Flemish Giant Rabbit How Long to Feed Before Butchering
1. Introduction
There are many species of rabbits in the world (Silvano et al. 2000; Sánchez-Trocino et al. 2013), but only European rabbits (Oryctolagus cuniculus f. domestica) are widely bred. Rabbits constitute a valuable source of easily-digestible and dietetic meat comparable to culinary beef (Dymnicka et al. 2004; Daszkiewicz et al. 2012). Medium breeds such as Californian (CAL), New Zealand White (NZW) and Termond White rabbits are generally regarded as most suitable for meat production. They are characterised by early development, a high growth rate, a satisfactory feed conversion ratio and high reproductive performance. Commercial rabbit farms in Europe mostly use selected hybrid lines produced by crossing the above breeds. CAL rabbits are used for cross-breeding and are also farmed extensively as a pure breed (Maertens et al. 2006).
To date, commercial rabbit breeding has not replaced traditional and organic small-scale farming systems which use various rabbit breeds and hybrids (Margarit et al. 1999). The Flemish Giant (FG), one of the largest rabbit breeds in the world, is widely used. It is bred mostly in small household farms, and according to some researchers, the progeny of FG does have a relatively high weaning weight (El-Bayomi et al. 2012). FG bucks are deemed good paternal components in commercial crossing (Lukefahr et al. 1982; Ozimba & Lukefahr 1991).
The aim of this study was to compare selected performance indicators in CAL and FG rabbits. Rearing rate, body weight, daily gains, carcass dressing percentage and the percentage of primal cuts in the carcass were studied. Nutrient digestibility, nitrogen balance and nitrogen retention parameters were also compared in these breeds.
2. Material and methods
The experimental material comprised FG and CAL rabbits from a breeding farm in northern Poland. The animals were kept on litter in outdoor cages measuring 0.8 × 0.7 m with a height of 1.0 m. Females with litter or two weaned animals of the same sex were kept per cage. Both breeds had unlimited access to complete pelleted diets which covered all the nutritional requirements (Lebas 2004). Additionally, does were fed ad libitum with meadow hay and small amounts of oats and root vegetables. The metabolisable energy (ME) of the diets was determined according to the formula proposed by Maertens et al. (1990). Chemical composition and energy value of diets are presented in .
Table 1. Chemical composition and energy value of diets.
The reproductive performance of rabbits in the breeding seasons of 2008/2009 and 2009/2010 was compared based on the available farm records. Breeding data were complied for 32 CAL females and 28 FG females, including for 14 CAL females and 11 FG females in 2009, and for 18 CAL females and 17 FG females in 2010. The rearing rate was calculated as follows:
Prior to slaughter, the animals were fasted for 24 hours and weighed. After slaughter, rabbits were skinned and eviscerated. Carcasses were chilled for 24 hours at 0–3°C, and carcass dressing percentage was calculated as follows:
Nutrient digestibility, nitrogen balance and retention parameters were analysed in six CAL males and six FG males aged 70 days. The animals were fed only complete pelleted diets (150 g d−1) with the described nutrient composition and energy value. The animals were placed in metabolism cages equipped for quantitative collection of faeces and urine. A 10-day experimental period proper was preceded by a 10-day adaptation period. The nutrient content of feed, nutrient excretion in faeces and urinary nitrogen were determined by standard methods (AOAC International 2006). Dry matter content was determined in a laboratory drier at 103°C. Crude ash content was estimated by sample mineralisation in a muffle furnace (Czylok®, Poland) at 600°C. Total nitrogen content was determined by the Kjeldahl method, in the FOSS TECATOR Kjeltec™ 2200 Auto Distillation Unit. Ether extract content was estimated by the Soxhlet method, in the FOSS SOXTEC™ SYSTEM 2043. Neutral detergent fibre (NDF) was determined according to procedure of Van Soest et al. (1991), in the FOSS TECATOR Fibertec™ 2010 System. The coefficients of nutrient and energy digestibility and nitrogen retention values were calculated using the balance method, as described by Li et al. (2011). Apparent nutrient digestibility coefficients were calculated as follows: a − b/a, where a is nutrient intake and b is nutrient excretion in faeces.
The results were processed by one-way ANOVA F-test in an orthogonal (–) and non-orthogonal () design using Statistica™ (StatSoft®, Inc. 2008) software.
Table 2. Reproduction parameters of rabbits (mean ± SD).
3. Results and discussion
The reproductive performance of female rabbits of both breeds is presented in . The average litter size of CAL females was 7.7 kittens and FG females was 7.4 kittens. Significant differences were noted in the number of kittens reared until the age of 35 days: CAL mothers reared an average of 6.2 kittens and FG mothers only 5.3 kittens. Rearing rates were determined at 80.5% in the CAL group and 71.6% in the FG group. In a study by Jaouzi et al. (2004), the average number of CAL rabbits born alive was 8.5 and the average number of weaned rabbits was 6.8, and the above results are similar to the reproductive parameters of CAL mothers reported in the first year of our study. In the work of Ozimba and Lukefahr (1991), the average size of purebred CAL litters reached 5.0 which was significantly below our findings, whereas FG crossbreds gave birth to an average of 5.4 kittens. The latter can probably be attributed to the highest heterosis effects on reproductive traits.
Our findings seem to validate the assumption that medium rabbit breeds are characterised by higher fertility and survival rates in comparison with large breeds. However, this statement may stem not only from physiological differences between the breeds compared in our study. Through their history CAL rabbits were often selected in commercial farms on the basis of their reproductive performance. Contrary to them, the FG breeders might rather prefer litters with few bigger kits, bearing in mind that the finest and the biggest rabbits originate from small litters, planned at the beginning of the year (Bolet et al. 2004). Furthermore, the reproductive performance of buck and doe rabbits can be modified to some extent by diets (Okab et al. 2013).
The body weights of rabbits aged 70–120 days are shown in . The values noted in FG rabbits were highly significantly higher in comparison with CAL animals. On day 70, the difference in body weights between the breeds was estimated at 335 g – on day 90 at nearly 600 g and on day 120 at 1000 g.
Table 3. Body weights of rabbits (mean ± SD).
In the study by Jaouzi et al. (2004), the average body weight of 77-day-old CAL rabbits was 2257 g, but in the cited experiment, the animals were fed only complete pelleted diets, and they probably descended from a commercial line of meat rabbits. The body weights of CAL rabbits reported by El-Bayomi et al. (2012) were also higher than in our experiment, and they were determined at 1925 g on day 70 and at 2132 g on day 84. In the cited study, FG rabbits weighed 1982 g on average on day 70, that is more than in our study, but on day 84, the average body weights of FG rabbits in our study were 131 g higher. Dabija and Macari (2011) determined the body weights of FG rabbits in monthly intervals. On day 90, the animals in the cited study weighed insignificantly more than in our experiment (2575 g vs. 2546 g), but on day 120, the rabbits in our study were 423 g heavier on average.
The body weights of rabbits may differ considerably subject to the applied production system, diet, breed and genetic line. In a study by Maertens et al. (2008), the average body weights of commercially bred hybrid rabbits were determined at 2640 g already at the age of 71 days. Tumova et al. (2004) reported body weights of 1918 g on day 63 and 3111 g on day 84 in the Hyplus hybrid line. In the work of Gugołek et al. (2011), F1 hybrids (FG × NZW) from different experimental groups weighed from 1762 g to 1774 g on day 77, from 2216 g to 2239 g on day 91, and from 2791 g to 2871 g on day 119.
In this study, the increasing differences in the body weights of rabbits resulted from higher daily gains in the FG group which were significantly higher than in the CAL group in each of the experimental periods (). Between days 70 and 120, the average daily gains of CAL rabbits were determined at 23.6 g and in FG rabbits at 36.9 g. Between experimental days 70 and 120, the body weights of CAL rabbits and FG rabbits increased by 79% and 101%, respectively. On days 70–84, 84–90 and 90–120, the body weights of CAL rabbits increased by 21%, 8% and 37%, respectively, and the body weights of FG rabbits increased by 27%, 10% and 44%, respectively, indicating that FG rabbits continued to grow more rapidly than CAL rabbits until the end of the experiment. Higher body weights of the FG rabbits are, certainly, determined genetically. It cannot be excluded, however, that part of these differences result from a lower number of weaned FG (5.3 on average) compared to the CAL rabbits (6.2 on average; ). In addition, young FG rabbits were reared by significantly larger mothers than the young CAL rabbits. However, this issue could be usefully explored in further research.
Table 4. Daily gains of rabbits, g (mean ± SD).
The increase in the body weights of CAL rabbits was nearly identical to that reported in animals of the same breed by Maj et al. (2009). In the cited experiment, the average daily gains of CAL rabbits were determined at 23.1 g until day 105. In our study, daily gains were determined between days 70 and 120, whereas in the work of Eady (2003), the growth rate of rabbits from weaning until day 70 was estimated at ca. 23 g for CAL rabbits and nearly 30 g for FG rabbits. Jaouzi et al. (2004) reported average daily gains of 35.1 g in CAL rabbits between days 28 and 77, whereas El-Bayomi et al. (2012) noted considerably lower daily gains of only 14.80 g in a commercial line of CAL rabbits between days 70 and 84.
Carcass dressing percentages and the percentages of primal cuts in the carcasses of rabbits sacrificed at the age of 90 and 120 days are presented in . On day 90, CAL rabbits were characterised by a significantly higher carcass dressing percentage than FG rabbits. The values of the analysed parameter increased throughout the experiment to reach 54.23 in the CAL group and 52.98 in the FG group on day 120, but the difference between breeds was statistically non-significant. Highly significant differences between the evaluated groups were noted in the percentages of primal cuts in the carcass which remained fairly constant between days 90 and 120. The loin, which is the most valuable cut, had a 24.76% contribution on day 90 and 26.93% contribution on day 120 in CAL rabbits, whereas its percentage in FG rabbits reached only 22.22% and 22.73%, respectively. The hind part had a greater share in FG rabbits (37.78% on day 90 and 38.07% on day 120) than in CAL rabbits (37.14% and 36.11%, respectively). The proportion of the least valuable fore part was higher in FG rabbits than in CAL rabbits, reaching 40.00% on day 90 and 39.20% on day 120 in the former and 38.10% and 37.50%, respectively, in the latter group.
Table 5. Carcass dressing percentage and the percentage of primal cuts in the carcass (mean ± SD).
It is worth mentioning that in the study by Eady (2003), carcass dressing percentages in both CAL and FG rabbits reached approximately 53% on day 70. Carcass dressing percentages in CAL rabbits were also investigated by Maj et al. (2009) whose results on day 105 were highly similar to our findings on day 120 at 54.6%. In the cited study, the percentages of primal cuts in the carcasses of CAL rabbits were as follows: fore part, 38.8%; loin, 23.2%; hind part, 37.9%, and the above results differed insignificantly from our findings. It should be noted, however, that the above authors performed cuts at different anatomical locations during the dressing procedure.
Nutrient digestibility parameters did not differ significantly between the compared rabbit breeds (), but protein and NDF digestibility values were somewhat higher in FG rabbits. In rabbits, nutrient digestibility values may differ by more than 10%, subject to the animals' age, health, diet and genetic line. Protein digestibility parameters reported in this study are consistent with the findings of other authors. In adult Dutch rabbits fed a complete diet, protein digestibility was observed at 65.18% (Li et al. 2011). In a study of 45-day-old rabbits of local non-descript breed, Ramchurn et al. (2000) determined protein digestibility at 74.2%. The work of Tumova et al. (2004) contributed interesting findings. In the above study, protein digestibility values in the Hyplus hybrid line increased from 68.6% on day 42 to 77.2% on day 56. This was accompanied by a drop in fibre digestibility parameters from 16.5% at the beginning of the experiment to 10.7% on day 56.
Table 6. Nutrient and energy digestibility (mean ± SD).
FG rabbits were characterised by a higher growth rate than CAL rabbits throughout the experiment (), as demonstrated by nitrogen balance and nitrogen retention parameters (). FG rabbits retained twice as much nitrogen daily as CAL rabbits (1.58 g vs. 0.78 g), and nitrogen retention as % of nitrogen intake and nitrogen digested was also considerably higher in FG rabbits (29.92% and 42.93% in the FG group as compared with 21.49% and 31.71% in the CAL group, respectively), which provides additional evidence that FG rabbits grew intensively throughout the experiment. Nitrogen intake was higher in the FG rabbits but, simultaneously, its retention was better.
Table 7. Daily balance and retention of nitrogen (mean ± SD).
4. Conclusions
In our study, CAL rabbits were characterised by better reproductive performance in comparison with FG rabbits. Despite the above-mentioned results, the observed daily gain values, daily nitrogen balance and retention parameters and carcass dressing percentages of the compared breeds suggest that FGs may be a good alternative to medium breeds such as CAL rabbits.
Source: https://www.tandfonline.com/doi/full/10.1080/09712119.2013.875905
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