Nutrition: Do feed interruptions affect grower-finisher performance?

Friday, August 8, 2008

Research conducted in Nebraska clearly suggests that grower pigs are more sensitive to out-of-feed events than finisher pigs

by JANICE MURPHY

Anyone who has had experience feeding grower-finisher pigs can relate to the constant struggle of keeping feed in front of pigs 24 hours a day. Working within modern production facilities presents a variety of challenges, but when it comes to the feeding system, the main culprits are human error, bridging of feed in storage tanks and equipment breakdown.

Human error is commonly associated with empty bins when feed is not ordered, prepared or delivered in a timely fashion. This is bound to happen as operations increasingly rely on external processing of feed and just-in-time delivery.

Bridging of feed in feed tanks is generally associated with "flowability," where the feed cannot flow freely out of the storage tank into the feed delivery system. This is most often an issue where meal diets are being fed. Finally, the incidence of equipment malfunction generally increases as facilities age and various components begin to wear out.

Regardless of the root cause, an out-of-feed event looks the same from the pig's perspective. Anecdotal information and experience suggest that when pigs receive feed after a period of deprivation, they tend to fight for a position at the feeder. Ultimately, the most aggressive pigs win out, therefore affecting the welfare of all pigs in the pen.

Previous research has shown that an inconsistent feed supply resulted in increased competition and aggression at the feeder during feeding time because the pigs were unsure when they would receive feed again. Short-term feed deprivation (24 hours) has also been proven to cause ulcers in growing pigs, so it is possible that interruptions in feed delivery could have a similar effect on pigs accustomed to eating whenever they please.

In the past, Drs. Bob Friendship and John Deen have suggested that producers investigate all possible causes of feed disruptions, since 24- to 48-hour feed withdrawals can cause stomach lesions, decrease performance and increase mortalities. Feed interruptions may also play a contributing role in hemorrhagic bowel syndrome.

If pigs miss a meal or two, they do not necessarily compensate by over-eating when feed does become available, so it is possible that repeated out-of-feed events could have an impact on performance and carcass composition. Research has shown that average daily gain was lower in pigs fed ad libitum and fasted on alternate days compared to pigs that were not fasted, with minimal impact on feed conversion.

However, the resulting carcass dressing percentage was lower due to a larger proportion of visceral mass at slaughter. In a separate experiment, backfat depth was greater in pigs fed on alternate days than in pigs fed once or twice daily.

Researchers in Nebraska recently examined the impact of repeated out-of-feed events on pig performance, carcass composition and animal welfare, as measured by the incidence of tail biting and skin lesions.

In each of two experiments, artificial 20-hour out-of-feed events were created by closing the feeder delivery devices from noon until 8 a.m. over a 16-week period. In Experiment One, barrows were assigned to one of four treatments – never out of feed, out of feed during one 24-hour period weekly, coarse (1,266 microns) or medium (1,019 microns) feed particle size. In Experiment Two, pens of barrows and gilts were assigned to one of four treatments – zero, one, two, or three random 20-hour out-of-feed events over a two-week period.

In Experiment One, weekly out-of-feed events resulted in an average daily gain of 68 grams per day lower for the grower phase (first eight weeks), with no effect during the finisher phase (last eight weeks). (See Table 1). This translated into 35-gram per day lower gain over the entire trial, compared to the never out-of-feed treatment.

Average daily feed intake for the grower phase was 132 grams lower in pens experiencing weekly out-of-feed events, but there was no effect during the finisher phase. Overall, average daily feed intake was 89 grams per day lower in pigs experiencing out-of-feed events compared to pigs which maintained access to feed. Limited access to feed had no impact on feed conversion results. 

As expected, feed conversion was better for pigs fed the medium feed particle size. The 250-micron difference in particle size between treatments translated into a 3.2 per cent difference in feed efficiency, or a 1.3 per cent change in feed efficiency per 100-micron change in particle size. These results are similar to what other researchers have previously reported (1.0-1.5 per cent for each 100-micron reduction in particle size).

Oddly enough, producers should not despair if they are not realizing the optimum particle size in every batch of feed. Despite careful planning, the researchers in this study had trouble achieving the desired particle size under controlled conditions. They originally intended to create coarse (> 1,100 microns) and fine (< 850 microns) particle-size diets but were not entirely successful, instead achieving 1,266 and 1,019 microns respectively.

The impact of the treatments on other parameters was minimal. There was little or no effect of any experimental treatment on carcass composition or skin-lesion scores. The out-of-feed events did not affect the tail-biting score, but pigs fed the medium diet did have a higher tail-biting score compared to the coarse diet. While tail biting tended to increase as the experiment progressed, the incidence remained low throughout the experiment.

In Experiment Two, there was a linear decrease in both average daily gain and average daily intake with increasing numbers of out-of-feed events during the grower phase, but this effect did not carry through to the finisher phase. (See Table 2). There was little or no effect of treatments on feed conversion or carcass composition. In contrast to some other research results, measurements of water consumption in this experiment showed that, during the out-of-feed events, the pigs did not increase their water intake in an attempt to achieve gut fill.

The results of these two experiments clearly suggest that grower pigs are more sensitive to out-of-feed events than finisher pigs. The number of out-of-feed events did not appear to alter this response. In spite of the deprivation, feed intake was the same for control and out-of-feed pigs for the first 24 hours after an interruption.

The researchers suggested a possible explanation; genetic selection for improved feed efficiency and decreased fat deposition may indirectly select for a limit on ad libitum feed intake, especially as the pig approaches maturity, when the rate of lean deposition decreases and fat deposition tends to increase.

Looking at alternative scenarios, the researchers admitted that their results could have been more drastic had the timing of the out-of-feed event been different. Under thermoneutral conditions, growing pigs start eating early in the morning, with a peak in consumption around mid-afternoon.

In light of this behavior, it is likely that by noon most pigs had consumed one or more meals. Had the feed interruption occurred earlier in the day, the out-of-feed event would most likely have had a bigger impact. BP

Source: Brumm M.C., Colgan S.L., Bruns K.J., 2008. Effect of out-of-feed events and diet particle size on pig performance and welfare. J. Swine Health Prod. 16(2):72–80.

Janice Murphy is a former swine nutritionist with the Ontario Ministry of Agriculture, Food and Rural Affairs who now lives and works in Prince Edward Island.