GENETIC AND ENVIRONMENTAL PARAMETERS FOR MATURE WEIGHT AND OTHER GROWTH MEASURES IN POLLED HEREFORD CATTLE

Variances and covariances were estimated for birth weight (BWT), weani ng weight (WW), yearling gain (YG), yearling weight (YW), yearling hei ght (YH), relative growth from birth to weaning (RGW) and weaning to y earling (RGY), and mature weight (MW). Field records on 572,446 Polled Hereford cattle were analyzed. Because multiple dam weights were coll ected on a cow the MW used in the analysis was calculated using a nonl inear regression correction factor computed by fitting a quadratic wit h a plateau to the data. If the cow had an observation(s) beyond the i nflection point (IP), the closest weight to that point was used. If th e cow only had observation(s) before the IP the closest weight to that point was nonlinearly adjusted to the plateau. The IP for this data s et was 1,506 d and the plateau was 554.7 kg. Heritabilities and geneti c and environmental correlations were calculated from the appropriate (co)variances and phenotypic correlations were computed. Heritability estimates for BWT, WW, YG, YW, YH, RGW, RGY, and MW were .49,.24,.23,. 30,.59, .24, .15, and .52, respectively. Genetic correlations between MW with BWT, WW, YG, YW, YH, RGW, and RGY were .64, .80, .76, .89, .73 , -.29, and .35, respectively, environmental correlations were .15, .4 3, .05, .40, 1.03, .32, and -.10, respectively, and phenotypic correla tions were .33, .32, .28, .46, .70, .00, and .07, respectively.