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Daily vaginal temperature in Girolando cows from three different genetic compositions under natural heat stress.

L. d. R. Carvalheira

Abstract:

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Daily vaginal temperature in Girolando cows from three different genetic compositions under natural heat stress.
L. d. R. Carvalheira*1, R. R. Wenceslau1, L. d. S. Ribeiro2, B. C. d. Carvalho3, �. M. Borges1, L. S. d. A. Camargo3. 1Departamento de Cl�nica e Cirurgia Veterin�rias, Escola de Veterin�ria, Universidade Federal de Minas Gerais Belo Horizonte, MG, Brazil, 2Departamento de Patologia e Cl�nica Veterin�ria, Faculdade de Veterin�ria, Universidade Federal Fluminense Niter�i, RJ, Brazil, 3Laborat�rio de Reprodu��o Animal, Embrapa Gado de Leite Juiz de Fora, MG, Brazil.

The present trial evaluated the effect of proportion of Holstein genetic on crossbred composition (H) and temperature-humidity index (THI) on vaginal temperature (VT) of Girolando dairy cows maintained under tropical pasture during warm seasons. Vaginal temperature was monitored from 615 Holstein x Gir cows (1/2 H = 284, 3/4 H = 248 and 7/8 H = 83) from 6 Brazilian farms from January to March of 2016 and 2017. VT of each cow at each hour of the day and the respective THI were averaged per hour across all monitoring days to generate an averaged value for VT and THI during 24h. A linear mixed model with repeated measures using REML method for (co)variance components estimation procedure was employed. The final model adjusted the VT for the effects of farm, year, pregnancy status, body condition score and milk yield. Fixed effects were evaluated by ANOVA and tested with Tukey test in R 3.6.1 software (R Core Team, 2019). Overall mean of VT, air temperature (AT) and THI were, respectively, 39.06 � 0.52�C, 25.63 � 0.40�C and 75.06 � 3.96. VT had moderate positive correlation with THI (r2 = 0.45, P < 0.001) and AT (r2 = 0.46, P < 0.001). The VT had estimated linear increase of 0.05 degrees of each THI unit increase (P < 0.001). The daily average VT was affected by the proportion of Holstein (H) on genetic composition (1/2 H = 38.95 � 0.06 a, 3/4 H = 39.08 � 0.06 b and 7/8 H = 39.09 � 0.06 b; P < 0.001). The difference of VT among the 3 crossbred groups varied in function of the time of the day, from 12:00 to 20:00 h (P < 0.001). 3/4 H and 7/8 H cows had similar VT and higher than 1/2 H cows during all this period. In conclusion, Girolando cows are subjected to heat stress in tropical condition during warm seasons and also, Holstein proportion higher than 3/4 reduces its thermoregulatory efficiency. Strategies to alleviate heat stress should be use in dairy farms that raise Girolando cows in tropical conditions.

Keywords: core body temperature, crossbreed, tropical environment.