INTRODUCTION

In Mexico, chicken meat production in 2020 was 3.952 million tons, representing two thirds of total meat consumption. Poultry farming constitutes 38.8% of the activities generating protein (meat) for human consumption (31 kg/per capita) (^{UNA, 2021}), and has played an important role in the family, especially during the pandemic, thus contributing to the welfare of the population. On the other hand, the annual production of balanced animal feed in the last 4 years has maintained 4% growth, which covers the demand required to guarantee quality animal protein for Mexicans. The Global Feedstuffs Survey mentions that Mexico, at the end of 2020, climbed to the 5th position worldwide with a production of 38 million MT (^{Alltech, 2021}; ^{CONAFAB, 2021}).

Within the total production price, feed is the item with the greatest impact, representing approximately 63% of costs (^{UNA, 2021}). Therefore, industries dedicated to feed formulation are in a constant search for economically viable resources that do not sacrifice diet quality and, therefore, production variables (^{UNA, 2021}). One of these possible resources could be giant squid meal (Dosidicus gigas), a cephalopod distributed throughout the American continent from California, United States, to southern Chile. Studies indicate that it has a high protein content, but the information that has been published on this aspect and others is scarce; in fact, it is not known how available this protein is for birds. Worldwide, Mexico is among the leading countries in giant squid (Dosidicus gigas) production (2.598 MT), with Sinaloa State being the main producer with 1.600 MT (^{De la Cruz et al., 2011}).

Squid consumption in Mexico is estimated at 0.53 kg/year/per capita, which represents 3.8% of seafood consumption, far below countries such as South Korea, Japan and Spain that consume more than 3.5 kg/year/per capita/year, as this is a product with high protein content, fatty acids and low cost (^{De la Cruz et al., 2011}). There is another market segment that can give added value to the squid fishery, this is to use the viscera and other parts of the squid or the whole specimen that does not meet the quality characteristics for human consumption for the production of meal for animal consumption, considering that this meal is a source of protein and fatty acids (^{Calvo et al., 2016}). Therefore, the objective of this research was to determine the metabolizable energy content and apparent ileal digestibility of amino acids of giant squid (Dosidicus gigas) meal to be incorporated as an alternative source of protein in broiler diets.

MATERIAL AND METHODS

The protocol was approved by the Institutional Committee for the Care and Use of Experimental Animals (CICUAE-FMVZ-UNAM) (approval: MC-2017/2-25) (^{NOM-062- ZOO-1999}). Experiments were conducted at the Center for Teaching, Research and Extension in Poultry Production of the FMVZ, UNAM, in Mexico City.

RESULTS

DISCUSSION

Since NNP (nucleic acids, urea, and amides) is not useful in the feeding of monogastrics, since they require preformed amino acids, its determination is important to avoid an overestimation of the protein of the ingredient (^{Caravaca et al., 2003}). No data on NNP and true protein content were found in other investigations with squid meal; however, (^{Ezquerra et al., 2007}) mention that of the total nitrogenous compounds (including protein) found in several squid species, the non-nitrogenous elements (trimethylamine oxide and other amines, free amino acids and octopine, arginine, glycine, betaine, alanine and nucleotides) represent 37%, although these authors do not specify whether the values were in fresh squid or meal, being similar to that reported by ^{Maza et al (2003)}, who mention that the NNP content is 39. 5% in fresh mantle of squid Dosidicus gigas. These figures are higher than the percentage obtained in this research (18.36%) for the same species.

The AMEn was 6.6% higher than that reported by ^{Remigio (Remigio, 2006)} (3151 kcal/kg) using viscera meal (68.75% CP) of the same species. Compared to other ingredients, it exceeds a fish meal (3037 kcal/kg and 60.3% CP) by 11% and soybean meal (2346 kcal/kg and 48% CP) by 44%, but becomes similar to yellow corn (3340 kcal/kg) and sorghum (3263 kcal/kg) (^{AMINODat, 2016}). Variations between results could be related to the amount of total protein in GSM, as amino acid skeletons can be converted to carbohydrate derivatives, which increase the energy value of the ingredients (^{Leeson & Summers, 2001}).

Digestibility coefficients at 21 days of age with diets formulated based on total amino acids showed similar behaviors to those reported by ^{Carranco (2020)} in laying hens, where there were no differences for feed intake, but in both works a higher feed conversion was detected. When analyzing the actual consumption of amino acids over the 21 days of the trial, it was observed that the highest consumption of lysine and arginine was for the control. However, when calculating the arginine:lysine ratio, it was found that the highest ratio was for the 16% inclusion (1:11) and ^{Leeson & Summers (2001)} report a normal ratio of 1:1 to 1.05:1, so the higher amount of arginine may have caused a lower absorption of lysine. Since lysine is almost totally destined for muscle formation (^{Campos et al., 2008}), these observations become factors to be considered to explain the behavior of the final weight variable, since the 65g difference between the control and 16% GSM treatments contributed to the 8.2% drop in the weight gain variable in the latter treatment.

The productive variables of the complete cycle (42 days) agree with what was reported by ^{Morales et al (2022)} that included 1.67, 3.34 and 5.01% of GSM based on a formulation with total amino acids and that at the end of the cycle (49 days) found no differences for the same variables. The average yield was 72.82% similar to that suggested for this strain (71.57%) (^{Aviagen, 2014}). Females had a higher yield than males, which is consistent with data from other authors, where females had higher proportions of breast and subcutaneous fat than males, but males outperformed males in proportion to leg and thigh ^{Rondelli et al., 2003}; ^{López et al., 2011}).

Since pigment deposition can be affected by decreased feed intake, the total consumption of yellow xanthophylls per treatment was calculated, however, considering the pigment added and the amounts of corn (lutein and zeaxanthin) used, as GSM inclusion was increased during the three study phases, these intakes did not agree with the behavior presented in b*, as the control diet consumed 273. 64 mg; with 16% GSM 297.72 mg and with 20% GSM 259.05 mg, data similar to that reported by ^{Muñoz et al (2012)} who observed b* units above those recorded in males, this could be explained because females have a greater capacity to deposit fat tissue. It is worth mentioning that the behavior observed in the treatment with 20% GSM inclusion could be due to the effect of the female because of the interaction tendency with sex. ^{Toyes (2016)} enriched with astaxanthin, 0.05 mg/100 g chicken egg, because he determined total carotenoid amounts of 11.5 mg/100 g in dried squid viscera meal of which 5. 4 mg/100 g were astaxanthin, this in turn differs with that reported by ^{Ezquerra et al (2007)} and ^{Aubourg et al (2016)} who in their studies on squid (Dosidicus gigas) skin extract ruled out the presence of carotenoids and melanins in the skin, but did find compounds of the omochrome type (used by animals for camouflage), also lipophilic, of which not enough information is available.

Sensory evaluation is an important point for consumers, since they can give their point of view on a food(s) by rating attributes such as taste, odor, texture, color, among others.

However, both flavor and aroma are main attributes that consumers consider for the acceptance of a food (^{Sánchez & Albarracín, 2010}).

It is important to mention, in this case, that in the production, processing and cooking of chicken meat, the sensory attributes tend to develop chemical changes of sugars, amino acids, thermal oxidation of lipids and degradation of thiamine. But there are also other factors that contribute to these sensory changes such as bird age, strain, feed, environmental conditions, rearing system, blanching temperature, cooling, labeling and storage (^{Alltech, 2021}). (Padilla, 2010).

When using unconventional seafood sources, there is concern about the fishy flavor attribute that develops in chicken meat. One example is a study in which herring meal was supplemented with 4, 8 and 12% herring meal in broiler diets, where these small amounts exerted an effect on flavor. Meat from birds fed 8% herring meal had unpleasant fishy, rancid, non-fresh flavors, which after cooking were less apparent, but 24 hours after refrigeration and re-evaluation, the fishy flavors increased (^{Poste, 1990}). In this research with cooked meat, none of the judges reported unpleasant tastes or odors (fishy), data that agree with those reported by ^{Morales et al (2022)} when using squid meal in broilers.

CONCLUSIONS

It is concluded that GSM can be an alternative source of protein in broiler diets, but more studies are needed.