GENETIC CORRELATIONS IN THE FEED CONVERSION COMPLEX OF PRIMIPAROUS COWS AT A RECOMMENDED AND A REDUCED PLANE OF NUTRITION

An experiment at the Agricultural University of Norway provided geneti c parameters of roughage corrected milk yield (FCM), smoothed BW (SW), weight change (WC), and energy balance (EB). Weekly measurements were averaged in four consecutive 6-wk periods after parturition for each of 331 primiparous Norwegian cows of 20 sires. Amount of concentrate f ed was adjusted according to stage of lactation and cows were randomly assigned to a normal or a low level. Animals were given ad libitum ac cess to grass silage. Multiple-trait animal models with all additive g enetic relationships incorporated were applied to the subsets of all a verages of one trait and all averages in one period. Each model contai ned for every trait 165 observations, 24 mo-year seasons of calving, a nd 313 additive genetic effects. (Co)variance components were estimate d by an EM-REML algorithm. The heritability of RI increased with negat ive energy balance from .25 to .86, whereas the estimates were approxi mately .2 for FCM, .6 to .7 for SW, and .03 to .4 for WC and EB. The c orrelations between RI and FCM were .37 to .58 phenotypically and -.11 to .88 genetically; between RI and SW they were .57 to .73 phenotypic ally and .7 to 1 genetically; between FCM and SW they were -.06 to .35 phenotypically and -.33 to .70 genetically; and between WC and EB the y were .52 to .92 phenotypically and -.09 to .88 genetically. Correlat ions between WC and EB and other traits were inconsistent over periods and had very high SE.