Photostimulation improves maturation of human photoreceptors.

To meet the energy demands of high-producing dairy cows in intensive production systems, energy-dense concentrate-rich diets are widely used. In grain-based formulations, these diets often increase the supply of rumen-degradable starch (RDS), which provides rapidly fermentable substrate for microbial fermentation and volatile fatty acid (VFA) production [, ]. However, when high-RDS supply is combined with insufficient physically effective fibre, unstable intake, or inadequate feeding management, ruminal acid load may exceed the capacity for buffering, absorption, and adaptation, increasing the risk of subacute ruminal acidosis (SARA) [–]. SARA has traditionally been associated with repeated or prolonged episodes of moderate ruminal pH depression. Nevertheless, it should not be interpreted as a disorder defined only by a single low-pH threshold. Reported pH cut-off values vary among studies because ruminal pH is affected by sampling site, sampling method, monitoring system, diet type, feeding time, and evaluation criterion [, , ]. In dairy cows, commonly used thresholds range from approximately pH 5.5 to 5.8, and SARA assessment often combines the selected threshold with the duration or area under the curve for which pH remains below that value [–]. Moreover, cows exposed to similar pH conditions may differ in feeding behaviour, epithelial adaptation, inflammatory responses, clinical signs, and production losses [, , ]. Thus, ruminal pH is better interpreted as a core indicator of acid-load exposure rather than as an absolute stand-alone diagnostic standard. Although ruminal pH monitoring remains the most direct method for identifying acidotic risk, conventional approaches are invasive or potentially stressful and are poorly suited for repeated herd-level application []. More importantly, SARA reflects broader disturbances in rumen fermentation, epithelial function, microbial stability, and host responses. These disturbances may contribute to reduced feed intake, impaired fibre digestion, altered milk production or composition, and increased risk of extra-ruminal health problems [, –]. Therefore, SARA is more appropriately viewed as a progressive failure of acid-load adaptation than as a simple low-ruminal-pH event.