Banca de DEFESA: GIOVANNA ARAUJO DE CARVALHO

Uma banca de DEFESA de MESTRADO foi cadastrada pelo programa.
DISCENTE : GIOVANNA ARAUJO DE CARVALHO
DATA : 26/07/2019
HORA: 10:00
LOCAL: Embrapa
TÍTULO:

Effect of thermal stress on thermoregulatory responses of grazing Girolando herd in Porto Velho, Rondônia

PALAVRAS-CHAVES:

crossbred bovines, bioacustic, thermal disconfort

PÁGINAS: 42
GRANDE ÁREA: Ciências Agrárias
ÁREA: Zootecnia
SUBÁREA: Nutrição e Alimentação Animal
RESUMO:

The purpose of this work was to investigate the effect of thermal stress on thermoregulatory responses of grazing Girolando cattle in Porto Velho, Rondônia. Two studies were carried out. The first study was performed for validation of bioacoustic as a methodology to estimate the respiratory rate (RR) of grazing bovines. Two trials were performed, the first with five heifers and the second with five lactating cows. RR was assessed by visual observation and bioacoustic at 08:00, 10:00, 13:00 and 15:00. The accuracy and precision of the methodology were verified by Willmott's confidence index (d), mean square error of prediction (MSEP) and mean systematic error (MSP). Data were collected regarding the ambient black globe temperature and relative humidity of the air for estimation of the black globe and humidity index (BGTI). The experimental design was completely randomized with four replications in time. The averages were compared by the Tukey-Kramer test at the 5% level of significance, where the methodologies, the evaluation schedules and their interaction were considered. Regression analysis of the effect of RR according to the BGTI was performed by the PROC REG program (SAS). High values for RR and BGTI were observed at 13:00 for both categories of animals studied. The regression analysis showed that for every 2.4 units of the ITGU, there is an increase of 1 mov / min in th heifer's RR. This effect was not significant in lactating cows (P> 0.05). There were no significant differences between visual and bioacoustics for heifers (84.46 vs. 81.48 mov / min, respectively) and for dairy cows (70.68 vs. 67.93 mov / min, respectively). nor between the methodology and time interaction (P> 0.05). The index d showed values of 0.99 and 0.98 when the methodology was applied in lactating and heifer cows, respectively. The MSEP and MSP indexes indicated high accuracy for the methodology when tested for both categories. The methodology of bioacoustics in the measurement of RR of dairy cattle showed reliability and applicability, mainly to pasture. To evaluate the effect of thermal stress on Girolando cattle, physiological and climatic data from previous experiments with heifers and lactating cows under different grazing conditions were used. RR was analyzed by hourly bioacoustics and internal temperature (IT) every 10 minutes, using data logger thermometers coupled in inert intravaginal devices, both for total periods of 48h. Climatic data (temperature and humidity) were collected through a meteorological station near the experimental area and from them the physiological parameters were calculated the temperature and humidity indexes (THI) and the thermal comfort of Benezra (BTC). The data were analyzed through the PROC MIXED (SAS) program with repeated measures over time. The effects of treatments (without soybean oil supplementation and with soybean oil supplementation and ICL and ICLF), evaluation times (00:00 to 23:00 hours) and their interaction were included as fixed effects. The Tukey-Kramer test for the comparison of means was used when the factor or interaction presented significance (P <0.05) or trend (P <0.1). In experiment 1, soybean oil had no influence on the physiological parameters of the animals (P> 0.05). The THI mean of 75.52 ± 2.93 indicated mild stress during the experimental period. BCT ranged from 3.0 to 3.6, with values higher than that recommended for animals in thermal comfort. In Experiment 2, animals allocated to the ICLF system demonstrated lower values of RR and IT compared to the ICL system (P <0.001). The THI values recorded did not present numerical differences between the evaluated systems (79.04 ± 4.84 in the ICL vs. 78.97 ± 4.36 in the ICLF). Both the ICL system and the ICLF presented ICB values above 2.0 (3.51 ± 0.55 vs. 3.31 ± 0.51, respectively). In both experiments we observed differences between the treatments evaluated for the RR and IT in the schedules from 07:00 to 09:00 and from 12:00 to 17:00 hours. Supplementation with soybean oil at 7% in diet DM did not influence the thermoregulatory parameters of grazing dairy cows Girolando. On the other hand, the shading promoted by the ICLF system benefited RR and IT of crossbred dairy heifers in a grazing system, providing thermal comfort. The THI and BCT indices indicated values above those recommended for thermal comfort, regardless of the treatment to which the animals were submitted.

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