Abstract
Thirty-six Angus and Brahman cows were subjected to an estrous synchronization program and mated by artificial insemination. Angus cows were mated to a single Angus sire, whereas Brahman cows were mated to two Brahman sires. Within breed type, cows were randomly assigned to full-term or one of five fetal age groups (n = 3). Fetuses were obtained by cesarean section at 6, 12, 24, 48, and 96 d prior to expected parturition of 282 and 292 d for Angus and Brahman, respectively. Fetal measurements obtained included empty body weight (EBW), crown to rump length, heart girth circumference, hip and shoulder height, and head width. The organ weights obtained included heart, liver, kidneys, adrenals, spleen, and empty gastrointestinal tract (GIT). Perirenal brown adipose tissue (BAT) was dissected, weighed, and analyzed for protein, lipid, and DNA. To examine total body composition, fetuses were analyzed for protein, lipid, and DNA content. Angus fetuses were heavier, and had longer crown to rump lengths and heart girth circumferences throughout late gestation compared to Brahman fetuses. The proportional weights of visceral organs relative to fetal EBW decreased as fetal age advanced for all organs except heart and GIT. Proportional weights of liver and heart were heavier for Angus than for Brahman fetuses from 200 to 240 d of gestation. Angus fetuses had heavier proportional adrenal gland weights than Brahman fetuses throughout late gestation. The proportional mass of the perirenal BAT deposit increased quadratically with fetal age, reaching maximal values at 240 d of gestation. The proportional mass of BAT was 14% greater (P < .05) in Brahman than Angus fetuses at 240 d of gestation. Angus fetuses had higher (P < .05) BAT lipid content than Brahman fetuses throughout late gestation. When examining fetal body composition, Angus fetuses had a higher DNA concentration at 200 and 240 d of gestation (P - .05) and a higher protein concentration at 240 and 280 d of gestation (P < .05) than Brahman fetuses. Major differences were found in fetal growth between Angus and Brahman fetuses, however minimal differences were found in visceral organ and BAT during late gestation.
McPhail, Eric Hadley (2000). Genotypic effects on bovine fetal ontogeny. Master's thesis, Texas A&M University. Available electronically from
https : / /hdl .handle .net /1969 .1 /ETD -TAMU -2000 -THESIS -M337.