Estimates Of Genetic Gain Research Articles

Genetic and Phenotypic Variation in Randombred White Leghorn Controls over Several Generations

IT IS A generally accepted fact that adequate controls are essential for the estimation of genetic gain in selection studies. Lerner (1950), Dickerson (1955), Goodwin et al. (1955), Gowe and Johnson (1956), King et al. (1959) and others have recognized and discussed the value of control strains for the separation of genetic and environmental effects. Gowe et al. (1959) clearly demonstrated the value of a control strain by comparing absolute trends of two selected strains with trends estimated by use of deviations from a control population. These workers also studied changes in this White Leghorn Control Population during six years by regressing annual means on generation number. No significant changes in hen-housed and survivor egg production, body weight at housing, March body weight or laying house mortality were noted. A significant increase in March egg weight and a significant decrease in sexual maturity were observed. King et al. (1963) investigated.

Estimation of genetic gain in milk yield by selection in a closed herd of dairy cattle

1. Methods of estimating the rate of genetic gain achieved in animal improvement are discussed and criticized. 2. A theoretical method of estimation of the maximum possible genetic gain of milk yield under direct selection is presented for a closed herd of dairy cattle. The maximum possible gain is approximately 1% of the average yield. 3. The method can also be used for the estimation of genetic gain from the selection practised in an actual, herd. An estimated gain of milk yield of 0.7% per year is given for one herd.