Submitted to: Journal of Chemical Ecology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/15/2001
Publication Date: 11/1/2001
Citation: ESTELL, R.E., TELLEZ, M.R., FREDRICKSON, E.L., ANDERSON, D.M., HAVSTAD, K.M., REMMENGA, M.D. EXTRACTS OF FLOURENSIA CERNUA REDUCE CONSUMPTION OF ALFALFA PELLETS BY SHEEP. JOURNAL OF CHEMICAL ECOLOGY. 2001. V. 27(11). P. 2275-2285. Interpretive Summary: Shrubs are increasing on arid grasslands at an alarming rate. These shrubs generally contain chemicals that render them unpalatable for livestock and wildlife. We are studying the role of plant chemicals in regulating shrub consumption by livestock. Previously we found that for tarbush, the amount of leaves eaten by livestock varied greatly among plants, and that chemicals on the leaf surface caused some of this variation. The present study was conducted to learn more about the compounds the deter consumption by livestock and how to isolate these chemicals. Chemicals were extracted from tarbush with three organic solvents (hexanes, ether, and ethanol) . Extracts were applied to alfalfa pellets and intake by lambs was compared to intake when no extracts were applied. When treatments were applied at the same ratio as that found in live plants, all three extracts reduced intake of alfalfa by nearly one-half. However, all treatments reduced intake to the same extent. Another experiment was conducted with the same extracts at a 10-fold dilution in an attempt to determine which extract was most potent for decreasing intake. However, none of the treatments reduced intake compared to untreated alfalfa pellets in that study. Because different extracts contain chemicals with different properties, yet all reduced intake in the first study, several compounds are probably responsible for the low palatability of tarbush for livestock. Systematic evaluation of extracts that alter shrub intake by livestock will help us identify specific chemicals responsible for deterrence and may ultimately help us find ways to alter the amount of a particular plant species eaten by livestock.
Technical Abstract: Effects of 3 extracts (hexanes, ether and ethanol) from tarbush on intake of alfalfa pellets by lambs were examined in 2 experiments. Forty-five ewe lambs were fed 1 of 5 treatments for 5 days. Treatments were alfalfa pellets (CON) or alfalfa pellets plus ethanol carrier (CAR), hexanes extract (HEX), ether extract (ETH), or ethanol extract (ETOH). Extracts were applied to alfalfa pellets at the same concentration as in an equivalent amount of tarbush in experiment 1 and at 10-fold dilutions of that concentration in experiment 2. Treatments were isolated from 36 kg of tarbush leaves using a sequential extraction with hexanes, diethyl ether and 100% ethanol. Extracts were obtained in batches (3 kg of leaves in 7 liters of solvent) with constant mixing (22 hr per solvent), filtered, solvents removed using a rotary evaporator and residue resuspended in ethanol. Lambs received 640 g of alfalfa pellets each morning and intake was monitored during a 20-min interval. In experiment 1, mean intake by lambs during the 20-min interval was 361, 393, 204, 212 and 228 g for CON, CAR, HEX, ETH and ETOH, respectively (SEM= 28.9). All 3 extracts decreased intake (P<.0001) compared to CON or CAR. Intake did not differ among the 3 extracts (HEX, ETH and ETOH) nor between the 2 controls (CON and CAR). Mean intake did not differ among treatments in experiment 2 (468, 455, 389, 381 and 431 g for CON, CAR, HEX, ETH and ETOH, respectively; SEM=30.5; P=.187). Because all 3 extracts decreased intake of alfalfa pellets at concentrations normally encountered in intact plants, several compounds are probably responsible for the low palatability and differential use of tarbush typically exhibited by livestock.