Effects of processing factors on in vitro ammonia release from cooked molasses blocks containing urea

Abstract Three studies were conducted to evaluate effects of processing factors on in vitro release of ammonia by ruminal microbes from cooked molasses blocks containing urea. Blocks were manufactured in a scraped-surface, steam-jacketed cooking vessel. Molasses was poured into the vessel, and the pH was adjusted. Other ingredients then were added, and cooking was initiated. Vapors were removed with mild vacuum throughout cooking. When vessel heating was discontinued, vacuum was increased for 3 min to approximately 635 mm Hg to remove additional water. Blocks were manufactured with sugar cane molasses as a base ingredient and contained 12% urea and 6% tallow. Manufacturing factors studied included the time of urea addition (i.e. beginning or end of cooking), molasses pH, addition of reducing sugars (i.e. glucose and fructose), treatment of molasses with invertase, addition of MgO after cooking, and post-processing storage temperature. Adding urea prior to cooking reduced ammonia release from blocks compared to adding urea after cooking. Initial pH of the molasses was positively related to in vitro ammonia release over the range of 4–8. Addition of reducing sugars reduced ammonia release, whereas addition of MgO after cooking had little effect. Post-manufacturing storage temperature impacted ammonia release, but blocks held at 82 °C released more ammonia than blocks held at 66 °C. Several factors, including final block pH and concentrations of sugars and urea may be useful for predicting the availability of N from cooked molasses blocks containing urea.