versão impressa ISSN 1405-3195
Agrociencia v.42 n.2 México feb./mar. 2008
The use of maize ear in rabbit diets: nutritive value and effect on fattenning performance
Empleo de mazorca de maíz en dietas de conejos: valor nutritivo y efecto sobre la engorda
Melida Martínez1, Vicente J. Moya2, Enrique Blas2 y Concepción Cervera2
1 Universidad Tecnológica del Chocó. Departamento Ingeniería Agroforestal. Barrio Medrano. Quibdó. Colombia.
2 Universidad Politécnica de Valencia. Departamento Ciencia Animal, Camino de Vera s/n. 46022 Valencia. Spain. (email@example.com)
Recibido: Enero, 2007.
Aprobado: Noviembre, 2007.
The nutritive value of maize ear for rabbits was determined by substitution of a standard diet (diet C) with 20 and 40% of maize ear (diets M20 and M40). Two experiments were carried out. In the first one, digestibility trials for dry matter (DM), crude protein (CP) and gross energy (GE) were performed with 24 rabbits. In the second experiment, 200 young rabbits were divided in two groups at weaning (28 d) and fed ad libitum with diets C and M20 up to 63 d of age. Feed intake and live weight gain were recorded from weaning to slaughter, and feed conversion ratio was calculated. The principal component of maize ear is the grain (88%) and, consequently, the chemical composition of maize ear is similar to corn, except for its higher fibre content. The digestibility coefficients of DM (64, 66 and 70% for C, M20 and M40) and GE (61, 65 and 70%) increased (p<0.001) with inclusion of maize ear in diet, but digestibility of CP was not affected. Digestible energy and digestible protein contents of maize ear were 15.2 MJ and 40 g kg1 DM. Rabbits fed with diet M20 presented lower feed intake than those fed with diet C (102 vs 107 g DM day1; p<0.05) but similar live weight gain (45 g day1) and, consequently, feed conversion ratio was lower in M20 group than in C group (2.28 vs 2.39; p< 0.001). Results from this experiment show that the inclusion of maize ear in the diet increases the digestible energy content, reduces the voluntary feed intake and improves feed conversion on fattening rabbits.
Key words: Rabbit, maize ear, nutritive value.
Se determinó el valor nutritivo de la mazorca de maíz a partir de una dieta estándar (dieta C), mediante la sustitución de 20 y 40% de la mezcla base por mazorca (dietas M20 y M40). Se hicieron dos experimentos. En el primero se determinó la digestibilidad de materia seca (MS), proteína bruta (PB) y energía bruta (EB) mediante un ensayo de digestibilidad con 24 conejos. En el segundo, doscientos conejos destetados a los 28 d de vida fueron divididos en dos grupos y alimentados ad libitum con las dietas C y M20 hasta los 63 días de edad, registrando la ingestión de alimento y la ganancia de peso vivo, y se calculó el índice de conversión. El grano es el principal componente de la mazorca (88%) y, por ello, la composición química de ésta es muy similar a la del maíz grano, pero con mayor contenido de fibra. Los coeficientes de digestibilidad de MS (64, 66 y 70% para C, M20 y M40) y de EB (61, 65 y 70%) aumentaron (psO.001) con la inclusión de mazorca en la dieta, pero no se afectó la digestibilidad de la PB. Los valores de energía digestible y proteína digestible de la mazorca fueron 15.2 MJ y 40 g kg1 MS. Los conejos alimentados con M20 mostraron una menor ingestión que los alimentados con la dieta C (102 vs 107 g MS día1; p<0.05) pero similar ganancia de peso (45 g día1) y, por ello, el índice de conversión fue menor para el grupo M20 que para el C (2.28 vs 2.39; p<0.001). Los resultados de este experimento muestran que la inclusión de mazorca de maíz en la dieta de conejos de cebo aumenta el contenido en energía digestible, reduce el consumo voluntario de alimento y mejora el índice de conversión.
Palabras clave: Conejo, mazorca de maíz, valor nutritivo.
Maize (Zea mays L.), wheat (Triticum vulgare) and rice (Oryza sativa) are the most important cereals in the world. Maize has advantage over other cereals in that it has a wide tolerance to different climates, the highest yield of grain per manhours of labour and resistance to depredation by birds (Heisey and Edmeades, 1999). Global maize production rises continually, with more that 580 millions t in 1997, and the demand is expected to increase by 50% by 2020 to around 837 millions t (Calvo et al., 1999). Finding cheap substitutes for maize grain in animal feeding is one of the main objectives in livestock development programmes (FAO, 2004).
The entire maize ear includes the corn and the cob with a relation 4:1 of the weight. Cob is low quality roughage, comparable to poor hay, containing 36% crude fibre (CF) and 87% neutral detergent fiber (NDF) (Kevelenge et al., 1983) and it is unpalatable. The cornandcob meal should be well dried, otherwise it is likely to mould in a hot climate. The inclusion of cob increases the crude fibre of maize ear in relation to corn and could significantly decrease DM digestibility and increase digestibility of CF in diets.
Maize ear is especially valuable for full grown ruminants, and there is almost no significant difference in the performance of feedlot animals receiving cornandcob meal and animals fed on shelled maize. Bacvanski (1976) recorded a higher consumption and poorer feed conversion in young fattening bulk fed ground ear compared to the diet based on ground grain. However, Malterre and Lelong (1976) concluded that maize ears dried or ensiled could replace corn as supplements to whole crop silage; indeed, maize ear has been used as the basis of the diets for beef production (FAO, 2004).
Maize ear is usually preferred to shelled maize for horses, since it is less likely to form a doughy mass in the stomach (FAO, 2004). Pigs can tolerate 2550% of maize ear in the diet depending on age, while the fibre content restricts its use in poultry diets (EMBRAPA, 1991).
For rabbit diets, maize ear could be useful due to its high energy content and increased fibre content, but the use of this product for rabbit diets has not been documented. Thus, the aim of this research was to determine the nutritive value of maize ear for rabbits and to examine the effect of its inclusion in the diet on the fattening rabbit performance.
MATERIALS AND METHODS
Maize ear was sampled for analysis daily along collection period (12 d) taking 3 units each d at random. The maize ears from each sample were weighed and divided in corn and cob, which were weighed separately in order to obtain the proportions of both parts in the maize ear. Samples of corn, cob and ear were analysed separately.
Three pelleted diets (Table 1) were formulated to determine the nutritive value of maize ear for rabbits. The control diet (C) was a standard diet including alfalfa, barley, soybean meal (SBM) and animal fat as major ingredients. The experimental diets were made by substitution with 20 and 40% maize ear (M20 and M40).
A digestibility trial for DM, crude protein (CP) and energy was performed with 24 rabbits 42 d old; diets were offered ad libitum during an adaptation period (7 d) and a faeces collection period (4 d), according to the methodology proposed by Pérez et al. (1995). Maize ear, corn, cob, diets and faeces were analysed according to the recommendations of the European Group of Rabbit Nutrition (EGRAN, 2001).
Digestible protein (DP) and digestible energy (DE) contents of maize ear were calculated by regression procedures using the digestibility coefficients of experimental diets, according to Villamide et al. (2001).
A fattening trial was performed using 200 young rabbits of the same genetic type (a threeway cross, males and females) divided in two groups at the weaning stage (28 d) and fed with C or M20 diets. Rabbits were placed in individual cages (45X30 cm) and had free access to water and diet. The daily minimum and maximum indoor temperatures averaged 14 °C and 20 °C, and a lighting schedule of 12 h of light was used. Feed intake and live weight gain were recorded from weaning to slaughter (63 d of age) and feed conversion (FC) ratio during this period was calculated.
A least squares analysis was performed using the GLM procedure (SAS, 1990). Sex way initially included in the model and found to be not significant for any of the variables studied, so the definitive model only included the diet as factor.
RESULTS AND DISCUSSION
The proportion and chemical composition of corn, cob and maize ear is shown in Table 2.
The principal component of maize ear is the corn (88%) and, consequently, the chemical composition of maize ear is similar to corn, although maize ear presents higher fibre content than corn. Cob and corn have a very different chemical composition: corn has higher content on starch and protein than cob, which has very high fibre content. These results of chemical composition are similar to those reported by Kevelenge et al. (1983) for cob and maize ear and by Maertens et al. (2002) for corn.
The results of digestibility trial are shown in Table 3. The digestibility coefficients of DM and gross energy (GE) increased (p<0.001) with inclusion of maize ear in the diet, due to both the increase in starch content in the diet and the decrease in feed intake.
Forage accounted for half of CP content of diets and showed a lower digestibility (60%) than concentrates and, consequently, the digestibility coefficients of CP were low for all diets. The inclusion of maize ear did not affect digestibility of CP, since the origin of the protein was similar in the diets (alfalfa and SBM, mostly).
The DE and DP contents of maize ear calculated from digestibility coefficients of diets were 15.2 MJ and 40 g kg1 DM (Table 2). The DE value of maize ear is very close to values reported for corn by de Blas et al. (2003) and Maertens et al. (2002), but the CP digestibility of maize ear was lower in our study than the value reported for corn by those authors (51% vs 65%). The nutritive value of any ingredient is essentially affected by the chemical composition and these results are in agreement with a chemical composition of maize ear very similar to corn.
The overall results of the rabbit fattening trial are shown in Table 4.
Rabbits fed with diet M20 presented lower feed intake (p<0.05) but similar live weight gain than rabbits fed with diet C; therefore, FC was lower in M20 group than in C group (p<0.001). Growing rabbits fed ad libitum modify their feed intake according to dietary energy content in order to achieve a constant energy intake (ParigiBini and Xiccato, 1998). Thus, the increase in growth rate and the decrease in feed intake observed for rabbits fed with diet M20 is likely due to the higher energy content of this diet (Table 3). Similar results have been reported by Blas et al. (1994) with increasing corn diets and by Pla et al. (2006) using the same diets, who recorded a similar improvement in FC (2.29 and 2.18 for C and M20 diets).
Chemical composition of maize ear and corn are similar, but maize ear has a higher fibre content than corn. Digestible energy and digestible protein contents of maize ear for rabbits were 15.2 MJ and 40 g kg"1 DM. The inclusion of maize ear in the diet for fattening rabbits increases the digestible energy content, reduces the voluntary feed intake and improves feed conversion ratio.
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