What could possibly be involved in feeder management that entails more than just adjusting up when the trough appears too empty and adjusting down when the trough appears too full? Managing a topping floor feeder is so apparently simple that the dynamics of its operation are taken for granted.
What factors affect the amount of feed dispensed by a feeder? Most feeders are designed to control feed flow by using a baffle or gate that restricts a space or gap through which feed must pass to be available in the trough to the hog. The hog is allowed a mechanism that when activated, an agitation of the feed near the gap occurs, and an increased flow of feed results through gravity. The most important factor affecting feed flow is width of gap. This seems straight forward; the wider the gap, the more the resulting feed flow. However, this factor of gap width is the only item under the control of the manager as the feeder is turned up and down. Other factors affect this situation, like weight of the hogs. The longer the hogs are in the pen, the larger they are, and the easier the task of feeder activation is for them. Bigger pigs get more feed out of the same gap than smaller pigs. It has been common knowledge that feeder gaps needed to be tightened as the hogs gained weight.
Another factor affecting feed flow is the quality of the pellets when pelletized rations are utilized. The greater the per cent of fines that exist in the feeder, the more the feed flow is restricted due to bridging near the gap. The effect of fines would be easily accommodated by merely increasing or decreasing the gap as fines in the feed increased or decreased, but this scenario is complicated to a greater extent by the tendency of pellets to separate to the center of the bulk bin causing the distribution of fines to occur unevenly between individual feeders. It is not uncommon for per cent of fines to differ as much as 30% between feeders and then change distribution the next day as a different portion of the bin is emptied. The more fines that are carried by the feed source, the more the fines at the level of the feeder will be a constantly varying value with wider swings. Poor pellet quality can be problematic while attempting to set feeders, especially on younger hogs.
Not all feeders are created equal. The activating mechanisms are designed the same, but will act differently between individual troughs. Therefore, some feeder mechanisms do a better job creating feed flow than others, because they make more agitation. For example, "agitation" is the difference between high and low position of the baffle plate on feeders when they are set up. When we examined 32 feeders, the agitation ranged from 1/8 inch to 1/4 inch. This factor of agitation means that every trough can respond differently. If a pelleted ration contained no fines and all hogs in a building weighed the same, there would still be a difference in feeder flow, even if every trough was set at the same aperture.
What determines if a feeder is delivering a reasonable flow? One manufacturer suggests a method of monitoring feed flow that is quite applicable to their feeder. They advise that the farm manager watches the extent of coverage on the trough bottom, as this associates enough to feeder flow that successful feeder settings can be achieved. Coverage can be expressed as the amount of trough bottom surface that has feed on it as compared to the total bottom. In other words, if 20% of the trough bottom has feed on it and the remaining 80% is a clean and shining steel surface; the coverage is 20%. The optimum coverage is assumed to be 50%.
Why is 50% coverage considered optimal? The quantity and quality of trough content is related to coverage. This can best be described by studying the 3 graphs of trough contents versus coverage (Figures 1,2,3). Notice that in Figure 1 the lowest trough moistures occur between 20% and 40% coverage. Moisture levels above 13% can easily lead to bacterial action and souring, which means refusal of the feed offered. The high spike at the lower coverages occurs because of 2 reasons: 1) The pigs attempt to lick to get more feed from under the baffle and 2) The pigs foul the troughs more at lower settings by urinating or dunging in them.
In Figure 2 the lowest amount of fines occurs between 20% and 40%, very similar to the moisture chart. Isn't it interesting that the trough content is closest to the feed source itself in fines and moisture only through this 20% to 40% coverage range. The high proportion of fines in the low coverage is suggesting that this material is the fines that stuck and dried to the corners and sides of the trough that the pig can't reach or may refuse to eat. The high proportion of fines of the higher coverage simply relates to the fact that hogs prefer pellets; when given the opportunity, the pigs eat the pellets and leave the fines. The high and low coverages seem to create a trough content that reflects more what the hog is not eating rather than what it is eating.
Next, relate this to Figure 3. The shape of this graph does a good job depicting what quantities can be found in the trough at different levels of coverage. The lower levels put minute weights of material in the trough, less than 3/4 of a pound. The coverage of 30% to 60% puts out a fairly consistent (flat line) amount of 1 to 3 pounds. After 60% the weight in the trough exponentially climbs. This is why 50% is the desirable coverage. The consistent amounts in this area (30% to 60%) allows some room for setting error, yet the material offered to the pig in the trough is the most like feed, as shown by the other 2 graphs. To farther enhance the coverage recommendation, it could be stated that optimal setting would achieve 50% coverage or slightly less. Fifty percent allows a reliable quantity and "slightly less" refers to the superior content quality achieved by 20% to 40% coverage.
The exponential weight climbs of coverages over 60% creates a state of its own. With 8 to 10 lbs. of a 90% fines material that has a moisture content of over 13% and has heated and soured; what are the chances that the hogs will clean up a high coverage trough? What they do is leave all the material set and eat from one or two small ares where fresh feed and pellets trickle out of the feeder. They fight over these small areas on the feeder, because the high coverage trough is in fact a restricted flow feeder due to all the unconsumed material that sits in it. This brings up the next issue.
What advantage is there to putting forth the extra effort to maintain 50% or slightly less trough coverage? The advantage has been shown in a recent study. Hogs eating at troughs set close to 50% (treatment 2) gain significantly faster than their counterparts who eat from coverages of less than 20% (treatment 1) or over 80% (treatment 3) (Figure 4). The restricted and excessive groups both gained the same; because, in truth, both were restricted groups.
Take-Home Message
In summary, an aspect of optimal feeder utilization can be attained on the feeder studied by setting for 50% coverage or slightly less. It will return faster gains.
