Photosynthetic cells contain chlorophyll and other light-sensitive pigments that capture solar energy. In the presence of carbon dioxide, such cells are able to convert this solar energy into energy-rich organic molecules, such as glucose.
Yes, you can add a little lemon juice or vinegar to the goat's milk to make it into a buttermilk or kefir. This will lower the pH of the milk, and allow it to release the CO2 stored in the sodium bicarbonate (baking soda), causing the bread to rise. Goat's milk generally has less fat and more vitamins.
The second option to substitute for buttermilk is to whisk together 1/2 cup of yogurt or sour cream with 1/2 cup of milk. If you only have Greek-style yogurt on hand, use 1/3 cup yogurt and 2/3 cup milk. This mixture may be slightly thicker than store bought buttermilk, but it has good acidity and a very similar flavor to buttermilk for baking.