Early milk-feeding regimes in calves exert long-term influence on the development of ovarian granulosa cells

We analysed effects of different feeding regimes of milk replacer (MR) during rearing on ovarian physiology with specific emphasis on the numbers of granulosa cells (GCs) as well as gene expression characteristics in GCs at the age of puberty onset. Animals of the 20% feeding group had a significantly higher body weight, but the proportion of animals having a corpus luteum at the time of slaughter was not different between groups, suggesting a similar onset of puberty. Calves of the 10% group showed a constant granulosa cell count regardless of the number of follicles (r = 0.23) whereas in the 20% group increasing numbers of GCs were detected with a higher follicle count (r = 0.71). The mRNA microarray analysis revealed a total of 557 differentially expressed genes in GCs (fold change > |1.5| and p<0.05). Among the top downregulated genes were OAS1X, MX2 and OAS1Z, whereas the top upregulated genes were BOLA, XCL1 and MT1E, which are known to be regulated by interferon. Subsequent signaling pathway analysis revealed the involvement of several immune response mechanisms in accordance with a number of interferons as upstream regulators. The results indicate that the plane of MR feeding in early life have an impact on the number and physiology of GCs later in life. This might influence the overall reproductive life initiated by the onset of puberty in cattle. In addition, the observed alterations in GCs of calves fed less MR might be a consequence of interferon regulated immunological pathways. Overall 10 samples were analyzed. Different feeding regimes (10% vs. 20% MR) in early life were compared with n=5 for each feeding group. Two groups of calves received either 10% or 20% of bodyweight MR per day during their first 8 weeks. After weaning, both groups were fed the same mixed ration ad libitum until slaughter at 8 months of age.