Effects of body condition score (BCS) on steroid-and eicosanoid-metabolizing enzyme activity in various mare tissues during winter anoestrus

Authors: OWEN, MEGAN - Mississippi State University; FERJAK, EMILY - Mississippi State University; CAVINDER, CLAY - Mississippi State University; MCCARTY, KEELEE - Mississippi State University; YANKEY, KALISHA - Mississippi State University; HART, CAITLIN - Mississippi State University; BURNETT, DERRIS - Mississippi State University; DINH, THU - Mississippi State University; LEMLEY, CALEB - Mississippi State University

Submitted to: Reproduction in Domestic Animals
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/25/2017
Publication Date: 11/8/2017
Citation: Owen, M., Ferjak, E., Cavinder, C., McCarty, K., Yankey, K., Hart, C., Burnett, D., Dinh, T., Lemley, C. 2017. Effects of body condition score (BCS) on steroid-and eicosanoid-metabolizing enzyme activity in various mare tissues during winter anoestrus. Reproduction of Domestic Animals. 53:296-303.

Interpretive Summary: Reproductive capabilities are dictated by the ability to maintain an adequate body condition, as measured by body condition scores (BCS), indicating nutritional maintenance has been met. However, excessive body condition, or amount of adipose cover, can also cause reproductive failures in various livestock species. These reproductive competencies can be heavily influenced by the production and metabolism of hormones within the body that are vital throughout the estrous cycle and gestation. Therefore, the objective of the current study was to determine the activity of steroid and eicosanoid metabolizing enzymes in horses with varying BCS. In addition, we examined tissue distribution of steroid and eicosanoid metabolizing enzymes in mares during winter anestrous. In the current work, activity of steroid and eicosanoid metabolizing enzymes does not provide an implication of BCS effects in horses. A wider range of horse BCS might provide a greater amount of diversity to detect BCS influences on hormone metabolizing enzyme activity. This is supported by the lack of differences observed in exsanguinated and eviscerated weights.

Technical Abstract: The objective of the current study was to determine the activity of steroid and eicosanoid metabolizing enzymes in horses with varying BCS. The BCS of twenty non-pregnant, anestrous mares were determined prior to euthanasia, and tissue samples were collected from the liver, kidney, adrenal gland, ovary, and endometrium. Cytochrome P450 1A (CYP1A), 2C (CYP2C), 3A (CYP3A), and uridine 5’-diphospho-glucuronosyltransferase (UGT) activities were determined using luminogenic substrates. The MIXED procedure of SAS was used to test the effect of BCS on enzyme activity and differences between tissues. Activity of CYP1A in adrenals was increased (p = .05) in BCS 5 versus BCS 4 and 6. Activity of CYP1A in liver was increased (p = .05) in BCS 4 versus BCS 5 and 6. Activity of CYP1A was 100-fold greater (p < .0001) in the liver than in the adrenal, ovary, and kidney. Activity of CYP2C was 100-fold greater (p < .0001) in the liver than in the adrenal, ovary, and endometrium. Activity of CYP3A was only detectable in the liver. Activity of UGT in the kidney was decreased (p = .02) in BCS 4 versus BCS 5 and 6. Activity of UGT was 3-fold greater (p < .0001) in the liver than in the kidney; whereas activity of UGT was 9-fold greater (p < .0001) in the kidney than in the ovary and endometrium. In general, BCS did not alter the activity of steroid and eicosanoid metabolizing enzymes in horses. However, tissue differences of these enzymes indicated abundant hepatic metabolism in horses, which is similar to other livestock species.