By Warren Rusche
When it comes to nutritional management of growing and finishing cattle, the scientific aspects tend to get the most attention. Hours are spent getting the formulations right and debating the merits of different ingredients and additives.
In truth, feeding cattle successfully is as much art and judgment as science. Judgment is required to balance between over- and under-feeding. Under-feeding limits performance and possibly Quality Grade. Feeding too much increases feed waste and more importantly can trigger acidosis, poor performance, and increased death loss.
Most commercial feeders use a “slick bunk” feeding strategy. The objective of this approach is to match dry matter intake to the cattle’s appetite as closely as possible. SDSU research has shown that compared to simply feeding cattle as much as they want, the slick bunk strategy required less feed for a similar ADG. The performance of the cattle within the slick bunk pen was also less variable, suggesting that some of the ad lib steers suffered from bouts of sub-clinical acidosis from over-consumption.
You need two things to successfully manage bunks: a record of how much feed has been delivered to the cattle and a way to keep track of intake and cattle behavior. It’s helpful to have a system or language that is easy to use and understand. Dr. Robbi Pritchard developed a bunk scoring system that lets managers can use to translate what they are seeing into a simple, descriptive tool to make decisions.
Table 1. SDSU Feedbunk Scoring System
| Score | Description |
| 0 | No feed remaining in bunk |
| 0.5 | Scattered feed remaining. Most of the bottom of the bunk exposed. |
| 1 | Thin, uniform layer of feed remaining. About 1 corn kernel deep. |
| 2 | 25 to 50% of feed remaining |
| 3 | More than 50% of feed remaining. Crown is thoroughly disturbed. |
| 4 | Feed is virtually untouched. Crown of feed still noticeable. |
Combine this information with a record of feed deliveries to the pen, and now we can determine how much to feed the pen of cattle. The goal is for cattle to score a zero most of the time, with perhaps a bunk score of ½ three or four days in a 10-d period. When using bunk scores, here are some “rules of thumb” or guidelines to keep in mind to keep cattle on track:
- Read bunks at a consistent time each day.
- Don’t increase amounts fed more often than every 3 – 5 days.
- Don’t increase amounts by more than about ¾ pound dry matter at a time.
- Cattle behavior and aggressiveness in coming to the bunk can tell us a great deal about whether or not the feed deliveries should be increased.
We also need to think about where the cattle are in terms of their actual intake and what their expected maximum might be. For instance, a group of yearling or backgrounded heifers such as those in the Fed Cattle Challenge program might hit their peak intake about somewhere around 30 to 35 pounds as fed, based on prior experience. If the cattle are eating almost that much feed, a good manager will be very careful about not being too aggressive when increasing the amount of feed offered. Those cattle may not get increased more often than every five days and perhaps only at 0.5 pounds dry matter at a time. On the other hand, if they had been on feed for about four to six week and have only been on the final diet for a short time, the manager may choose to bump deliveries every 3 d by 0.75 pounds DM each time.
Getting cattle started right is very closely related to topic of bunk management and feed delivery. We want to adjust the energy content of the diet so avoid overloading the rumen with more starch than the rumen microorganisms can easily handle. Most feedlots use a serious of step-up diets before cattle reach the final or top-diet that they will eat for the majority of the feeding period. Usually cattle will be started on a lower-energy diet fed at a certain percentage of body weight, for instance perhaps about 2% on a dry matter basis. From there cattle will move from one starting diet to the next scheduled step-up. On yearlings this process may take 30 to 45 d, with calves usually on a slower schedule. It’s important not to get “out ahead” of the cattle; we want to make sure that there is still an opportunity to increase intake when the cattle reach the final diet.
Finally, changing weather conditions can play havoc on consistent feed deliveries and meeting bunk management goals. Cattle often eat more when it’s cold and less during heat waves. Adjusting feed deliveries based on forecasts and not getting fooled by weather related changes help to minimize digestive upsets and losses in performance.