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Background: Heat stress and fescue toxicosis caused by ingesting tall fescue infected with the endophytic fungus Epichloë coenophiala represent two of the most prevalent stressors to beef cattle in the United States and cost the beef industry millions of dollars each year. The rate at which a beef cow sheds her winter coat early in the summer is an indicator of adaptation to heat and an economically relevant trait in temperate or subtropical parts of the world. Furthermore, research suggests that early-summer hair shedding may reflect tolerance to fescue toxicosis, since vasoconstriction induced by fescue toxicosis limits the ability of an animal to shed its winter coat. Both heat stress and fescue toxicosis reduce profitability partly via indirect maternal effects on calf weaning weight. Here, we developed parameters for routine genetic evaluation of hair shedding score in American Angus cattle, and identified genomic loci associated with variation in hair shedding score via genome-wide association analysis (GWAA)., Results: Hair shedding score was moderately heritable (h 2  = 0.34 to 0.40), with different repeatability estimates between cattle grazing versus not grazing endophyte-infected tall fescue. Our results suggest modestly negative genetic and phenotypic correlations between a dam's hair shedding score (lower score is earlier shedding) and the weaning weight of her calf, which is one metric of performance. Together, these results indicate that economic gains can be made by using hair shedding score breeding values to select for heat-tolerant cattle. GWAA identified 176 variants significant at FDR < 0.05. Functional enrichment analyses using genes that were located within 50 kb of these variants identified pathways involved in keratin formation, prolactin signalling, host-virus interaction, and other biological processes., Conclusions: This work contributes to a continuing trend in the development of genetic evaluations for environmental adaptation. Our results will aid beef cattle producers in selecting more sustainable and climate-adapted cattle, as well as enable the development of similar routine genetic evaluations in other breeds.

Twenty-three male lambs were intoxicated with 2.5 ppm aflatoxins in their feed for a period of 3 weeks. Thirteen lambs were maintained as a control group (0 ppm aflatoxins in their feed). The coagulation profiles were determined from blood samples that were obtained at 0, 7, 14 and 21 d during the intoxication period and at 1, 2, 4 and 8 d of an 8-d clearance period. Aflatoxicosis in the animals was characterized by an increase in prothrombin time (P < 0.01) from d 14 of the intoxication period until the end of the experiment. An increase (P < 0.05) in fibrinogen concentration was detected beginning on d 21, instead of the expected decrease. This was probably due to the inflammation found in the lungs of the intoxicated animals. No difference in activated partial thromboplastin time was found between intoxicated and control animals. These results suggest that there was a significant change in some coagulation factors of the extrinsic pathway in the intoxicated lambs and that prothrombin time determination could be used as an indicator of aflatoxicosis in lambs.