Prediction of mature cow carcass composition from live animal measurements.

Two trials were conducted with mature cows to develop prediction equations for estimating carcass composition from live animal measurements. Trial 1 involved 82 animals that were used to develop these equations. Subjective criteria (frame and condition scores) also were utilized along with live weight in development of prediction equations. Equations using subjective independent variables predicting energy and carcass tissue weights apparently were slightly more variable in precision (R2 = .69 to .91) than those developed with objective variables (R2 = .74 to .90). Equations predicting percent compositions from subjective variables had lower coefficients of determination (R2 = .49 to .76) than those developed with objective variables (R2 = .63 to .83). Forty-one animals similar to those used in Trial 1 served as a test group in Trial 2. Measured carcass composition was regressed on composition predicted by equations developed in Trial 1. These equations generally had slopes and intercepts with confidence intervals that included 0 and 1, respectively, indicating that most of the prediction equations were unbiased. This work indicates that carcass composition can be predicted from both objective and subjective measurements, with some accuracy and precision.

Growth patterns of Angus, Hereford and shorthorn cattle. I. Comparison of inbred and noninbred lines, changes in patterns over time and effects of level of inbreeding and reproductive performance.

Mature weight (A) and rate of maturing (K) were estimated for 283 Angus, 140 Hereford and 280 Shorthorn cows utilizing the asymptotic regression equation Yt=A(1-Be-Kt). The Yt was weight of the individual at age t; and B was an estimate related to early life weight changes and provided for a Y-intercept (A-B). Each breed consisted of four inbred and two noninbred lines. Regression of estimated growth curve parameters on levels of inbreeding of the individuals and of their dams and effects of early reproductive performance (EREPRO) were studied as sources of variation in addition to line differences and trends in line values over years. Considered jointly with inbreeding of the dam and with EREPRO, inbreeding of the individual was negatively related (P less than .01) to estimates of A in the three breeds and unrelated (P greater than .10) to estimates of K. Each 1% increase in inbreeding of the individual was associated with about 2 kg decrease in estimated mature weight. An increase in inbreeding of the dam of an individual was negatively related to estimates of K in Angus (P less than .01) and Shorthorns (P less than .05). Inbreeding of dams was positively related to estimates of A in the three breeds, but only in Shorthorns could the relationship be declared significant. Estimates of A were about 46 kg heavier and estimates of K about .010 less for each year an individual failed to produce a calf during her first three opportunities. In general, A values declined in all three breeds during the study. Significant changes were observed in all Hereford analyses and after inbreeding was included in the Angus analysis, while inclusion of inbreeding in the Shorthorn analysis caused the change to become unimportant. The K values increased in all three breeds during the study; however, the change could be declared significant only in Herefords.

Growth patterns of Angus, Hereford and shorthorn cattle. II. Relationship of growth patterns of dams with progeny performance.

Relationships between estimated growth curve parameters of dams and performance traits of their progeny were studied in Angus, Hereford and Shorthorn herds, each divided into four inbred and two noninbred lines. Growth curve parameters were calculated from the growth function Yt=A(1-Be-Kt), where Yt was weight at age t, A was estimated mature weight, B was an estimate related to early life weight changes and provided for a Y-intercept term and K was estimated general rate of maturing. Least-squares analyses of progeny variables were calculated separately for each breed and sex. Line differences did not influence any of the progeny variables except weaning type score of Shorthorn males (P less than .01). Birth year exerted a curvilinear effect on birth weights of Angus female progeny (P less than .01), a linear influence on 205-d weights of Shorthorn male progeny (P less than .05) and a curvilinear effect on weaning type scores of Angus and Shorthorn male progeny (P less than .01). Regression coefficients on weaning age indicated that calves born earlier in the calving season had lighter birth weights and that older calves at weaning received higher type scores. Inbreeding of the progeny negatively influenced (P less than .05) birth weights of Angus male and Hereford female progeny. Hereford male and Shorthorn female 205-d weights were negatively affected (P less than .05) by inbreeding, while weaning type scores of Shorthorn female progeny were negatively influenced (P less than .001) by inbreeding. Regression coefficients of all progeny variables on inbreeding in all analyses indicated negative trends.(ABSTRACT TRUNCATED AT 250 WORDS)