Effects of two different forage sources on mammary gland growth, mammary cell turnover and activity in early lactation dairy cows

Abstract

The objective of this study was to evaluate the effects of two different forage sources on mammary gland growth, mammary cell turnover and activity in early lactation dairy cows. Twelve early lactation cows were randomly assigned to a CS (33.8% corn straw as sole forage) or MF diet (3.7% Chinese wildrye + 28.4% alfalfa hay + 26.5% corn silage as mixed forage). All cows were fed from Week –3 to Week 8, and mammary biopsies were taken on 16 days postpartum. Mammary cell proliferation and apoptosis were determined by immunohistology, and genes expression in mammary were detected by real-time PCR. Results showed that cell proliferation, gene expression of milk proteins and proteins involved in the synthesis of milk components did not differ between two dietary treatments (P > 0.05). However, cows fed the MF diet had a higher IGF-1 receptor (IGF-1R) expression (P = 0.02), and lower rate of cell apoptosis (P = 0.003) relative to cows fed the CS diet. Collectively, these results suggest that the mammary secretory activity probably was not affected by the dietary treatments, but high quality and mixed forages led to the increased expression of IGF-1R and a larger number of cells in mammary glands, which may be responsible for the higher milk production in early lactation dairy cows.