In Vitro and Nylon-Bag Digestibilities of Reindeer and Caribou Forages

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Abstract
Two microdigestion techniques for estimating dry matter digestibility (DMD) were compared for 31 plant species consumed by reindeer and caribou (R. 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 spp.), 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.