Early induction of angiogenetic signals in gliomas of GFAP-v-src transgenic mice.
Angiogenesis is a prerequisite for solid tumor growth. Glioblastoma multiforme, the most common malignant brain tumor, is characterized by extensive vascular proliferation. We previously showed that transgenic mice expressing a GFAP-v-src fusion gene in astrocytes develop low-grade astrocytomas that progressively evolve into hypervascularized glioblastomas. Here, we examined whether tumor progression triggers angiogenetic signals. We found abundant transcription of vascular endothelial growth factor (VEGF) in neoplastic astrocytes at surprisingly early stages of tumorigenesis. VEGF and v-src expression patterns were not identical, suggesting that VEGF activation was not only dependent on v-src. Late-stage gliomas showed perinecrotic VEGF up-regulation similarly to human glioblastoma. Expression patterns of the endothelial angiogenic receptors flt-1, flk-1, tie-1, and tie-2 were similar to those described in human gliomas, but flt-1 was expressed also in neoplastic astrocytes, suggesting an autocrine role in tumor growth. In crossbreeding experiments, hemizygous ablation of the tumor suppressor genes Rb and p53 had no significant effect on the expression of VEGF, flt-1, flk-1, tie-1, and tie-2. Therefore, expression of angiogenic signals is an early event during progression of GFAP-v-src tumors and precedes hypervascularization. Given the close similarities in the progression pattern between GFAP-v-src and human gliomas, the present results suggest that these mice may provide a useful tool for antiangiogenic therapy research. (+info)
Morphometric study of the equine navicular bone: variations with breeds and types of horse and influence of exercise.
Navicular bones from the 4 limbs of 95 horses, classified in 9 categories, were studied. The anatomical bases were established for the morphometry of the navicular bone and its variations according to the category of horse, after corrections were made for front or rear limb, sex, weight, size and age. In ponies, navicular bone measurements were smallest for light ponies and regularly increased with body size, but in horses, navicular bone dimensions were smallest for the athletic halfbred, intermediate for draft horse, thoroughbreds and sedentary halfbreds and largest for heavy halfbreds. The athletic halfbred thus showed reduced bone dimensions when compared with other horse types. Navicular bones from 61 horses were studied histomorphometrically. Light horses and ponies possessed larger amounts of cancellous bone and less cortical bone. Draft horses and heavy ponies showed marked thickening of cortical bone with minimum intracortical porosity, and a decrease in marrow spaces associated with more trabecular bone. Two distinct zones were observed for the flexor surface cortex: an external zone composed mainly of poorly remodelled lamellar bone, disposed in a distoproximal oblique direction, and an internal zone composed mainly of secondary bone, with a lateromedial direction for haversian canals. Flexor cortex external zone tended to be smaller for heavy ponies than for the light ponies. It was the opposite for horses, with the largest amount of external zone registered for draft horses. In athletic horses, we observed an increase in the amount of cortical bone at the expense of cancellous bone which could be the result of reduced resorption and increased formation at the corticoendosteal junction. Cancellous bone was reduced for the athletic horses but the number of trabeculae and their specific surfaces were larger. Increased bone formation and reduced resorption could also account for these differences. (+info)
Estimating the effective number of breeders from heterozygote excess in progeny.
The heterozygote-excess method is a recently published method for estimating the effective population size (Ne). It is based on the following principle: When the effective number of breeders (Neb) in a population is small, the allele frequencies will (by chance) be different in males and females, which causes an excess of heterozygotes in the progeny with respect to Hardy-Weinberg equilibrium expectations. We evaluate the accuracy and precision of the heterozygote-excess method using empirical and simulated data sets from polygamous, polygynous, and monogamous mating systems and by using realistic sample sizes of individuals (15-120) and loci (5-30) with varying levels of polymorphism. The method gave nearly unbiased estimates of Neb under all three mating systems. However, the confidence intervals on the point estimates of Neb were sufficiently small (and hence the heterozygote-excess method useful) only in polygamous and polygynous populations that were produced by <10 effective breeders, unless samples included > approximately 60 individuals and 20 multiallelic loci. (+info)
The importance of genetic diversity in livestock populations of the future.
Farm animal genetic diversity is required to meet current production needs in various environments, to allow sustained genetic improvement, and to facilitate rapid adaptation to changing breeding objectives. Production efficiency in pastoral species is closely tied to the use of diverse genetic types, but greater genetic uniformity has evolved in intensively raised species. In poultry, breeding decisions are directed by a few multinational companies and involve intense selection, the use of distinct production lines, and very large populations. In dairy cattle, the Holstein breed dominates production. Intensive sire selection is leading to relatively rapid inbreeding rates and raises questions about long-term effects of genetic drift. Key questions in management of farm animal genetic diversity involve the distribution of potentially useful quantitative trait locus alleles among global livestock breeds. Experiments with tomato, maize, and mice suggest that favorable alleles can exist in otherwise lowly productive stocks; this cryptic variation may potentially contribute to future selection response. Genetic improvement under relatively intense unidirectional selection may involve both increases in the frequency of favorable additive alleles as well as the progressive breakdown of homeostatic regulatory mechanisms established under the stabilizing selection that is characteristic of natural populations. Recombination among closely linked regulatory loci and new, potentially favorable mutations are possible sources of long-term genetic variation. A greater understanding of the potential that these alternative mechanisms have for supporting long-term genetic improvement and of genetic relationships among global livestock populations are priorities for managing farm animal genetic diversity. (+info)
Evaluation of carcass, live, and real-time ultrasound measures in feedlot cattle: I. Assessment of sex and breed effects.
Carcass and live-animal measures from 1,029 cattle were collected at the Iowa State University Rhodes and McNay research farms over a 6-yr period. Data were from bull, heifer, and steer progeny of composite, Angus, and Simmental sires mated to three composite lines of dams. The objectives of this study were to estimate genetic parameters for carcass traits, to evaluate effects of sex and breed of sire on growth models (curves), and to suggest a strategy to adjust serially measured data to a constant age end point. Estimation of genetic parameters using a three-trait mixed model showed differences between bulls and steers in estimates of h2 and genetic correlations. Heritability for carcass weight, percentage of retail product, retail product weight, fat thickness, and longissimus muscle area from bull data were .43, .04, .46, .05, and .21, respectively. The corresponding values for steer data were in order of .32, .24, .40, .42, and .07, respectively. Analysis of serially measured fat thickness, longissimus muscle area, body weight, hip height, and ultrasound percentage of intramuscular fat using a repeated measures model showed a limitation in the use of growth models based on pooled data. In further evaluation of regression parameters using a linear mixed model analysis, sex and breed of sire showed an important (P < .05) effect on intercept and slope values. Regression of serially measured traits on age within animal showed a relatively larger R2 (62 to 98%) and a smaller root mean square error (RMSE, .09 to 8.85) as compared with R2 (0 to 58%) and RMSE (.31 to 67.9) values when the same model was used on pooled data. We concluded that regression parameters from a within-animal regression of a serially measured trait on age, averaged by sex and breed, are the best choice in describing growth and adjusting data to a constant age end point. (+info)
Comparison of three weaning ages on cow-calf performance and steer carcass traits.
An experiment was conducted to compare three weaning ages on cow-calf performance and steer carcass traits. Crossbred steers (n = 168; 1/2 Simmental x 1/4 Angus x 1/4 Hereford) were randomly assigned to three treatments with eight pens per treatment: groups were 1) weaned at an average of 90 d of age (90 +/- 13 d) and placed in the feedlot, 2) weaned at an average of 152 d of age (152 +/- 13 d) and placed in the feedlot, and 3) weaned at an average of 215 d of age (215 +/- 13 d) and placed in the feedlot. The number of days steers were finished decreased by 55 and 38 d (linear, P = .0001) as weaning age increased when slaughtered at a constant fat end point (.81 cm). Weaning at an average of 90 and 152 d of age improved overall ADG by .15 and .07 kg/d, respectively, over weaning at an average of 215 d of age (linear, P = .005). Over the entire finishing period, intake increased (linear, P = .0006) and efficiency was poorer (linear, P = .004) as weaning age increased. Owing to differences in finishing days and intake, total concentrate consumed increased (linear, P = .03) as weaning age decreased. No differences (P > .21) were observed for carcass weight, longissimus muscle area, or yield grade. No differences (P > .19) were observed in marbling score or percentage of steers grading greater than or equal to Choice or Average Choice. Cow body condition score improved (linear, P = .0001) as weaning age decreased. Pregnancy rate improved 12 percentage units (linear, P = .15) for cows on the 90-d weaning treatment. In this study, early weaning improved gain and feed efficiency, but it increased total concentrate consumed. (+info)
Effects of milk yield on biological efficiency and profit of beef production from birth to slaughter.
Effect of milk yield (MY) on biological efficiency and gross margin as an indicator of profit potential of beef production from birth to slaughter was determined. Data included 9 yr of spring-born single male calves. Biological efficiency was calculated as carcass weight/total feed energy intake, including nonlactating and lactating intakes of cow and creep and feedlot intakes of calf. Slaughter end point was finish constant at 9 mm of fat thickness. Gross margin was determined as returns minus feed costs. Three breeding systems were analyzed: purebred Hereford (HE), large rotational (LR), and small rotational (SR). Analyses were performed separately by breeding system when differences in the effect of MY among breeding systems were significant. Increased MY was associated with increased preweaning gain (P < .001), increased weight at start of feedlot trial (P < .001), and increased hot carcass weight (P < .05). No significant (P > .10) effect of MY on age at slaughter or on carcass weight per day of age at slaughter was found. Increased MY was associated with increased cow lactating energy intake (P < .10) and negatively associated with calf creep intake (P < .01). No effects of MY on intake of the cow during the nonlactating period, calf feedlot intake, or total feed intake were found. Increased MY was associated with a reduction in backfat thickness of the cow during the lactating period (P < .01) with no change in body weight. In the subsequent nonlactating period, increasing MY was associated with increased backfat thickness (P < .10) and body weight (P < .05). No effect of MY on change in backfat or weight of cow from calving to the end of the next nonlactating period was found. No effect of MY on biological efficiency to slaughter was detected. Milk yield was positively associated with gross margin from birth to slaughter (P < .05); results were similar when cow feed prices were reduced by 30%. Increased MY was associated with increased biological efficiency to weaning in HE (P < .01) and SR (P < .10), with no effect found in LR. When feeding cows to requirements, milk yield has a positive effect on the profit potential of beef production from birth to slaughter. (+info)
Modulation of allospecific CTL responses during pregnancy in equids: an immunological barrier to interspecies matings?
Maternal immune recognition of the developing conceptus in equine pregnancy is characterized by the strongest and most consistent alloantibody response described in any species, a response directed almost exclusively against paternal MHC class I Ags. This work investigated the cellular immune response to paternal MHC Ags in pregnant and nonpregnant horses and donkeys, and in horses carrying interspecies hybrid mule conceptuses. We observed profound decreases in classical, MHC-restricted, CTL activity to allogeneic paternal cells in peripheral blood lymphocytes from both horse mares and donkey jennets carrying intraspecies pregnancies, compared with cells from nonpregnant controls. This is the first evidence in a randomly bred species for a generalized systemic shift of immune reactivity away from cellular and toward humoral immunity during pregnancy. Surprisingly, mares carrying interspecies hybrid mule conceptuses did not exhibit this transient, pregnancy-associated decrease in CTL activity. The failure of interspecies pregnancy to down-regulate cellular immune responses may be a heretofore-unrecognized, subtle barrier to reproductive success between species. (+info)