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Eleven papers were compared for absorption of whey and for digestibility in vitro. Papers were squared, ground, and soaked in whey for 1,5, and 15 min and for 1, 6, 24, 48, and 72 h. Digestibility in vitro was determined on minimum and maximum whey absorption of each squared and ground paper sample. Whey absorption by squared papers increased with time. Ground samples absorbed more whey than squared ones and maximum quantities were absorbed within 1 to 5 min. Mean percent absorptions for ground telephone book covers, glossy magazines, computer cards, computer printout sheets, daily newsprint, telephone directory yellow pages, cardboard box, feedsacks, brown bags, telephone directory white pages, and coasters were: 31.0, 35.2, 35.4, 36.5, 43.9, 47.9, 51.0, 51.4, 51.7, 55.6, and 67.4. For seven papers, addition of whey increased digestibility. Four papers were either unchanged or decreased in digestibility. This depression of digestibility may have resulted from the high fat content of whey used. Based on in vitro digestibilities, we conclude that it is possible to recycle selected paper/whey combinations through ruminants.

In vitro dry matter disappearances were determined for 11 paper sources and three complete rations containing 0, 10, and 20% newsprint. Inoculum was from an alfalfa hay-fed steer. Alfalfa hay, brome hay, and Solka Floc were reference substrates. Brown wrapping paper and brown cardboard had the highest dry matter disappearances of 90.8 and 77.8%; whereas four glossy or slick magazine papers had significantly lower values of 46.1, 45.1, 41.3, and 41.0%. Newsprint with black ink, without ink, and with colored inks had dry matter disappearances of 33.2, 32.6, and 26.5%, which were significantly lower than those of the glossy magazine papers. Lowest dry matter disappearances of 24.0 and 20.1% were from two magazine papers. The complete rations had 77.9, 80.1, and 81.8% dry matter disappearances for the 0, 10 and 20% paper rations. These data indicate substantial differences in digestibilities of various paper sources.