Free radicals are unstable molecules that have an unpaired electron in their last orbital, which makes them highly unstable agents. In medicine, it has been discovered that they play an important role in cell signaling and without them some cells such as leukocytes or sperm could not perform their biological functions. To protect itself from these oxidizing agents, the cell has a defense system based on antioxidants; however, when this balance is lost and oxidizing agents exceed the cellular antioxidant capacity, the cell enters oxidative stress, which affects cellular components such as proteins, nucleic acids, lipids, amino acids, and carbohydrates, among others. In the case of spermatozoa, due to their high metabolic rate, they produce large quantities of oxygen reactive species (ROS), decreasing sperm motility, alterations in cytoplasmic components, modifications in genetic material, or sperm death. In this chapter, a review is made of a brief history of how the toxicity of oxygen and free radicals was discovered, the oxidative stress in cells, and the effect of oxidative stress in the cytoplasmic sperm membrane, in the spermatic mitochondria, in the spermatic acrosome, in the sperm DNA, and in the fertility of the female and the male.

El clembuterol, Químicamente se describe como polvo blanco, anhidro, muy soluble en agua y altamente estable a temperatura ambiente, su punto de fusión es de 174 a 175.5 ºC. También es un derivado sintético perteneciente a una clase de medicamentos análogos fisiológicamente a la adrenalina, tiene la capacidad de interactuar con receptores adrenérgicos,  generalmente  del  tipo  ß2    (β  agonista),  es  uno  de  los  modificadores metabólicos más conocido en el área de producción de carne, debido al alto grado residual que deja esta sustancia en los tejidos comestibles y sus posibles repercusiones en la salud pública. En este trabajo, se describen los principales actores de la cadena productiva en la engorda  de  ganado  que  deben  participar  para  prevenir  el  uso  de  clembuterol.  La información fue recopilada de información científicas y publicaciones de las autoridades competentes, tales como: SENASICA, SAGARPA, COFEPRIS y Ley Federal de Sanidad Animal.

Objetivo: El objetivo de este trabajo fue valorar el efecto de la raza del toro sobre la calidad espermática del semen descongelado. Diseño/metodología/aproximación: Se utilizaron 10 pajillas plásticas de 0.5 ml de semen congelado de tres diferentes razas de toro, las cuales se adquirieron en una empresa comercial. Las razas de toro utilizadas fueron Charolais, Brahman y Simbrah. Las pajillas fueron descongeladas a 37°C durante 40 segundos. Inmediatamente después se valoró motilidad, viabilidad e integridad acrorosomal (NAR). Resultados: Los resultados fueron para motilidad 75.0, 87.5 y 85.0 %; para viabilidad 74.5, 74.5 y 72.5 %; y para NAR 97.1, 96.9 y 96.9% para las razas Charolais, Brahaman y Simbrah, respectivamente. Limitaciones/implicaciones: Las pajillas utilizadas se obtuvieron de una empresa comercial dedicada a la venta de semen congelado de bovino. Hallazgos/conclusiones: Las tres razas de toros mostraron buena calidad espermática después de la descongelación, las cuales pueden ser recomendadas para ser utilizadas en la inseminación artificial sin ningún problema.

During seminal freezing, sperm undergo oxidative stress, reducing their motility, viability, and acrosomal integrity. To prevent these damages, antioxidants have been added at the time of seminal freezing. The objective was to assess the antioxidant effect of the combination of α-tocopherol with quercetin, added to the diluent for the freezing of boar semen. The semen of boars of the Pietrain and York/Pietrain breeds was frozen in 0.5 ml straws, before freezing α-tocopherol in a concentration of 4 mg/ml (T1), quercetin in concentrations of 25, 50 and 100 µM (T2, T3 and T4), α-tocopherol + Quercetin in concentrations of 4 mg/ml + 25 µM, 4 mg/ml+50 µM and 4 mg/ml + 100 µM (T5, T6 and T7) and the control group (T8) without antioxidant. The straws were frozen in liquid nitrogen for 7 days and thawed at 42 °C for 12 seconds. 5 repetitions were performed analyzing motility, viability, and NAR. the results were analyzed using a completely randomized design in factorial arrangement comparing the means with a Tukey test. The best percentage of motility was for T5, T4 and T1 with 39.44, 38.06 and 37.33%, respectively, there was a significant difference with T8; the best percentage of viability were T5 with 51.41%, there was a significant difference with T3 and T8; and the best NAR percentages were for T8 with 94.90%, with a significant difference for T1. In conclusion, the addition of α-tocopherol and quercetin separately or in combination protects the motility, viability, and NAR of spermatozoa from frozen-thawed boar semen.