ABSTRACT
The study was carried out to determine the x-chromatin status of different breeds of rabbit and their crosses. The genotypes were Newzealand (NZW) x Newzealand (NZW), Dutch Black (DTB) x Dutch Black (DTB), (NZW) x DTB, and DTB x NZW. One hundred and sixty-nine offsprings from the mating were screened. Blood samples were collected with heparin sample bottles fortified with EDTA anti-coagulant via the ear veins and blood smears were made on clean glass slides. They were stained with Geimsa, rinsed in distilled water and air dried. With the aid of microscope, 200 polymorphonuclear neutrophils were examined for the presence of drumstick appendages. The result revealed that the females had the average x-chromatin status of
2.09%, 2.00%, 2.28% and 2.07% for NZW x NZW, DTB x DTB, NZW x DTB and DTB x NZW genotypes respectively while the males had the average x-chromatin status of 0.00%, 0.05% 0.00% and 0.00% for NZW x NZW, DTB x DTB, NZW x DTB and DTB x NZW genotypes respectively. These values were within the normal range of 2.00 – 12.00% for females and
0.00% – 2.00% for males. It was concluded that these animals were free from x-chromatin related physiogenetic problems. The body weight measurement of the rabbits at 4, 8, 12 and 16 weeks of age showed significant differences at (p<0.05) across the genotypes. The linear body measurements of males and female rabbits at 4, 8, 12, and 16 weeks of age showed significant differences at (p<0.05) across the genotypes. From this experiment it could be concluded that the Main crosses ((NZW) x DTB) and the Reciprocal crosses (DTB x NZW) came out better since they explored the advantages of cross breeding and it is advised that farmers should practice cross breeding of rabbits rather than breeding pure lines.
CHAPTER ONE
1.0 GENERAL INTRODUCTION
1.1 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.
1.2 Objective of the Study
The objectives of the study are:
1. To screen rabbits for the presence of aberrant x-chromatin incidence as a way of determining their reproductive potentials.
2. To determine the genotype with highest incidence of x-chromatin appendage.
3. To determine the effect of the presence of drumstick appendage on the body weight and linear measurements of rabbit.
Justification of the Study
The application of the principle of animal breeding and genetics is one of the answers to livestock development in Nigeria. However, breeding and breed improvement can effectively take place if a large number of animal and farms are involved so that any genetic improvements are quickly spread through the participating farms (Nwosu, 1990). Achieving animal protein requirement for the masses should be the utmost concern of animal scientists and livestock farmers in developing country like Nigeria. Thus, the result of this experiment will:
i. Provide rabbit farmers with useful information on the best genotypes to consider for rapid production with a view to maximizing profit and reducing the acute shortage of animal products that has bedeviled developing countries. ii. Reduce the high risks of producing genetically defective rabbits
This material content is developed to serve as a GUIDE for students to conduct academic research
CYTOGENETIC SCREENING OF DIFFERENT BREEDS OF RABBIT FOR GROWTH POTENTIALS IN A WARM HUMID TROPICAL ENVIRONMENT
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