1.0 GENERAL INTRODUCTION
The total world production of rabbit was estimated to range from 1,311,000 to 1,516,000 tonnes for the top 22 producer countries. From this figure, Italy had 300,000 tonnes, Russia 250,000 tonnes, France 150,000 tonnes, China 120,000 tonnes, Spain 100,000 tonnes, Indonesia 50,000 tonnes, Nigeria 50,000, tonnes, United States 35,000 tonnes and Germany 30,000 tonnes (WRP, 1990).
Rabbits are basically reared for meat, fur and cool production (TNAU, 2008). Rabbit production is very essential in improving animal protein intake in developing countries. This is because rabbit is very prolific as determined by the number of kits born alive at kindling and birth to weaning viability (Orunmuyi et al., 2006).
Alleviation of poverty, attainment of food security and provision of adequate nutrition are some of the millennium development goals that Nigeria has to meet. Rabbit farming can be one effective objective that can be used not only in Nigeria but also in other Africa countries (Cliford, 2009).
Advantages of rabbit farming are enormous considering the fact that they can be fed with high forage, low grain diet that is largely non-competitive with human food and they have high feed conversion efficiency. Rabbits have the potential to being in constant state of reproduction and can be mated within 24 hours of kindling. They have high growth rate attaining market weight of about 2kg at 12 weeks of age. Rabbit meat is a highly nutritious, tasty and excellent in quality. It is rich is protein, low in fat, cholesterol and sodium and thus can be recommended for cardiac patients (TNAU, 2008).
Cliford (2009) also summarized in Africa Rural Connect that Rabbits are prolific in reproduction, have high growth rate and therefore high turnover, required minimal space to keep and meager resources to maintain since they can flourish on forages that are disdained by humans.
The feeding habit of rabbit offers no appreciable competition with man. This is because it can subsist on green as basal diets. The combination of these characteristics is unique. In addition to these, rabbits have a number of other characteristics that might be advantages on subsistence farming system such as their small body size, short generation interval with relatively short gestation period average of 30-31 days. The daily weight gain is high in proportion to the body weight which gives them a rapid growth rate and sexual maturity is early. These factors result in rabbit reaching the weight of a sexually mature animal 30% faster than other animals (Ajayi et al., 2005) and also make rabbits suitable as meat producing small livestock in developing countries (Arijeniwa et al., 2000).
Ensminger (1991) identified problems facing reproduction of some farm animals to include repeat breeding, still birth, abortion, poor libido and poor semen quality. It had been documented that in the study of ruminant and human infertility that chromosomal abnormalities were the major causes of infertility and pre-natal losses of foetus. As observed by Berepubo et al. (1993); Omeje et al. (1994); and Wekhe (1998), chromosomal abnormalities lead to sub-fertility or total infertility, neo-natal deaths, repeat breeding, anoestrus, congenital defects, poor libido, poor semen quality as well as stunted growth and general poor performance in young animals.
Chromosomal abnormalities have been implicated for all these reproductive problems as observed by direct karyotyping of embryos from infertile or sub-fertile dams or sire (Long and Williams, 1980; Hares et al., 1980; Berepubo and Long, 1983; King and Linares, 1983; Berepubo, 1985; Murray et al., 1985). X-chromatin screening for the presence of drumstick appendages has proved to be one of the very many techniques for diagnosing chromosomal defects. Similar studies have revealed the presence of chromosomal abnormalities in affected farm animals (Otuma et al., 2005; Parkaryi et al., 2008; Nyeche et al., 2010).
In modern genetic term, X-chromatin evaluation refers to the analysis of X-chromosome only without reference to the Y-chromosome. The X-chromosome has been successfully used in domestic animals to predict the cytogenetic or genetic merit of various economically important species. These include early detection of potential sex chromosomal and developmental anomalies which considerably impair fertility and also the prediction of the growth potential of neonates (Wekhe, 1998).The investigation of the sex chromatin in animals is based on the fact that it represents the sexual status (XX and XY) chromosomes of a particular animal.
As suggested by Bhatia and Shanker (1984), much would be saved by farmers if animals with abnormal reproductive traits were identified and culled early. Hence, the relevance of this work.