Important! This text corresponds to the INRA-AFZ 2002 Tables and has not been updated yet.
The nutritional values published in previous feed tables for rabbits diverge greatly, even for the most common feed materials (NRC, 1977; Cheeke, 1987; INRA, 1989; Maertens et al., 1990; Perez et al., 1998b). Furthermore, the underlying concepts are often different, notably for the estimation of energy values: these values can be calculated through a global approach using efficiencies of energy utilisation, or by a simple general equation integrating digestible constituents. The differences between the existing tables essentially arise from long-standing methodological problems in the evaluation of rabbit feeds. In particular, due to the lack of standardisation, each laboratory developed its own methodology. Besides, in the rabbit – as opposed to other monogastrics (pigs and poultry) – it is often necessary to work with complex diets and low substitution rates (due to mandatory fibre requirements). This means that even small inaccuracies in diet measurements can cause very large errors in the estimation of the digestibility coefficients for feed materials (Villamide et al., 1998). Over the last few years, the measurement methodology of the nutritional value of feedstuffs has been the topic of concerted studies at European level, with particular emphasis on the standardisation of in vivo methods (Perez et al., 1995a) and on the harmonisation of analytical methods for feeds and faeces (EGRAN, 2001). This resulted in the adoption of a European reference method to determine the digestibility of diets (Perez et al., 1995b) and in the harmonisation of the procedures used to calculate the nutritional value of feed materials within mixtures of feedstuffs (Villamide et al., 2001).
Selection of nutritional criteria
Our aim in producing these tables was to provide reliable data, rather than to change the fundamental concepts of rabbit feeding. Therefore we had to select the most relevant nutritional criteria and discard parameters such as ileal amino acid digestibility or phosphorus availability, which, though interesting, have not yet proven to be suitable in rabbit feeding due the lack of experimental data. In addition, fibre digestibility (crude fibre and Van Soest cell wall fractions) was not introduced into the tables, because the available experimental data are very imprecise and were judged to be too discordant to be able to produce reliable average values.
For nutritional values, three major criteria were used:
- apparent faecal digestibility of crude protein (Nd)
- digestible energy (DE)
- metabolisable energy (ME).
Since the DE system may lead to an overestimation of the energy value of protein-rich feed materials, it is recommended that formulation of diets should be performed on a ME basis, by taking into account an average estimation of energy losses in urine and fermentation gases.
Because nitrogen (principally in urea form) is a dominant fraction of urinary excretion, the ME value depends both quantitatively and qualitatively on the supply of nitrogen (balance of amino acids). Therefore, to avoid any interference between the expression of energy and nitrogen nutrition, we propose a ME corrected for a zero nitrogen balance (MEn). Due to the difficulties encountered when making measurements on rabbits, the ME was calculated directly using the DE values given in the tables and a ME/DE coefficient dependent on the characteristics of the feed material. We applied a correction factor based on the ratio DCP/DE (DCP = digestible crude protein) rather than on crude protein. This ratio corresponds to a nitrogen balance relative to energy. Assuming a zero nitrogen balance, 1 g of digestible protein corresponds to a loss of 0.16 g of urinary nitrogen. If we estimate at 30.1 kJ the loss of energy corresponding to 1 g of urinary nitrogen (Jentsch et al., 1963), the correction is 4.81 kJ per g of DCP. A fixed value of 0.5% of the DE can be used to correct for the losses in gaseous form. A more rigorous approach would be to use a correction factor (yet to be established) based on cell wall content and cell wall digestibility, since the losses of gas depend on these parameters. However, these losses remain low in the rabbit. We propose the following equation, which estimates ME value from a DE value obtained in animals:
MEn = DE x ME/DE
with ME/DE = 0.995 – 0.00481 x DCP (in g) / DE (in MJ)
When formulating feeds, this method of calculation has the advantage of creating a hierarchy between feed materials that represents more accurately the way energy is used by rabbits in balanced diets.
Selection of nutritional data
In the present work, we have tried to be as precise as possible by using literature data first, and then, systematically, our own data. Therefore, the values presented are the product of a inclusive survey of international literature, completed when necessary by as yet unpublished results. The tables of nutritional value of feedstuffs for rabbits resulting from a collaboration between several European researchers (Perez et al., 1998b) were used as the starting point for this update. We selected the final data after a comprehensive review of the publications and a comparison of all of the experimental results. For some feed materials, the nutritional data appeared to diverge greatly between experiments. In this case, the values were chosen after an in-depth critical analysis of the methods used in each in vivo experiment, such as the technique used to measure digestibility, the number of repetitions, the level of inclusion of the feed material in the experimental diets, the calculation procedures, the precision of the estimation etc.
Coherence with the chemical composition
The final average values were chosen after paying particular attention to the consistency between chemical and nutritional parameters. Therefore, for each feed material, the proposed nutritional value was adjusted by taking into account the average chemical composition published in the tables. For feeds materials with a large variability, the users can correct the nutritional values through specific equations based on analytical parameters. This was the case of alfalfa using the crude fibre content (CF in % dry matter):
Nd (%) = 78.7 – 0.69 CF (Perez, unpublished) (n = 12; r = -0.8; RSD =2.1)
DE (MJ/kg dry matter) = 13.94 – 0.196 CF (Perez et al., 1998a) (n = 16; r = -0.94; RSD = 0.30)
- Cheeke P. R., 1987. Rabbit feeding and nutrition. Academic Press Inc., Orlando, USA, 376 p.
- EGRAN (European Group on Rabbit Nutrition: Gidenne T., Perez J. M., Xiccato G., Trocino A., Carabaño R., Villamide M. J., Blas E., Cervera C., Falcao e Cunha L., Maertens L.), 2001. Technical note: attempts to harmonize chemical analyses of feeds and faeces for rabbit feed evaluation. World Rabbit Sci., 9, 57-64.
- INRA, 1989. L’alimentation des animaux monogastriques : porc, lapin, volailles. INRA Editions, Paris, 282 p.
- Jentsch W., Schiemann L., Hofmann L., Nehring K., 1963. Die energetische Verwertung der Futterstoffe. 2. Die energetische Verwertung der Kraftfutterstoffe durch Kaninchen. Arch. Tierernähr., 13, 133-145.
- Maertens L., Janssen W. M. M., Steenland E., Wolters D. F., Branje H. E. B., Jager F., 1990. Tables de composition, de digestibilité et de valeur énergétique des matières premières pour lapins. 5èmes Journ. Rech. Cunicole Fr., Paris, 12-13/12/1990. Communication n°57. ITAVI Ed., Paris.
- NRC, 1977. Nutrient requirements of rabbits (2nd Ed.). Nat. Acad. Sci., Washington, DC, USA, 30 p.
- Perez J. M., Cervera C., Falcao e Cunha L., Maertens L., Villamide M. J., Xiccato G., 1995a. European ring-test on in vivo determination of digestibility in rabbits: reproducibility of a reference method in comparison with domestic laboratory procedures. World Rabbit Sci., 3, 171-178.
- Perez J. M., Lebas F., Gidenne T., Maertens L., Xiccato G., Parigi-Bini R., Dalle Zotte A., Cossu M. E., Carazzolo, A., Villamide M. J., Carabaño R., Fraga M. J., Ramos M. A., Cervera C., Blas E., Fernandez J., Falcão e Cunha L., Bengala Freire J., 1995b. European reference method for in vivo determination of diet digestibility in rabbits. World Rabbit Sci., 3, 41-43.
- Perez J. M., Lamboley B., Béranger C., 1998a. Valeur nutritive de différentes luzernes déshydratées utilisées seules ou en mélange dans le régime du lapin en croissance. 7èmes Journ. Rech. Cunicole Fr., Lyon, 13-14 mai 1998. ITAVI Ed., Paris, 129-132.
- Perez J. M., Maertens L., Villamide M. J., De Blas C., 1998b. Tables de composition et de valeur nutritive des aliments destinés au lapin: conclusions d’un groupe de travail européen. 7èmes Journ. Rech. Cunicole Fr., Lyon, 13-14 mai 1998, ITAVI Ed., Paris, 141-146.
- Villamide M. J., Maertens L., De Blas C., Perez J. M., 1998. Feed Evaluation. In: The Nutrition of the Rabbit, De Blas C. and Wiseman J. (Eds), Chap. 6, p. 89-101. CABI Publishing, CAB International, Wallingford, UK.
- Villamide M. J., Maertens L., Cervera C., Perez J. M., Xiccato G., 2001. A critical approach of the calculation procedures to be used in digestibility determination of feed ingredients for rabbits. World Rabbit Sci., 9, 19-25.