Abstract
Breed differences in adult animals are determined during fetal development. If interventions are to be developed that influence growth of muscle and fat, it is important to know at which time during gestation breed differences appear and are fixed. The objective of this study was to characterize fetal development in cattle of different breeds. Pregnant cows of 4 cattle breeds with different growth impetus and muscularity were slaughtered under normal processing conditions and the fetuses were removed. German Angus, a typical beef cattle; Galloway, a smaller, environmentally resistant beef type; Holstein Friesian, a dairy type; and Belgian Blue, an extreme type for muscle growth were used. Fetuses of each breed were investigated at 3, 6, and 9 mo of gestation. Fetuses were weighed and dissected into carcass, organs, and muscles. Body fat weight was obtained using the Soxhlet extraction method. Fetal weight increased most rapidly in the third trimester of gestation mainly due to the accelerated muscle and fat deposition. The organ weight to body weight (BW) ratios decreased and the muscle and fat weight to BW ratios increased. At 3 mo of gestation, Galloway fetuses had the significantly smallest BW, half-carcass weight, leg weight, organ weight, muscle weight and shortest leg length. In contrast, Holstein fetuses had the significantly greatest BW, liver, kidney, and lung weights and significantly longest leg length among the 4 breeds, but no differences between Holstein Friesian and Belgian Blue were detected in half-carcass and leg weight. Indeed, Belgian Blue fetuses had the significantly greatest half-carcass weight, leg weight, and muscle weight at 9 mo of gestation, and Galloway had a significantly greater body fat to BW ratio than Holstein Friesian and Belgian Blue. These differences were not evident at 3 and 6 mo of gestation. These data show that the profound increase of tissue and organ weights occurred in later gestation in cattle fetuses even though breed differences were evident as early as 3 mo of gestation. Depending on the tissue of interest, impacting fetal growth likely needs to occur early in gestation before the appearance of breed-specific differences.
Highlights
Fetal growth and development is a complex process related to interactions among genetic potential, environmental factors, and nutrient supply
Prior and Laster (1979) reported that the growth of normally developing cattle fetus follows an exponential equation with a body weight (BW) gain of 25 g/d up to 4 mo of gestation, and the maximal rate of BW gain of 352 g/d by 7.6 mo
A similar measured from the femoral head to the tarsal joint of the result is shown in ovine fetal growth by Osgerby et al
Summary
Fetal growth and development is a complex process related to interactions among genetic potential, environmental factors, and nutrient supply. Berg et al (1978) studied the influence of genotype on growth patterns of muscle, fat, and bone in cattle fetuses, and found a distinct pattern of growth under appropriate nutrient supply and environmental conditions. Different growth patterns for BW, organs, muscles, and body fat, expressed relative to BW in cattle, were reported by Ferrel (1991) and Godfredson et al (1991) and in sheep by Osgerby et al (2002). To understand the growth of cattle, especially the postnatal muscle and fat development, which influences the amount and quality of meat, a characterization of normal prenatal development of cattle is necessary. Differences in the development of organs and muscles in the fetus were expected between dairy and meat
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