Genotype effects on body temperature in dairy cows under grazing conditions in a hot climate including evidence for heterosis |
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Authors: | S Dikmen L Martins E Pontes P J Hansen |
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Institution: | 1.Department of Animal Science, Faculty of Veterinary Medicine,University of Uludag,Bursa,Turkey;2.Department of Animal Sciences,University of Florida,Gainesville,USA;3.Faculdade de Medicina Veterinária e Zootecnia,Universidade de S?o Paulo,S?o Paulo,Brazil |
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Abstract: | We compared diurnal patterns of vaginal temperature in lactating cows under grazing conditions to evaluate genotype effects
on body temperature regulation. Genotypes evaluated were Holstein, Jersey, Jersey × Holstein and Swedish Red × Holstein. The
comparison of Holstein and Jersey versus Jersey × Holstein provided a test of whether heterosis effects body temperature regulation.
Cows were fitted with intravaginal temperature recording devices that measured vaginal temperature every 15 min for 7 days.
Vaginal temperature was affected by time of day (P < 0.0001) and genotype × time (P < 0.0001) regardless of whether days in milk and milk yield were used as covariates. Additional analyses indicated that the
Swedish Red × Holstein had a different pattern of vaginal temperatures than the other three genotypes (Swedish Red × Holstein
vs others × time; P < 0.0001) and that Holstein and Jersey had a different pattern than Jersey × Holstein (Holstein + Jersey vs Jersey × Holstein)
× time, P < 0.0001]. However, Holstein had a similar pattern to Jersey (Holstein vs Jersey) × time, P > 0.10]. These genotype × time interactions reflect two effects. First, Swedish Red × Holstein had higher vaginal temperatures
than the other genotypes in the late morning and afternoon but not after the evening milking. Secondly, Jersey × Holstein
had lower vaginal temperatures than other genotypes in the late morning and afternoon and again in the late night and early
morning. Results point out that there are effects of specific genotypes and evidence for heterosis on regulation of body temperature
of lactating cows maintained under grazing conditions and suggest that genetic improvement for thermotolerance through breed
choice or genetic selection is possible. |
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Keywords: | Holstein Jersey Swedish Red Crossbreeding Heat stress Milk yield |
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