Using Metabolomics to Understand Selective Breeding of Goats that Enables Tolerance of Plant Secondary Compounds
Authors: Tolleson Douglas R. , Campbell Erika S. , Welsh Thomas H. 
Published: May 2024

The objective of this study was to determine aspects of liver function in goats with a divergent propensity to consume juniper ( Juniperus spp.), a terpene -containing woody plant. Goats represent a significant contribution to sustainable food production and local economies worldwide. Climate change in arid and semiarid regions has led to a transition of grasslands to woodlands. Goats ( Capra hircus) are adapted to utilize woody plants as a food source; however, herbivory can be limited by plant secondary compounds (e.g., monoterpenes). Estimated breeding values (EBV) have been determined for domestic goats based on their propensity to consume above (H: EBV = 13.1 ± 0.2) or below (L: EBV = −14.8 ± 0.5) the herd average for proportion of juniper in the diet of free-ranging animals. To investigate the physiological and metabolic mechanisms enabling increased intake and tolerance of juniper, H and L adult male Spanish goats within young (2-yr-old) and old (3-5-yr-old) groups that spent their life grazing pastures containing juniper were randomly selected from our research herd. Twenty goats (n = 5 of each age and juniper consumption combination) were weighed and harvested. Serum samples and multiple organs (i.e., liver, kidney, heart, spleen, adrenal, testis) were collected, weighed, and preserved for analyses. With an initial focus on the liver, samples (200 mg) were submitted to Metabolon, Inc. (Morrisville, NC) to identify metabolites by ultra-high-performance liquid chromatography/tandem high resolution/accurate mass spectrometry chromatography methods. Data were analyzed using the PROC MIXED procedure of Statistical Analysis System (SAS Institute Inc., Cary, NC). Goat body weight (BW), relative organ weight (g/kg BW), and serum constituents were analyzed using a model that included age (O, Y), treatment (H, L), and the age x treatment interaction. Animals were the experimental unit and error degrees of freedom = 16. Statistical significance was determined at P ≤ 0.05. Multiple differences in metabolites of the lipid and protein pathways were identified. For example, the relative intensity of 19 monoacylglycerol metabolites was greater (P < 0.05) in H than L goats. This report, however, focuses on the gamma-glutamyl amino acid (GGAA) pathway due to its role in diagnosis of liver dysfunction. Relative liver weight (g/kg BW) was numerically greater (P = 0.15) in H (15.80 ± 0.75) than L (14.58 ± 0.39) goats. Serum gamma glutamyl transferase (U/L) was within the clinically normal range but was greater (P < 0.0001) in H (59.2 ± 2.1) versus L (44.3 ± 2.2), and in Y (55.3 ± 2.9) versus O (48.2 ± 3.2) goats. Of the 18 GGAAs identified from the GGAA super- and sub-pathways, the relative intensities of 11 metabolites were greater (P < 0.05) in liver from H than L; 8 were greater in HY versus LY, and only 2 were greater in OH versus OL goats. The increased expression of serum and liver components of the GGAA pathway for the goats with a positive estimated breeding value for juniper consumption may be indicative of metabolic mechanisms and biomarkers associated with increased tolerance of plant secondary compounds. Texas A&M AgriLife Research. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.