The German total index RZG has changed its formula. Compared to the former RZG, the portion of production has decreased from 45% to 36%, the fitness portion increased from 40% to 49% and type remains at 15%. RZS (somatic cell) dropped out of the RZG formula, while RZGesund (18%) and calf vitality (3%) are included for the first time.
To achieve the maximum overall genetic gain in dairy cattle breeding, a Total Merit Index is applied to improve all traits according to their relative importance in the breeding goal. This Total Merit Index is called RZG (Relativ Zuchtwert Gesamt) and is applied to Holstein and Red Holstein. The derivation of the Total Merit Index (RZG) is based on selection index theory. This is providing the optimum overall selection response in all traits. The relative breeding values (composites or indices) are considered as information traits.
The RZG is only published if a bull has an official index for production (RZM), somatic cell score (RZS), functional herd life (RZN) and conformation traits (RZE). The RZG is standardized to a mean of 100 in the base (cow base with all cows who are 4-6 years old) and a genetic standard deviation of 12 points. The official ranking of Geman top bulls is by RZG. Breeding values of Holsteins and Red Holsteins in Germany are estimated three times a year.
