Effect of thermal stress on basic seminal characteristics of Gyr bulls
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ORIGINAL PAPER
Effect of thermal stress on basic seminal characteristics of Gyr bulls Anielly de Paula Freitas 1 & Guilherme Felipe Ferreira dos Santos 2 & André Rabelo Fernandes 3 & Gabriela Geraldi Mendonça 2 & Claudia Cristina Paro de Paz 1,2 & Anibal Eugênio Vercesi Filho 4 & Lenira El Faro 2 Received: 25 July 2019 / Revised: 26 May 2020 / Accepted: 27 May 2020 # ISB 2020
Abstract The objective of this study was to evaluate the influence of thermal stress indices and minimum temperature on the semen quality of dairy Gyr bulls and to determine whether the minimum night temperature is able to balance the thermal stress that occurred during the day. A total of 922 semen samples were collected from 391 bulls aged between 15 and 49 months, which participated in progeny pretest trials, from December 2011 to April 2017. Semen characteristics (ejaculate volume, gross motility, sperm motility, sperm vigor, sperm concentration, and percentage of total defects) and scrotal circumference were analyzed. Meteorological data were recorded daily by the National Institute of Meteorology. The analyses were carried out using mixed models. The following fixed effects were included in the model: test, month of sample collection, scrotal circumference, the age of the bull at sampling as covariate (linear regression), and the climatic variables (equivalent temperature index [ETI], temperature and humidity index [THI], or minimum temperature). The effect of the bull nested within the test was included in the model as a random effect. Two periods were considered to evaluate the effect of the climatic variables on sperm quality: 7 days before collection (period 1) and the day of collection (period 2). There was an effect of ETI on sperm vigor and concentration in both periods and on volume and percentage of total defects only in the second period. The THI exerted a significant effect on volume in both periods and on sperm motility and concentration only in the second period. There was an effect of the minimum temperature on ejaculate volume, sperm motility, sperm concentration, and percentage of total defects only in the second period, which corresponds to the day of semen collection. Taken together, the results show that there was sufficient thermal stress to negatively affect semen quality. However, the minimum temperature during the night was a significant factor that balanced these negative effects of THI and ETI on semen traits of Gyr bulls. Keywords Environmental conditions . Spermatogenesis . Semen quality . Gyr
Electronic supplementary material The online version of this article (https://doi.org/10.1007/s00484-020-01945-6) contains supplementary material, which is available to authorized users. * Lenira El Faro [email protected] 1
Ribeirão Preto Medical School, University of São Paulo, Av. Bandeirantes, 3900, Monte Alegre, Ribeirão Preto, SP CEP 14049-900, Brazil
2
Beef Cattle Research Center, Animal Sciences Institute/APTA/SAA, Rodovia Carlos Tonanni, km 94, Sertãozinho, SP CEP 14160-900, Brazil
3
Technical Superint
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