to adapt to heat stress. In areas of high temperature, such as the tropics, rabbits consume large quantities of water and consume less feed than in temperate climates. Their productivity is reduced because of the lower feed intake. Provision of adequate water is critical under these conditions. Rabbits that begin to pant or develop extreme wetness around the nose and mouth are in severe heat stress, and immediate corrective action should be taken.
An ideal environmental temperature is 10° to 15°C. This is known as the “comfort zone.” At higher or lower temperatures than this, the animal has to expend energy to maintain its body temperature. Rabbits are much more tolerant of low temperatures than high temperatures. A major consideration under low temperatures is that feed consumption is increased so the animal can maintain its body temperature. Thus, the lower the environmental temperature, the poorer the feed conversion, because a greater quantity of feed energy is being used to maintain body temperature. When limited feeding is practiced, provision must be made to provide extra feed in cold weather. It is significant that, because of the increased feed intake, water consumption also increases as the temperature drops. Restricted availability of water under cold conditions (e.g., from frozen water lines) will reduce performance more than restriction at the comfort zone, because rabbits will not eat if they don’t have sufficient water.
An interesting response to cold temperature occurs in some breeds such as the Californian, Siamese Satin, and Sable. If the newborn kits are exposed to cold temperature, or if fur on an adult is shaved and then the rabbit is exposed to cold, the fur will temporarily grow in black in areas where it is normally white (Fig. 5.21). This occurs because the cold stimulates the melanin pigment in the hair follicles, which causes the hair to be black.
Fig. 5.21. The Californian rabbit on the right had a patch of hair shaved off its rump and was then kept in a cold environment for a few days. The hair grew back in as pigmented fur. (Courtesy of OSU Rabbit Research Center)
Fluctuations in temperature may trigger outbreaks of enteritis. Enteritis outbreaks are sometimes noted following the start of a cold snap. One possibility to account for this is that a sudden drop in temperature triggers an increase in feed intake. This could cause carbohydrate overload, leading to proliferation of pathogens in the gut, with the production of lethal toxins. Restricting feed at the beginning of a cold spell may reduce the incidence of enteritis.
Light
Optimal lighting conditions for rabbit production have not been established. It is believed that the winter decline in fertility that is often observed in some regions of the world may be due, at least in part, to decreasing day length. Use of lights to maintain a total day length equal to the longest day at the particular latitude is recommended. In most places in the United States, that is in the range of 14 to 16 hours. As discussed in Chapter 4, commercial rabbitries should have lights on a timer and use supplementary lighting both in the morning and the evening to help maintain normal breeding during the fall and winter. It is possible that the spectrum of the light source may also have an influence on animal performance.
Hypnosis
You can readily “hypnotize” a rabbit (put it to sleep) by laying it on its back and gently stroking the chest, abdomen, and sides of the head. When asleep a rabbit is in a trance-like state (Fig. 5.22). Hypnosis may have some value as a means of restraining animals for minor surgery; probably it is mainly used to get the attention of 4-H Club members touring the rabbitry!
Fig. 5.22. A rabbit that has been hypnotized. (Courtesy of D.J. Harris)
Breeding Herd Replacements
An extremely important part of herd management is providing adequate replacements for the breeding herd. In commercial rabbitries it is common to replace 100 to 125 percent of the breeding does each year. This does not mean that every doe in the herd is replaced yearly, but it does mean that if you have a 100-doe breeding herd, you will add to this herd 100 to 125 junior does per year. Some cages will have had two or three does during the year, whereas other cages will have the same doe for two years. In fact, if you are not replacing a sizeable portion of the breeding herd annually, you are probably not improving the quality and health of the herd as rapidly as you should. Snuffles, sore hocks, malocclusion, mastitis, poor reproductive performance, and many other reasons will result in breeding animals being removed from the herd. As a general rule, save one replacement doe per month for every 12 does in production, and one replacement buck for every five bucks in service. The continual replacement of old bucks with young bucks is extremely important. Since each buck is bred to many does, his influence on the genetic quality of the herd is much greater than that of an individual doe. Young bucks tend to have greater libido and will work harder than old bucks. The criteria used in selection of young stock are covered in Chapter 15
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