Organ weights and metabolic indicators in male goats differing in genetic propensity to consume juniper

Our objective was to determine if there was a cost of fitness associated with selecting Spanish x Boer goats for their propensity to consume above (H) or below (L) the herd average for proportion of juniper (Juniperus spp.) in the diet. Organ weights and metabolic parameters were compared among adult male goats (young [2-year-old] and old [3–5-year-old]) that spent their life grazing pastures containing juniper at the Texas A&M AgriLife Sonora Research Station. In June 2019, body weights were recorded, and serum samples collected by jugular venipuncture from 20 animals (n = 5 of each age and juniper consumption combination) 2 days prior to harvest. At harvest, organ weights (i.e., liver, kidney, heart, spleen, adrenal, testicle, epididymis) were obtained and later analyzed as relative organ weights (organ to body weight ratio). Analysis of variance was used to determine if differences in organ weights (g/kg BW) and serum parameters were detected between young (Y) and old (O), and H and L goats. Body weights (kg) did not differ by treatment group but were greater (P < 0.03) for O (76.0 ± 3.72) than Y (66.3 ± 1.9). Total testicular, epididymal, adrenal, and heart organ weights (g/kg BW) were not affected (P > 0.10) by age nor juniper consumption group. Total kidney weight (g/kg BW) was greater (P < 0.05) in H (2.53 ± 0.09) than L (2.19 ± 0.08) and liver weight (g/kg BW) trended (P = 0.15) in the same pattern, with H (15.80 ± 0.75) greater than L (14.58 ± 0.39). All serum parameters were clinically normal. Serum urea nitrogen (mg/dL) did not differ by treatment (P > 0.1) but was greater (P < 0.004) in O (12.9 ± 1.3) than Y (8.2 ± 0.5). NEFA (mEq/L) was greater (P < 0.02) in H (0.33 ± 0.04) than L (0.26 ± 0.02), but not differ between O and Y. Total globulin (g/dL) was greater (P < 0.007) in L (4.34 ± 0.35) than H (3.40 ± 0.16), and in O (4.29 ± 0.38) than Y (3.45 ± 0.12). Gamma glutamyl transferase was elevated (P < 0.0001) in H (59.2 ± 2.1) versus L (44.3 ± 2.2), and in Y (55.3 ± 2.9) than O (48.2 ± 3.2). In summary, under adequate nutritional conditions, length of exposure (via advancing age) and preference for juniper did not incur an acute cost of fitness in goats. However, the observed metabolic and organ differences indicate that under more challenging chronic conditions (e.g., drought or disease), consumption of monoterpene-defended plants may become problematic. Research to define these eco-physiologic bounds is needed.