EFFECTS OF BIOSTIMULATION ON BEHAVIOUR GROWTH AND REPRODUCTION OF RABBITS

ABSTRACT

A 16-week study was conducted to evaluate the effect of biostimulation on behaviour, growth, and reproduction of rabbits. Seventy five (crossbreds) mature rabbits (2.6 -2.70 kg), comprising of 50 nulliparous does aged, 6-7 months old and 25 bucks, (8-10 months old), were used for this study. The rabbits were allocated into five treatment groups in a completely randomised design (CRD). Each treatment consisted of 10 nulliparous does and five bucks. The study plan involved an exposure ratio of one buck to two does, implying five replications per treatment and each replicate containing two does and one buck. However, the does in the control group were not exposed to any buck. The does in the treatment groups were placed in opposite cages separated by a distance of 2.5 cm to the bucks at a ratio of 2 does: 1 buck for 7,14,21 and 28 days of exposure. The results showed that the behavioural response of the does ranging from flattening at a corner, circling, mounting without lordosis and mounting with lordosis differed significantly (P<0.05) across treatments. The frequency of vulva colour occurrence varying from white, red to pink across treatments were observed. The reproductive performance of the biostimulated does also differed significantly (P<0.05) as gestation length, pregnancy rate and average litter weight at weaning were higher in the treatment groups. Reaction time, sperm motility, percentage live sperm, percentage dead sperm and percentage coiled tails of the exposed bucks differed significantly (P<0.05) from the control. There were evidence of linear increase in hormonal profiles (estradiol and testosterone), as duration of exposure advanced to 7 and 14 days, respectively. Therefore, this study suggests that biostimulation can be a veritable tool for improving reproductive performance in rabbits. Also, it was noted that exposing rabbit does to rabbit bucks longer than 7-14 days prior to mating may adversely affect their reproductive performance. Hence, it is recommended that farmers should expose rabbit does to rabbit bucks 7 days prior to mating or artificial insemination for higher reproductive performance.

CHAPTER ONE

INTRODUCTION

The increasing demand for animal protein has aroused so much interest in the production of animals with short generation intervals like rabbits (Obinne and Okorie, 2008). The expansion of the livestock industry in Nigeria can hold great promise to bridge the gap in the supply and demand of animal protein in the country (Apantaku et al.,1998) if attention is given to microlivestock such as rabbit. The composition and quality of rabbit meat is comparable to poultry and superior to meat of larger animals (ruminants), It is highly palatable with less fat, sodium and cholesterol (Atteh, 2004). Rabbits are commonly raised to provide tender meat for human consumption. Besides, high prolificacy is the most important economic factor in rabbit production (Belhadi, 2004; Nofal et al., 2005). In addition to this, rabbits have a number of other good characteristics that are advantageous to subsistence farming, such as their small body size and short gestation period of 30-31 days. The daily weight gain is directly proportional to the body weight which gives them rapid growth rate and early sexual maturity. These factors are responsible for rabbits attaining the weight of sexual maturity 30 % faster than other animals and makes them suitable as meat producing small livestock in developing countries (Arijeniwa et al., 2000, Ajayi et al., 2005).

The profitability of rabbit production depends on the reproductive intensity and the number of kits weaned from a litter (Castellini et al., 2010). Although rabbits are reflex ovulators, the ovulation following instant mating sometimes does not result in successful conception. The inherent prolificacy in rabbits is currently facing biochemical, biophysical and environmental challenges which depresses their performance, therefore there is need for the application of some biological strategies to enhance their reproductive efficiency. Biostimulation methods are natural and cheaper alternatives to improve the reproductive performance of animals. Such methods have been found or tested in bulls (Bailey et al., 2005), bucks (Bonanno et al., 2011), hamsters (Cooke et al., 2001) and rams (Kasimanickam et al., 2007). Other approach to promote a steady reproductive performance in animals is the application of hormonal protocols (Rebollar et al., 2006). This however, increases labour cost and possible adverse effects on health due to residual effects.

The use of exogenous products such as hormones and antibiotics to improve livestock production goes against the perception of the consumers. Castellini et al. (2006) reported that the European Community Policy might impose a restriction on the use of hormones in relation to their residues in meat, animal welfare and the desire to preserve a natural meat quality. For these reasons, serious efforts have been made by the International Rabbit Reproduction Group (IRRG, 2005) to set up alternative methods which do not require the use of hormones in rabbit production in order to increase sexual receptivity at the time of insemination or natural mating. Several biostimulation approaches such as animal manipulation (doe-gathering) at the time of semen collection, dam-litter separation, evaluation of different reproductive rhythms or re-mating intervals, adoption of different feeding programs, buck effect and photoperiods have been tried  in an attempt to obviate the use of hormones in animal reproduction (Ojeda and McCann, 2000). These biostimulation methods are believed to stimulate the release of gonadotropins, luteinizing hormone (LH) and follicle stimulating hormone (FSH) through visual, olfactory (pheromonal) and tactile cues from the anterior pituitary gland under the influence of some releasing factors from the hypothalamus (Ojeda and McCann, 2000). The release of LH and FSH provides steroidal feedback to the hypothalamus which ensures the continuation of normal ovarian cyclicity (Frink, 1998). However, the exact effects and mechanism of biostimulation techniques and the subsequent behavioural responses on the reproductive performance of rabbit does and bucks have not been properly elucidated. Therefore, the present study was designed to evaluate the effect of biostimulation on the reproductive performance of nulliparous rabbit does as well as to ascertain its effects on semen characteristics of the bucks.

    Justification

In order to contain the pressure of increased human population on the demand for meat and meat products, rabbit (Oryctolagus cuniculus) production is a viable option, because of their prolificacy, early maturity, fast growth rate, high genetic selection potential, high feed conversion efficiency and economic utilization of space (Hassan et al., 2012). To ensure a sustained rabbit production and development of the sector, rabbit breeds and breeding practices should be explored and challenges identified. However, poor response of rabbit does during service and subsequent decrease in ovulation and/or conception has necessitated the emergence of possible and cost effective techniques in improving reproduction in rabbits. Sexual responses of female rabbits to visual, acoustic/auditory and olfactory stimuli from the male have not been properly investigated, but ovulation is believed to be induced by mating through a neuro- endocrinological reflex which provokes an LH surge (Bakker and Baum, 2000).

Frank (1966) reported the possibility of certain pheromones secreted by the sebaceous glands of rabbit bucks to induce sexual receptivity in the does. It has also been suggested that rabbit does emit specific signals containing information on her sexual state that attracts male rabbits  (Hudson and Distel, 1990). Till date, the precise nature of the pheromones or signals supposedly exchanged between the male and female rabbits remain obscure. However, it appears that male presence is beneficial to receptivity and fertility in nulliparous does (Berepudo et al., 1993) but not in lactating does (Kustos et al., 2000; Eiben et al., 2001; Bonanno et al., 2003). Biostimulation is one of the techniques which has been tested on other species and appears to be promising in enhancing fertility in animals (Theau-Clement, 2005). In addition, several evidences have shown that the use of exogenous gonadotropic hormones such as equine chorionic gonadotropin (eCG) to improve reproductive performance in rabbits has resulted in resistant effects, with subsequent decrease in conception rate and increase in mortality rate following frequent and/or high dosage treatment (Theau-Clément, 2007). Therefore, a practical and potent non-hormonal approach in improving fertility in rabbits remains imperative. This study aimed at evaluating the effect of different durations of exposure on the reproductive performance of rabbit does and bucks towards finding the best duration of exposure for optimum performance.