Seasonality and fresh semen quality from Pantaneira and Nellore bulls raised in Brazilian Pantanal

Abstract Text: Taurine cattle (Bos taurus) when subjected to tropical conditions have reduced fertility compared to zebu cattle (Bos indicus). The Pantaneira breed (Bos taurus) was recently recognized as a Brazilian native breed adapted into climatic conditions of Brazilian Pantanal. However,  the seminal parameters of this breed are unknown. Thus, the aim of this work were knowing the seminal parameters Pantaneira breed and evaluate what breed (Pantaneira or Nellore breed) raised on pasture in the southern Brazilian Pantanal region is more adapted to regional climatic conditions. Seven Pantaneiro bulls and three Nelore bulls were used. Semen was collected by electroejaculation. Immediately after collection were evaluated: sperm motility (MOT), vigor (VIG) , primary defects (PRIMDEF) , secondary defects (SECDEF) and total defects (TOTDEF) semen concentration (CONC) , sperm viability (SVIAB) and integrity of acrosomal membrane (ICM).The experiment was conducted in a 2x2 factorial arrangement (2 breed and 2 seasons) and data were analyzed by ANOVA and Tukey test , with α = 5 %. Seminal parameters in Pantaneira bull are within recommended standards for bovine. SVIAB was lower in winter in both breeds (95.76 ± 1.77 % vs . 87.07 ± 4.78 % P = 0.03). Nellore bulls showed a higher amount of sperm with SECDEF in summer (2.16 ± 1.09% vs 0.57 ± 0.31%; P = 0.02) , and higher percentage of PRIMDEF (61.91 ± 5.92 % vs . ± 26 % 3.83 P = 0.01) and TOTDEF (62.58 ± 5.63 % vs . 27.33 ± 3.91 % P = 0.03) in winter . Were not found effects of breed, season, or interaction  (P > 0.05) in other parameters evaluated. Although Pantaneira breed to be considered a taurine breed (Bos taurus), it passed a  natural selection process by about 300 years, adapting to high temperatures in central Brazil and probably has become more resistant to testicular degeneration process. In contrast, Nellore bulls appear to be more sensitive to heat stress by cold. Therefore, it is concluded that Pantaneira breed is most suitable breed to edaphoclimatic conditions in the Brazilian southern Pantanal.

Keywords: sperm morphology, heat stress, fertility