INTRODUCTION

In recent years and due to the environmental concern of society, agribusiness must be sensitive to environmental issues, seeking the increasing development of a social conscience, which requires not to produce at the expense of the planet, but in a sustainable way. Due to the above, the nutritional characteristics of the by-products of the agro-industry have been studied, for the elaboration of food rations, in cattle (^{Escorza et al., 2019}). The best strategy to achieve higher productivity is to establish a food supplement program, using the available material, human and financial resources. Since the decision to complement represents an additional cost to the producer, the use of those supplements that provide the maximum productive and economic response must be considered (^{Cury et al., 2017}).

Industries that process agricultural products must find a final destination for by-products, which meet two minimum requirements; that it is not polluting the environment and that the costs of processing and transportation are covered by the sale price thereof and do not generate additional costs to production (^{Bisang, 2017}). Among the different by- products, there is a high variability in the chemical composition available; some can be very regular in composition, because the industrial processes that generate them are highly controlled. While others may present an important variation, so it is necessary to know the nutritional contributions at the time of formulating the rations (^{Berenguer, 2000}). Once the contributions to be made through supplementation have been determined, it should be taken into account that many by-products can simultaneously provide energy and protein (^{Lagos and Castro, 2019}); others, on the other hand, may be lacking in some nutrient. It is important to highlight that animal feed from by-products are substitutes and are also considered as alternatives that producers can choose, according to their economic possibilities and geographic distribution, in order to increase weight gains, feed conversion and greater economic profitability (^{Campos and Arce, 2016}).

Citrus fruits are widely cultivated in subtropical or Mediterranean climate areas, and to a lesser extent in tropical areas. Most of the increases in production have been due to the growth of the areas of the orange crop, and to the fact that productivity has increased, thanks to the improvement of the exploitation practices; by applying fertilizers and irrigation, controlling pests and diseases, grafting trees, replacing poorly located orchards and planting the varieties with the highest resistance (^{Hernández, 2015}).

Valencia orange (Citrus sinensis var.valencia), is one of the most consumed products worldwide, and just over 10% of total production, approximately 6.5 million tons, is exported to other countries , such as: France, United Kingdom, Germany, Russia, Saudi Arabia, among others. It is one of the world's most consumed products and a little more than 10% of total production (^{Gómez et al., 2019}). In Mexico, citrus production is destined for domestic consumption (88%), and the rest is mainly exported to the United States (^{Valencia and Duana, 2019}).

Oranges rank fifth on the list of most produced or exported agricultural products, surpassed only by bananas, apples, tomatoes and onions, in terms of international trade. Mexico is in twenty-fifth place with $ 19,449 and contributes 0.4% of total exports (^{Triana et al., 2014}).

The state of Veracruz has almost 50% of the country's harvested area (^{Barrón and Hernández, 2014}) and produces 50% of the juice orange nationwide (^{SADER, 2018}). Álamo municipality of, located in the north of the state of Veracruz, is considered the capital of the orange; producing variety of late valence, super late valence and early valence; as well as the table ones (zarzuma, monica and tangerines), among others. It also has juicers that process the orange and that add value to the derived by-products (^{Sarah et al., 2018}), such as the pulp or citrus waste; composed of the juice, bagasse, seeds and the husk (^{Espinoza et al., 2019}) to produce silage.

Fresh bagasse, due to its high water content and its potential for polluting the environment, generates a problem at the level of industrial plants, but at the same time offers an opportunity for supplementary feeding for ruminants, especially cattle (^{Bermúdez et al., 2015}).

Derived from the high production of orange in the area, these by-products come to be supplied by the owners of cattle ranches in times of high production. A large part of these citrus fruits are destined for the production of juice, obtaining annually about 70,000 tons of pulp that are discarded by the juicer.

Due to the above and due to the high demand for by-products of the orange, this work aimed to prepare a food concentrate with by-products of Valencia orange (Citrus sinensis var. Valencia) as a supplement for fattening young bulls in the north of Veracruz state.

MATERIAL AND METHODS

RESULTS

Regarding the nutritional recommendations indicated by the National Research Council (^{NRC, 2001}), the values between 10-18% of Crude Protein (PC) and 65% of Total Digestible Nutrients (TND), are considered desirable (Table 4). Therefore, in this investigation, these parameters were met, intended for the stalled bulls of 300 kg, with values of 10.0 -13.0 % PC provided in the ration.

The productive behavior of the animals in the different treatments, related to weight gain (kg/day) was significantly different (P <0.05), between the treatments (T2, T3 and T4), with respect to the control (2.66, 2.70 and 2.97 kg.) (Table 5).

DISCUSSION

The orange pulp from the juicer presented a protein value of 10-13 %; These crude protein (PC) values could be increased and improve daily weight gain, by adding medium quality protein, such as urea, chicken manure, chicken manure or some bypass protein; such as soybean paste, harinoline, cottonseed, among others (^{Lagos and Castro, 2019}). In feed rations with citrus by-products for ruminants (^{Hernández et al., 2015}), it has been observed that the gain in weight, quality of the carcass and the content of milk fat increases, which gave similar results with the supply of cereals in the food ration provided in this study. The difference in feed consumption resulted in T1 animals consuming 12.6 Mcal; while the animals that consumed orange by-products (T2, T3 and T4), ingested between 27.89 and 29.9 Mcal of net energy of production/day (table 5).

It is highlighted that the animals that received only energy nutrients presented higher kilograms gained/animal to the addition of the orange by-product (240.1, 243.4 and 267.4 kg, for T2, T3 and T4, respectively), compared to the treatments supplemented only with fiber (T1), those with a significantly lower response (P <0.05). Likewise, the performance of the cold carcass (55.3%) is notable, which was significantly higher in the animals supplemented with corn silo. The above is related to what was reported by ^{Cury et al. (2017)}, who recognize that the daily production per animal is determined by the combination of effects between the availability and quality of the food (energy-protein supplementation); as well as the animal's appetite and genetic potential.

Currently, in the field of nutrition of meat-producing cattle, protein is not only important, since the level and quality of protein is fundamental in the productive response of animals, and is the key to achieving the highest profits in any livestock production unit, under confinement conditions and the productive behavior of animals in the different treatments.

In relation to the total weight gain/day, there were increases of 2.66, 2.70, 2.97 kg for T2, T3 and T4, in the young bulls that received orange by-products with respect to the control treatment. The difference in feed consumption (T1: grass) was 10.30 Mcal of metabolizable energy/day. While the young bulls supplemented with orange by-products, consumed 27.89, 27.92 and 27.94 Mcal (T2, T3, T4, respectively); equivalent to a difference of 40%, which is reflected in the same proportion on the live weight gain between the treatments. These differences were due to a better nutritional contribution and the effect that the inclusion of an energy source in the rumen has for the production of volatile fatty acids (VFAs), such as acetic acid, propionic acid, butyric and valeric, essential on feed intake, daily live weight gain, and increased meat and conformation production (^{Jarvis and Moore, 2010}).

Regarding the quality of the orange silo (T4), good quality silage was obtained; Due to its yellowish green and light brown color, a slightly acidic, ripe fruit smell and a firm texture, without deforming when pressed with the fingers; which indicates that the adequate management of the silo increased the nutritional and organoleptic properties of the food. It should be noted that the amount of food offered to treatment animals 2, 3 and 4, was totally consumed; this due to the palatability of the orange by-product, which was demonstrated by not leaving residues inside the feeders. Therefore, it could be attributed that the consumption of dry matter is total in all the treatments, except in T1 (fresh forage), in this it was observed that, although it was consumed, it was not attractive, compared to the orange by-products. This may be due to the increase in digestible sugars that stimulate palatability, compared to green or dry forages, as they have more carbohydrates. Lactic acid bacteria generate a greater amount of biochemical compounds that enrich the substrate, improving taste conditions and sensory stimulating through their characteristic lactic acid odor and the sensitive organs of animal smell (^{Wadhwa et al., 2015}).

The results of the present work were similar to those reported by ^{Triana et al. (2014}), who worked with Valencia orange by-products, appreciating in the silo a light brown and light mustard color through fermentation times. The silo produced in this study complies with the organoleptic characteristics associated with high-quality silages; in this case an aromatic, sweet, pleasant fermented wine smell that characterizes lactic acid. This could be attributed to the fact that the orange peels, in addition to the natural fragrance of essential oils, have acids that generate a pleasant odor that, accompanied by the increase of lactic bacteria in the fermentation process, gave the silage a slightly pleasant odor.

Currently, in the field of nutrition of meat-producing cattle, protein is not only important, since the level and quality of energy is fundamental in the productive response of animals and is the key to achieving the highest profits in any livestock production system, under confined conditions. Importantly, energy provides the body with the ability to do work. In rations for fattening cattle, energy is required for activities such as growth and maintenance; so energy is a nutrient required by livestock in large quantities. The primary sources of energy in forage are cellulose and hemicellulose, and in grains starch. Fats and oils have a higher energy content, but are usually added in small amounts in the diet.

CONCLUSIONS

It was very notable that the stalled bulls that received the orange silo by-products had a daily weight gain of 2.97 kg. The accumulated weight gain at 90 days was 267.4 kg and the treatment for the young bulls with fresh fodder from African star grass was lower, with 139.7 kg. The low price and easy elaboration of concentrates with orange by-products is attractive and a viable option, as a complement for ruminants in periods of low water (drought and winter), given the availability of citrus in the north of Veracruz state.