Effects of administering exogenous bovine somatotropin to beef heifers during the first trimester on conceptus development as well as steroid and eicosanoid-metabolizing enzymes

Authors: SANFORD, CARLA - Montana State University; OWEN, MEGAN - Texas A&M University; OOSTHUIZEN, NICOLA - Texas A&M University; FONTES, PEDRO - University Of Georgia; VONNAHME, KIMBERLY - North Dakota State University; NELSON, MEGAN - North Dakota State University; REYAZ, ARSHI - North Dakota State University; LEMLEY, CALEB - Mississippi State University; DELORENZO, NICOLAS - University Of Florida; LAMB, GRAHAM,CLIFF - Texas A&M University

Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/10/2021
Publication Date: 2/15/2021
Citation: Sanford, C.D., Owen, M.P., Oosthuizen, N., Fontes, P.L., Vonnahme, K.A., Nelson, M., Reyaz, A., Lemley, C.O., Delorenzo, N., Lamb, G. 2021. Effects of administering exogenous bovine somatotropin to beef heifers during the first trimester on conceptus development as well as steroid and eicosanoid-metabolizing enzymes. Journal of Animal Science. 99, 3, 1-7. https://doi.org/10.1093/jas/skab050.
DOI: https://doi.org/10.1093/jas/skab050

Interpretive Summary: Offspring survival and performance are major determinants of profitability in livestock production systems. Fetal programming plays a large role in both survival and future performance, as nutrient availability to the fetus during gestation has lasting impacts on offspring development. Fetal growth is supported by the placenta, which secretes hormones including placental lactogen, placental growth hormone, and growth factors that alter development. This study was designed to evaluate the administration of bovine somatotropin (bST) and its effects on fetal and placental development. In the present study, the administration of bST every other week through early gestation was successful at increasing circulating concentrations of IGF-1 in gestating beef heifers. However, no effects were detected on body weight, average daily gain, carcass quality grade, yield, or weight between BST and the CTL heifers. Likewise, the treatment failed to alter measured fetal parameters or ovarian and uteroplacental weights and therefore bST may not be a feasible option at improving fetal development in cattle.

Technical Abstract: The aim of this study was to evaluate the effect of bovine somatotropin (bST) on fetal and placental development during the first third of gestation in beef heifers. Angus heifers (n = 97) were randomly assigned to either receive a 500-mg injection of bST (BST) biweekly on days 0, 15, 29, 43, and 57 of gestation or not receive bST (CTL) throughout the experiment. Body weight (BW) was assessed on days -9, -3, 0, 15, 22, 29, 43, 50, 57, 64, and 77, while blood samples were collected on days 0, 22, 50, and64. Pregnancy status was determined via transrectal ultrasonography on days 29 and 64. A subset of pregnant heifers (BST,n = 7; CTL, n = 5) were harvested on day 84, and complete gravid reproductive tracts and liver tissue were collected for analysis. Cytochrome P450 1A (CYP1A), 2C (CYP2C), 3A (CYP3A), and uridine 5'-diphospho-glucuronosyltransferase (UGT) activities were determined. Mean change in BW and average daily gain of heifers between fixed-time artificial insemination (day 0) and day 77did not differ between treatments (P = 0.05). Mean concentrations of insulin-like growth factor 1 (IGF-1) were greater (P < 0.001)in BST (347 ± 27.7 ng/mL) compared with CTL (135 ± 32.8 ng/mL) heifers. Mean placental weight, fetal membrane weight, uterineweight, and ovarian and corpus luteum (CL) weights, as well as fetal morphometric data, did not differ (P = 0.05) between treatments. However, BST heifers had greater (P = 0.03) quantities of combined fetal fluid compared with CTL (521.6 ± 22.9 vs. 429.6 ± 27.14 g, respectively). Tendencies were observed for BST heifers to have reproductive tracts with fewer placentomes (P = 0.08) and fetuses with greater umbilical diameters (P = 0.09) compared with CTL. The activity of CYP1A did not differ (P = 0.05) within the maternal and fetal liver, caruncle, cotyledon, or CL tissue samples between treatments. Furthermore, CYP3A activity was only observed in maternal liver samples and was not different between treatments (P = 0.05). Interestingly, CYP2C activity was greater (P = 0.01) in the liver of BST vs. CTL heifers, and UGT activity was greater (P = 0.02) in the CL from BST heifers compared with CTL. In conclusion, the administration of bST during the first third of gestation increased plasma concentrations of IGF-1, which resulted in an increase in fetal fluid, decrease in placentome number, and greater umbilical diameter, but failed to alter fetal development.