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Indexes in retrospect to determine situations in which no change in gestation length would be expected
Data for the first three cycles of the Germ Plasm Evaluation (GPE) program at the Meat Animal Research Center (MARC) were used to determine indexes in retrospect, for Angus and Hereford cattle, to explain the lack of change in gestation length (GL). Estimates of variance components, heritabilities, and genetic correlations between pairs of traits were obtained. Birth weight (BWT), weaning weight (WWT), yearling weight (YWT), and mature weight (MWT) were used to determine indexes for Angus sires and calving difficulty (CD), BWT, WWT, and YWT were used for Hereford sires. Calves with two-year old dams typically have greater variation for CD and BWT. In addition to CD and BWT of calves of dams of all ages, CD and BWT for calves of two-year-old dams were analyzed separately as well as with all traits. A total of four indexes were calculated for both Angus and Hereford sires. Indexes 1 and 2 consisted of two known components, the genetic (co)variance matrix (G), and genetic selection differentials (ΔG), from which the selection index weights (b) can be found. Indexes 3 and 4 used the phenotypic (co)variance matrix instead of the G matrix. Indexes 1 and 3 were derived from records of calves of two-year old dams for CD and BWT and records of calves from all ages of dam for all other traits. Indexes 2 and 4 were derived from records of calves of all ages of dams for all traits. Expected correlated responses were calculated using the weights (b) for the indexes in retrospect. To determine factors that influence GL, changes in ΔG were made until the correlated response for GL was zero. For most indexes, WWT appeared to have the largest influence on GL. ^
Agriculture, Animal Culture and Nutrition|Agriculture, Animal Pathology
Senneke, Sandra L, "Indexes in retrospect to determine situations in which no change in gestation length would be expected" (2005). ETD collection for University of Nebraska - Lincoln. AAI3180817.