In Vitro Model of Milking Pulses and Stretching Cycles: Assessing Mechanical Effects on Bovine Mammary Cells

Culture models of mammary glands can be significantly enhanced by simulating physical forces, including those experienced by the tissue during milking or nursing. In particular, in vitro biophysical studies of bovine mammary cells can provide novel insights into the effects of milking pulses on cellular function, which are currently not well understood. We introduce here a system for modeling uniaxial stretching cycles in culture such as those exerted by vacuum pulses during milking. Bovine mammary epithelial cells (MECs) were cultured under several conditions in stretchable silicone chambers and monitored before and after applying various protocols of stretching pulses. Image processing was conducted for detailed analysis of thousands of MECs in each condition. In the stretchable chambers and upon stretching pulses the bovine MECs maintained high viability, normal proliferation and expression of fat globules, indicating that this system is suitable for tracing functional aspects. We demonstrated usage of the stretching pulses methodology in two possible fields of interest. The first is the fundamental study of the reaction of isolated bovine MECs to stretching cycles, in which we observed cell rounding under various stretching protocols, while maintaining surface adherence and high viability. In the second branch we imitated physiological conditions of mammary epithelium under milking pulses and found that morphological homeostasis was maintained as well as high production of lipid globules with preserved size distribution. Furthermore, our analysis suggests that in collagen-coated chambers and differentiation medium, milking pulses enhance the extracellular release of fat globules. Collectively, the data in this section reflected the ability of mammary epithelium to maintain structural integrity, function effectively, and potentially enhance functionality under milking pulses.