There isn’t exactly a clear-cut answer to whether one is better than the other. Horse milk, or mare milk, is said to be lower in fat and calories and is much gentler on the digestive system. However, cow’s milk is more widely available and is a well-rounded package of nutrients such as calcium and vitamin D. Cow’s milk also comes in lower-fat, skim, and lactose-free options if whole milk doesn’t fit your dietary preferences.