Everyone knows that hogs should always have constant access to feed. But in the real-world feeders do run dry.

The question is, how much impact does this have on your pigs? Do you know what it is costing you; or how often your pigs find the feeders empty? Do you know how best to avoid this problem?

Mike Brumm, University of Nebraska Extension swine specialist, defines an out-of-feed event as anything that causes a disruption in the normal feed distribution, or that prevents pigs from having unrestricted access to feed.

"Everyone has an out-of-feed event at one time or another," says Brumm.

Most out-of-feed events are resolved before any hogs die, but that doesn't mean these events don't cause problems. Animal growth, health and welfare are all impacted to a degree.

"A pig doesn't necessarily compensate for the feed intake it missed when the feeder was empty," says Brumm. According to his research, the pigs don't appear to eat a much bigger meal the next time they step up to the feeder. "An out-of-feed event means the pigs permanently miss a meal or a part of a meal, so there's a negative effect on average daily gain."

An increase in growth variation is another potential negative effect of out-of-feed events, says Brumm. There's a good chance the larger, more dominant hogs will get much of the feed once it starts flowing again, leaving the more passive pigs without feed for even longer periods of time. This results in the big pigs getting bigger while the slow-growing pigs take another step backward.

In terms of animal health, an out-of-feed event stresses pigs, which can trigger disease episodes. It's also been shown to create ulcers, and there's speculation that running out of feed can cause other health concerns such as hemmoragic bowel syndrome, illeitis and tail biting.

Leaving pigs without feed for more than a couple of hours could prompt aggressive behavior and fighting among pigs, which brings up additional animal-welfare concerns. The pigs can get unruly and agitated when they are hungry, causing damage to equipment and the hogs themselves.

"As an industry, we say we provide for the pigs' every need by raising them inside buildings; if out-of-feed events become common, we're not doing that," says Brumm.

Another question mark is how long the pigs can go without feed before problems start to surface? Assuming pigs were eating normally before the out-of-feed event occurred, Brumm says the pigs are probably alright for four to six hours. Much longer than that and you will likely see more aggressive behavior at the feeder.

Often out-of-feed events go on much longer and are much more frequent than necessary. Brumm shares one case, where the grower was responsible for ordering feed from the local mill, but if he didn't give them 24 hours notice they charged an additional $3 for delivery. The owners saw these constant charges and charged it back to the grower. Unfortunately, that didn't mean the grower started ordering his feed further in advance. Instead, the pigs went longer without feed. Brumm says incidents like this are becoming more prominent with fewer producers grinding their own feed today.

There are three main causes of out-of-feed events:

1. Human error. This could involve forgetting to order feed until it's too late, the feed truck breaking down or other random events that cause an   out-of-feed event. "With good management these out-of-feed events caused by human error should be almost non-existent," says Brumm.

2. Feed bridging in the bins or feeder can cause an out-of-feed event.

3. Equipment failure, such as mixing or auger problems, among others.

"You can eliminate most out-of-feed events by good planning, equipment maintenance and training employees," says Ken Purser, director of nutritional and technical services for Prince Agri Products.

Bridging feed is another story. Bridging can happen at any time and usually requires someone actually beating on the bin with a mallet or poking the feed down with a stick. It's not the difficulty of the task, but the fact that someone has to be present when it occurs that causes problems. After all, it could happen at 3:00 a.m.

"As you move to finer ground feeds and add more fat, you increase the likelihood of bridging," says Brumm. "But finer ground feeds help increase feed conversion, so there's an economic incentive there."

Most swine nutritionists agree that finer particle size also increases digestibility, but causes more bridging, so the two factors are at odds, says Purser.

Adding fat to swine diets in summer months adds to the feed bridging problem as well. All the more reason to keep an eye out for bridging problems in the months ahead.

There are only a handful of options to try to reduce bridging. You could add a flow agent to your rations, but you should first determine if bridging is a serious enough problem to justify the added costs, says Brumm.

Some common flow agents include calcium alumina silicate and sodium bentanite. Costs vary from 5 cents per pound to 75 cents per pound for the flow agents, however, costs per ton of complete feed varies with inclusion rates, says Purser.

Pelleted diets are another option, producing little to no bridging.

New technologies are being offered - like bins equipped with vibrating parts that could help reduce bridging, but they are expensive, says Brumm. The bin vibrator costs about $2,000, which is expensive for a bulk tank that typically costs about $1,000.

"There are a lot of questions when it comes to bridging," says Brumm. "Do you spend the money to add a flow agent? Do you switch to a coarser grind and give up feed efficiency?"

"Typically, producers make swine diets as fine as possible, within the limits of their grinding equipment," says Purser. "Then the bins at the farm become the most common bridging problem area."

There's not much you can do about equipment failure, other than following regular maintenance, says Brumm. An equipment failure might occur during a weekend, and you won't be able to get the necessary parts until Monday, causing problems. But Brumm stresses that feed equipment is very reliable and such situations are rare.

"Out-of-feed events happen more often in older barns, because older equipment is less reliable. Also, producers get more complacent with time," says Brumm. "The more times an out-of-feed event happens without a producer noticing an immediate effect, the less the producer worries about it."

The lack of knowledge and awareness about this topic is a concern, but that might be changing. Brumm has applied for funds to study out-of-feed events, with the hope of shedding more light on the exact costs to the industry.

"Producers know they have out-of-feed events, and many are frustrated by it. But until we can show them the economic losses, they won't aggressively deal with the problem," says Brumm.

For now, logic and experience tells you that when a pig faces an empty feeder, there is a long-term price to pay. Regardless of the exact economic impact, a little more attention to detail, and a higher priority on feed flow could greatly reduce the number of out-of-feed events that your pigs face.