The climate and food have not so much influence on the human species as on animals; and the reason is plain: man can defend himself better than any other animal from the intemperance of the climate; he is lodged and clothed suitably to the seasons; in his food also there is more variety, and consequently it cannot influence all individuals in the same manner. The defects or excesses which arise from these two causes, and which are so constantly and so sensibly felt in animals, are much less conspicuous in men. Besides, as there have been frequent migrations, as nations are mixed, and great numbers travel and are dispersed every where, it is no wonder that the human race should appear less subject to the influence of climate, and that there should be men strong, well-made, and even ingenious in all countries. Nevertheless, we may believe, from experience much further back than memory can trace, that men formerly knew the misfortunes which resulted from alliances with the same blood; since in the most uncivilized nations, it has rarely been permitted for the brother to marry the sister. This custom, which among Christians is a divine law, and which is practised by other people from political views, is perhaps grounded on this observation. Policy is never extended in so general and absolute a manner, unless supported by physical principles: but if men once discovered by experience that their race degenerated, when intercourse was admitted between children of the same family, they would soon have looked upon alliances with other families as a law of nature, and agreed in not suffering a mixture of blood among their children. In short, from analogy it may be presumed, that in most climates men would degenerate, as well as animals, after a certain number of generations.
Another influence of the climate and food is, the variety of colours in the coats of animals: those which are wild, and live in the same climate, are of the same colour, which becomes a little lighter, or a little darker, in the different seasons of the year; on the contrary, those which live in different climates are of different colours, and domestic animals vary so much, that there are horses, dogs, &c. of all colours, while the stags, hares, &c. are almost uniformly of the same. The injuries of the climate, always the same, and constantly eating the same food, produce, in wild animals, this uniformity. The care of man, the comforts of shelter, the variety of food, efface and vary the colour in domestic animals; as does also the mixture of foreign racers, when no care has been taken to assort the colours of the male and female, which sometimes produces beautiful singularities, as we see in pied horses, where the black and the white are so whimsically mixed that they sometimes do not seem the work of nature, but rather the fancy of a painter.
In coupling horses the colour and height should be attended to; the shapes should be contrasted, the race should be mixed with opposite climates, and horses and mares bred in the same stud should never be coupled together. All these are necessary cautions, and there are still some others not to be neglected; for example brood-mares ought never to be docked, because, being unable to defend themselves from the flies, they are continually tormented, and the constant agitations which the stings of these insects occasion diminish the quantity of their milk, which has great influence on the temperament and size of the foal, which in every respect will be more vigorous as the mother is more capable of nursing it. It is also preferable to choose brood-mares from such as have always been kept at grass, and have never been hard worked. Mares which have been kept in stables on dry food, and are afterwards put to grass, do not immediately conceive; they must have time to accustom themselves to this new kind of nutriment.
Although the usual season of mares is from the beginning of April to the end of June, yet it frequently happens that some are so before that time; but which it would be better to let pass off, because the foal in such case would be brought forth in winter, and suffer both from the intemperance of the season, and badness of milk; and also, if a mare does not become proud till after the month of June, she should not be suffered to take horse, because the foal being produced in summer, cannot acquire strength enough to resist the injuries of the ensuing winter.
Many people, instead of conducting the stallion to the mare, let him loose in a park, where a number of mares are kept, and leave him at liberty to single out those which are in season: this method is good for the mares, and they will breed with more certainty; but the stallion is more hurt in six weeks than he would be well managed in as many years.
As soon as the mares are with foal, and their bellies begin to grow heavy, they must be separated from those which are not so, lest they should be injured. They usually go with foal eleven months and some days; they bring forth standing upright, while almost all other quadrupeds lie down: in some cases, when the delivery is difficult they require assistance, and when the foal is dead, it is extracted with ropes. The foal generally presents its head first, as do all other animals; it breaks the membranes in the birth, and the waters flow out abundantly; at the same time there is voided several solid pieces of flesh formed by the liquor of the allantoides: these pieces, which the ancients have called the hippomanes, are not, as they say, pieces of flesh fastened to its head; but, on the contrary, separated by the amnios. The mare licks the foal after its birth, but she does not meddle with the hippomanes, notwithstanding the assertion of the ancients, that she devours it immediately.
It is the usual custom to have the mare covered nine days after she has foaled: not to lose time, and to make all they can from the stud; yet it is certain, that the mare having a foal and f[oe]tus to provide for, her strength is divided, and she is not able to give them so much nourishment as if she had only one; it would, therefore, be better, in order to have excellent horses, to let the mares be covered but once in two years; they would last longer, and would not be so liable to drop their foals; for in common studs it is a great thing when, in the same year, half or two thirds produce foals.
The mares, when with foal, can bear to be covered, though there is never any fresh conception: they usually breed till the age of 14 or 15 years, and the most vigorous not longer than 18. Stallions, when they have been taken care of, may engender till they are 20 years old, or upwards. The same remark has been made of these animals as of men, viz. that those who have begun too early are soonest incapacitated; for large horses, which sooner arrive at their growth than delicate ones, are frequently incapable before they are fifteen.
The duration of the life of horses, like that of every other species of animals, is proportioned to the time of their growth. Man, who is above 14 years in growing, lives six or seven times as long, to 90 or 100. The horse, who attains his whole growth in four years, lives six or seven times as long, that is, to 25 or 30. There are so few exceptions to this rule that we cannot draw any precedents from them; and as robust horses are at their entire growth in less time than delicate ones, they also live less time, seldom exceeding 15 years.