The birth weight of rabbits: Influencing factors and effect on behavioural, productive and reproductive traits: A review

The maternal effect plays an important role in several productive traits of rabbits because the length of gestation is one month and till the age of 3 weeks (wk) kits consume only their mother's milk, and weaning occur at the age of 4 or 5 wk. Fetuses are fed by the mothers through the blood supply; their growth depends on the number of fetuses and their position in the uterine horn, on the number of blood vessels per fetus, and on placental blood flow. The largest fetus is found at the ovarian end of the uterine horn and a decreasing size tendency can be observed in the direction to the cervical end, while a fetus of average weight is located in the last position (next to the cervix). The number of fetuses in the other uterine horn affects the weight of fetuses on the examined side. The body weight of does determines the birth weight of kits, with large differences between small and large breeds. Nulliparous does kindle smaller kits than multiparous ones. High ambient temperature has a significant negative effect on birth weight; however, its effect can be reduced by cooling the drinking water, by specific feeding strategies, or by shearing the hair of does. Generally, feed restriction adversely affects the birth weight; however, switching to ad libitum feeding in the last third of gestation may have a positive effect. Selection for within-litter homogeneity of birth weight induces a significant decrease in birth weight variability, without any influence on the average birth weight but with a positive effect on the survival of kits.Heavier kits have more brown fat tissue, which acts as energy fuel, they occupy the warmer central part of the nest, hence maintaining higher body temperature, and they consume more milk and grow faster than their smaller littermates. Rabbits with larger birth weight have higher body weight at their first mating, as well as during their reproductive career, than those with smaller birth weight. Low birth weight in itself is detrimental to viability, but this effect is even more aggravated by the factors listed above. To reduce mortality and to achieve a more balanced growth in litters and flocks, it is advised to raise kits with lower weight in smaller litters and those with larger weight in larger litters. In addition, care should be taken to cover the nest with a sufficient amount of hair. Limited results are available on the effect of birth weight on slaughter traits and meat quality of growing rabbits and on the reproductive performance of rabbit does.