Năng lượng tối là dạng năng lượng chưa quan sát và nghiên cứu đầy đủ được, lấp đầy không gian vũ trụ, là nguyên nhân sự giãn nở của vũ trụ. | 70 energy a beginner s guide that usually worked for less than ten years compared to 15-20 for horses were more difficult to train and did not have the endurance of horses Certainly harnessing oxen is cheaper they do not need metal shoes and they are not as excitable but the key reason is energetic. Ruminants have a highly specialized digestive system and can with the help of microbes that reside in their rumen metabolize cellulose which other mammals are either unable to digest or can use only poorly and in limited amounts. Ruminants do not compete for their feed either with other animals or with people. Moreover one bovine species water buffalo is a perfect fit for the tropics able to walk well in muddy terrain feed on aquatic plants and metabolize its feed more efficiently than cattle. And all bovines eventually yield meat and leather and their manure is a recyclable and welcome source of nutrients for the fields. That is why oxen and even working cows were always preferred by poor farmers despite the fact that horses make far better draft animals. DRAFT HORSES Some reasons for the superiority of horses as draft animals are obvious others are subtle and peculiar. Many horse breeds are much heavier than oxen and hence more powerful and they also have greater endurance. But what may not be immediately apparent is that their fronts are heavier than their rears by a ratio of 3 2 giving them a greater forward inertia. They also live longer than cattle and thanks to a unique attribute they do not use any additional energy while standing the suspensory ligaments and tendons lock their legs so they do not have to tension their long leg muscles as other animals do . For centuries these advantages remained largely irrelevant. Even more efficient harnesses and iron horseshoes were not enough to make horses the dominant prime movers in at least some regions that shift took place only once crop yields increased enough to allow sufficient production of grain feed and a more .
