Effect of grain sorghum particle size and digest “M” enzyme treatment on performance of growing steers

A 73-day growing study utilizing 203 crossbred steers (681 lb) and a digestion trial examined the effect o f sorghum grain particle size on rumen fermentation, ration digestibility, and performance of growing steers fed 37% grain and 63% ground alfalfa. Dry-rolled grain sorghum p article sizes in both trials were about 2000, 1500, and 1000 microns, for the coarse(CR), medium(MR), and fine-rolled (FR) treatments , respectively. Coarsely rolled corn (2000 microns) was included as a positive control. In the growing study, half of sorghum was treated at feeding time with an enzyme product, Digest "M". The rations were 35 to 37% dry grain plus ground alfalfa hay and supplement. Total ration dry matter, neutral detergent fiber, and starch digestibilities increased linearly (P<.02) with decreasing sorghum grain particle size. Rumen pH, ammonia and total volatile fatty acid concentrations, and acetate-to-propionate ratio were unaffected by grain type or particle size. Dry matter intake was not influenced by grain types or particle size. Steers fed FR sorghum gained 9% faster (P<.03) during the first 28 days and tended to gain faster (5%, P<.14 ) over the entire trial than those fed CR sorghum , with gains on MR sorghum being intermediate. FR sorghum produced 6% more efficient gains (P<.07) than CR, and MR grain was intermediate. Digest "M" enzyme treatment of the sorghum grain had no influence. Feed con versions of CR, MR, and FR sorghum were 93, 94, and 99% of corn. This research indicates that grain sorghum in high roughage backgrounding programs should have a maximum average particle size of 1000 microns.

Appreciation is expressed to the Kansas Grain Sorghum Commission for partial funding 1 of this research and to Loveland Industries, Loveland, CO for the Digest "M" used in this study.

Summary
A 73-day growing study u t ilizing 203 crossbred steers (681 lb) and a digestion trial examined the effect o f sorghum grain particle size on rumen fermentation, ration digestibility, and performanc e of growing steers fed 37% grain and 63% ground alfalfa.Dry-rolled grain sorghum p article sizes in both trials were about 2000, 1500, and 1000 microns, for the coarse-(CR), medium-(MR), and fine-rolled (FR) treatments , respectively.Coarsely rolled corn (2000 microns) was included as a positive control.In the growing study, half of sorghum was treated at feeding time with an enzyme prod uct, Digest "M".The rations were 35 to 37% dry grain plus ground alfalfa hay and supplement.
Total ration dry matter, neutral detergent fiber, and starch diges t ibilities increased linearly (P<.02) with decreasing sorghum grain particle size.Rumen pH, ammonia and total volatile fatty acid concentratio ns, and acetate-to-propionate ratio were unaffected by gr a in type or particle size.Dry matter intake was not influenced by grain types or particle size.Steers fed FR sorghu m gained 9% faster (P<.03) during the first 28 days and tended to gain faster (5%, P<.14 ) over the entire trial than those fed CR sorghum , with gains on MR sorghum being intermediate.FR sorghum produced 6% more efficien t gains (P<.07) than CR, and MR grain was intermediate.Digest "M" enzyme treatment of the sorghum grain had no influence.Feed con versions of CR, MR, and FR sorghum were 93, 94, and 99% of corn.This research indicate s that grain sorghum in high roughage backgroundin g programs should have a maximum average particle size of 1000 microns.

Introduction
Grain sorghum is used widely for growing cattle and normally is dry-processed by either roller or hammer mill.Samples c ollected across Kansas indicate that particl e size is often coarse.Although the effect o f sorghum particle size has been studied in finishing rations, it has not been studied in higher roughage, growing rations.We investigated the influence of grain particle size on growing cattle performance and ration digestibilit y and also evaluated the effect of Digest "M" , an enzyme product that has shown potential to improve sorghum digestibility.

Experimental Procedures
Digestion Trial.Sixteen ruminally fistulated steers (944 lb) were assigned randomly to four treatments : 1) dry-rolled corn (CO) with an average particle size of 2172 microns as a positive control, and 2) fine-rolled (FR, 1040 microns) , 3) medium-rolled (MR, 1371 microns), and 4) coarse-rolled ( CR, 2008 microns) grain sorghum.These particle sizes were selected to cover the spectrum of grain particle sizes typically observed in cattle rations.Feedstuff composition is shown in Table 1.Diets consisted of 37% of the respective grain and 63% ground alfalfa.Steers were housed in an individual tie stall barn, with free access to water and a trace mineral salt block.Steers were fed once daily at 7 AM with dry matter intake limited to 2.25% of body weight.They were adapt-ed to rations for 11 d ays.On day 12, ruminal fluid sampl es were taken at feeding and at 3, 6, 9, and 12 hours postfeeding.Begin n ing on day 13, feed samples were taken daily.Any feed refused was weighed back and sampled.On day 14, steers were fitted with fecal bags for total fecal collection to measure digestibility.Fecal samples were taken twice daily for 7 consecutive days.Growing Steer Trial.Two hundred and three thin, short yearling, crossbred steers (681 lb) were weighed unshrunk on 2 consecutive days, blocke d by breed type, and assigned randomly by weight to the same grain treatments described for the digestion tri a l, except that one-half of each sorghum particl e size treatment was treated with Digest "M".This d e sign resulted in seven treatments with five pens per treatment and five to six head per pen.Pens were roofed partially and had concrete floors.Digest "M" application followed manufacturer's recommendations, including the addition of 5% water to the grain.Steers wer e fed a totally mixed ration (Table 1) once daily.The exper i ment started on February 27, 1996, and steers were weighed every 28 days.On days 73 and 74, the steers were weighed off-test, with the average serving as the final unshrunk weight.

Results and Discussion
Sorghu m particle size did not influence rumen fermentation (Table 2).Corn produced a rumen fermentation profil e similar to that with grain sorghum, except f or a higher (P<.10) concentratio n of valerate than the FR and MR sorghum treatments.Ration starch and NDF digestibilitie s (Table 2) increased linearly (P<.02 ) with decreasing sorghum particle size, and dry matter digestibility increased linearly (P<.01 ) as a direct result of the increased digestibility of starch and fiber.
Becaus e no interactions occurred between effects of grain particle size and enzyme treatment on steer performance, both were pooled (Table 3).Feed intake was not affected by grain type or particle size.Steers on FR sorghum g ained (9%) faster (P<.03) than those on CR sorghum during the first 28 days; with gains on MR sorghum being intermediate .Feed conversions were 10 and 4% better for FR and MR than CR sorghum (P<.01 and P<.06, respectively) during the first 28 days, and the FR treatment was 6% more efficient (P<.07) than CR sorghum during the entire 73-day trial.Steers carried considerable mud and fecal matter during the middle of the trial, which affected the apparent gains toward the end.Digest "M" had no effect on intake or performance (Table 4).Decreasin g grain sorghum particle size in high roughage, growing rations increased total ration star ch, NDF, and dry matter digestibility, which improved feed conversion.In fact, the fine-rolle d grain sorghum produced feed efficiencie s equal to those with dry-rolled corn.These results indicate that producers should strive to process grain sorghum to a maximum, average, particle size of about 1000 microns.

Table 1 . Composition of Diets and Feedstuffs Used in the Digestion and Steer Growing Trials
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Table 3 . Effect of Grain Sorghum Particle Size on Dry Matter Intake, Average Daily Gain, and Feed Efficiency of Growing Steers
Grain particle sizes were: corn , coarse = 2235 microns; sorghum, coarse = 1956 microns, medium 1 = 1514 microns, and fine = 1077 microns.Means in same row not sharing the same superscript differ (P<.03).
ab Means in same row not sharing the same superscript differ (P<.07).cd