Determining optimum flake density for feedlot heifers Determining optimum flake density for feedlot heifers

Escalating costs of natural gas and electrical utilities have greatly increased the cost of flaking grain for feedlots. Energy demand for flaking is inversely related to bulk density of flaked grain; the lighter, more highly processed flakes typically require longer steaming times and greater roll pressures, which ultimately decreases mill. Corn is most commonly flaked to a density of about 28 lb/bushel, and published research results indicate that levels less than 28 lb/bushel afford no further advantage with respect to animal performance. Little information is available concerning the relative feed value of grains flaked to heavier bulk densities. Flaking grains to heavier bulk densities could make it possible to increase mill throughput and reduce energy costs associated with flaking. In this study, our objective was to evaluate milling efficiency and cattle performance when grains were flaked to densities of 28, 32, and 36 lb/bushel.


Introduction
Escalating costs of natural gas and electrical utilities have greatly increased the cost of flaking grain for feedlots.Energy demand for flaking is inversely related to bulk density of flaked grain; the lighter, more highly processed flakes typically require longer steaming times and greater roll pressures, which ultimately decreases mill.Corn is most commonly flaked to a density of about 28 lb/bushel, and published research results indicate that levels less than 28 lb/bushel afford no further advantage with respect to animal performance.Little information is available concerning the relative feed value of grains flaked to heavier bulk densities.Flaking grains to heavier bulk densities could make it possible to increase mill throughput and reduce energy costs associated with flaking.In this study, our objective was to evaluate milling efficiency and cattle performance when grains were flaked to densities of 28, 32, and 36 lb/bushel.

Experimental Procedures
Heifers (n = 358) were allocated to 48 feedlot pens, each containing six to eight cattle.Pens were assigned to one of three treatments (16 pens per treatment), which consisted of finishing diets made from steamflaked corn processed to densities of 28, 32, or 36 lb/bushel.Cattle were fed once daily throughout the 115-day finishing trial.At the termination of the study, cattle were weighed as pens and subsequently transported to a commercial abattoir in Emporia, KS, for harvest.Information was collected for severity and incidence of liver abscesses; hot carcass weight; back fat over the 12th rib; kidney, pelvic, and heart fat percentage; yield grade; marbling score; and quality grade.
In addition to animal performance and carcass quality attributes, data also were collected to evaluate milling efficiency when corn was processed to the three different densities.Total mill throughput in tons per hour was determined for each grain, and this information was used to calculate energy expenditure associated with processing grains to different densities.Particle size was measured daily for flaked grain samples and weekly for total mixed rations using a Ro-Tap (W. S. Tyler, Mentor, OH) sieving machine equipped with a series of seven sieves with openings ranging from 9,500 to 1,180 μm.

Results and Discussion:
Starch availability ranged from a high of 47% for corn flaked to a density of 28 lb/bushel down to 35% for corn flaked to a density of 36 lb/bushel.As bulk density increased, mill throughput increased fairly dramatically.Increasing flake density also increased the average particle size of flakes and improved durability of the flaked grain throughout the mixing process, as evidenced by the decreased proportion of small particles that tend to accumulate in feed bunks.However, these improvements in flake integrity did not positively improve cattle performance.Processing corn to heavier bulk densities resulted in small decreases in gain, as well as slightly higher feed intakes.Carcass traits were mostly unaffected by degree of grain processing.Overall, efficiency tended to improve with more rigorous processing of the grain.Compared with cattle fed 28-lb flakes, feeding corn flaked to densities of 32 or 36 lb/bushel yielded gain efficiencies that were 2 to 5% poorer than those of cattle fed the 28-lb flakes.Using an estimated feed cost of $200/ton (dry basis), the poorer efficiency of under-processed flakes increased cost of production by $0.01 to $0.03 per pound of gain, equating to approximately $0.03 to $0.08 per animal daily.

Implications:
Improvements in mill efficiency that are attributable to flaking grain to heavier bulk densities do not offset increased costs associated with poorer feed conversion efficiency.

Table 2 . Influence of Bulk Density on Dry Matter and Available Starch of Flaked Grain and Mill Efficiency
Efficiency is expressed as a percentage relative to grain flaked to a density of 28 lb/bushel. 2

Table 3 . Growth Performance of Yearling Heifers Fed Finishing Diets Containing Corn Flaked to Different Densities
Statistics were performed as gain:feed, reported as feed:gain. 2

Table 5 . Particle Size Distribution, Geometric Mean Diameter, and Geometric Mean Di- ameter Standard Deviation of Steam-flaked Corn Where Flake Densities were 28, 32, or 36 lb/bushel
1 Percentage of sample remaining on screen. 2 GMD = geometric mean diameter. 3GSD = geometric standard deviation.

Table 6 . Particle Size Distribution, Geometric Mean Diameter, and Geometric Mean Di- ameter Standard Deviation of Complete Diets Where Flake Densities were 28, 32, or 36 lb/bushel
2 GMD = geometric mean diameter. 3GSD = geometric standard deviation.