THE INFLUENCE OF CORN SILAGE FEEDING LEVEL ON BEEF STEER GROWTH PERFORMANCE AND CARCASS QUALITY Summary P.L. McEwen Ridgetown College, University of Guelph Other growth rate and feed intake comparisons were similar (silages @ 34 to 35 percent DM). One hundred and seven large and medium frame steers (332.00+41 kg BW) were divided randomly into eight diet groups. One half of the steers were fed a processed silage while the remaining animals were offered a nonprocessed product. One of four silage levels (20, 40, 60 or 80 percent silage DM) were also incorporated into each diet. Rations were balanced to a 14 percent crude protein level. Mineral, vitamin and ionophore fortification levels were also similar for each diet. Individual steers were sent to an abattoir and slaughtered after a 6 mm backfat reading (ultrasound) was achieved. Silage level influenced steer growth rate and days to market. Steers fed diets with 80 percent silage grew at a slower rate and required more days to finish. Growth rates and days on feed were similar for the other three groups, however. Total dry matter intake was also greater for the high silage diet while average dry matter intakes per day were similar for each group. Feed efficiency estimates were therefore increased (kilograms DM/kg gain) for the high silage cattle. All carcass traits were similar for each silage level with the exception of marbling score. The two intermediate rations produced cattle with higher marbling scores when they were compared to the low silage-high concentrate diet. A 4.2 percent improvement in feed efficiency was noted for the processed silage fed cattle. Introduction Historically, corn silage varieties have been selected on their grain and dry matter yield capabilities. However there is evidence that corn silages can also differ in digestibility. Previous trial results at Ridgetown College (1995-7) indicated that steer growth rates could be influenced by differences in silage grain content and estimates of digestibility. The results were based on high levels of corn silage feeding (85 to 92 percent of diet dry matter).therefore the primary objective for the present trial was to compare the performance of cattle fed different levels of corn silage when the silage was known to be highly digestible. A second objective was to evaluate the effect of silage processing on cattle performance. Materials and Methods The corn hybrid, Cargill 3427, was planted to evaluate the effect of grain level and silage processing on beef steer growth performance and carcass quality. Twelve hectares of the variety were planted at 79,330 seeds per hectare. The planting was completed on the same day, in 76 centimetre rows, to minimize environmental differences. The silage was then harvested over a two day period. On the first day a self propelled harvester with a silage processor harvested every other four rows across the twelve hectare field. A similar method of harvest was employed on the next day to produce an unprocessed silage. Silage weights and dry
matter percentages were recorded on each wagon load of silage during the harvest process. The two silages were stored in four adjacent upright silos. Therefore the main difference between the two silages was due to the harvest method (processed versus unprocessed). Two steer groups were purchased for the feeding period (first group purchased in December - second group purchased in February) from an Ontario livestock sales facility. A strict health protocol was followed for each group. After arrival the cattle were weighed, divided into groups of six and assigned to their respective pens. A two week adjustment period was needed for both groups to adapt to the Calan feeding system. Eight diets (2 corn silage process types * four corn silage levels) were formulated for the feeding period. One half of the steers were fed diets containing unprocessed silage while the remaining animals were fed a processed (finer cut with cracked kernels) product. One of four silage levels was also incorporated into each diet. Each ration contained either 20, 40, 60 or 80 percent corn silage on a dry matter basis. A constant supplement (56 percent CP) inclusion rate was incorporated into each diet to ensure that ionophore (monensin @ 33 ppm) and vitamin fortifications were similar. Mineral and crude protein levels (14 percent crude protein) were also standardized across ration. Silage moisture levels were monitored on a biweekly basis. Rations were then adjusted (if needed) to reflect changes in silage dry matter content. A second group of silage and complete diet (composite) samples were also mixed biweekly for later nutrient analysis at Agri-Food Laboratories and the University of Guelph. The cattle were gradually introduced to their respective diets over a three week period and were being fed to appetite before the trial officially began. The first group began their feeding period in January while the second group was started in March (70 day difference in starting date). Each animal remained on their assigned diet for the duration of their feeding period. Steer initial weights were determined by averaging two consecutive day weights for each animal. The cattle were also implanted (both groups) at one hundred day intervals (if needed) with an estradiol implant. The amount of feed offered at each feeding was automatically recorded with feed refusals (weighbacks) recorded weekly. The cattle were weighed every 14 days during the trial to assess total weight gains. Ultrasound measurements for fat cover (between the 12th and 13th rib) were also taken to determine a market endpoint for each animal. Each steer was sent to a federally inspected abattoir (in groups) after achieving a (ultrasound) 6 mm backfat reading. This endpoint was chosen to ensure that all slaughtered cattle met the required level of fat cover for an A grade (4 mm or greater). All carcasses were federally graded. Minimum fat measurements in the last quadrant over the longissimus and ribeye area (square inches) tracings were also taken by college staff. Results and Discussion Covariables were included in each final model if they were found to significantly influence the dependent variable of interest (tables 2, 3 and 4). Significant covariables were identified and included in each final analysis to more precisely compare the diets based on animal performance, feed intake and carcass measurements. Laboratory analysis for the processed and unprocessed corn silages are summarized in table 1. As would be expected, silage analytical and yield (34.43 for processed versus 32.18 tonnes/hectare) differences were relatively small.
The average starting weight for the trial cattle was 332.00 kg (table 2). The second group was 54.82 kg heavier (304.84 versus 359.66 kg) due to a 70 day later starting date. Final weights were 45.50 kg greater for the first group however, indicating that a fat deposition advantage was present for the smaller framed cattle. Average days on feed were also less for the second group (130.06 versus 207.65 days). Silage level influenced steer growth rates and days to market. Steers fed diets with 80 percent silage grew at a slower rate and required more days to finish. Growth rates and days on feed were similar for the other three silage levels, however. Total dry matter intakes were also greater for the high silage cattle while average dry matter intakes per day were similar for each group. Feed efficiency estimates were therefore increased (kg DM/kg gain) for the high silage diet while other rations were similar in efficiency. A reduced level of available energy in the high silage diet was probably the primary reason for these observed differences. The dependent variables, hot carcass weight, dressing percent, ribeye area, and yield index were not significantly influenced by silage level. Conversely marbling scores were higher for the two intermediate diets (60 and 40 percent silage) when they were compared to the low silage - high concentrate ration. Cattle fed diets with 80 percent silage were intermediate in score. The lower marbling associated with the high concentrate diet was probably due to (cattle) genetic differences as growth rate and feed efficiency estimates were similar for the intermediate and low silage groups. The relationship between marbling score and dietary energy content appears to be low if the steers are marketed at a similar backfat thicknesses. Unfortunately the amount of silage harvested for the control (unprocessed) silage diets was insufficient for the total feeding period. Therefore cattle fed the control silage were switched (if they were still on feed) to the processed silage after a 140 or 210 day feeding period. Table 3 indicates the performance differences associated with the processed and control silages across the four silage feeding levels. A subset of the available data appears in table 4 for cattle fed diets with either 60 or 80 percent silage dry matter. A slight daily gain advantage (table 3) coupled with a small reduction in dry matter intake produced a significant 4.2% improvement in feed efficiency (6.24 versus 5.98 kg DM/kg gain) for the processed silage. Although statistically not significant, a similar advantage (processed versus unprocessed) was also observed for the high silage fed cattle (table 4). More research work is needed to substantiate the effect of silage processing at various moisture levels. Feed efficiency differences might become more pronounced as the corn stalk and kernel become more mature. Significance to the Industry The trial indicated differences in steer growth rate, feed efficiency and days to market dependent on the corn silage level fed. However differences in performance were eliminated when diets were 60 percent silage or less. The results were somewhat surprising as they generally contradict previous research findings (more concentrate = higher growth rate). A more digestible silage (low lignin + high in vitro digestibility) could be one of the plausible reasons for the above results. Future trial endeavours will help substantiate the economic importance of these initial research findings. The effect of corn silage processing on beef steer performance also requires additional investigation. The present trial indicated that a
slight improvement in feed efficiency was possible if the silage was processed. More research work is needed (processed versus unprocessed) when the silages are at a similar or higher dry matter level (more mature) to clarify the performance differences associated with silage processing. Acknowledgments During silage harvest assistance from Anton and John Noorloos was very much appreciated. The author would like to thank Gary Brien and his staff in the Ridgetown Beef Centre for their continued support. Advise and support from Dr.Jock Buchanan-Smith and Cheryl Campbell was also very much appreciated. Table 1. Average nutrient analysis for both the processed and unprocessed silage samples. Analysis Corn Silage Corn Silage (Unprocessed) (Processed) Dry Matter (%) 35.55 34.74 Crude Protein (%) 8.55 8.47 Dry Matter Digest. (%) 70.85 71.15 NDF (%) 43.04 43.89 ADF (%) 23.13 23.56 Starch (%) 27.35 27.40 Lignin (%) 1.57 1.54
Table 2. EFFECT OF CORN SILAGE LEVEL ON BEEF STEER GROWTH PERFORMANCE AND CARCASS QUALITY. Ration Type 80% Corn Silage (CS) 20% Concentrate 60% CS 40% Conc. 40% CS 60% Conc. 20% CS 80% Conc. Significant Model Variables Growth Performance Number of Calves 26 25 28 28 Ave. Initial Weight Ave. Final Weight Corrected Final Weight 318.18 333.92 335.14 339.98 597.41 594.29 587.41 596.42 605.80 590.78 588.00 589.53 initial weight and cattle group Days to Market 193.60 a 162.89 b 157.58 b 166.76 b initial weight, cattle group and ration Average Daily Gain 1.46 a 1.61 b 1.65 b 1.63 b initial weight and ration Feed Intake Measurements Total Dry Matter Intake Average Dry Matter Intake (kg) Percent Dry Matter Intake (%) Feed Efficiency DM/ kg Gain 1815.26 a 1580.45 b 1558.95 b 1535.00 b ration, cattle group and ration * group 9.75 9.87 10.19 9.72 initial weight, group and ration * group 2.08 2.15 2.21 2.11 cattle group 6.69 a 6.19 b 6.19 b 5.96 b initial weight, process type and ration Carcass Measurements Grade Fat (mm) 6.68 7.45 7.46 6.79 Hot Carcass wt. 332.73 325.23 327.98 327.31 initial weight and cattle group Dressing Percentage 56.40 55.11 55.60 56.12 Yield Group 1=Y1;2=Y2;3=Y3 1.11 1.13 1.21 1.08 Yield Index (%) 60.34 59.92 60.04 60.26 cattle group Ribeye Area inches 2 12.77 12.28 12.60 12.47 initial weight and cattle group Marbling Score 1=A; 2=AA; 3=AAA 1.79 ab 1.96 a 1.87 a 1.48 b initial weight, ration and cattle group a and b LS means within row that do not share a common superscript differ significantly (p < 0.05). - LS means without a superscript are similar within row (p < 0.05).
Table 3. Effect of corn silage processing on beef steer growth performance and carcass quality. Corn Silage (Normal Cut) CornSilage (Processed) Significant Model Variables Number of Animals 56 51 Avg. Initial Wt. (kg) 330.37 333.79 Avg. Intermediate Weight (kg) 568.75 582.76 Average Number of Days 154.25 154.96 Average Daily Gain (kg) 1.58 1.62 ration and process type * cattle group Total Dry Matter Intake (kg) 1471.21 1469.98 initial weight, group and ration * cattle group Average Dry Matter Intake (kg) 9.81 9.67 initial weight and cattle group Dry Matter Intake Percent 2.17 2.12 cattle group Feed Efficiency (DM/ kg Gain) 6.24 a 5.98 b initial weight a and,b LS means within row that do not share a common superscript differ significantly (p<0.05). - LS means without a superscript are similar within row (p.<0.05). - maximum number of days on feed was 210 days for the first group and 140 days for the second group. - diets contained either 20, 40, 60, or 80 percent corn silage.
Table 4. EFFECT OF CORN SILAGE PROCESSING ON BEEF STEER GROWTH PERFORMANCE AND CARCASS QUALITY (60 or 80% Silage DM) Corn Silage (normal cut) Corn Silage (processed) Significant Model Variables Number of Animals 28 23 Ave. Initial Weight 325.88 325.92 Ave. Intermediate Weight kg) 568.86 574.85 Ave. Number of Days 160.50 162.52 Ave. Daily Gain 1.51 1.54 initial weight and ration Total Dry Matter Intake 1508.15 1447.34 cattle group Average Dry Matter Intake (kg) 9.67 9.29 initial weight and group Dry Matter Intake Percent 2.16 2.08 cattle group Feed Efficiency (DM/ kg Gain) 6.36 6.06 cattle group and ration * process type a and b LS means within row that do not share a common superscript differ significantly (p.(0.05). - LS means without a superscript are similar within row (p < 0.05). - maximum number of days on feed was 210 days for the first group and 140 days for the second group. - diets contained either 60 or 80 percent corn silage on a dry matter basis.