4 Linear regression coefficients for the moisture content (g/kg) of NZW and CAL male and female rabbits exposed to dietary protein levels over a period of 56 days. 6 Linear regression coefficients for ash content (g/kg) for NZW and CAL male and female rabbits exposed to dietary protein levels over a period of 56 days.
- Background
- Problem statement
- Objectives
- Hypothesis
Measure the response in growth performance (feed intake, body weight gain and feed conversion efficiency) to dietary protein levels. Measure response in carcass composition (moisture, ash, lipids and protein) and changes in physical growth (carcass and skin weight) to dietary protein content.
- Introduction
- Amino acid requirements for maintenance and growth
- Ideal protein concept
- Amino acid imbalances
- Factors affecting amino acid utilization
- Factors influencing the response of growing rabbits to dietary protein
- Effect of genotype
- Effect of environment
- Discussion
- Conclusion
An accurate assessment of the amino acid requirements of growing animals requires an accurate assessment of how efficiently these animals use amino acids (Reis et al., 2018). According to some authors, the efficiency of amino acid utilization for birds should be approximately 80% (Martin et al., 1994).
Introduction
Response of broilers to balanced dietary proteins was recently studied by Azevedo et al. The present study was then designed to measure the response of growing rabbits of two breeds and sexes in growth performance to various levels of balanced dietary protein in order to determine the optimum economic amounts of dietary protein levels to be included in feeds.
Materials and methods
- Ethical consideration
- Study Site
- Experimental design
- Animal housing and management
- Experimental diets
- Chemical composition of experimental diets
- Growth performance measurements
- Statistical analysis
The rabbits were monitored twice a day, in the morning and in the afternoon, to ensure that feed and clean water were always available. Chemical analysis (AOAC, 1990) of experimental diets was carried out in duplicate at the University of KwaZulu-Natal, Animal and Poultry Science Laboratory, Pietermaritzburg, South Africa. A Retch ultracentrifugal mill was used to grind the experimental pelleted diets through a 1 mm sieve.
The food remaining at the end of the week was weighed again to calculate food intake, and the container was refilled and weighed. Food intake was calculated as the initial food weighed in the dish minus the food remaining in the feeder and in the dish. Body weight gain was calculated as the final body weight minus the initial body weight of the rabbit.
Analysis of variance was used to determine treatment means, and appropriate regression analysis was used to describe responses to dietary protein content on the variables of interest.
Results
- Growth performance parameters
5 Mean feed intake (g/d), final body weight (g) and feed conversion efficiency (FCE, ggain/kg feed) of female and male New Zealand White (NZW) and Californian (CAL) rabbits fed a range of dietary protein levels for a period of eight weeks. 6Average daily body weight gain of the NZW and CAL rabbits fed dietary protein levels over 56 d period. 7Linear regression coefficients describing feed intake (g/d) of male and female NZW and CAL rabbits over 56d period.
8 Exponential regression coefficients describing the body weight gain (g/d) of male and female NZW and CAL rabbits over 56 d period. 9Linear regression coefficients describing the final body weight of male and female NZW and CAL rabbits over 56 d period.
Discussion
This observed interaction could also mean that the feed intake of these breeds was dependent on the level of protein in the diet. The lowest feed intake was observed at the lowest dietary protein content (126 g/kg) in male and female CAL rabbits, while, conversely, the lowest feed intakes in female and male NZW rabbits were observed at the highest protein level (213 g/kg kg) or 178 g/kg dietary protein. Male New Zealand White rabbits had greater feed intake than NZW females at all dietary protein levels, whereas the opposite was observed in CAL rabbits.
The difference in response to feed intake between the NZW sexes means that the optimal dietary protein levels to include in the feed of these different sexes within this breed would differ to meet their needs. The highest final body weight was observed in NZW female rabbits receiving the lowest amount of feed, while the highest body weight in CAL female rabbits was observed at the highest level of dietary protein. However, this was not the case for CAL males, as higher female body weights were observed at all dietary protein levels except the highest dietary protein.
Only female NZW rabbits had lower FCE at the highest level of dietary protein.
Conclusions
In a study by Maertens et al. 1997), it was also found that dietary protein levels for different ages during growth must be considered to meet the protein requirements of growing rabbits. Apart from lowering protein levels during the growth phase to meet the needs of growing animals, there are other advantages to this approach. One of the widely known benefits is the reduction of nitrogen release into the environment.
It has also been emphasized that reducing protein content in animal feeds is beneficial at high ambient temperatures by increasing feed intake and thus performance (Waldroup, 1982). The performance of heat-exposed broilers also appeared to improve with the low-protein diet and the ideal protein concept (Faria Filho et al., 2007).
Introduction
- Study Site
- Experimental design
- Animal housing and management
- Experimental diets
- Chemical composition of feeds
- Slaughter procedure and carcass analysis
- Carcass composition parameters
- Statistical analysis
Rokonuzzaman (2018) also reported significant variations in wing moisture content of three broiler strains and thigh fat and protein composition. It is well known that the chemical and physical composition of the body changes systematically as the animal grows (Emmans, 1995). In order to determine changes in the weight of different chemical components of the body at different stages of growth, genotypes must be accurately characterized.
The chemical composition of the feed was also described in the Slaughter Procedure and Carcass Analysis section. A total of eight (8) NZW rabbits (four males and four females) were sampled on arrival for physical and chemical analysis to estimate the initial carcass composition of the NZW rabbits prior to being subjected to dietary treatments. The moisture content was then determined as the initial weight of the sample (150 g) minus the weight after freeze-drying divided by the weight of the initial sample multiplied by 1000, with initial weight of the sample W1, weight after freeze-drying (W2) ) (AOAC 930.15).
Protein analysis was performed using the Dumas combustion method, which quantifies sample nitrogen.
Results
- Response in carcass composition to balanced dietary protein
Significant interactions were observed between the females of the two breeds in carcass and pelt weights. 1Mean moisture, ash, lipid and protein content in the carcass of NZW (initial and final) and CAL female and male rabbits fed a range of dietary protein levels over a period of 56 days. 2 Mean carcass and pelt weights of NZW (initial and final) and CAL male and female rabbits fed a range of dietary protein levels over 56 d period.
3 Exponential regression coefficients describing carcass moisture content (g/kg) of female and male NZW and CAL rabbits over the 56 d period. 4 Linear regression coefficients of moisture content (g/kg) of male and female NZW and CAL rabbits subjected to dietary protein levels over the 56-day period. 5 Exponential regression coefficients describing carcass ash content (g/kg) of female and male NZW and CAL rabbits over the 56 d period.
6Linear regression coefficients for ash content (g/kg) in NZW and CAL male and female rabbits exposed to dietary protein levels over a period of 56 days. 9 Exponential regression coefficients describing carcass protein content (g/kg) in male and female NZW and CAL rabbits over a period of 56 days. 12Linear regression coefficients for carcass weight (g) of male and female NZW and CAL rabbits exposed to dietary protein levels over a period of 56 days.
Discussion
However, the highest ash content was found at the highest dietary protein levels in the NZW breed and CAL females, while the high ash content was observed at 178 and 196 g/kg in the CAL males. As expected according to Gous et al. 2012), NZW rabbits (both male and female) showed the highest lipid content at the lowest (126 g/kg) and second lowest (143) dietary protein levels than at the highest protein level. As mentioned above, both males and females of the NZW breed had the highest fat content at the lowest and second lowest dietary protein levels.
Regarding CAL rabbits, female and male CALs had the highest fat content at a dietary protein content of 161 g/kg and the second highest protein content (196 g/kg). The highest body protein content was observed at the highest level of dietary protein in both sexes of NZW and male CAL rabbits. The highest protein deposition in the NZW breed was in rabbits receiving the highest dietary protein content (213 g/kg) in both females and males.
However, this higher body protein content found at the highest dietary protein level was expected as high dietary protein content results in an increased body protein content (Bogosavljević-Bošković et al., 2010 ).
Conclusions
Significant interactions (protein x breed x sex) and (breed x sex) were observed in carcass and skin weights in females of the two breeds. New Zealand White females increased carcass and skin weights in response to decreased dietary protein, while CAL females decreased their carcass and skin weights with decreasing protein. The maximum carcass weights of NZW females were therefore recorded at the low dietary protein levels (126g/kg and 143g/kg), whereas the highest carcass weights of CAL females were recorded at the high dietary protein levels (178g/kg, 196g/kg) and 213g /kg).
The results of improved carcass weights of the NZW females in response to reduced dietary protein content are consistent with the findings of Nørgaard et al. 2014), who observed increased pig carcass weights in response to reduced crude protein content.
- General discussion
- Future research
- Study limitations
- References
A model for predicting and predicting the response of laying hens to amino acid intake. Efficiency of amino acid utilization in the growing pig at suboptimal levels of intake: lysine, threonine, sulfur amino acids and tryptophan. A formal method to determine the dietary amino acid requirements of laying-type pullets during their growing period.
Organ weight and body composition in chickens in relation to energy and amino acid requirements: effects of strain, sex and age. Re-estimation of soluble amino acid requirements of male and female broilers based on different ideal amino acid ratios in the initial period. Effects of dietary amino acid levels on performance and carcass composition of 42- to 49-day-old chickens.
The effect of the nutritional level on the optimal amino acid pattern in the diet of growing pigs.
