ABSTRACT
Data on a full diallel cross involving three rabbit breeds
and its effects on some growth and reproductive traits were studied. Data on
two thousand and thirteen (2,013) rabbits comprising eight hundred and five
(805) purebred bunnies kindled in 60 litters and one thousand, two hundred and
five (1,205) crossbred bunnies from 86 litters bred from 2010 to 2014 in five
parities were first corrected for the fixed effects of sex, season of kindling
and the does‘ age using the least significant differences (lsd) before the
analysis was run using the Generalised Linear Model. Of the three breeds, the
Chinchilla showed superior performance in both the reproductive and growth
performance while the BV X CH crossbred showed superior performance in most of
the economic traits that were assessed compared to the other crosses. The BV X NZ and NZ X CH crossbreds recorded
significantly (p = < 0.05) higher litter size at birth (6.8±0.1) and at
weaning (6.9±0.1) respectively. The heterotic effects of both the main and
reciprocal crosses were quite desirable for most of the economic traits.
Notable among them was the age at sexual maturity, kindling interval and
mortalities which recorded varying levels of negative heterosis. The reciprocal
crosses exhibited some level of superiority in the growth traits (bunny weight
at birth and the post-weaning growth rate) that recorded positive heterosis.
The Chinchilla and BV X CH crossbred comparatively exhibited a higher level of
superiority in the general and specific combining abilities in a number of the
economic traits that recorded significant differences. The positive heterotic
effects encourage the application of crossbreeding schemes in rabbit production
for improved productivity within the coastal savannah agro-ecological zone of Ghana.
CHAPTER ONE
INTRODUCTION
Background of the Study
Globally, there has been an
increasing demand for animal protein; more significantly, in the developing
countries of sub Saharan Africa. This soaring demand for animal protein has
been attributed not only to the ever-increasing global human population, but is
also an acknowledgement of the essential role of animal protein in human
development and well-being. Improved economic status, urbanisation and
industrialisation, particularly in the developing economies have all
contributed to the increased demand for protein from animal sources (Karikari,
Darkoh & Deku, 2011). There have been several interventions geared towards
meeting this increasing demand. These interventions include improved management
and production systems, improved nutrition, efficient utilisation of genetic
resources and agro-industrial by-products, as well as rise in backyard or
non-commercial animal production (Onifade & Tewe, 2010). More importantly,
these interventions also seek to guarantee security in food supply for the
marginalised in society (Fayeye & Ayorinde, 2010).
Over the period, poultry in
particular has played a significant role in this regard, although the
persistent and ever-widening gap between demand and supply of animal protein
has not yet been bridged. This has necessitated the need to make more use of
alternative sources of animal protein via the development of non-conventional
livestock. The rabbit, in recognition of its high prolificacy, rapid growth
rate, early sexual maturity, short gestation period (28-31days), good ability to
utilise forage feed, high meat yield, comparatively low production cost, lower
space requirement, limited cultural and religious prohibitions on its
production and consumption, as well as the high nutritive value of its meat,
has been identified as a promising food animal (Fayeye, 2013; Obiajulu, Eze,
Amadi, & Odoemena, 2016; Sivakumar et al., 2013).
Considering the potential for
rabbit production in Ghana, and the success story of some neighbouring West
African countries, the National Rabbit and Grasscutter Projects were initiated
by Newlove Mamattah, in 1971. With the introduction of some improved rabbit
breeds, breeding herd was approximately 1,478 by 1978 (Lukefahr, 1998;
Lukefahr, 2000). Individuals, particularly women, children and rural folk who
showed keen interest in this species, recorded tremendous successes. This
initiative notwithstanding, performance records of rabbits have over the period
not only been sub-optimal, but also continued to follow a downward trend. With
time a number of individuals and governmental institutions (like the Rabbit
Unit of the Animal Research Institute of the Council for Scientific and
Industrial Research) abandoned the programme entirely, focusing only on the
traditional livestock species. It is thus not surprising that efforts primarily
geared towards enhancing the general performance (reproductive and growth) of
rabbits through improved nutrition and management practices, have not yielded
the expected results.
An important intervention or tool
that has greatly influenced output of not only livestock species but also plant
species as well has been crossbreeding. Crossbreeding is basically the mating
of individuals of different breeds. The exercise results in the
alteration of genetic variance, and allows combining the valuable traits of
parent lines in their progeny. It has also been found to be a major tool for
the full exploitation of genetic variation in rabbits (Lukefahr, 1998), being
identified as one of the best options to increase profits of the warren or
colony because of its particular impact on productivity and adaptation to the
environment (Akinsola et al., 2014; Fayeye & Ayorinde, 2010; Mbanasor,
& Wogu, 2006; Obiajulu et al., 2016). Baselga (2004) has indicated that due
to the nature of their productive traits, rabbits offer a higher degree of
kindness (productivity) when improved via cross breeding.
Diallel crossing is a crossbreeding
system that involves crossing each of several individuals with two or more
others in order to determine the relative genetic contribution of each parent
to specific characters or traits in the offspring. It has been identified as
one of the best approaches to facilitate the selection of an ideal genotype,
primarily because of the combining ability of the genotypes. Likewise, diallel
crossing permits the estimation of heterosis among all pairs of breeds. This
has been found to be useful in the evaluation of breeds which are already
indigenous to a region or for a limited number of breeds chosen on the basis of
prior top cross evaluation (García, Ponce de León & Guzmán, 2012). Aside
offering the opening to assess the varied genetic aspects of the parents‘
performance, diallel crossing helps in taking objective decisions in the
different improvement programmes right from the identification of superior
genotypes and promising combinations for the desired economic traits (Ramos et
al., 2006). It is thus not surprising that the diallel crossing is considered
as an efficient means of assessing the full genetic and heterotic potential of
different breeds or lines.
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