Growth factors in milk: interrelationships with somatic cell count.

Growth factors are thought to play a decisive role in the course of inflammatory processes. The aim of the present study was to characterize a potential interrelationship between the concentrations of insulin-like growth factor-1 (IGF-1), basic fibroblast growth factor (bFGF) and somatic cell count (SCC) in normal milk, and to investigate the presence of these growth factors in mammary secretions of cows suffering from clinical and subclinical mastitis. Quarter secretions of cows with spontaneous acute clinical mastitis and of cows with subclinical mastitis were analysed radioimmunologically for their concentrations of IGF-1 and bFGF. During two relocation trials with normally lactating Brown Swiss cows, dramatic changes in milk somatic cell count were obtained following a short-term change (5 d) of location and housing system. The animals were relocated from their familiar loose housing system with concrete slatted floor to a separate stanchion barn with long stalls and straw bedding, and vice versa. The concentration profile of IGF-1, but not of bFGF, corresponded well with SCC during the relocation trials, the positive correlation between the characteristics being highly significant, as determined by regression analysis (r = 0.60; P < 0.001). The results provide evidence that significant changes in SCC and growth factor content may be caused by environmental factors other than infection. The concentrations of both IGF-1 and bFGF were greatly elevated in secretions of quarters affected by acute clinical mastitis compared with the corresponding clinically healthy quarters. Subclinically affected quarters with high SCC, as compared with non-affected quarters with low SCC, also had elevated milk IGF-1, but unchanged bFGF. Measuring of growth factor profiles in milk may have value in the near future in monitoring the state of udder health in addition to SCC.