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ARS Home » Plains Area » Clay Center, Nebraska » U.S. Meat Animal Research Center » Livestock Bio-Systems » Research » Publications at this Location » Publication #412805
Research Project: Applying Nutritional Strategies to Improve Early Embryonic Development and Progeny Performance in Beef Cows

Location: Livestock Bio-Systems

Title: Relationship of length of the estrous cycle to antral follicle number in crossbred beef heifers

Author
item Cushman, Robert - Bob
item KAPS, M - University Of Veterinary Medicine
item Snider, Alexandria - Alex
item Crouse, Matthew
item Woodbury, Bryan
item Keel, Brittney
item MCCARTHY, K - University Of Nebraska

Submitted to: Translational Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/19/2024
Publication Date: 4/30/2024
Citation: Cushman, R.A., Kaps, M., Snider, A.P., Crouse, M.S., Woodbury, B.L., Keel, B.N., McCarthy, K.L. 2024. Relationship of length of the estrous cycle to antral follicle number in crossbred beef heifers. Translational Animal Science. 8. Article txae074. https://doi.org/10.1093/tas/txae074.
DOI: https://doi.org/10.1093/tas/txae074

Interpretive Summary: In women, length of the menstrual cycle is positively associated with markers of size of the ovarian reserve. If this pattern is consistent in cattle, this could be a value-added benefit to automated activity monitors that are used to determine estrous status. The current study was designed to determine if there was a relationship between length of the estrous cycle and follicle number in beef heifers. Contrary to results in women, length of the estrous cycle is not a predictor of follicle number in beef cattle. While automated activity monitors can help cow-calf producers with reproductive management, in its current form, the data produced will not provide an alternative method to ultrasonography or hormonal profiles for predicting the size of the ovarian reserve.

Technical Abstract: Length of the menstrual cycle was positively associated with antral follicle number in women. If this pattern is consistent in cattle, a value-added benefit to using automated activity monitors to determine estrous status could be the ability to predict antral follicle count (AFC). We, therefore, hypothesized that as inter-estrous interval increased ultrasonographic AFC would be greater in crossbred beef heifers. Over three years, crossbred beef heifers (n = 1394) were fitted with automated activity monitors for 81 d. From d 42 to 46, heifers were submitted for ultrasonographic examination to determine AFC. From d 60 to 81, heifers were visually observed twice daily for 45 min for signs of behavioral estrus. Heifers that had a behavioral estrus that coincided with a sensor-based estrus and had a previous sensor-based estrus between 15 and 26 d earlier were used for the analysis (n = 850). A combination of regression analyses and correlation analyses were applied to understand the association between data collected by sensors and follicle number determined by ultrasonographic examination. Antral follicle count was analyzed using the GLM procedure of SAS with estrous cycle length (15 to 26 d) as a fixed effect. Estrus was more likely to initiate in the early morning hours and peak activity was greater (P < 0.0001) when estrus initiated between 0200 h and 0800 h then when estrus initiated at other times of the day. Antral follicle count did not differ due to length of the estrous cycle (P = 0.87). Thus, length of the estrous cycle obtained from three-axis accelerometers cannot be used to predict follicle number in crossbred beef heifers; however, machine learning approaches that combine multiple features could be used to integrate parameters of activity with other relevant environmental and management data to quantify AFC and improve reproductive management in beef cows.