Date of Award
Doctor of Philosophy
W.T. Butts, R.R. Shrode, J. Philpot, D.O. Richardson
The objectives of this study at the University of Tennessee were to estimate the effect of the following factors on growth curve parameters: (1) age, (2) season and frequency of weighing. (3) reproductive status at three age intervals and (4) condition of the cow at early age. The final objective was to evaluate the relationship of mature weight and general rate of maturing with performance of progeny.
The main body of data consisted of the growth curve parameters, mature weight (A) and rate of maturing (K), as determined by asymptotic regression of several series of weights on 102 mature Angus cows. The growth model described by Brody (1945) was used as the basis of the asymptotic regression. The study was divided into two phases. The first phase was designed to evaluate growth curve parameters derived from weights taken from birth to specified ages ranging from 1.5 years to 8.5 years of age plus one set of estimates derived using lifetime weights. The second phase was used to determine the influence of season of year on the parameters estimated from weights taken at various times of the year.
In Phase I the mean estimates of mature weight (A) were 539, 503, 465, 473, 481, 485, 484 and 482 kg for ages 1.5 through 8.5 years, respectively. The mean estimates of rate of maturing (K) were .061, .069, .073, .069, .065, .062, .061 and .061 for the same ages. The mean estimates of A and K using lifetime weights were 497 kg and .056, respectively. Correlations between estimates of A at the various ages were low until 4.5 years of age, at which time the correlation tended to stabilize. The same trend was shown between estimates of K. Early reproductive status of each cow was coded as (1) if the cow calved at two and three years of age, (2) if the cow calved just at three or (3) if the cow calved at two and was open at three. The least-squares analyses of A and K showed a significant age-reproduction interaction. The-cow-within-reproduction component was highly significant, indicating significant independent variation with which to work in animal breeding projects.
In Phase II eight weight-age curves were calculated for each animal—one group of four sets of estimates using weights to five years of age and another group using lifetime weights. Within each group one set of parameters was estimated using all weights to the respective age. The other three sets were based on weights from birth to yearling plus one weight per year—summer, fall or winter. The symbols A and K are used with the following subscripts: 0 or 5 as a first digit to represent lifetime and five years of age, respectively; 0. 2. 3, or 4 as a second digit to represent all weights, summer weights, fall weights or winter weights, respectively. Mean estimates of mature weight were 496, 492, 522, 483, 478, 487 and 508 kg for A00, A02, A03, A04, A50, A52, A53 and A54, respectively. Mean estimates of rate of maturing were .0573, .0583, .0614, .0545, .0646, .0642, .0642 and .0602 for K00, K02, K03, K04, K50, K52, K53 and K54, respectively. Correlations among the estimates of mature weights were all positive and larger than .7. Correlations among the rates of maturing were larger than .5 except for those involving the relationship of K00 and estimates of the parameters derived using weights up to five years of age. This study indicated that a single annual weight from one to five years of age is adequate for estimating growth curve parameters.
Morrow, Ronald Edwin, "Age, frequency and season of weighing, and reproduction as factors influencing growth curve parameters in Angus cows. " PhD diss., University of Tennessee, 1974.