INTRODUCTION

Productive performance in animals can be improved by feed additives or feeding strategies. It is mentioned that the maximum animal growth rate is limited by its genetic potential, physiological and nutritional factors. In the nutritional sense, energy is an important requirement in ruminants. It contributes to heat generation, growth, activity and production. Energy is often the first and most important consideration when selecting an ingredient; in addition to the current high and fluctuating prices of ingredients, which have prompted the search for alternative feed sources. It is possible to take advantage of agro- industrial by-products and discarded agricultural resources for human consumption with high nutritional potential for animal feed (^{Romero-Huelva et al., 2017}; ^{De Evan et al.,2020}; ^{Moghaddam et al., 2019}; ^{Ruiz-Hernández et al., 2019}). Mexico is a leader in avocado production and contributes 30% of total production in the world (^{SIAP, 2017}). This has led to the existence of a large amount of this fruit considered as waste, which results from the elimination of large quantities during this fruit packing process.

Avocado discarded for human consumption due to physical damage or size, it is considered an important source of energy for animals (^{Grageola et al., 2010}; ^{Van Ryssen et al., 2013};), mainly due to its fat content (10-30%), in addition to maintaining lipid and cholesterol homeostasis (^{Solís, 2012}; ^{Hernández-Lopez et al., 2016}). The addition of lipid sources to the diet has effects on performance and carcass characteristics, these include lower feed intake, increased palatability, growth rate, feed conversion and carcass (^{Azain, 2001}). In a study in broilers, the inclusion of avocado oil extraction by-product reduced feed intake and growth (^{Van Ryssen et al., 2013}). ^{Hernández-López et al. (2016)}, reported that including 30% of waste avocado on a wet basis reduced intramuscular fat content in fattening pigs.

On the other hand, ^{Fránquez et al. (2017)} , offering 21% fresh avocado paste to fattening pigs improved feed conversion, but decreased weight gain by reducing voluntary feed intake. Regarding the use of avocado meal and paste in ruminants, there is little information that focuses on compositional aspects, digestibility and in situ rumen degradability (^{Eliyahu et al., 2015}). In a recent study in dairy goats when including a fresh mixture of avocado pulp and peel in the diet, they concluded that it is a by-product with high moisture content, but its dry matter is rich in unsaturated fat which influenced milk fat content and quality (^{De Evan et al., 2020}). However, there is no evidence of the use of whole avocado meal in sheep on aspects of productive performance.

The aim of this study was to evaluate the effect of different levels of avocado meal during different feeding times on growth performance and carcass characteristics in sheep.

MATERIAL AND METHODS

RESULTS

In the productive performance in sheep growth and carcass characteristics after the experimental days, significant differences were observed (p<0.05) (Table 2), it was observed that the final weight and slaughter weight increased with the 10% AM inclusion level, compared to the 0% control diet. In the weight gain per day, daily feed intake, carcass weight and intramuscular fat variables, the highest values were presented with statistical equality in the inclusion of 10% and 0% AM. Although the treatment with a 10% AM inclusion presented high values in carcass weight, the carcass performance (%) was low; similar to the diets with AM inclusion, which could be due to a greater accumulation of visceral fat that was not quantified in this work. No statistical differences were observed in FC, nor in DM and CP efficiencies. It was observed that the greater AM inclusion, the lower the efficiency in the use of dietary energy, as well as the carcass performance compared to the 0% control diet.

According to the feeding time (FD) in the use of diets with AM, seven variables were different (p <0.05). The longer the feeding time (56 and 84 days), weight gain per day, daily feed intake, DM, CP and energy feed efficiencies increased and FC decreased. For the final weight and carcass weight variables, no modifications were observed with feeding time.

In the interaction of AM inclusion and FD feeding time, it was observed that the longer the feeding and inclusion time, the better the final weight; something similar occurs with the daily weight gain, contrary to the DM feed conversion, which is higher in the first days of feeding influenced; perhaps due to the change in feeding due to the greater contribution of avocado meal in the ration. For feed and protein efficiency, the same effect was observed, with an improvement as the time of flour inclusion increased. In energy efficiency, it was observed that the lower amount of meal in the ration (control and 2.5%) and the longer feeding times showed the best interaction, perhaps influenced by the lower amount of fat in the rations compared to diets with 5% and 10% of AM. For slaughter weight, an interaction was observed in the avocado meal inclusion in the three percentages of AM inclusion, improving at 56 days. This was contrary to what occurred in carcass performance (%) where without the inclusion of AM (0 %) there was a positive effect over a longer period of time.

Response results of the surface regression, by the AM inclusion at different levels and FD, can be seen in Table 3, where it is observed that the highest calculated responses were found in the maximum values of inclusion of 10% AM and 84 FD, with the exception of energy efficiency, carcass performance and intramuscular fat, which are higher at 0% AM. However, very low R² values were observed for the feed conversion, slaughter weight, average leg weight and intramuscular fat variables. The rest of variables present intermediate R² values, which indicate moderate prediction.

DISCUSSION

Sheep production is a common activity in tropical areas of Mexico, where hair breeds are used for their hardiness, fertility and adaptation to the climate; in this sense, the Pelibuey and Dorper breeds are the most widely distributed in this country; however, in these breeds the birth weight and pre-weaning development of lambs is low compared to other breeds. Consequently, the sheep feeding system could be a factor limiting the expression of genetic potential to produce sheep (^{Chay-Canul et al., 2019}). Various efforts to employ agricultural and livestock by-products have been used in feeding, in this sense ^{Mejía-Haro et al. (2011)} , report values of 71 g/day/ sheep when they used a silage containing 25 % nopal for the preparation of multinutritional blocks; however, no significant statistical differences were appreciated in the final weight of sheep. ^{Rivas-Jacobo et al. (2017)} achieved average gains of 138 g/day/sheep when using 500 g/day/sheep of brewery bagasse, which was supplied after grazing. Authors such as ^{Ortiz et al. (2007)} evaluated the inclusion of three levels of poultry manure made with coffee husks; they reported that with the inclusion of 20% of poultry manure in a fattening with young sheep, they achieved maximum values of 118 g/day/animal; these same authors report the highest final weight with the inclusion of coffee husk manure, achieving a linear effect on production. ^{Gómez-Gurrola et al. (2017)} evaluated the inclusion of 12 % of Guazuma ulmifolia and Tithonia diversifolia at different levels, in a ration with Pennisetum grass, where they achieved the highest daily weight gain at the highest level (40 %), with an average of 159 g/day/animal, where the highest level of inclusion achieved the highest final weight. The aforementioned values are considered low in comparison to those obtained in this study, where with the inclusion of 10 % AM reached the maximum averages of 260 g/day/bovine.

In this experiment it was observed that the AM inclusion at the highest level of 10% did not affect daily intake, but according to ^{Lemus-Flores et al. (2020)} higher levels affect intake and digestibility. The AM inclusion did not significantly affect feed conversion, similar to what ^{Partida-Hernández et al. (2019)}) reported, when including alfalfa at 55 % and Guazuma ulmifolia at 8 % in lamb diets. It has been documented that the tannin content in feeds does not influence feed intake (^{Méndez-Ortiz et al., 2018}); however, authors such as ^{Zamora-Beltrán et al. (2018)} indicate that an intake higher than 40 % of Ricinus comunis leaf meal affects dry matter intake and feed efficiency. In this experiment, neither FC nor DM and CP use efficiencies are affected, but energy use efficiency decreases when including values of 5 and 10 % AM. On the other hand, ^{Rodríguez-Ruiz et al. (2018)} evaluated the selection and consumption of Enterolobium cyclocarpum and Caesalpinia coriaria fruit meals in sheep, where they achieved maximum intakes of 100 and 80 g/day/sheep respectively, perhaps influenced by the content of anti-nutritional factors in Caesalpinia; contrary to what occurred in this evaluation where maximum intakes of 117 g/day/sheep were achieved at AM inclusion10 %, with no negative effects on daily weight gain and carcass weight. When considering the results of ^{Ly et al. 2021}, who indicate that the digestibility of the whole avocado fruit is high, so that at levels up to 10% inclusion, they did not affect the daily intake nor the FC and feed efficiencies of DM and CP, which makes its use feasible in sheep fattening for a longer time of consumption. In this sense (^{De Evan et al., 2020}) evaluated the inclusion of avocado pulp and peel in goats, they reported an increase in the percentage of fat in the milk of goats fed avocado and a reduction in live weight.

In the present experiment, carcass performance was affected, since the three treatments where AM was included yielded an average of 3.7% less and at the time of slaughter of the sheep there was a greater accumulation of visceral fat, which must have influenced the aforementioned reduction.

In an evaluation on the quality and carcass performance of grazing lambs supplemented with fermented sugar cane, ^{Frías et al. (2011)} reported values of 42 % in the carcass; in carcass performance, values were not favored by the AM inclusion, which reached values higher than 50 %. In this evaluation, the control treatment presented the highest performance with 53.76 %. In the reports presented in this section, feeding times range from 45 to 90 days, which are necessary to reach a slaughter weight above 40 kg. Providing AM for longer (56 and 84 days), improves results in most of variables evaluated for performance and carcass characteristics.

The interaction of the AM inclusion with feeding time showed that it does improve daily weight gain and slaughter weight of sheep, as well as feed efficiency of DM and CP; however, carcass performance did not show a positive effect, similar to what was reported with the use of vegetable oils in sheep diets by ^{Martínez-Marín et al. (2012)}, who concluded that it is possible to include moderate amounts of vegetable oils rich in unsaturated fatty acids in the diet of small ruminants, without causing negative effects on nutrient digestibility, which could happen in this experiment with the use of avocado meal, which is rich in unsaturated fatty acids, in agreement with the reports of authors such as ^{De Evan et al. (2020)} and ^{Lemus et al. (2017)}.

CONCLUSIONS

The use of avocado meal up to maximum levels of 10% does not have a negative effect on the productive behavior in the growth of sheep. Consumption and daily weight gain are not affected; even final weight and slaughter weight are improved; however, it will be necessary to evaluate the quality of meat from sheep fed avocado meal.