In vitro and nylon-bag digestibilities of reindeer and caribou forages.

Two microdigestion techniques for estimating dry matter digestibility were compared for 31 plant species consumed by reindeer and caribou (Rangifer tarandus). To estimate in vivo digestibility and obtain rumen liquor for a 2-stage estimate of digestibility in vitro, 2 reindeer were fed a diet containing 67% lichens (5 species), 25% bromegrass (Bromus spp.), and 8% cured sedge (Carex aquatilis), and were fitted with rumen fistulae for the insertion of nylon bags containing vegetation samples. For 2 of 3 mosses and 7 of 8 graminoid species tested, dry matter digestibility was 1-16% higher with the in vitro than with the nylon-bag system. The digestibility estimates for the 12 lichen species were highly variable and were 2-53% higher in nylon bags than in vitro. The digestibilities of 6 shrub species were 26-46% higher in nylon bags than in vitro. For both microdigestion systems, digestibility of heterogeneous diet could be estimated from the sum of digestibilities of individual components. When liquor was obtained from a relevant dietary source, the estimated digestibility by the usual in vitro method could be used to rank the in vivo DMD of mosses and graminoid species. Reasons for differences between in vitro DMD values are discussed. Comparison of in vitro and nylon-bag estimates of digestibility can be used to screen forages for digestive inhibitors. J. WILDL. MANAGE. 44(3):613-622 Reindeer (R. t. sibericus) and barrenground caribou (R. t. groenlandicus) inhabit tundra ranges and usually consume a highly heterogeneous diet. In summer, grasses, sedges, lichens, fungi, and shrubs, including leaves of willows (Salix spp.) and birches (Betula spp.), are important dietary constituents (Murie 1935, Banfield 1954, Bergerud and Russell 1964, Skoog 1968, Klein 1970, Gaare and Skogland 1975, White et al. 1975). The winter diet consists of up to 50% perennial plants and shrubs, but generally lichens are dominant (Kelsall 1968, Gaare and Skogland 1975). Limited data are available concerning the nutritional value of these forage species in North America. G. H. Kennedy and H. W. Titus (unpubl. rep. ca. 1932) and Palmer (1944) studied in vivo digestibilities of various lichen mixtures. Nordfeldt et al. (1961), den Braver (1969, unpubl. manuscr. 1974), Jacobsen and Skjenneberg (1975), plus a review by Presthegge (1954) reported digestibilities of a number of forage species used by reindeer in Scandinavia, and Aksenova (1937) reported on forage digestion in Siberia. Courtright (1959) summarized earlier work on chemical composition of many summer forages, as well as several lichens, and Scotter (1965, 1972) and Pegau (1968) studied the chemical composition of plant species important to reindeer and caribou. Digestibility per se, however, has not been reported for summer forages or for individual lichen species in North America. This study reports on estimating digestibility of dietary components by using 2 microtechniques: the in vitro digestibility technique was compared with the "nylon-bag" technique in which plant samples are suspended in nylon 1This work was supported by the U.S. Atomic Energy Commission Contract AT(45-1)-2229. Additional support was Grant GB-29342 under auspices of the U.S. Tundra Biome Program from the Office of Polar Programs and the International Biology Program of the National Science Foundation. 2 Present address: Department of Biology, Lake Superior State College, Sault Ste. Marie, MI 49783. J. Wildl. Manage. 44(3):1980 613 This content downloaded from 157.55.39.37 on Thu, 28 Apr 2016 05:36:21 UTC All use subject to http://about.jstor.org/terms 614 DIGESTIBILITY OF RANGIFER FORAGES * Person et al. bags within the rumen. In vitro and nylon-bag estimates of digestibility were made with a number of shrubs, grasses, sedges, mosses, and lichens that are consumed by reindeer and caribou. MATERIALS AND METHODS Animals and Feeding Regimes.-The 2 adult reindeer used were a rumen-fistulated bull (No. 2) and cow (No. 9). To provide as diversified a rumen microflora and fauna as possible, the diet was gradually changed over 2 weeks from a Cattle Starter #1 (PCS, Ralston Purina Co.) to a "mixed reindeer feed" (MRDF) diet that contained 67% lichens (25-30% [dry weight] Cladonia alpestris, 45-55% C. arbuscula, 15-20% C. rangiferina, 3% Cetraria spp., 1% Stereocaulon spp., and 1% unidentified), 25% bromegrass, and 8% sedge. All components were air dried, ground in a hammer mill, thoroughly mixed, and stored at 0 C until fed to the reindeer. After this 2-week period, the reindeer were fed MRDF ad libitum for 2 weeks prior to the 1st experiment. Both animals were maintained at 5 C at ambient photoperiod during April-March. Forages.-All plant samples except 5 lichens were collected near Nome, Alaska, in September 1972. Three lichen species were collected on the Kenai Peninsula and 2 others were collected near Cantwell, Alaska. All samples were ground through a 20-mesh screen in a Wiley Mill before testing. A mixture of several species, called the standard reindeer forage (SRF), was used in all trials to indicate between-animal and between-day variation. The SRF was composed of 40% (dry weight) lichens (20% Stereocaulon alpinum, 10% Cetraria islandica, 10% Cladonia arbuscula), 20% grass (Festuca altaica), 15% cottongrass (Eriophorum vaginatum), 10% sedge, 10% shrub (Salix pulchra), and 5% moss (Sphagnum magellanicum). In Vitro Digestibility.--This was determined using the method of Tilley and Terry (1963) as modified by Person (1975) and Person et al. (1975). Briefly, the determination consisted of a 48-hour incubation in rumen liquor and "artificial saliva" buffer (McDougall 1948). Care was taken to keep the liquor anaerobic and minimize dry matter content by straining through a nylon hose. After the 48-hour incubation the entire solution was frozen and stored. When convenient, the solution was thawed and centrifuged. The supernatant fluid was then decanted and the sediment was incubated for 48 hours with an HCl-pepsin solution. The solution was then filtered, washed, and the undigested particles were dried and weighed to determine dry matter digestibility (DMD). Nylon-Bag Digestibility.--This was obtained using modifications of the technique described by Van Keuren and Heinemann (1962) and Pegau and Bos (1972). Approximately 1 g of forage was sealed into each tared 3 x 7-cm bag of parachute nylon. Twenty-two to 27 bags were then connected to a piece of perforated flexible plastic tubing and placed into the rumen through a 2.5-cm cannula. Several bags contained steel ball bearings to prevent the bags in each group from floating to the top of the rumen contents. After 48 hours in the rumen, the bags were removed, washed to remove particles clinging to the outside, dried at 100 C, and weighed. DMD was calculated as change in dry weight of the contents of the bag.