A description of the chemical and physical growth of New Zealand white and chinchilla rabbits.

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.