By P.L. McEwen, Ridgetown College and J. Fregeau-Reid, Agriculture and Agri-Food Canada, Central Experimental Farm, Ottawa
At the present time there is an increased interest in feeding soft endosperm corn to grain fed veal calves. An initial trial, conducted at Ridgetown College, indicated that feed efficiency differences were possible between varieties with similar starch content. The observed difference in feed efficiency was then presumed to be due to differences in kernel structure. Unfortunately the two grain varieties fed during this preliminary study were not tested for endosperm or structural differences. A second trial was therefore needed to corroborate or disprove the initial conclusions and assumptions.
Medicating diets with an ionophore has been a standard practice in the feedlot industry for a number of years. Various feedlot trials have shown an improvement in feed utilization when diets were medicated with an ionophore. However very few comparisons have been specifically initiated for grain fed veal calves. Therefore the primary trial objective was to compare the performance of calves fed three different grain corn varieties. A second objective was to investigate the effectiveness of two ionophore treatments based on calf growth rate, feed intake and carcass merit.
Materials and Methods
Fifty-four Holstein bull calves were purchased for the experiment. They were divided into groups of six by weight and were randomly allotted to a pen and Calan feeder. Diet combinations (3 corn varieties x 3 ionophore treatments) were then randomly assigned to six Calan feeders within the barn.
Upon arrival the calves were fed a traditional heavy calf diet of whole shelled corn and supplement. The calves were then introduced to their experimental diets over a two week period. A soft endosperm (soft starch) variety (Pride 6355) was fed to one third of the calves. A second group of calves (18 calves) received a hard endosperm (hard starch) variety (Pride K407) while an intermediate variety (Pride K286) was a diet component for the remaining animals. One of three ionophore treatments was also assigned to each diet (3 ionophore treatments and 3 grain corns). One third of the calves were fed diets medicated with monensin (0.73 kg of Rumensin/tonne of supplement). A similar number were offered rations medicated with lasalocid (1.06 kg of Bovatec/tonne of supplement) while the remaining calves were fed non-medicated rations. The medicated diets were formulated to contain either monensin at 33 ppm or lasalocid sodium at 36 ppm.
Diets formulated with the soft starch variety were 76.1 percent grain corn, 22.7 percent commercial supplement (36% crude protein) and 1.2 percent soybean meal pellets (as fed basis). Diets with the intermediate variety were 77.3 percent grain corn and 22.7 percent supplement. The third diet was 77.0 percent grain corn, 22.7 percent commercial supplement and 0.3 percent (48% CP) soybean meal pellets. The rations were designed to contain 15.0 percent crude protein on a dry matter basis. All calves remained on their respective diet (grain corn and ionophore treatment) until they were marketed.
During the experimental period the calves were fed twice daily. The amount of ration offered to each calf at each feeding was automatically recorded. Feed refusals or weighbacks were recorded weekly. Therefore total weekly intakes were recorded for later analysis. All animals were fed to appetite for the duration of the trial.
Complete diet samples were taken during the trial period for nutrient analyzes while supplement samples were tested for their ionophore level. Nine grain samples (3 per variety) were also sent to Agriculture and Agri-Food Canada for laboratory analyzes. Five tests per sample were then conducted in triplicate. The samples were evaluated for stress cracks, kernel density, hardness (Stenvert Hardness Test) and external hardness (TADD Test) and hard to soft endosperm ratio.
The animals were weighed on two consecutive days at the start of the feeding period. They were then weighed every fourteen days for the duration of the experiment. Ultrasound measurements for fat cover and (between the 12th and 13th ribs) longissimus muscle area were also taken at the start of the feeding period and before the calves were slaughtered. After achieving a 300 kg live weight each calf was weighed off the trial by two consecutive day weights. They were then shipped to an abattoir and slaughtered in groups (17 to 19 calves per group). A hot carcass weight was recorded on each calf after the slaughter process was completed. Two of the three groups were also graded by the Canadian Meat Grading Agency (CMGA) for carcass merit.
Results and Discussion
Covariables were included in each final model if they were found to significantly influence the dependent variable of interest (table 1 and 2). 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. Two-way interaction terms were also included in each model if they were found to significantly influence the dependent variable.
Complete ration protein (14.9 to 15.2 percent CP) and corn starch levels (76.1 to 77.1 percent) were similar for each diet. Conversely, Stenvert Hardness Tests (time to collect 17 ml of ground corn) indicated a significant increase in grind time for the 20 gram Pride K407 samples (12.5 and 12.8 versus 16.2 seconds) while the TADD tests indicated similar levels of external kernel hardness. Hard to soft starch ratios also differed for each variety (0.69, 0.94 and 1.42:1 respectively). True differences in endosperm hardness (percent hard starch – figure 1) were therefore present for comparison. The percent and severity of kernel stress cracks were also higher for the hard endosperm variety (table 1 and 2).
The calves were on trial for 65, 76 or 97 days before they were transported to an abattoir and slaughtered. Weight gains per day (table 1), feed intake and efficiency estimates were similar for each grain corn. Hot carcass weights (192.7 to 196.0 kg), dressing percentages, fat thicknesses, ribeye areas and veal carcass grades (C.B.G.A.) were also comparable. The results tend to contradict previous findings published in Beef Research Update, 1997 edition (pg. 38 to 41) where differences in calf performance were related to kernel variety. Unfortunately (kernel) endosperm and external layer hardness tests were not conducted during this experiment. Endosperm differences were assumed to be present for the two fed varieties. The present results tend to lessen the validity of this previous assumption. However, measured differences in crack kernel content (present trial) might be a contributing factor to the lack of difference in calf performance. The variety with the highest hard starch content (Pride K407) also had the highest level of stress cracks (figure 2). Conversely Pride 6355 with an elevated soft starch fraction had the lowest overall crack percentage. This observed relationship might be reducing feed intake and efficiency differences to a non-significant level. Therefore more research work is needed before precise conclusions can be made about the effects of endosperm hardness on veal calf performance.
Three ionophore treatments were also compared during the feeding period. Supplement inclusion rates were determined to be from eighty-four to one and nine percent of their prescribed levels. Average daily gains (table 2), feed intakes and carcass measurements were similar for the three treatment groups. Feed intake and efficiency results support previous veal research findings at Ridgetown College (Beef Research Update 1997, pg. 38 to 41).
Significance to the Industry
There are a number of grain corn types with different endosperm thicknesses presently on the market. To this point in time the industry has assumed that the calf can digest different corn types with similar efficiency. The present results (although preliminary) are in agreement with this hypothesis. Unfortunately the present results are not consistent with a previous research endeavor. Therefore more research work is needed before precise conclusions can be made about the effects of endosperm hardness on veal calf performance.
Partial funding of the project by the Ontario Veal Association was very much appreciated. The carcass grades provided Mr Gary Hasson from the Canadian Meat Grading Agency were also very much appreciated. I would also like to thank the technical and barn staff at Ridgetown College for their continued service.