THE INFLUENCE OF CORN SILAGE HYBRID VARIETY ON BEEF STEER GROWTH PERFORMANCE P.L. McEwen 1 and J.G. Buchanan-Smith 2 1 Animal and Poultry Science Department, Ridgetown College of Agricultural Technology 2 Department of Animal and Poultry Science, University of Guelph Summary Three corn hybrids ( 3427, 3477 and 3777) were planted to evaluate the effects of hybrid and their chemical analysis on beef steer performance. Each variety was harvested at a similar maturity and moisture level. They were then fed to a group of one hundred and eight steers (42 Holstein and 66 Limousin crossbred animals) over an eighty four day period. Three diets were formulated with one silage variety used as the sole roughage source per diet. Therefore the primary difference between the three rations was the corn silage variety used per diet. Mineral, vitamin and ionophore fortifications were comparable for each ration. Calves within breed were randomly assigned to ration, pen and implant treatment. They were then fed to appetite, twice daily, for the duration of the trial. Corn silage variety, breed and implant treatment were found to significantly influence the dependent variable, weight gain per day. hybrids 3427 and 3477 produced comparable steer growth rates while animals fed 3777 grew at a slower rate. Feed efficiency and backfat measurements also favoured the 3427 and 3477 varieties. Limousin crossbred steers had an 8.4 percent advantage in growth rate. Conversely, dry matter intakes were 9.93 percent greater for the Holstein animals. Therefore the Limousin crossbreds were more feed efficient (16.7 percent advantage) due to a lower dry matter intake but higher average growth rate. Ribeye areas and backfat thicknesses were also greater for the Limousin group. Introduction Historically corn hybrids have generally been selected on their grain and dry matter yield capabilities. However there is evidence that corn hybrids can also differ in their whole plant digestibilities. Presently in vitro and chemical techniques are being used to determine various quality parameters (dry matter digestibility and NDF values). Higher animal growth rates should be achieved as the contents of the plant become more digestible. Forage NDF values are commonly used to predict dry matter intake levels. Therefore they will also influence the animal's performance in conjunction with the energy level of the corn silage. At the present time there is also a renewed interest in feeding Holstein steers for beef in Ontario. The relatively high price for beef replacement cattle and their availability has tended to increase the interest in Holstein steer information and research. With an Ontario Holstein cow population of approximately 400,000 head the use of Holsteins as feedlot animals may become more common in the future. Therefore the objectives for the trial were to (1) determine if differences in whole plant energy and digestibility estimates would influence beef steer performance in a high corn silage feeding program and (2) to compare the performance of Holstein and Limousin crossbred steers on a high roughage diet. Materials and Methods Three corn hybrids were planted ( 3427, 3477 and 3777) to evaluate the effects of hybrid and their chemical analysis on steer performance. Each silage variety was planted in two locations. The first location contained 4.2 acres of each hybrid with 1.8 acres of each variety planted in the second area. Field conditions were comparable for each variety. The hybrids were randomly assigned to locations within the fields at 30,200 seeds per acre. Varieties within field were planted on the same day. The two fields were planted eight days apart, however. Before harvesting each silage the number of plants found in 50 foot lengths was counted per variety. Fourteen, fifty foot lengths were counted per variety to determine the number of plants per hectare. Ten plants per site were then randomly removed and weighed. Each bundle was weighed to determine an estimated yield per hectare. Stalk weights and moistures were then determined after the cobs were removed. Twenty ears per variety were also dried in a forced air oven over a forty eight hour period. Cob and stalk dry matter
percentages were then recorded for later use. One hundred and eight steers (42 Holstein and 66 Limousin crossbred animals) were purchased for the feeding period. The Holstein calves were purchased approximately five months before the arrival of the Limousin animals. The Limousin crossbred steers were purchased 35 days before the start of the official feeding period. After arrival a standard vaccination and medication program was administered to each calf. During the first two weeks, both breed groups received a high roughage feedlot starter diet. The Holstein calves were then switched to a high corn silage grower diet for a four month period. They were then introduced to the experimental diets over a seven day period after the Limousin crossbred steers arrived. The crossbred cattle were more gradually introduced to their respective diets over a three week period. Three diets were formulated for the eighty four day feeding period. One silage variety was used as the sole roughage source per ration. Therefore the primary difference between the three diets was the corn silage variety used per diet. The diet formulation is outlined in table one. Table 1 Ingredient Inclusion Rates For The Diets (dry matter basis) Corn silage 84.8 Soybean Meal (48) 11.4 Calcium Phosphate 0.2 Limestone 0.6 Trace Mineralized Salt 0.5 Premix 2.5 Total 100 ** 13 crude protein, 0.5 Calcium and 0.3 Phosphorus on a dry matter basis. The premix for each diet contained dried corn (96 percent), vitamin\mineral premix (2.907 percent) and Monensin (1.112 percent). The two breed groups were randomly assigned to their respective pens. Therefore each pen contained either six Holstein or six Limousin crossbred calves. Calves within breed were also assigned to an implant and diet at random. The animals were then arbitrarily assigned to their individual Calan feeders. They were then weighed onto the trial after a 24 hour fasting period. On the first day of the experiment, the cattle were implanted with either Ralgro, Synovex-S or they were not implanted for the control group. Therefore there were eighteen different treatment combinations (2 breeds x 3 corn varieties x 3 implant treatments) represented. The calves were fed to appetite twice daily for the duration of the trial. The amount of feed offered to each calf at each feeding was automatically recorded. Feed refusals or weighbacks were recorded weekly. The steers were weighed every 14 days to assess total liveweight gain for later calculations of average daily gain. Ultrasound determinations of backfat and longissimus muscle area were also taken two weeks before the completion of the feeding period. The two measurements were taken between the 12th and 13th ribs. The steers were then weighed off the eighty four day feeding period after a 24 hour fast. One silage sample per variety was taken daily. The samples were then packaged and frozen. Two weekly composite samples were then taken per variety, one was delivered to the University of Guelph for chemical analysis while the second sample was submitted to the Agricultural and Food Laboratory Services branch for percent dry matter determination. Therefore, when needed rations were adjusted weekly to reflect silage moisture changes. Covariables were included in each final analysis if they were found to influence the dependent variable. Interaction terms were included in the initial analysis but they were routinely eliminated from the models due to their nonsignificant effects on the dependent variables of interest. Results and Discussion Unfortunately one crossbred steer was lost during the feeding period. Therefore his initial measurements were eliminated from the data set. The average starting weight for the trial animals was determined to be 270.04 kilograms. The Holstein steers were 35.96 kilograms heavier than their Limousin crossbred counterparts. Corn hybrid variety, breed and implant treatment were found to influence the dependent variable, weight gain per day (table 3). hybrids
3427 and 3477 produced comparable steer growth rates while animals fed 3777 grew at a slower rate. Conversely, hybrid variety was not a factor in determining the amount of dry matter consumed during the trial. Average dry matter intakes as a percentage of body weight were also similar. Therefore feed efficiency estimates (kilograms of dry matter per kilogram of gain) were lower for the 3427 and 3477 varieties. Their slightly higher starch and digestibility values coupled with lower ADF percentages (table 2) produced a cumulative effect on animal growth rate and backfat cover. Conversely, ribeye area measurements were not influenced by the energy content of the silages. Silage yields per hectare ( 3427, 3477 and 3777) were determined to be 46.85, 51.60 and 51.08 tonnes respectively. After allowing for a ten percent ensiling loss and the dry matter and feed efficiency estimates tabulated for each silage, the amount of live beef produced per hectare was noticeably greater for the 3477 variety ( 2823.6, 3348.5 and 2880.5 kilograms of weight gain). Differences in dry matter yield and the energy content of the silages were the primary reasons for this weight gain advantage. future trial endeavours will more precisely determine reasons for the above differences in steer performance. Two breed groups were also compared during the feeding period. The Limousin crossbred group had a decisive advantage in steer growth rate, feed efficiency, backfat cover and ribeye area measurements. Therefore the results will help cattle producers, project costs and returns associated with Holstein steers on a high roughage feeding program. Acknowledgements Assistance from Hybrid Seeds was very much appreciated. Work done by staff at Ridgetown College, the University of Guelph and the Agricultural Laboratory Services branch located at Ridgetown College were also very much appreciated. Breed Differences After adjusting for corn hybrid variety and implant treatment, Limousin crossbred steers had an 8.4 percent advantage in growth rate over their Holstein counterparts (table 4). Conversely average dry matter intakes for the eighty four day trial were 9.93 percent higher (727.07 versus 661.42 kilograms) for the Holstein animals. Dry matter intakes per day as a percentage of average body weight were also greater for this prominent dairy breed (11.3 percent greater). Therefore the Limousin animals were more feed efficient (16.7 percent advantage) due to a lower daily dry matter intake but higher growth rate. Both carcass measurements taken by ultrasound techniques produced breed differences. Average backfat thicknesses were 17.5 percent greater for the Limousin group. Ribeye areas were also larger after accounting for differences in initial weight. A twenty two percent advantage was observed for this important trait. Significance to the Industry The trial results indicated substantial differences in steer growth rate, feed efficiency and fat cover dependent on the corn silage variety fed. It is hoped that
Table #2 Average Analysis for Corn Silage Varieties Variety D.M. C.P. Starch A.D.F. N.D.F. Lignin D.M. Digestibility Cob DM 3427 34.26 7.82 21.11 25.47 45.43 2.95 76.73 49.42 3477 36.77 7.83 21.90 24.17 41.98 2.54 76.82 47.63 3777 34.23 7.56 18.38 28.13 47.01 3.14 75.49 43.94 Table #3 Corn Silage Variety Comparison Based on Beef Steer Performance Hybrid Variety Number Other Model Variables 3427 3477 3777 Number of Animals 35 38 34 Average Initial Weight (kgs) 266.54 273.05 270.29 Average Final Weight (kgs) 386.41 390.32 379.35 Weight Gain/Day (kgs) 1.41 a 1.39 a 1.29 b Implant Treatment Feed Intake Analysis Dry Matter Intake (kgs) Over 84 Day Period 705.10 691.70 685.79 Breed and Initial Weight Average Percent Dry Matter Intake( of Avg. Body Weight) 2.55 2.51 2.52 Breed and Initial Weight Feed Efficiency, Dry Matter Intake/Gain 6.01 a 6.01 a 6.44 b Initial Weight Carcass Measurements Backfat Thickness (mm) 2.55 a 2.68 a 2.22 b Corn Hybrid and Breed Ribeye Area (inches) 2 8.76 8.90 8.68 Breed and Initial Weight a and b LS means that do not share a common superscript differ significantly (p < 0.05) within rows.
Table #4 Breed Comparisons Based on Beef Steer Performance Breed Type Holstein Limousin Crossbred Cattle Number of Animals 42 65 Other Model Variables Average Initial Weight (kgs) 291.89 255.93 Average Final Weight (kgs) 401.57 375.21 Wt. Gain/Day (kgs) 1.31 a 1.42 b Implant Treatment Feed Intake Analysis Dry Matter Intake (kgs) Breed Over 84 Day Period 727.07 a 661.42 b and Initial Weight Average Percent Dry Matter Intake ( of Avg. Body Weight) 2.66 a 2.39 b Breed and Initial Weight Feed Efficiency, Initial Dry Matter Intake/Gain 6.63 a 5.68 b Weight Carcass Measurements Backfat Thickness (mm) 2.29 a 2.69 b Breed Ribeye Area (inches) 2 7.91 a 9.65 b Breed and Initial Weight a and b LS means that do not share a common superscript differed significantly (p < 0.05) within rows.