Dairy cattle

Evaluation of heat resilience genomic predictions for first service conception in US Holstein cows

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Abstract

Heat stress poses a significant challenge on dairy production and reproductive performance in Holstein cows. Exposure to elevated temperatures and humidity prior to breeding can disrupt normal estrous cycles, reduce oocyte quality, and impair fertilization, ultimately lowering conception rates. To partially address this a genetic evaluation was developed for fertility heat resilience. The genetic evaluation was conducted using single-step genomic BLUP methodology, applying the algorithm for proven and young animals. An animal's genetic ability to conceive per unit increase of Temperature-Humidity Index (THI) is reported as a genomic predicted transmitting ability (GPTA). The objective of this retrospective study was to evaluate the efficacy of genomic prediction for fertility heat stress resilience and its impact on first service conception rate (FSCR) during critical periods prior to insemination in Holstein cows. Data were collected on lactating Holstein cows (n = 50,731) from twenty-two commercial dairy farms across the United States. Cows enrolled did not contribute phenotypes to the genomic evaluation. Weather data extracted from the National Oceanic and Atmospheric Administration database were used to calculate daily THI values. THI exposure windows were established with cow reproductive records for 21, 14, and 7 days prior to first insemination. Daily average THI points above 70 were summed for all days in the exposure window to classify treatments: thermoneutral (0 total points above THI 70; TN), mild (1-25 total points above THI 70), extreme ( >75 total points above THI 70). Statistical analyses were conducted using a generalized linear mixed model, with semen type, lactation group, and first service conception rate GPTA included as fixed effects and herd as a random effect. Estimated response in FSCR per increase in Fertility Heat Resilience GPTA varied by exposure window prior to breeding and level of heat stress. For mild heat stress, the response in FSCR was 10.2% per GPTA (P P = 0.087). The estimated response in FSCR per GPTA was 18.5% (P = 0.094) for exposure to extreme heat stress 21 d prior to breeding. These results demonstrate Fertility Heat Resilience GPTA as an informative genomic predictor for fertility heat stress resilience, underscoring its utility for dairy producers as a tool for improving reproductive efficiency and climate resilience in their herds.

Keywords: 2026

How to Cite:

Beard, J., Weigel, D. & Fessenden, B., (2026) “Evaluation of heat resilience genomic predictions for first service conception in US Holstein cows”, World Congress on Genetics Applied to Livestock Production Digital Archive 2026(1): 2287205. doi: https://doi.org/10.31274/wcgalp.24234

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