Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/9/2008
Publication Date: 6/4/2008
Citation: Estell, R.E., Fredrickson, E.L., Anderson, D.M., Remmenga, M.D. 2008. Effects of cis-ß-ocimene, cis-sabinene hydrate, and monoterpene and sesquiterpene mixtures on alfalfa pellet intake by lambs. Journal of Animal Science. 86:1478-1484.
Interpretive Summary: The conversion of grasslands to shrublands in the western United States and in arid regions throughout the world is a serious concern to livestock producers and ecologists. This process of desertification not only reduces available forage for livestock and wildlife, but also leads to increased soil erosion and reduced biodiversity. These shrubs often contain chemicals that make them unpalatable to browsing animals. We have been conducting a long-term study on the impact of volatile plant chemicals such as terpenes on shrub consumption by livestock. Our previous work showed that for a common shrub in the northern Chihuahuan Desert (tarbush), animals exhibited a variable preference for different plants that was partly explained by the concentration of volatile leaf surface chemicals. In this study, we applied two chemicals and two chemical mixtures to alfalfa pellets and fed them to lambs to determine if they affected intake when applied at concentrations approximating those found in tarbush. The two individual chemicals (cis-ß-ocimene and cis-sabinene hydrate and the monoterpene mixture (borneol, camphene, camphor, 1,8-cineole, limonene, myrcene, and a-pinene) did not affect intake of alfalfa pellets by lambs, and therefore do not appear to be related to low preference for tarbush. However, the sesquiterpene mixture (ß-caryophyllene, caryophyllene oxide, a-copaene, and a-humulene) tended to decrease intake by lambs. This trend for decreased intake as concentration of the sesquiterpene mixture increased suggests sesquiterpenes may be partly involved in the avoidance of shrubs by livestock. Information about chemicals that control intake will help us identify mechanisms to alter how much of a particular plant species is eaten by livestock.
Technical Abstract: The transition of grasslands to shrub-dominated scrubland reduces livestock productivity and contributes to impoverished human conditions in arid and semiarid regions worldwide. Many shrubs increasing in dominance contain secondary compounds that deter herbivores. Knowledge concerning the effects of specific compounds on herbivore diets is limited but may provide useful insights into desertification. Flourensia cernua is a dominant shrub in the northern Chihuahuan Desert that contains an abundance of terpenes. Four experiments were conducted to determine the effects of individual terpenes (cis-ß-ocimene and cis-sabinene hydrate; Exp. 1 and 2) or mixtures of monoterpenes (borneol, camphene, camphor, 1,8-cineole, limonene, myrcene, and a-pinene; Exp. 3) or sesquiterpenes (ß-caryophyllene, caryophyllene oxide, a-copaene, and a-humulene; Exp. 4) on intake of alfalfa pellets by lambs. Forty-five lambs (9 lambs/treatment) were individually fed treated alfalfa pellets for 20 min each morning for 5 days. Five treatments (0X, .5X, 1X, 2X, and 10X; multiples of the concentrations of the same terpenes in Flourensia cernua) were applied to alfalfa pellets (637 g, DM basis) in an ethanol carrier. Experiments were preceded by a 10-d adaptation period to untreated pellets. Except during the 20-min test, lambs were maintained outdoors and fed untreated alfalfa pellets (total mean intake = 4.7% of BW, DM basis). Day × treatment interactions were detected (P < 0.04) in Exp. 1 and 4, due to greater intake for 0X than other treatments on day 1 (Exp. 1) and lower intake for the 10X treatment on day 1 and 2 (Exp. 4). A trend for decreased intake (g/kg BW) as concentration of the sesquiterpene mixture increased was observed in Exp. 3 (P = 0.093 for the linear contrast). Although there was a tendency for the sesquiterpene mixture to decrease intake, cis-ß-ocimene, cis-sabinene hydrate, and the monoterpene mixture did not appear to affect intake by lambs. Thus, sesquiterpenes may exert antiherbivory properties under certain conditions that may contribute to shrub dominance with extended periods of livestock foraging.