FIGURE 4–2. Phase II: Post-Absorptive Nutrient Use (Boyd and Bauman, 1991).

High-producing lactating dairy cows have higher concentrations of blood somatotropins than do lower producing dairy cows, but these levels are elevated only during lactation. This is because during lactation, the secretion rate of somatotropin from the pituitary gland is higher in high producing dairy cows (Hart et al., 1980). Injecting somatotropin in lactating dairy cows mimics rate of genetic progression. Somatotropin does not affect basal metabolic requirements

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