A maternal productive index for beef cows

Abstract

To evaluate beef cows on their reproductive performance a maternal productive index (M.P.I.) was developed as an alternative to their evaluation in terms of simpler traits, or in terms of a conventional selection index based on simple traits. Data on M.P.I. were obtained from Hereford cows on three grazing treatments each containing three groups of cows differentiated by last breeding season (i.e. presence and age of calf at foot). The same cows were also scored for coat type on two occasions in late spring and early summer. The magnitude and change of coat score are explained by the hypothesis that nutritional stress delays the cycle of shedding of winter coat and its replacement by a sleek coat. Analysis of the correlations between coat score data and M.P.I. shows that low M.P.I. is also associated with a delay in change of coat type. This suggests that M.P.I. is an indication of adaptation of cows to their environment with poorly adapted animals suffering a greater stress. Because M.P.I. is a direct measure of a very important goal of beef cattle breeding it should be used widely in selection (or culling) of beef cows. Whether genetic progress will be faster than through the use of simpler traits, may be judged once genetic parameters have been estimated for M.P.I.