137 Randel Lecture: Genetic control of thermotolerance in cattle at the whole-animal and cellular level

Abstract

Abstract Research by Randel and others has revealed the extensive genetic diversity in thermotolerance existing in cattle. Genetic differences in resistance to heat stress involve genes that affect body temperature regulation and that stabilize cellular function during hyperthermia. There are large differences between breeds in ability to regulate body temperature during heat stress. There is also genetic variation in thermoregulatory ability within breeds that arose in cold climates – the estimate of heritability of rectal temperature during heat stress in Holsteins is 0.17. Efforts are underway to identify genes conferring increased thermoregulatory ability in thermotolerant breeds and transfer these to thermosensitive breeds. One such gene is the prolactin receptor gene (PRLR). Several mutations in PRLR exist in criollo-type B. taurus that result in formation of a truncated receptor protein. Cattle with this mutation, which is dominant, have a short sleek hair coat and are referred to as “slick”. The slick mutation has been introduced into Holsteins by crossbreeding with Senepol cattle and in Red Angus by gene editing. Slick Holsteins are less affected by heat stress than wild-type Holsteins with respect to rectal temperature, milk yield and reproduction. Genetic variation also exists in cellular responses to elevated temperature (i.e., heat shock). Exposure of preimplantation embryos to heat shock, for example, causes a greater reduction in subsequent development of Angus, Holstein, Angus x Holstein or Jersey embryos than embryos from Brahman or Nelore (B. indicus) or Romosinuano (criollo). One gene with alleles affecting cellular resistance is the heat shock protein 70 gene HSPA1A. A mutation in the promoter region of HSPA1Ais associated with increased transcription of the encoded protein and enhanced survival of lymphocytes exposed to heat shock. Identification of other genes conferring thermotolerance will result in the increased ability to produce thermotolerant lines of cattle via genetic selection or gene transfer.