Selection for longevity and yield in dairy-cows using transmitting abilities for type and yield

A dynamic programming model was used to derive economic values for the goal traits milk, fat and protein yield and longevity. The economic values derived were pound 3.37 per complete lcatation four (conditional on having a molk record in the first lcatation) and pound-0.03, pound 0.60 and pound 4.04 per kg for milk, fat and protein yield respectively. In terms of genetic standard deviations the weight for protein, fat, milk and longevity were 1.0, 0.21, ¸-0.25 and 0.55, respectively. Using economic values and genetic (co) variances, weights were derived from milk fat, protein and four linear type traits (chosen out of fifteen on the basis of the genetic correlation with longevity): angularity (angular), foot angle (sleeper), udder depth (shallower) and teat length (shorter). Three additive indices were derived, assuming that the breeding goal was for. (i) yield only (PIN), (ii) longevity only (LIN) or (iii) yield and longevity, hence economic merit (ITEM). Selection on ITEM is expected to give a 2genetic progress compared with selection on PIN. Efficiency of using ITEM was larger than 0.97 compared with the optimum index, when the real individual economic values increased or decreased by a factor 1.5 or 2.0. Weights for ITEM were calculated assuming that predicted transmitting abilities (PTAs) from complete multivariate analysis were used as index measurements. In the practical situation that index measurements come from (i) separate univariate best linear unbiased prediction (BLUP) evaluations of (ii) two multivariate BLUP evaluations (one for type and one for yield), efficiency of ITEM (compared with the optimum index) decreased with decreasing accuracy of the PTAs and with increasing ratio between number of records for type and yield, or vice versa, but remained close to 100 the (not practical) situation where accurate PTAs for type and inaccurate information for yield were combined, did the efficiency of ITEM drop as low as 0.44, due to a change of sign for udder depth in the optimal index.