Introduction

One of the main factors that contribute today to maintain the quality of the environment, is the use of by-products of animal origin; so it is a priority to look for alternative nutritional sources that reduce costs without adversely affecting production. Agroindustrial activities generate waste that can be reincorporated into the food chain, after physical-chemical treatment (^{Castañeda et al., 2010}).

Within the last report made by ^{INEGI-Mexico (2010)}, it was analyzed that of the livestock products (Table 1) those obtained from cattle report an annual production of 665 thousand tons/year, mainly in some regions where livestock that is practiced is intensive type; a part of the byproducts obtained is destined for export, mainly due to the high quality of the product (^{Abdul-Kalil et al., 2006}). The pigs are produced in 28 states of the country through intensive and extensive farms; as well as 500 thousand tons of by-products of this species, which are used annually for national consumption. With respect to sheep and goats, the average national production is 10,000 and 11,000 tons/year respectively, in this case the farms are extensive and they are carried out in 28 of the 32 entities of the country; there is only a slight deficit in the production of goats, which is covered by the import. The national production of consumer birds represents 30,000 to 40,000 tons/year, being one of the most technified in the country. Most of these farms are located in areas close to urban centers that consume most of this production (^{Gutiérrez et al., 2013}).

On the other hand, the existing deficit in the production of grains and the relative abundance of agricultural waste, make these along with other organic waste and livestock by-products become an acceptable and low-cost nutritional alternative that can be used in the feeding of ruminants as a source of non-degradable protein in rumen (^{Gómez, 2006}).

An answer to this situation is found in the poultry industry, which is the source of a great miscellany of by-products with an enormous nutritional potential, which is evident as long as the transformation technologies applied propitiate the bioavailability of its nutrients. Thus, the use of organic waste generated by this industry can contribute to the nutrient reduction cost in balanced feed for the preparation of ruminant diets (^{Ockerman et al., 2005})

Material and Methods

This investigation was developed in a commercial ranch of the North of Veracruz state, in the municipality of Platón Sánchez, geographically located in the meridians 21° 16 "north latitude and 98 ° 22" west longitude, at a height of 60 meters above the level of the sea (m a.s.l) and average annual temperature of 19-36 °C.

30 Cebu x Suizo heifers were used, weighing approximately 300 kg and 30 months of age, which were assigned under a completely randomized design in three treatments. T1 (control) concentrated without poultry by-product; T2 concentrated + 30% poultry manure and T3 concentrated + 30% poultry meal. The composition of the energy concentrate was based on ground sorghum, corn grain, wheat bran, ground bale, mineral salt with 11% crude protein and 70% TDN (Total digestible nutrients. The nutritional values were analyzed by the method of Van Soest and Wine (Ockerman and Hanen 1995).

The energy concentrate was stirred daily according to treatment in the following proportions (T1 = 100% concentrated), (T2 = 70% concentrated + 30% poultry manure) and (T3 = 70% concentrated + 30% poultry meal). This was supplied in dry matter twice a day at a rate of 3% of live weight (^{NRC, 2007}) during the 90 days that the experiment was developed; the consumptions of food corresponded in average to 10.5 kg/animal. The rations were offered in 3 stages, which were initiation, transition and finalization. The initiation stage lasted 8 days and the ration was made up of 21% forage from ground star hay (Cynodon plectostachium) ground and 79% concentrated feed. The transition stage lasted 8 days and it was made up of 15% forage and 85% concentrate; while, for the 74-day completion stage, 11% forage and 89% concentrate were supplied. The management of the animals consisted of vaccination, deworming, identification and application of vitamins A, D and E intramuscularly. The variations in the weight of the animals were recorded in fortnightly periods. Once the fattening period was over, the animals were slaughtered in the TIF (Federal Inspection Trace) refrigerator, determining the cold carcass yield (RCF).

The data were processed in the statistical package SPSS version 10, through the analysis of variance and the differences between treatments were detected by the Duncan test. The level of significance was 5%.

Results and Discussion

The nutritional values analyzed (Table 2) by the method of ^{Van Soest and Wine (1994)}, fulfilled the nutritional recommendations indicated by the National Research Council (^{NRC, 2007}), with 11-18% of Crude Protein (PC) and 70% of Total Digestible Nutrients (TDN) for heifers with weight between 300-350 Kg. Determining that the experimental rations made from aviary by-products in the present work contained different levels of protein (manure and poultry meal), which they expected an unequal growth of the animals according to the treatment.

The productive performance of the animals in the different treatments (Table 3), in relation to the total weight gain / day, was significantly higher (p ≤ 0.05) in the groups that received avian by-products with respect to the control (.964; 1.04 and 1.15 kg, for T1, T2 and T3, respectively). Also, the heifers of the study that received only the supplement based on energy nutrients, had lower accumulated weight gain; compared with the treatments supplemented by avian by-products (T2 and T3), which had a significantly higher response (p ≤ 0.05) to the addition of manure and poultry meal (86.8, 94.3 and 104.0 kg, for T1) , T2 and T3, respectively).

The difference in food consumption resulted in the consumption of T1 animals consuming 14.6 Mcal. of metabolizable energy / day; whereas the animals of the supplement + poultry meal (T3) treatment consumed 23.8 Mcal, equivalent to a difference of 40% that is reflected in the same proportion of the live weight gain between treatments. These differences were due to a better nutritional intake and the effect on the rumen of the inclusion of a true source of protein, with an adequate balance of amino acids on feed intake and live weight gain (^{Stewart and Bryant, 2008}).

The age at which heifers were slaughtered (Table 4) and the quality of the nutritional supplementation influenced most of the carcass characteristics; this behavior was observed in the present study, registering a yield of 52.03% for the hot carcass yield, which was higher due to the effect of adding 30% of the poultry meal to the daily diet supplied (T3).

In the evaluations of the carcasses visibly and tactilely (Table 4), it was determined that the distribution of fat on the carcass surface and thickness in the eye area of the loin were slightly moderate in those females that received a supplementation based on poultry manure and meal, reaching a standard and select classification degree for the carcass (T2 and T3). With regard to marbling, it was located at the level that was little covered, covered and fatty for the T1, T2 and T3 respectively; while the color of the carcass remained with a dark, light and cherry red color. Muscularity (muscular profile and costal eye area) did not show statistical differences in favor of a treatment, although the supplemented animals showed a better silhouette (straight vs. slightly concave profiles of the control).

Conclusions

The supplementation based on 30% of poultry by-products (manure and poultry meal), promoted a better productive performance in farmed heifers, achieving weight gains of up to 1.0 kg / day. In the same way, balanced supplementation with optimal levels of protein and energy in the diet, significantly improved the quality of the carcass, obtaining yields greater than 52.30%, surpassing the control and giving it a high degree classification. In this context, poultry meal is a poultry byproduct considered a source of protein with high biological value. Taking into account their nutritional characteristics and their availability in large quantity; the inclusion of this protein source in commercial diets for ruminants would contribute to a significant reduction in the production price; allowing at the same time the use of a good quality poultry by-product.