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Title: Effects of Milk Replacer Formulation on Measures of Mammary Growth and Composition in Holstein Heifers

Author
item DANIELS, K - VA POLYTECHNIC INST
item Capuco, Anthony
item MCGILLIARD, M - VA POLYTECHNIC INST
item JAMES, R - VA POLYTECHNIC INST
item AKERS, R - VA POLYTECHNIC INST

Submitted to: Journal of Dairy Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/12/2009
Publication Date: 12/1/2009
Citation: Daniels, K.M., Capuco, A.V., Mcgilliard, M.L., James, R.E., Akers, R.M. 2009. Effects of Milk Replacer Formulation on Measures of Mammary Growth and Composition in Holstein Heifers. Journal of Dairy Science. 92(12):5937-5950.

Interpretive Summary: Overfeeding prepubertal heifers may impair mammary growth and development, and reduce milk production. Similarly-aged pre-weaned Holstein heifers were fed different milk replacer formulations to achieve various BW gains. Heifers were harvested at 65 d and mammary tissue was evaluated. Diet had no effects on mammary parenchyma, which eventually becomes the secretory portion of the gland. However mass and composition of mammary fat pad were directly affected by increased nutrient intake. Implications with respect to future milk production remain to be determined.

Technical Abstract: Overfeeding prepubertal heifers may impair mammary parenchymal growth and reduce milk production, but dietary impacts in pre-weaned heifers are unknown. This study was to evaluate effects of milk replacer (MR) composition on: mass and composition of mammary parenchyma and fat pad (MFP), growth hormone (GH)/insulin-like growth factor-I (IGF-I) axis gene expression, and putative mammary epithelial stem cells. The hypothesis was that the positive effects of faster rates of gain during the pre-weaning period alter the development, persistence, or activity of populations of putative mammary epithelial stem cells, possibly through involvement of GH/IGF-I axis molecules. Twenty-four newborn heifers were fed one of four MR diets (n=6/diet): CON (20% CP, 21% fat MR fed at 441 g DM/d), HPLF (28% CP, 20% fat MR fed at 951 g DM/d), HPHF (27% CP, 28% fat MR fed at 951 g DM/d), and HPHF+ (27% CP, 28% fat MR fed at 1431 g DM/d). Water and starter (20% CP, 1.43% fat) were offered ad libitum. Animals were harvested on d 65 and mammary tissue was subjected to biochemical, molecular, and histological examination. Diet had no effect on mammary parenchyma, but mass and composition of MFP were directly affected by increased nutrient intake. Neither GH/IGF-I axis gene expression nor putative mammary epithelial stem cell abundance were affected by diet when heifers were assessed at a common chronological age. We conclude that diet is not important for regulating the expression of local GH/IGF-I axis components or stem cell populations in the developing heifer MG. Implications with respect to future milk production remain to be determined.