Ovarian Function/Dysfunction
Session: Poster Session B
Kennedy Hill
Graduate Teaching Assistant
University of Tennessee
Knoxville, Tennessee, United States
Kennedy Hill1, Pablo Fioravanti1, Ian E. Batey1, Rebecca R. Payton1, Micheal O’Neil2, F. Neal Schrick1, Saulo Menegatti Zoca1, Sarah E. Moorey1, and J. Lannett Edwards1
1. Department of Animal Science, The University of Tennessee Institute of Agriculture and AgResearch, Knoxville, TN, USA, 37996
2. Office of Innovative Technologies-Research Computing Support, The University of Tennessee, Knoxville, TN, USA, 37996
Abstract Text: Intensity of ‘estrus’ estimated by pedometers/accelerometers has been associated with higher pregnancy outcomes per AI and higher progesterone levels in dairy and Bos indicus beef cattle. Because standing to be mounted is a defining feature, study objective was to determine if a relationship exists between standing estrus intensity at fixed-time artificial insemination (FTAI) and D11 progesterone levels. Data are from a multiyear study conducted at three locations where suckled Bos taurus beef cows (n=1,481) were administered GnRH, and a controlled internal drug release (CIDR) device (1.38 mg progesterone) was inserted intravaginally. Seven days later, CIDR was removed (CIDRout), cows were administered prostaglandin F2α (PGF2α), and an Estrotect breeding indicator was affixed to tailhead and remained in place until FTAI (~53-63 h after PGF2α). Standing estrus intensity score (EPS) was based on amount of breeding indicator rubbed off (EPS 1-none of indicator rubbed off; EPS 2 ~25% rubbed off; EPS 3 ~50-75% rubbed off; EPS 4 majority/all rubbed off; EPS 0-indicator missing). Cows were administered GnRH at FTAI. Blood samples were collected at CIDRout, FTAI, and 11 days after FTAI. Hierarchical linear regression was performed using a forward stepwise approach (SAS 9.4). Toward a best fit model, cow, follicle, hormone, and other independent variables were utilized as covariates; final model included EPS and significant covariates (P<0.05). Factors associated with D11 progesterone (R2=0.25) included EPS, pregnancy status, ovulatory follicle size, change in ovulatory follicle size (CIDRout to FTAI), estradiol at FTAI, change in progesterone (CIDRout to FTAI), cow weight and age. Specific to standing estrus, D11 progesterone increased as intensity increased (3.1a, 3.4a, 3.9b, 4.6c and 4.5c ng/mL for EPS 1, 2, 3, 4 and 0, respectively; SEM=0.2; P< 0.0001). Cows determined pregnant (~34 days after FTAI) had higher D11 progesterone (3.7 vs 4.1 ng/mL; SEM=0.1; P=0.0003). Day 11 progesterone was interactively influenced by EPS and pregnancy status (P< 0.002). Specific for cows not engaging in standing estrus (EPS-1), D11 progesterone was higher in pregnant cows (2.7 vs 3.5 ng/mL; SEM=0.2). In contrast, D11 progesterone in cows engaging at the highest intensity of standing estrus was similar in pregnant and nonpregnant animals (4.6 vs 4.6 for EPS-4 and 4.3 vs 4.6 for EPS-0, respectively; SEM=0.2). Day 11 progesterone was positively related to ovulatory follicle size (P< 0.0001) and serum estradiol (P< 0.003) at FTAI. Per each unit increase, D11 progesterone increased by 0.2 and 0.02, respectively. Change in ovulatory follicle size (P< 0.04) and progesterone concentration (P< 0.0001) from CIDRout to FTAI also influenced D11 progesterone. Cow weight (P< 0.0002) and age (P< 0.003) were negatively related to D11 progesterone. Per each unit increase in age and weight (kg), D11 progesterone decreased by 0.06 and 0.001, respectively. In summary, D11 progesterone was positively related to standing estrus intensity (EPS) at FTAI and was influenced by pregnancy status. The size of the ovulatory follicle and estradiol concentrations at FTAI were other factors that positively impacted D11 progesterone. Whether relatedness of standing estrus intensity at FTAI with D11 progesterone reflects direct or indirect effects on periovulatory follicle components or simply reflects differences in timing of ovulation provides the basis of ongoing and future efforts. This research was supported by Agriculture and Food Research Initiative Competitive Grant no. 2022-67015-36374-USDA National Institute of Food and Agriculture, USDA Multistate NE2227, UT Institute of Agriculture-Animal Science Department.