Rabbit Production. James I McNitt
5.20. A white fungus is often observed growing on rabbit manure beneath the cages. (Courtesy of P.R. Cheeke)
Shedding or Molting
The rabbit’s coat is prime when the hairs have a good sheen, are tight, and have attained their maximum length. The skin is white and the hair flows back into place evenly when the coat is rubbed from the rump to the shoulders.
Unprimeness is indicated by a dull, uneven coat and loose hair. The hair does not flow back evenly when the coat is rubbed from the rump to the shoulders. Patches of new fibers can be seen, and these new fibers will appear in a growth pattern that varies from animal to animal. The skin of these new hair growth areas is dark and easily detected on rabbits with colored coats.
The pattern of shedding in rabbits has not been definitely established. There is a juvenile molt that begins when a rabbit is about two months old and lasts until it is four to six months of age. Heavy feeding of the young tends to cause the molt at an earlier age. In addition, there is the annual molt with mature rabbits. This molt varies in time of appearance in different geographical areas. Rabbits may be thrown into molt by disease, going “off feed,” the sudden occurrence of unseasonably high temperatures, or other stresses. Evidence of molting in the herd is the accumulation of loose hair on the wire sides and in the corners of the cages and the droppings being bound together by embedded fibers.
Shedding first occurs on the sides of the rump and the thighs, followed by the back, then increasingly in areas down over the sides. There is a pronounced degree of similarity in the size and location of the ingrowing new coat areas on both the right and left sides of the rabbit.
A high quality diet and high feed intake promote molting. The growth rate of hair is more rapid with a high nutrient intake, so the rate of turnover of hair is greater. Restricted feeding of adult show animals reduces the amount of hair shedding and keeps the fur in prime condition for a longer period. Some rabbit raisers claim that molting adversely affects reproductive performance, but this belief is not well substantiated. In fact, little attention is paid to molting in commercial meat rabbit operations.
Environmental Effects on Rabbit Performance
Temperature
Rabbits are very susceptible to heat stress because they have few functional sweat glands and have difficulty in eliminating body heat when the environmental temperature is high. Heat stressed animals stretch out to maximize body surface area for heat elimination. Animals respond differently to a sudden acute exposure to high temperature than to chronic exposure when reared under high environmental temperatures. In the tropics, rabbits can be successfully raised under conditions in which the temperature is consistently 32° to 35°C, whereas rabbits adapted to the cool conditions of the Pacific Northwest of the United States may die of heat stress when the temperature on rare occasions exceeds 32°C. Animals routinely kept under high temperatures develop metabolic mechanisms 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