An Sci 361 1st Edition Lecture 19 Outline of Last Lecture I. Genetic GainII. Selection Intensitya. Criterionb. Processc. Measuringd. Theoretical ApproachIII. Genetic VariationIV. Generation IntervalV. Selection Pathsa. Maleb. FemaleOutline of Current Lecture I. Generation IntervalII. Selection Pathsa. Maleb. FemaleCurrent LectureGeneration Interval- Generation Interval (L) is average age of parents when offspring are born - Typically measured in years of ageo To calculate L, simply add across all progeny the ages of their sires and dams; calculate average age of parents L = (average age of sires + average age of dams)/2o Using younger parents reduces generation interval and increases genetic gain peryear- Is limited by reproductive characteristics of species, e.g. age at puberty, gestation length,litter size, etc.- Can be managed by breeders- To determine generation interval, consider:o Life Cycleso Number of Paritieso Ages of parents when progeny are bornThese notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.o Reproductive cycleso Herd or flock age structureo Gestation LengthsCommon Generation Intervals for Farm AnimalsSpecies Generation Interval (yr.)Horses 8 to 12Dairy Cattle 4 to 6Beef Cattle 4 to 6Sheep 3 to 5Swine 1.5 to 2Chickens 1 to 1.5Refined definition of Generation Interval (L) = average age of parents when offspring that are potential replacements are born- Which herd has the shorter generation interval?o A dairy herd that breeds heifers to Angus bullso A dairy herd that uses only dairy bulls2 Selection Paths: Males and Females- Accuracy, intensity, and generation interval may differ between sires and damso Fewer males are needed than females, i.e. greater selection intensity in maleso If selection is based on progeny test results, males will have more progeny than females, i.e. greater accuracy in male selectiono Progeny tested males may be older than females, i.e. greater generation interval for males - ΔBV / YR = Sum of male & female selection responses / Sum of male & female generation
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