments for pregnancy rate ( -90% ). The P group had the most compact lambing season, while median breedmg dates for M and R groups were delayed by one cycle. In those groups, the mtroduct1on of breedmg rams was later found to have been too late. M and R differed s1gmficantly for probable conception date but not for lambmg dates. Circa 30% of M ewes dtd not have a short 6 day ovulation cycle after the first ovulation, which resulted m a less concentrated lambmg season than the other methods. Although no s1gmficant differences m htter size were seen among the 3 treatments, M had the highest group average, 2.25. The ewes m this study were not m very deep anestrous m the middle of August. This supports the conclusion that treatment with exogenous hormones ts not necessary to breed Swedish Landrace Fmewool ewes successfully m late August/early September ewes; breeding season; reproductive performance.

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Heritability and Sire Genetic Trend for Litter Size in Swedish Sheep Estimated with Linear and Threshold Models

Acta Agriculturae Scandinavica, Section A - Animal Science, 1995

AGRIS record. Record number, DK9720947. Titles, Heritability and sire genetic trend for litter si... more AGRIS record. Record number, DK9720947. Titles, Heritability and sire genetic trend for litter size in Swedish sheep estimated with linear and threshold models. Personal Authors, Gates, PJ (Sveriges Lantbrukshoegskola, Uppsala (Sweden)),Urioste, JI. Publication Date, (Nov 1995 ...

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Non-Genetic and Breed Variation in Litter Size in the Swedish Sheep Recording Program

Acta Agriculturae Scandinavica, Section A - Animal Science, 1993

AGRIS record. Record number, DK9321025. Titles, Non-genetic and breed variation in litter size in... more AGRIS record. Record number, DK9321025. Titles, Non-genetic and breed variation in litter size in the Swedish sheep recording program. Personal Authors, Gates, PJ. Publication Date, (Aug 1993). AGRIS Subj. Cat. Animal genetics and breeding;Animal physiology - Reproduction ...

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