Two completely random digestion trials were conducted, each with 12 beef steers (325 kg initial weight), to measure changes in digestibilities of fat and of forage components when fat was added to diets containing 62 to 76% wheat straw. Trial 1 diets contained either no added fat or 6.3% added fat from whole cottonseed (30% of the diet), cottonseed oil or animal fat; diets were formulated to contain equal levels of cottonseed hulls and cottonseed meal. Trial 2 diets contained 0, 2, 4 or 8% added animal fat. In all forms and at all levels, added fat increased apparent digestibility of dietary lipid (P less than .05). However, estimated true digestibility of lipid decreased (from 94 to 71%) as added fat was increased from 0 to 8% (P less than .05). Up to 6.3% added fat increased digestible energy (DE) content of the diet. Fat additions of 2 and 4% increased daily DE intake (P less than .05) and did not depress digestibility of diet components (P greater than .05). Fat additions of 6.3% or greater, either as free fats or as whole cottonseed, reduced (P less than .05) mean acid detergent fiber digestibility from 40 to 28%. In addition to depressing fiber digestibility, 8% added fat reduced (P less than .05) digestibilities of dry matter (from 54 to 47%), organic matter (60 to 52%) and gross energy (60 to 51%). Oil fed as whole cottonseed caused digestibility depressions similar to free fat addition at the same level.(ABSTRACT TRUNCATED AT 250 WORDS)

No abstract

Monensin was fed at levels of 0 and 33 ppm in a series of digestion and metabolism trials to determine its effect on utilization of high grain diets and on ruminal parameters in yearling steers. Monensin had no effect (P greater than .05) on apparent digestibility of dry matter, gross energy or starch when fed with a 90% corn diet (10.5% crude protein, dry matter basis). Monensin in this corn-based diet tended to increase crude protein digestibility (63.4 vs 61.3%) and decrease ruminal ammonia concentration (2.5 vs 6.5 mg/100 ml) measured 3 hr postprandially (P greater than .05). In metabolism trials with a 76% sorghum grain diet (11.7% crude protein, dry matter basis), monensin improved apparent digestibility of crude protein (P less than .05) but not dry matter or gross energy (P greater than .05). Retention of nitrogen, expressed as a percentage of nitrogen intake, tended to improve (24 vs 20%) in response to monensin addition to the sorghum grain-based diet (P greater than .05); a similar trend was observed (P greater than .05) for nitrogen retention expressed as a percentage of nitrogen absorbed (41 vs 36%). Total ruminal volatile fatty acid (VFA) concentrations measured 3 hr postprandially were not altered by monensin fed with either diet. The proportion of acetic acid d-creased (P less than .05) and that of propionic acid increased (P less than .05) in response to monensin fed with the corn-based diet. Monensin did not appreciably alter proporations of VFA when fed with the sorghum grain-based diet. Results suggest that a possible improvement in N utilization may account for some of the benefits of feeding monensin with high grain diets.

No abstract

No abstract