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The phenotype of an individual is the manifestation of that individual's genotype, environment, and the interaction of that genotype and environment. The genotype is attributable to nuclear genetic material equally contributed by the sire and the dam. The in utero environment and(or) the genotype of the dam (maternal effects) have long been known to have an influence on fetal and postnatal development. These effects were documented by Walton and Hammond (1938), who described the growth of Shetland pony-Shire horse reciprocal crosses. The physiology of the individual (e.g., enzyme activities, endocrine secretion and function) is the phenotypic expression of that individual's genotype and environment just as much as grossly observed characteristics such as color, height, and weight.
The objective of the present study was to investigate the effects of genotype and prenatal maternal environment on the secretion of two metabolically important hormones [growth hormone (GH)and prolactin (PRL)]and the growth of individual calves of Angus-Red Poll genotype. Through embryo transfer, the confounding of the effects of maternal genetic contributions and prenatal maternal environment was eliminated.