Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/28/2011
Publication Date: 7/1/2011
Citation: Chavez, S.J., Huntington, G.B., Burns, J.C. 2011. Use of Plant Hydrocarbons as External Markers to Measure Voluntary Intake and Digestibility in Beef Steers. Journal of Animal Science. 139:245-251. Interpretive Summary: Dry matter intake of grazing ruminants is difficult to determine because animals select what they eat. Eating patterns can change from shifts in animal behavior and may be attributed, in part, to forage on offer. Environmental conditions can influence canopy structure and density of forage present thereby changing intake patterns and rate of passage. Various markers have been used to predict intake; however, each marker has strengths and weaknesses. Alkanes have been used as markers for sheep, goats, and cattle by evaluating the ratio of odd-chain to even-chain alkanes in the plant. Plants have higher concentrations of odd-chain alkanes, with little (but measurable) to no even chained alkanes. Alkanes can be administered into the rumen in the form of a controlled release capsule (CRC) or they can be administered via treated material, such as cellulose or a feedstuff. In the former case the manufacturer provides a release rate for the CRC. However, the CRC has some constraints with the fact that 1) the CRC cartridge remains in the animal for life, unless the animal is fistulated, and 2) release rate may not be consistent for all rations and hence rumen environments. Other methods of administering alkanes include once daily offering of pelleted material previously treated with alkanes or the use of gelatin capsules filled with alkane-treated cellulose. Also, feed components can be treated with alkanes such as cottonseed meal or milled hay in aqueous suspension of xantham gum or forage can be used that has been treated or sprayed with alkanes. Two experiments were conducted to validate analytical methods used to extract alkanes from oven-dried and freeze-dried samples and to compare measured and predicted intakes and digestibility using either CRC or alkane treated supplement in fistulated steer as well as and predicting dry matter intakes in beef steers fed mixed hays. We found that Cattle will eat alkane treated soy hulls mixed with corn within minutes after feeding. A once daily feeding of alkanes allows for a constant delivery of alkanes similar to the constant release from a CRC. Soy hulls were a good medium for providing alkanes as external markers in cattle. Further, alkanes can be analyzed in feed and feces to predict intake, digestion and diet composition in cattle when fed for 14 d with 5 d of fecal grab samples beginning on the tenth day. Fecal grab samples are easier and faster to collect and resulted in the same predicted intake compared to total fecal collection using the traditional stall intake and digestibility procedures.
Technical Abstract: Calculating dry matter intake of grazing herbivores has been an issue in determining factors such as efficiency and digestibility of forages. Two experiments were conducted using alkanes to validate analytical methods with oven-dried and freeze-dried samples, to compare and contrast measured and predicted intake and digestibility using a controlled release capsule (CRC) or supplement. In the first trial, 7 beef steers consuming either alfalfa or switchgrass hay received either a CRC or supplement in a random crossover design. Each period lasted 20 d with fecal grab samples taken the last 10 d and total fecal collection the last 5 d. In the second trial, 12 beef cattle were fed a blended switchgrass and alfalfa hay and fed a once daily alkane supplement. Fecal grab samples were collected the last 5 d over the 14 d experiment. In the first experiment, steers fed switchgrass hay ate less and digested a smaller proportion of total diet (P < 0.02) than steers fed alfalfa. There was no difference (P < 0.35) between predicted intake and measured intake. Fecal concentrations of alkanes were not affected (P < 0.13) by drying method and no difference (P <0.40) was seen between fecal grab samples and total fecal collection. Either dotriacontane (C32) or hexatriacontance (C36) can be used for predicting DMD. In the second experiment, there was no difference between measured and predicted intake (P < 0.35). There was no day effect in fecal alkane concentrations and predicted intake. There was no difference (P < 0.65) between fecal alkane concentrations when duplicate samples were analyzed. Alkanes can be used to predict intake in grazing cattle. Fecal grab samples are sufficient to reduce labor and result in adequate predicted intake.