Digestibility and Associative Effects of Protected Tallow

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Abstract
Two Guernsey heifers were fed 3 mixtures: corn silage and a wheat-corn-soybean concentrate at 35 or 55% dry matter or this concentrate at 35% plus a protected tallow product at 18%. Food intakes and fecal outputs were measured daily for 5-day periods and then pooled for analysis. Digestibilities were calculated for each ration and were solved by simultaneous equations. For protected tallow, digestibilities were dry matter 78%, energy 83%, fat 91%, protein 86%, N-free extract 83%, acid-detergent fiber -24%, Ca -76% and Mg -5%. Gross energy of protected tallow was calculated from analysis, 6.34 Mcal/kg and digestible energy was 5.28 Mcal/kg. The heifers were weighed at the start and finish of each period and changes in body weight were related to intakes of digestible energy above maintenance, 7.1 .+-. 3.3 Mcal digestible energy/kg change in body weight. The negative associative effects on fiber, Ca and Mg warrant further investigation because they may determine the upper limit of protected tallow in ration formulation.