PERFORMANCE OF HOLSTEIN BULL CALVES FED A WHOLE CORN DIET
Forty two Holstein bull calves weighing 168.2 kg were divided randomly into two groups. The first group was fed a conventional red veal diet. The second group was fed whole roasted soybeans as a supplemental protein source. Two diets were utilized during the feeding period per group. Whole shelled corn was the major feed ingredient for all diets. Calves remained on the trial until a live weight average of 283 kg was achieved for both groups. Both groups were fed for a total of 67 days before they were sent to an abattoir and slaughtered. Hot carcass weights, backfat thicknesses, ribeye areas and meat colour grades were then taken.
Final calf weights were similar for both groups. Average weight gains per day, backfat thickness, ribeye areas, dressing percentages and lean meat colour grades were also similar. However, calves fed diets with roasted soybeans consumed 5.5 percent less dry matter per day and required approximately seven percent less dry matter per kilogram of gain. Reductions in feed intakes were found to be comparable to the higher NE gain values associated with the diets containing roasted soybeans.
Roasted soybeans have traditionally been used in a number of livestock rations as a protein and energy source. Approximately one half of the protein in roasted soybeans is degradable in the rumen while the remaining fraction is undegradable. Beef diets which contain roasted soybeans as a primary supplement are usually higher in undegradable protein than rations fortified with more soluble protein sources. Many trials have reported an improvement in animal growth rates when undegradable intake protein levels were increased due to a more efficient use of total dietary protein. Energy levels are also usually improved when soybeans are added to most rations. Therefore, the primary objective for this trial was to investigate the use of roasted soybeans as a supplemental protein and energy source for red veal calf diets.
Materials and Methods
Forty two Holstein bull calves were purchased for the trial. After arrival, a standard vaccination and medication program was administered to each calf. A health protocol was also developed and strictly followed for animals showing characteristic disease symptoms or signs.
For the first three days, all calves received a high roughage feedlot "starter" diet. Calves were also given a limited amount of hay. Each calf was then introduced to one of two diets over a ten day period. Calves were assigned to the Calan feeders and diets at random. One half of the calves received a conventional red veal diet while the remaining twenty-one calves received an experimental diet that contained roasted soybeans as the main supplemental protein source.
Whole shelled corn was the primary feed ingredient for both diets. A high quality commercial supplement (36% crude protein) was also incorporated into the control diet. The first control diet contained four parts of whole corn to one part commercial supplement. Whole roasted soybeans and a custom made eleven percent crude protein premix were added to the experimental diet. The experimental diet contained 17.5 percent roasted soybeans on an as fed basis. Both diets were 15.8 percent crude protein on a dry matter basis. Each calf remained on their first diet until the animal weighed 210 kg or greater. A second diet for each group (14.8 percent crude protein) was then introduced and fed to the calf for the remainder of the trial.
The two initial diets were very similar in mineral, vitamin and ionophore fortifications. The two final diets were also nutritionally similar. However, the experimental diets were 3.8 and 3.2 percent higher in NE gain than their control diet counterparts. They were also 3.7 and 4.4 percent higher in NE maintenance. Metabolizable protein estimates were eighteen to twenty percent higher for the rations with roasted soybean supplementation. Soluble protein levels were higher for the control diets.
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. All animals were on full-feed for the length of the trial.
Calves were weighed on two consecutive days at the start of the feeding period. They were then weighed every fourteen days for the first four weeks. Calf weights were then recorded weekly. Two consecutive day weights were also taken at the end of the feeding period before the animals were shipped to an abattoir and slaughtered. On the day after slaughter, fat cover and ribeye measurements were taken from each carcass. The measurements were taken between the tenth and eleventh ribs. A within-abattoir grade was also assigned to each carcass based on lean meat colour. A grade of one indicated a lighter meat colour while a grade of two was indicative of a darker colour.
Results and Discussion
Unfortunately, two calves died during the feeding period, one from each group. Therefore, their initial information was eliminated from the final analysis and data set. All calves were marketed together when their average weight was 286.7 kg. Final average weights were similar for both groups (Table 1). Weight gains per day, backfat thicknesses, ribeye areas, dressing percentages and lean meat colour scores were also found to be similar. Therefore, carcass quality differences were not significantly influenced by diet.
Covariables were included in each final model if they were found to influence the various dependent variables listed in Table 1. Significant covariables were identified and included in each final analysis to more precisely compare the two diet types based on animal performance or feed intake measurements.
Differences in feed intake measurements were found to exist between the two diet groups. Average dry matter intakes per day were 5.5 percent higher for calves fed the control diets. Daily dry matter intakes as a percentage of animal body weight were also greater for control calves. Calves fed diets containing roasted soybeans, required approximately seven percent less dry matter per kilogram of gain after adjustments were made for calf starting and final weights. Reductions in feed intakes were comparable to the higher energy estimates tabulated for the diets with roasted soybeans as part of their formulation. Therefore, the experimental diets with roasted soybeans tended to reduce average daily feed intakes while growth rates were maintained. The additional oil content of the experimental diets was not conducive to an increased growth rate or carcass fat cover.
Significance to the Industry
Roasted soybeans are commonly used in various dairy and swine rations to increase energy and protein levels. They are usually considered to be a very palatable and readily available source of protein and energy. The trial indicated that the incorporation of roasted soybeans into a calf's diet would tend to reduce the amount of feed needed per kilogram of weight gain while maintaining animal growth rate. However, further work is needed on the feeding of roasted soybeans to veal calves before more precise feeding recommendation can be made to the industry.
Assistance from staff at Shur-Gain in diet formulation and custom premix preparation was very much appreciated.
Table 1. Performance of Holstein bull calves fed a commercial supplement versus roasted soybeans as a supplemental protein source.
* Significantly different.