Browsing by Author "Gaines, James A."
Now showing 1 - 7 of 7
Results Per Page
Sort Options
- Alcohol consumption, wantedness, and support of pregnant adolescentsShortt, Sandra Small (Virginia Polytechnic Institute and State University, 1982)The purpose of this study was to explore relationships between pregnant teens' use of alcohol before and during pregnancy and several personal and social variables, including the wantedness of the pregnancy, support of the pregnancy by significant others, pregnant teens' reasons for drinking, the context of their drinking, and the use of alcohol by significant others. This information is needed to plan and evaluate effective prenatal education and intervention programs related to the use of alcohol during pregnancy. Such programs are important in light of increasing numbers of pregnant teens, the number of female adolescent drinkers, and findings about the effects of moderate and binge drinking on fetal development. Subjects consisted of 14 to 19 year old patients of the High-Risk Ob/Gyn Clinic at Roanoke Memorial Hospitals. These patients were predominantly low income urban and suburban teens, with some referrals from areas outside Roanoke City and County. Subjects responded anonymously to a written questionnaire. One-fourth of the subjects were classified as drinkers according to their binge drinking before and during pregnancy. Higher percentages of drinkers than abstainers were white, married, had been pregnant at least once in the past, and intended to become pregnant. Proportionately fewer drinkers indicated religious preferences or attended church services on a regular basis. Drinkers were more likely to smoke and smoked more than abstainers. Personal effects reasons for drinking, consumption in settings where adults were not present, and weekly consumption by peers and boyfriends/husbands were reported by significantly higher percentages of drinkers than nondrinkers. Wantedness and support of significant others were significantly related. Knowledge of the potential harm that all types of alcoholic beverages pose to fetal development was reported by over 70% of the sample. Key sources of knowledge about alcohol and fetal risk were subjects' mothers, pamphlets or books, school health class, the RMH Clinic and television. Boyfriends were also a key source of information for drinkers. Implications of these findings for clinical and educational practice are discussed.
- Correlated response and sexual dimorphism in bidirectional selection experimentsCarte, Ira Franklin (Virginia Tech, 1968-02-05)This dissertation involved two experiments, (1) the study of realized heritabilities of correlated traits, and (2) the study of the inheritance of sexual dimorphism or body weight. The first experiment included data from four generations of double two-way selection for body weight and breast angle at eight weeks of age. Breast angle was considered a correlated trait in the weight subpopulation and body weight a correlated trait in the angle subpopulation. There was a significant divergence between lines for both selected traits. The response to direct selection for breast angle was asymmetrical with the response in the narrow direction being greater then that in the broad direction. The response of body weight to two-way selection was symmetrical through the F₄ generation. Divergence of body weight between the lines selected for breast angle was significant in the F₁, F₃, and F₄ generations. Divergence of breast angle between the lines selected for body weight was significant in the F₂ and subsequent generations. Heritabilities of the unselected traits were obtained by the cumulative difference between lines divided by the expected secondary selection differential and by the regression of the cumulative difference between lines on expected secondary selection differential. The correlated realized heritability of breast angle was greater in the weight lines than was the correlated realized heritability for body weight in the angle lines. Examination of the components of the correlated realized heritability showed that they were the ratio of the genetic to phenotypic covariances of the two traits. The second experiment involved the investigation of sex dimorphism for body weight at eight weeks of age. The heritability estimate for sex dimorphism of this trait was .02, and the genetic correlation of it in males and females was .98. The genetic variability (.02) in sex dimorphism was evidenced by a greater response in males to selection for eight-week body weight than in females. The biological reason for this was additive sex-linkage.
- Density estimation and some topics in multivariate analysisGaskins, Ray Allen (Virginia Tech, 1972-05-15)Part I, entitled "A test of goodness-of-fit for multivariate distributions with special emphasis on multinornality", investigates a modification of the Chi-squared goodness-of-fit statistic which eliminates certain objectionable properties of other multivariate goodness-of-fit tests. Special emphasis is given to the multinormal distribution, and computer simulation is used to generate an empirical distribution for this goodness-of-fit statistic for the standardized bivariate normal density. Attempts to fit a four-parameter generalized gamma density function to this empirical distribution were only partially successful. Part II, entitled "The centroid method of numerical integration", begins with a discussion of the often slighted midpoint method of numerical integration, then, using Taylor's theorem, generalized formulae for the centroid method of numerical integration of a function of several variables over a closed bounded region are developed. These formulae are in terms of the derivatives of the integrand and the moments of the region of integration with respect to its centroid. Since most nonpathological bounded regions can be well approximated by a finite set of simplexes, formulae are developed for the moments of general as well as special simplexes. Several numerical examples are given and a comparison is made between the midpoint and Gaussian quadrature methods. FORTRAN programs are included. Part III - entitled "Non-parametric density estimation," begins with an extensive literature review of non-parametric methods for estimating probability densities based on a sample of N observations and goes on to suggest a new method which is to subtract a penalty for roughness fron the log-likelihood before maximizing. The roughness penalty is a functional of the assumed density function and the recommendation is to use a linear combination of the squares of the first and second derivatives of the square root of the density function. Many numerical examples and graphs are given and show that the estimated density function, for selected values of the coefficients in the linear expression, turns out to be very smooth even for very small sample sizes. Computer programs are not included but are available upon request. Part IV, entitles "On separation of product and error variability," surveys standard techniques of partitioning the total variance into product (or item) variance and error (or testing) variance when destructive testing makes replication over the same item impossible. The problem of negative variance estimates is also investigated. The factor-analysis model and related iterative techniques are suggested as an alternative method for dealing with this separation when three or more independent measurements per item are available. The problem of dependent measurements is discussed. Numerical examples are included.
- Effect of age on the accuracy of selection among beef calves for growth rate and typeMeyerhoeffer, David Clyde (Virginia Tech, 1960-06-05)The data for this study were taken from the calf crops born from 1950 through 1958 at the Beef (Battle Research Station, Front Royal, Virginia. These included 556 Angus, 556 Hereford, and 590 Shorthorn calves.
- The growth pattern of various body and carcass parts and proportions of beef steers as influenced by different planes of nutritionDe Ramos, Mariano Bauyon (Virginia Tech, 1968-12-15)Ten attributes representing various body and. carcass measurements of beef steers were considered for statistical analysis. The slaughter data were obtained from an experiment conducted at Blacksburg, Virginia, by members of the Animal Science Department of the Virginia Polytechnic Institute, described by Kelly et al. (1968). The objective of the study was to obtain estimates of the effects of slaughter time (age), and of the energy level of the ration fed, on the body proportions and carcass composition of beef steers from approximately 7 to 30 months of age. The nutritional regimens used were: Ration I - maintenance; Ration II - full feed of hay; Ration III - limited concentrate plus full feed of hay; Ration IV - full feed of a fattening ration. According to the design of the experiment, the linear model included the general mean, the effects of slaughter time, breed, trial, slaughter time by trial interaction and slaughter time by breed interaction, and an error term. The first part of the investigation dealt with the analysis of variance of the percentage hot carcass to determine whether the effects of breed and trial were significant. In the second part, only the general mean, the slaughter time effect, and an error term were included in the model. When the slaughter time was found significant or highly significant, the sum of squares due to slaughter time was divided into regression components to determine which polynomial regression model best described the relationship between the body component mean and age. The results of the statistical analyses were as follows: 1. Breed and trial effects on the percentage hot carcass were insignificant in all but ration II, in which trial was significant. 2. Slaughter time by trial interaction effect was significant in all rations; slaughter time by breed was not. 3. The percentage hot carcass behaved in a parabolic manner with age, which was concave upward at lower planes of nutrition; the pattern changed to cubic at higher planes. 4. Age had no effect on the mean empty-body weight with steers on ration I; the effect was linear on ration II; quadratic on rations III and IV. Similar growth pattern was obtained for the percentage meat. 5. The percentage of front quarter to total carcass increased proportionately with age in all rations; the opposite trend was obtained for the percentage hind quarter. 6. The relationship of weight of the head, expressed as percentage of the live weight, with respect to age or slaughter time was linear with positive slope on rations I and II and negative on rations III and IV. 7. The percentage moisture in the meat showed a quartic regression with age on ration I presumably due to random fluctuation of the means. For rations II and III, the relationship was quadratic and concave downward; for ration IV, it was linear with negative slope. 8. The percentage crude protein and the percentage ash behaved similar to that of the percentage head, while opposite pattern was obtained for the ether extract.
- Heterosis from crosses among British breeds of beef cattle : straightbred versus crossbred cowsGaines, James A.; Hill, C.; McClure, William H. (Virginia Agricultural Experiment Station, 1985)The second phase of a long-term beef cattle crossbreeding experiment involving the Angus, Hereford and Shorthorn breeds was conducted at the Shenandoah Valley Research Station, Steeles Tavern, Virginia. Records of 604 matings and 567 births from 120 cows were collected over five successive calf crops. Comparisons were made between crossbred and straightbred dams, backcross and three-breed cross calves, three breeds of straightbred cows, six kinds of crossbred cows, various combinations within the backcross and three-breed cross calves, and the general combining abilities of the three breeds. Calves from crossbred cows were heavier at birth and weaning, and had higher weaning grades. Crossbred cows were 31.9 kg heavier than straightbred cows. There were 2.0% more calves born, but 0.2% fewer calves weaned from the crossbred cows. Crossbred cows weaned more kg of calf per year, but fewer units of calf per 100 units of cow, and fewer units of calf per 100 units of cow per cow year. There were increases of three-breed cross over backcross calves for all measures of growth, leading to the conclusion that three-breed crossing would increase production over backcrossing. Differences existed among the three breeds of cows for every calf performance trait, and for cow weight. Differences were found among the kinds of crossbred cows for all calf traits. Crossbred cows out of Hereford dams excelled over the reciprocal matings. The breeds did not differ in general combining ability.
- Linear body measurements and other birth observations on beef calves as predictors of preweaning growth rate and weaning type scoreFlock, Dietmar K. (Virginia Tech, 1960-05-05)Since birth type showed only a low association with weaning type and preweaning gain, it is of no practical interest whether or not type at birth can be expressed by certain body proportions, which themselves are not high enough correlated with the two weaning traits to be of any predictive value. The high association between birth weight and the linear body measurements suggests that birth weight is as good a measure of a calf's merit at birth as any other birth observation. Birth weight should be considered a useful selection criterion for Angus and possibly Hereford calves, but not for Shorthorns, except that extremely small calves should not be kept as breeding stock. Neither body measurements nor type at birth can be recommended as selection criteria as their use would not be likely to result in an improvement of the more important weaning traits.