Abstract
The objective of this study was to determine the effects of dietary energy and recombinant bovine somatotropin (bST) injection to identify genes that might control mammogenesis. Total RNA was extracted from the parenchymal tissue of 32 heifers randomly assigned to one of four treatments: two diets (a standard diet and a high energy, high protein diet), each with or without bST. To perform microarray experiments, RNA samples were pooled (2 animals/pool) before reverse transcription and labeling with Cy3 or Cy5. A 4-node loop design was used to examine the differential gene expression among treatments using a bovine-specific cDNA microarray (National Bovine Functional Genomics Consortium Library, NBFGC) containing 18,263 unique expressed sequence tags (EST). Significance levels of differential gene expression among treatments were assessed using a mixed model approach. Injection of bST altered the expression of 12 % of the genes on NBFGC slide related to tissue development, whereas 6% were altered by diet. Administration of bST increases the expression of genes positively related to cell proliferation and mammary parenchyma to a greater extent than a high energy diet.
Highlights
The establishment of milk yield potential is critically determined during the prepubertal phase of mammary development (Sejrsen & Purup, 1997)
The bovine somatotropin (bST) injection altered the expression of 620 genes, while high energy andprotein diet altered the expression of 463 genes (P
The authors of the present study aimed at identifying bST and/or high-energy diet-regulated genes, involved in the induction or inhibition of parenchymal tissue development
Summary
The establishment of milk yield potential is critically determined during the prepubertal phase of mammary development (Sejrsen & Purup, 1997). It is well accepted that nutrition plays an important role in mammary development and subsequent milk production. Several reports have shown that feeding heifers with high-energy diets during the prepubertal period is detrimental to mammary development, with subsequent permanent reduction in milk production (Sejrsen & Purup, 1997). Radcliff et al (1997) did not find a decrease in mammary parenchymal tissue mass or DNA when prepubertal heifers were fed high energy diets combined with high protein levels. Animals fed the same prepubertal diet produced 14% less milk during first lactation when compared with animals receiving a standard diet (Radcliff et al, 2000)
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