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An early study by Sorensen [30] showed that attainment of puberty in heifers was more influenced by weight than age. He found that heifers on a higher plane of nutrition reached puberty at an earlier age than similar heifers with lower average daily gain [30]. However, heifers may have similar body weights but vary in frame size, indicating they have differing body composition. For any given frame size, heifers that are heavier reach puberty at an earlier age. Body weight at puberty has a heritability coefficient of 0.40 [31]. Overall, heifers reared on higher planes of nutrition are heavier but younger than nutritionally restricted animals at puberty [32]. However, puberty does not occur at similar body composition or metabolic status in all heifers [33] but is positively correlated with body fat percentage and negatively correlated with carcass moisture percentage [33]. The precise mechanisms involved in the relationship of body composition and puberty are not clearly defined. However, it is known that somatotropin and the insulin‐like growth factor (IGF)‐I system are involved [34]. This fact was demonstrated by Armstrong et al. [35] who immunized heifers at three or six months of age against growth hormone releasing factor. By 14 months of age 75% of control heifers but only 22% of immunized heifers had reached puberty and had significantly fewer follicles >7 mm by six months of age^.