Body temperature and respiratory rate of lactating dairy cattle under field and chamber conditions.

A coordinated field and chamber experiment assessed breed, sire, and cow differences in body temperatures and respiratory rates. During each of 4 yr, 10 lactating Ayrshire, Guernsey, Holstein, and Jersey cows, 40 animals per yr, were observed in the field on 10 d when the air temperature approached 32 degrees C. For the first 3 yr, each cow also was exposed in a controlled atmospheric chamber at 40 degrees C and 34 mm Hg vapor pressure. Significant breed differences were found for body temperature and respiratory rate. The order of tolerance to hot conditions was Jersey, Guernsey, Ayrshire, and Holstein both in the field and chamber. Significant sire differences, interpreted as genetic, were found for the field measures but not in the chamber. Repeatability of individual field observations for a cow on different days in a year ranged from .38 to .55. Correlations between the average of 10 observations for a cow in the field during a year and the chamber evaluation were positive but lower than the repeatability values. Correlations of ambient temperature with body temperatures and respiratory rates were highest; those for radiation were next, followed by vapor pressure and air movement.

Efficiency of feed utilization in Holsteins selected for yield.

Feed intakes were obtained for d 71 through d 120 postpartum for 36 first lactation selection and 32 control cows during the last 3 yr of a 16-yr selection experiment for FCM yield in Holsteins. The ration consisted of concentrates fed according to production, limited alfalfa hay, and ad libitum corn silage. The higher estimated net energy intake by selection cows was due primarily to their significantly higher silage intake. Grain intake was slightly higher for the selection animals, but the control animals had a slightly higher hay intake. Neither differences was statistically significant. Only small and statistically nonsignificant differences in BW and weight change were found between the two groups. Selection animals had a 7.6% advantage in gross efficiency for the 50-d trial. Selection for yield gave a desired correlated change in gross feed efficiency.

Measuring genetic change in a dairy herd using a control population.

A selection experiment was conducted to assess the change in production resulting from selection with artificial insemination using a randomly maintained control. The experiment continued for 16 yr with approximately 20 lactations in each of the two breeding groups annually. Selection and control production was compared using 1) intraseason herdmate comparisons (weighted) and 2) mixed model maximum likelihood estimates of year-season effects (adjusted). The regressions of differences in milk yield on years for the two approaches were 110 kg for milk (weighted) and 108 kg for milk (adjusted), corrected for inbreeding. The regressions for fat were 3.9 kg for fat (weighted) and 4.2 kg for fat (adjusted). These regression coefficients were 1.6 and 1.5% of the least squares means for milk (6987 kg) and fat (259 kg), respectively. Definitive trends were not evident for differences between the two groups in percent fat, percent SNF, days open, final type classification score, or heart girth. Even with the limited numbers in the closed control population, inbreeding, and nonrandomness in culling of females or in the choice of dams of bulls appeared to have little impact on control mean during the 16 yr.

Correlated response in skeletal traits and replicate variation in selected lines of mice.

Correlated responses in caudal vertebrae number (VN), lengths of eighth and ninth caudal vertebrae (V8 and V9, respectively), femur length (FL) and femur weight (FW) were evaluated in lines of mice which had been selected for six-week body weight (WK6) and/or six-week tail length (TAIL). Ten males and ten females were randomly sampled from each of ten selected lines (two replicates each of five selection treatments) after seven generations of selection. Sexes and lines were significant (P < .01) sources of variation in all seven traits. Sex x line interactions were unimportant except for V8 and V9. Male mice of both replicate lines selected for increased WK6 and decreased TAIL had shorter vertebrae than females, whereas the reverse was true for all other lines. Multiple regression and canonical correlation analyses indicated a high phenotypic relationship of FL with both WK6 and TAIL. Examination of the correlated responses indicated that FL was the only skeletal trait that showed a substantial correlated response to single trait selection for both WK6 and TA IL. Thus, the genetic relationships among the three traits also appeared to be high. Between replicate variation was not significant for randomly selected control lines. However, about onethird of the statistical tests between selected replicates were significant. This was taken to indicate a joint effect of selection and drift in causing variation between replicate lines. Replicate variation was further examined by canonical variate and generalized distance analyses. The first two canonical variates accounted for most of the generalized variance. Graphically, the first two canonical variables discriminated among selection treatments, whereas the replicates tended to cluster. Thus, although between replicate differences were significant for several traits, the differences were relatively small compared with the variation between lines having different selection criteria.

An experimental evaluation of genetic correlation.

Heritability and genetic correlations realized from both single-trait and antagonistic index selection were compared with paternal half-sib estimates. Primary attention was focused on the genetic correlation between six-week body weight and six-week tail length. Parameters realized from single-trait selection were in excellent agreement with paternal half-sib estimates. However, the realized genetic correlation between six-week body weight and six-week tail length obtained from index selection was significantly greater than the other estimates. Differential inbreeding levels and realized selection intensities were considered and rejected as being causative factors for these results. Linkage disequilibrium probably was not a factor either, as the base population had been randomly mated and randomly selected with a large effective population size for many generations. It was concluded that with antagonistic index selection, the pleiotropic effects of genes may be more powerful in retarding response in aggregate genotype than current theory would suggest. Replication of all selected and control lines allowed the use of between-line estimators of sampling variances of realized genetic parameters in the above comparisons. Generally, standard errors of realized genetic parameters were much smaller than corresponding paternal half-sib standard errors. Thus, selection was an efficient method of estimation.

Effects of population size and selection intensity on correlated responses to selection for postweaning gain in mice.

Correlated responses to selection for postweaning gain in mice were studied to determine the influence of population size and selection intensity. Correlated traits measured were three-, six- and eight-week body weights, litter size, twelve-day litter weight, proportion infertile matings and two indexes of reproductive performance. In general, the results agreed with observations made on direct response: correlated responses in the body weight traits and litter size increased as (1) selection intensity increased and (2) effective population size increased. Correlated responses in the body weight traits and litter size were positive in the large population size lines (16 pairs), as expected from the positive genetic correlation between these traits and postweaning gain. However, several negative correlated responses were observed at small population sizes (one and two pairs). Within each level of selection intensity, traits generally associated with fitness tended to decline most in the very small populations (one and two pairs) and in the large populations (16 pairs) for apparently different reasons. The fitness decline at the small effective population sizes was attributable to inbreeding depression. In contrast, it was postulated that the fitness decline at the large effective population size was due to selection moving the population mean for body weight and a trait positively correlated genetically with body weight (i.e., percent body fat) away from an optimum.

Comparison of growth functions within and between lines of mice selected for large and small body weight.

Several criteria have been suggested for comparing different nonlinear growth functions to determine which function gives the best quantitative description of a given set of observed sigmoid growth curves. These criteria were then used to compare the logistic, Gompertz and Bertalanffy functions within and among lines of mice: a control line (C 1) and lines selected for large (H 6) and small (L 6) body weight at six weeks of age.A general comparison of the three growth functions was based on the differences in residual variances of the respective functions fitted to the growth data of individual mice. Since the three functions differ primarily in the fixed proportion of the asymptotic weight at which the inflexion point occurs, the growth function which will provide the minimum residual variance among the three considered is the one which most closely approximates the observed proportion. The results of this comparison indicated that the logistic function gave the best fit for both sexes of the H 6 and C 1 lines. While no significant differences in residual variances were evident in L 6 males, the Bertalanffy function had the smallest residual variance in L 6 females.The four derived traits of each growth function analyzed individually were the asymptote (A), age at inflexion (t (*)), rate at which a logarithmic function of body weight changes with time (k) and mean absolute growth rate with respect to body weight increase (v). The coefficient of variation among individuals within full-sib families was used to compare the relative variability of the analogous traits estimated from the three growth functions. The coefficients of variation of A, t (*) and k calculated from the logistic function were significantly (P < .01) smaller than those from both the Gompertz and Bertalanffy functions in all three lines, while there were no significant differences in the relative variability of v among the three lines. The genetic and phenotypic correlations between the analogous traits estimated from two different growth functions were sufficiently high in most cases to conclude that the same trait was being measured by the three growth functions. Each derived trait was analyzed for variation in lines, sexes, seasons and respective interactions. The sources of variation generally exhibited similar levels of significance for the analogous traits estimated by the three functions, although a few exceptions were found. These results suggest that although the logistic function provided the best description of the growth data, the same general conclusions about differences within and among the three lines would have been reached with any of the three functions. The four derived traits of the logistic curve were used to describe quantitatively the differences in growth among the H 6, L 6 and C 1 lines.

Rate, composition and efficiency of growth in mice selected for large and small body weight.

Mice selected for high (H6) and low (L6) 6-week body weight and a randombred control population (C1) were characterized for rate, composition and efficiency of growth. Individual body weights were obtained from birth to 8 weeks of age on 682 mice representative of the three lines. Individual whole carcass determinations of water, fat, ash and protein (residual) were obtained for 180 mice sampled weekly from 3-8 weeks of age. Efficiency of feed utilization was estimated from individual body weight and feed consumption data obtained on 189 mice from 3-8 weeks of age. Growth curves for body weight and gain in body weight, constructed by line and sex, showed a temporary retardation of maximum growth rate in the L6 line, which was attributed in part to an extended depression in growth following weaning. The composition of growth yielded no evidence that the more rapid growth rate in the H6 line resulted from an increase in fat deposition relative to the other carcass components. A decrease in fat percent at 7 weeks of age in the H6 and C1 lines was not evident in the L6 line until 8 weeks of age. Females had a higher percentage carcass fat than did males during the 4-7 weeks growth period, but this difference was essentially reduced to zero by 8 weeks of age. Percentage water was highly correlated negatively with percentage fat. Percentages protein and ash were essentially constant across lines and ages. A positive relation between rate and efficiency of growth was observed between lines. Consistent sex differences, males more efficient than females, were observed prior to 6 weeks of age, but were not evident in the later (6-8 week) data.