A description of the chemical and physical growth of New Zealand white and chinchilla rabbits.
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Date
2024
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Abstract
This study investigates two key aspects in animal science: (i) describing the growth potential and
chemical composition of two commercially bred rabbit strains, in order to optimize the
composition of their feed based on variables predicted by simulation modelling; (ii) testing the
hypothesis that the allometric relationship between body parts remains consistent across different
strains, sexes, and body protein levels. In other words, the research assesses whether animal scientists
have faced challenges in modifying the proportional relationship between the weight of different
body parts of rabbits and their body protein weight. The primary goal of the study was to outline
the physical and chemical transformations in the body composition of two commercially bred
rabbit breeds, namely New Zealand White and Chinchilla, over a 126-day growth period. The key
focus was on investigating how the growth performance of developing rabbits is affected by sex and
age, considering the influence of body protein. Moreover, the research examined alterations in
growth and variations in the physical and chemical elements of the body.
To achieve the objectives, series of studies were conducted: In this experiment, a total of 220
rabbits, consisting of both New Zealand White and Chinchilla strains, were utilized. Weekly
weighing of 100 rabbits from each strain were conducted, starting from day 14 (due to the fragility
of the kittens at birth) and continuing until day 140, in order to assess the growth potential of
each rabbit. Additionally, samples were collected from 120 rabbits from each strain at specific
ages: day 14, 21, 28, 35, 42, 56, 70, 84, 112, and 140. Before slaughter, the animals underwent
weighing to determine their weight exclusive of internal organs. Post-slaughter, their weight was
measured again to discern the weightof internal organs, skin, and the weight without the skin. The
dissected body parts were weighed, labeled, and stored in a freezer for subsequent thawing and
mincing. The specimens were then subjected to freeze-drying to extract water content. Following
this, they underwent further grinding before being analyzed for protein, lipid, and ash.
Moreover, the Gompertz equation was applied to individual body parts and the protein weight of
each body component. The parameters of the Gompertz equations were defined as the final weight
of these components, their rate of maturation, and the time required to achieve the peak growth
rate of each component. By utilizing data from each individual rabbit, allometric regressions were
employed to establish the relationship between the weights of physical and chemical components.
The natural logarithm of body protein weight served as the independent variable, while the natural
logarithm of body component weight served as the dependent variable.
A significant allometric relationship was found between body weight and pelt weight, as the weight
growth process occurs continuously from birth to maturity. Body weights and chemical
composition of males and females (bucks and does) of the two strains remained similar throughout
the trial. Mature body weights for both strains (New Zealand White and Chinchilla) at 140 days
averaged 1760 g and 1558 g; mature body protein weights averaged 95 g/kg and 61 g/kg; and
mature body lipid contents averaged 40 g/kg and 55 g/kg, respectively. Rates of maturing per day
of body weights for males and females of both strains averaged 0.0241 and 0.251; pelt-free, 0.0294
and 0.0251, and body lipid was 0.0441 and 0.0225, respectively. The rates for body protein differed
between New Zealand White females and Chinchilla females (0.0172 vs 0.0256/d). Separate
equations were needed for males and females to describe the allometric relationships between lipid
and protein in the pelt-free body. The rate of maturing of pelt in the New Zealand White was higher
in females than in males (0.0249 vs 0.0214/d), and the mature weight was lower in females than in
males (45vs 52 g/kg), respectively. Common values of the sexes for both strains are represented
when there were no apparent variations in the constant terms and regression coefficients. The saddle
weights, regardless of the protein content in both sexes of the New Zealand White, can be described
by a single constant term of 1.0193, and a lower single constant term value of -1.1070 in the
Chinchilla rabbit. The goodness of fit (R2) for both strains was highest in the saddle with 0.974 and
0.957 in the New Zealand White and Chinchilla gigantas rabbits, respectively, while it was lowest
(0.922) in the pelt of New Zealand White and hindlimb (0.892) of the Chinchilla gigantas rabbits.
Sexes differed in the allometric relationships of all component parts measured in both breeds. A
common relationship between the two strains could be used to predict the weights of all rabbit
major component parts. Further studies are recommended to confirm the findings of this study.
Keywords: Chemical, Chinchilla, Components, Physical, New Zealand white, Rabbits.
Description
Doctoral Degree. University of KwaZulu-Natal, Pietermaritzburg.