Effect of bovine somatotropin (BST) on the efficiency of dairy breeding schemes

Abstract

A free access to bovine somatotropin (BST) in recorded dairy herds would bring some disturbances into dairy breeding schemes. The existing numeric simulation results show that cow selection as well as bull selection would be affected. The overall effect would be a reduction of annual genetic gains and most of all, a misevaluation of the true efficacy of breeding schemes. Optimistic or pessimistic views of the selection scheme would result according to the screening policy for BST treatment. Consequently, correcting the data for a possible treatment is of the utmost importance. Simulations show that to keep some reliability in any circumstance, these corrections should proceed from within animal comparisons between treated and untreated monthly records. Since the relevant methodology does not exist yet and since the accuracy of such corrections is not yet known, the only immediate possibility would be for treated cows to extend part lactations preceding the first BST injection. On the long run, if corrections are not implemented for reasons described within the text, selection work should be concentrated within contracted herds, using intensive reproduction techniques.