No description available.

Assisted reproductive technologies such as estrus synchronization and embryo transfer can aid producers in meeting their goals of improving genetics, calve one calf per cow per year, and wean heavy calves. Most estrus synchronization protocols follow a GnRH-PGF-GnRH sequence. Ovulation prompted by exogenous gonadotropin releasing hormone (GnRH) may cause the release of sub-mature oocytes and lead to decreased pregnancy rates. Inclusion of estradiol benzoate (EB) improved pregnancy rates in some studies. The objective of this study was to determine if EB affects blood perfusion of follicles, corpus luteum (CL), or uterus, concentrations of estradiol and progesterone, or incidence of standing estrus.

No description available.

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. / Ph. D.

Beef cattle production in Virginia has increased steadily during the last few years. This increase has been brought about in a large part by the increase in the price of beef by a definite trend toward more livestock to provide profitable utilization of non-productive lands and to serve as a good source of cash income. / Master of Science

The objectives of this study were: (1) to estimate the effects of certain non-genetic sources of variation in weight, gnde, and condition of beef cows; (2) to estimate the heritability of weight, grade. and condition of beef cows; and (3) to estimate the genetic, phenot;rpic, and environmental correlations between weight, grade, and condition of beef cows. Weights, grades., and condition scores taken on 1371 Angus cows were used to evaluate the genetic and environmental nature of these traits. This sample of cows represented 365 sire groups. Four models were used in this study: 1. Model A - Cow weight and grade were considered dependent variables; herds and sires within herds were considered random independent variables; and season, age, condition, nursing status, and their interactions were considered fixed independent variables. Least-squares procedures involving Henderson's (1953) Method II were used to adjust tor fixed effects and to obtain variance and covax-iance components. Heritability estimate and correlation coefficients were obtained by paternal half-sib analysis. 2. Model B differed from Model A in that condition 3 score was considered a dependent variable instead of an independent variable. 3. Model C was the same as Model A except that the coefficients (kₒ and k₂) for the within sire (σw²) component of variance included in the among sire and herd adjusted expected mean squares (EMS) were considered unity whereas as in Model A they were calculated according to Method II of Henderson. 4. Model D - Heritability estimates were computed by doubling the estimate of intra-sire regression of offspring on dam from 198 dam-daughter pairs representing 63 sire groups. The dam-daughter pairs were part of the group or 1371 cows. The results of this study indicated that season, age, condition score, nursing status, and age by nursing status remain significant when condition score was not considered as a fixed environmental effect (Model B). However, a comparison of the magnitude of the mean squares for these effects in Models A and B indicated that season, age, and nursing status are highly confounded with condition score. Season and flesh condition were found to have a significant effect on grade of beef cows when they were included in the same model (Model A). When condition score was not included (Model B) age had a significant effect on grade. Age, season, and nursing status were found to have a significant effect on flesh condition (Model B). Paternal half-sib heritability estimates for cow weight using Models A, B, and C were 0.38 ± 0.11, 0.29 ± 0.11, and 0.56.± 0.11, respectively. Estimates for grade from the same models were 0.49 ± 0.11, 0.43 ± 0.11, and 0.67 ±0.12, in that order. Estimates from Model A should be the most reliable. The differences in the estimates from Models A, B, and C, illustrate that variation in heritability estimates is not entirely due to genetic differences. Considerable variation can occur depending on how much adjustment has been made to fixed effects, and the methods used in estimating the variance and covariance components. The heritability estimates of cow weight and grade obtained by intra-sire regression of offspring on dam were 0.22 ± 0.14 and 0.10 ± 0.06, respectively. The paternal half-sib heritability estimate for condition score was 0.31 ± 0.11, which implies that adjusting cow weights and grades for condition may actually involve adjusting for genetic differences as well as differences due to environmental influences. The correlation between weight and grade or beef oowe was found to be largely genetic whereas the correlation between condition and cow weight or grade was primarily environmental. / Ph. D.

A series of four trials over the grazing season were conducted to evaluate the nutritional status of beef cows grazing reclaimed strip-mined pastures in southwestern, Virginia. Blood samples, esophageal fistula forage samples and hand plucked forage samples were taken in each trial. An external marker, Ytterbium, and an internal marker, indigestible neutral detergent fiber (INDF) were used to estimate organic matter intake, fecal output and digestibility. In addition to samples taken during the trials, blood samples and hand plucked forage samples were taken monthly for 11 mo prior to the trial period. In late summer esophageal masticate samples had a low fiber fraction (ADF and NDF), high crude protein and total nonstructural carbohydrates (TNC) which contributed to a high organic matter digestibility. Hand plucked forage samples had higher TNC than esophageal masticate samples. Organic matter digestibility predicted by the internal marker was highest in late summer 61.6%, similar in spring and late fall, and lowest in mid-summer, 52.6% (p < .01). Fecal output was highest in mid-summer and lowest in spring (p < .05). Estimated intake was not significantly different in any of the trials. Although data was variable, forage quality was higher in May, June, October and November samplings, as indicated by highest CP, TNC, and lower NDF and ADF values, compared with July and August data when forage quality was lowest. Packed cell volume, BUN and serum P and Mg concentrations fell within normal ranges for beef cattle. Low BUN values were observed in spring and late fall which corresponded to low crude protein values observed in the esophageal masticate samples for the same trials. Serum Cu was on the low end of normal values in the late spring and decreased to .6 ppm by late fall. Serum K levels were above the expected values for beef cattle. Serum Na concentrations were lower than normal with lowest values observed throughout spring and summer months. / M.S.

The growth performance of Angus-Polled Hereford F₁ calves was compared to the expected progeny differences (EPD) estimated by the American Polled Hereford Association to evaluate the usefulness of EPD estimates for improving commercial beef production. Polled Hereford sires were selected from the high accuracy sires listed in the American Polled Hereford Association's sire summary. Four types of sires were used: 1) Sires with high yearling weight and high maternal EPD's; 2) Sires with high yearling weight and low maternal EPDâ s; 3) Sires with low yearling weight and high maternal EPD's; and 4) Sires with low yearling weight and low maternal EPD's. The resulting progeny were weighed at birth, approximately 135 d, weaning and approximately 1 yr. Hip heights were also measured at weaning. Linear regressions of progeny performance on EPD indicated that birth and yearling weights were accurately predicted by their respective EPD estimates. Weight and height at weaning were not accurately predicted by weaning weight EPD. Partial regressions of progeny performance on yearling weight and maternal EPD's were also calculated. Regression of progeny performance on yearling weight EPD resulted in .16 ±.09 kg/kg for 135-d weight, .28 ± .09 kg/kg for weaning weight, .073 ± .020 cm/kg for weaning hip height and .93 ±.19 kg/kg for yearling weight. Comparable regression values for maternal EPD were .44 ± .18 kg/kg, .31 ± .17 kg/kg, .100 ± .040 cm/kg and .22 ± .36 kg/kg for 135-d, weaning weight, weaning hip height and yearling weight, respectively. These results indicate that maternal EPD values predicted some differences in preweaning growth that were not predicted by yearling weight EPD. The progeny performance data was also used to calculate independent EPD estimates for birthweight, weaning weight, and yearling weight. Correlations between these EPD estimates and those made by the American Polled Hereford Association were .49 for birthweight, .26 for weaning weight and .66 for yearling weight. The low correlation between weaning weight EPD estimates was significantly below expectation and indicates that the American Polled Hereford Association estimates were inadequate for predicting preweaning growth differences in these crossbred calves. / Master of Science

Data collected on weight, feed consumption, and daily gain of 66 steers and 121 bulls were studied by analyses of variance, covariance, correlation, and partial regression. The bulls were of Hereford, Angus, and Shorthorn breeds, and the steers were the offspring of fast and slow gaining bulls that were progeny tested. The feeding tests for the bulls were from 112 to 170 days, and for the steers, approximately 200 days. The bulls and steers were on full feed for the test period, and all animals were fed individually. The first four groups were hand fed and the remaining groups were self fed. / Master of Science

This study assessed the effects of prenatal androgen exposure during three periods, of gestation on the external genitalia, estrous cyclicity, postnatal growth, social dominance and sexual behavior of female beef cattle. Pregnant cows received 17a methyl-testosterone (250 mg/d, sq) on d 40 to 100 (group 1), 70 to 130 (group 2) or 100 to 160 (group 3) of gestation. Control cows (group 0) received no treatment. Group 1 females exhibited completely masculinized external. genitalia. No vulval opening was present and the ano-genital distance (A-g) was similar to that of control male calves. Group 2 females exhibited small vulval openings and enlarged clitoral structures while group 3 females exhibited normally appearing female external genitalia. Anogenital distances for the heifers in groups 2 and 3 were similar to those of the control heifers. Androgen exposure during the three periods of gestation did not affect age at puberty (P<.80), estrous cycle length (P<.63) or postnatal growth (P<.60) of the heifers. At 9, 16 and 21 mo of age, social dominance values (SDV) were determined for each heifer by 3 min random pair contests for a restricted feed source. The animal with the greatest feed source control time was awarded a win. Social dominance value was calculated as 10 times the number of wins divided by the number of competitions for each animal. Group 3 heifers had significantly greater SDV values than group 1 and 2 females (P<.03). SDV did not differ among groups at 16 mo of age (P<.59). Group 1 females had greater SDV than group 2 females at 21 mo of age (P<:.04). At 9, 16 and 21, mo of age, sexual behavior of the heifers was characterized by exposure of the heifers to a teaser female in estrus. Sexual behavior, as indicated by the number of mounts, head placements and interest time, was lower for group 3 females compared to females in groups 1 and 2 at 9 mo of age (P<.04). There were no treatment differences for any sexual behavior variable at 16 or 21 mo of age. These results indicate that there is little potential for increasing postnatal growth or altering the estrous cyclicity of female cattle by exposure of the fetus to testosterone during the periods of gestation selected in this study. External genitalia of females were masculinized by androgen exposure during d-40 to 100 of gestation. Social dominance values were increased and sexual behavior was reduced in females by exposure to androgen during d 100 to 160 of gestation. / Master of Science