Abstract The effect of climatic factors on ovarian activity and reproductive behavior (RB) was evaluated in 46 Bos indicus cows kept under grazing conditions. Temperature-humidity index (THI) was used as an indicator of stress and divided in alert, damage and emergency levels. Fat thickness (FAT) was taken during the last trimester of gestation (LTG) to approximately 90d postpartum (PP). At 30d PP animals received a progesterone (P4)-releasing device (CIDR) which was withdrawn 9d later. Ovarian activity was assessed by blood progesterone on days 21, 24, 27, 30, 49, 51, and 54 PP. Animals were divided into three groups, higher, and moderate RB and non-behavior. Sixty percent presented a THI >74 increasing dramatically from June to September up to >78. During LTG, animals lost 27% of their body reserves contrasting to PP where an increase of 2.6% (P=0.002) was observed. The percentages of cyclic and non-cyclic animals were 57 and 43%, respectively (P> 0.05). Seventy-two percent displayed RB and 28% were non-behavior (P<0.05). A negative correlation (r = -0.307; P = 0.038) between THI and RB, and a positive correlation (r = 0.427; P = 0.003) between the onset of ovarian activity and RB were observed. Differences in THI during the LTG (P<0.01) were observed between cyclic and non-cyclic animals. Non-behavior cows in the LTG had a higher THI (P <0.05). High levels of THI have a negative effect on the resumption of ovarian activity and RB in Bos indicus especially if high THI occurs during the last trimester of gestation.

Foi administrada dexametasona para indução de degeneração testicular experimental em touros de uma raça taurina pura (Aberdeen Angus) e de sua sintética derivada (Brangus-Ibagé). O objetivo deste estudo foi o de averiguar a diferença de sensibilidade na função gametogênica em frente à degeneração experimental. Para tal, foram avaliados os aspectos físicos e morfológicos do sêmen. Os dados obtidos foram analisados considerando o dia de coleta e genótipo. Os resultados revelaram que os dois grupos raciais comportaram-se semelhantemente ao longo das coletas. A despeito do número de animais empregados, o uso da degeneração testicular experimental possibilitou evidenciar que não há diferença entre as duas raças quanto à intensidade da degeneração e tempo necessário para o restabelecimento do quadro espermático normal.

Testicular degeneration was induced by dexamethasone injection in bulls from a European breed Aberdeen Angus and a derived synthetic crossbreed (Brangus-Ibagé). Aiming to investigate differential sensibility on gametogenic function in these genotypes, physical and morphological semen characteristics were evaluated. The data analysed considered the day of the semen samples and the breed. Our results reveal that both breeds behave similarly during the experimental period. Even considering the number of bulls used in this experiment, the employed methodology gives no evidence of any difference between breeds, intensity of degeneration or time required to the reestablishment of normal sperm frequencies after experimental induction of testicular degeneration.