INTRODUCTION

The need for animal protein in developing countries has generated growing interest in the study of alternative, cheap and available food sources for animal production (^{Nieves et al, 2011}; ^{Malavé et al, 2013}). In tropical areas around the world, a wide variety of plant species with potential for feeding herbivores, such as rabbits, have been identified, considering their availability, biomass production and chemical composition (^{Nieves et al, 2011}; ^{Malavé et al, 2013}). Different studies conducted in Latin America and the world, show that the inclusion of tropical forages in the feed of fattening rabbits allows obtaining satisfactory productive yields (^{Nieves et al, 2011}); however, the information generated on the preference of these resources in rabbits is still scarce (^{Safwat et al, 2014}; ^{Hafsa et al, 2016}). Feed consumption and preference in rabbits have been evaluated under farm and laboratory conditions, demonstrating that it is influenced by multiple factors, including fiber content, digestible energy, fat, amino acid composition, gut fill, and the physical form of the consumed material and environmental conditions (^{Prebble & Meredith 2014}). The simultaneous forage offering method is the closest to reality for determining forage preference in rabbits (^{Safwat et al, 2014}). The study of forage preference may favor the development of local resource-based rabbit production in tropical areas (^{Safwat et al, 2014}; ^{Ozakwe & Ekwe, 2017}).

The objective of the present study was to evaluate the preference of tropical forages in fattening rabbits and the relationship with chemical composition.

MATERIAL AND METHODS

RESULTS

Table 1 shows that the highest CP content in forages corresponded to Guazuma ulmifolia (17.70%), followed by Gliricidia sepium (15.84%); the lowest CP content was found in Brachiaria humidicola (9.00%). Regarding fibrous content, the genus Brachiaria presented the highest values of ADF (40.80-48.55%), Guazuma ulmifolia had the lowest value of ADF with 22.72%; also, the FDN content was higher in the genus Brachiaria forages (67.7- 70.45%); the forages Guazuma ulmifolia and Gliricidia sepium obtained values of 37.61% and 41.74%, respectively.

Table 2 shows that Gliricidia sepium was the species with the highest intake with 51 g (p<0.05) per day, followed by commercial feed (37 g) and Brachiaria mutica (36 g); the lowest intake was observed with Guazuma ulmifolia and Paspalum notatum. Likewise, Gliricidia sepium showed a higher total DM intake of 16.5 kg and total crude protein intake of 2.7 kg (p <0.05). Brachiaria mutica was the second highest total DM intake 11.20 kg. With respect to NDF and ADF intake, Brachiaria mutica showed the highest total intake with 8.49 kg and 5.85 kg, respectively (p <0.05), compared to the other species evaluated.

Table 3 shows that the correlation coefficient between total forage intake and CP, NDF and ADF content is low (P> 0.05); therefore, there is no relationship between the elements.

With respect to the relative preference index, Table 4 shows that Gliricidia sepium had the highest consumption preference (P<0.05), while Brachiaria mutica, Brachiaria humidicola, Paspalum notatum and Guazuma ulmifolia forages did not show significant variations (P>0.05) in consumption preference during the experimental period.

DISCUSSION

In the present study, the simultaneous forage offering method and the relative preference index were used to measure consumption preference. Gliricidia sepium tree forage had higher consumption and preference compared to Brachiaria mutica grass, Guazuma ulmifolia tree, and Paspalum notatum and Brachiaria humidicola grasses (P <0.05). (^{Kontsiotis et al, 2015}), as well as (^{Clauss & Hatt, 2017}), mention that the diet composition of wild rabbits is composed of different plants and food types (grasses, shrubs, herbs and leaves), depending largely on the availability and quality of food resources in the environment. According to the results of (^{DeJaco & Batzli, 2013}), cottontail rabbits (Sylvilagus floridanus) prefer in their diet herbaceous plants such as: Trifolium pratense, Medicago sativa, Persicaria vulgaris, Aster ericoides and Viola pranticola; as well as woody plants, which it may preferentially consume depending on their availability. (^{Ozakwe & Ekwe, 2017}) indicate that preference measured through forage consumption (palatability) in rabbits, is a phenomenon influenced by dietary and environmental factors. However, (^{Bobadilla et al, 2020}) points out that the trophic selection of rabbits is positive for grasses, while forages and shrubs are avoided; however in these animals the consumption of more nutritious plants (rich in protein) can be of great importance in ecosystems where the available plants have low nutritional value. In this sense, it has been shown that the consumption of woody species by rabbits increases when the availability of grasses decreases, due to seasonal variations.

Regarding the relationship between consumption and chemical composition of diets, according to (^{Franz et al, 2011}) and (^{Somers et al, 2008}) rabbits are selective consumers, so they prefer parts with high protein content, since in nature the consumption of protein- rich materials guarantees a higher nutritional value of a low-energy diet. For their part (^{Crowell et al, 2018}), points out that in the wild, pygmy rabbits (Brachylagus idahoensis) and cottontail rabbits (Sylvilagus nuttallii) employ behavioral strategies to consume materials with specific characteristics, such as low or high amount of fiber according to the availability in the meadow, or with higher crude protein content to decrease exposure times to predators and obtain food of higher nutritional quality; or to regulate or decrease the amount of secondary metabolites present in the plants they consume. According to (^{Wallage Drees & Deinum, 1985}), the nutritional composition of the diet of wild rabbits represents crude fiber (CF) levels of 25 to 30% (DM) and neutral detergent fiber (NDF) levels of 50 to 60%. (^{Ogbuewu et al, 2017}) (^{Ozakwe & Ekwe, 2017}) indicate that there is a relationship between crude protein content and the preference of rabbits in consumption terms. The authors found that forages with high crude protein content such as Centrosema pubescence, Calopogonium mucunoides and Elaeis guinensis were the most consumed in a cafeteria trial. (^{Lush et al, 2017}) report that rabbits prefer short grasses with lower fiber concentration and select forages for higher quality rather than higher quantity to meet their nutritional needs. However (^{Safwat et al, 2014}) and (^{Abubakar et al, 2015}) reported a large variability in the response of rabbits to forage supplementation; besides, (^{Kontsiotis et al, 2015}) and (^{Lush et al, 2017}), note that changes in feeding strategies are likely an adaptation to seasonal changes imposed by environmental conditions, which affect both forage availability and quality and that the diet of herbivorous mammals such as rabbits, can be affected by a myriad of factors such as resource availability, forage quality, area available for foraging and the presence of predators. (^{Lush et al, 2017}) note that lagomorphs such as rabbits and hares are selective consumers, capable of consuming large amounts of low quality food and adapting to the availability of resources with higher nutritional quality.

In the present study, the content of crude protein, acid detergent fiber and neutral detergent fiber in the forages studied (crude protein, ADF and NDF) did not affect the preference in terms of consumption in any of the consumption periods evaluated (I1, I5, I10, I15) (P> 0. 05); which is contrary to that reported by (^{Ulappa et al, 2014}), who point out that the odds of a forage being consumed increase 1.64 times for every 1% increase in crude protein content. According to (^{Somers et al, 2008}), the selection of higher nutritional quality diets is a behavioral adaptation by which herbivores maximize their nutrient intake by selecting plants with high crude protein content. (^{Schmalz et al, 2014}) reports that pygmy rabbits (Brachilagus Idahoensis) prefer to feed on sagebrush (Artemisa vulgaris); which has higher crude protein and lower fiber content (ADF-NDF); such preference may be associated more with the energy density it presents, being richer in protein than fiber, which may be especially important during winter when pygmy rabbit diets are 99.1% sagebrush, because energy requirements are especially high for thermoregulation at low temperatures, which could be contrary in tropical areas where temperatures are high. On the other hand (^{Hernández et al, 2017}) and (^{Carpio et al, 2017}) point out that the differences observed in consumption preference in rabbits, may be related to the presence of secondary metabolites such as saponins, flavonoids, total phenolic compounds and tannins, in cover crops and some fruits, which were not quantified in the foods studied in the present work. (^{Malavé et al, 2013}) and (^{Ogbuewu et al, 2017}) point out that the study and use of resources with high protein content in tropical areas, represent a viable option for rabbit feeding without relying on commercial feeds.

CONCLUSIONS

The CP, NDF and ADF content of tropical forages did not modify the consumption preference in fattening rabbits. Gliricidia sepium forage was preferred by fattening rabbits compared to Brachiaria mutica, Guazuma ulmifolia, Paspalum notatum and Brachiaria humicola forages. The study of forage preference in rabbits and its relationship with nutrient content is necessary to improve the use of these resources in tropical areas.