Recent studies have demonstrated that finishing pigs fed using wet-dry (WD) feeders improves average daily gain (ADG), average daily feed intake (ADFI), and final body weight (BW) when compared to conventional dry (CD) feeders. However, feed conversion (feed/gain, or F/G) responses have been inconsistent.

Wet-dry feeders also influence carcass characteristics and water usage of finishing pigs. Higher backfat levels and lower lean percentage in pigs fed with a WD feeder compared to those fed with a CD feeder can reduce carcass price and the economic benefits of using a WD feeder. The inconsistency of feed efficiency responses and impact of WD feeders on carcass traits are major factors to consider when selecting a feeder.

To gain a better understanding of the pros and cons of WD feeders vs. CD feeders, a comprehensive search was conducted to evaluate the influence of WD feeders on growth performance, carcass traits and water usage of growing-finishing pigs. The criteria for selecting data included experiments conducted with complete randomized design or randomized complete block design, replicated treatments, and a clear description or diagram of the WD feeder to confirm that the water source was indeed located within the feeder.

The search resulted in 15 trials with growth performance data; eight trials that measured carcass characteristics (carcass weight, backfat, loin depth, percentage carcass yield); nine trials that reported lean percentage; five trials listing water disappearance; and three trials that included diet type (meal vs. pellet) in their comparison of feeder types.

Means for feeder type (CD and WD) within trial and diet type (pellet or meal) were the experimental units for all data analysis. There were two observations per feeder type in the three trials that fed both meal and pellet diet forms. Pen replicates per observation ranged from six to 24. Backfat, loin depth and lean percentage in each study were adjusted using hot carcass weight (HCW) as a covariate.

From the meta-analysis results, the growth performances and carcass characteristics were used to calculate an income over feed cost (IOFC) of feeding with WD vs. CD feeders. IOFC is a method to measure an economic value by assuming that other costs, such as utility and labor, are equal. Feed cost was valued at $278/ton, carcass price at $0.88/lb., and $1.50 for 1% of reduction in lean percentage. The advantage or disadvantage of feeding with a WD vs. CD feeder was evaluated by the difference in IOFC.

The meta-analysis indicated that pigs fed with WD feeders had greater ADG (0.09 lb./day) and ADFI compared with those fed with CD feeders, but no difference was observed in F/G (Table 1). As a result of improved growth rate, final BW and HCW of pigs fed with WD feeders were 3.2% greater than when pigs were fed with a CD feeder.

For carcass traits, backfat was greater and percentage lean was lower in pigs fed with WD feeders compared with those fed with CD feeders. Carcass yield and loin depth did not differ by feeder type. Water usage for pigs fed with WD feeders was 0.4 gal./pig/day less than for pigs using CD feeders.

Economic analysis shows that WD feeders would provide an advantage of $0.74/pig. If the reduction in lean percentage was not discounted by the processor, the economic advantage would increase to $1.60/pig. Notably, some experiments found a negative impact of WD feeders on F/G (0.03 to 4.60%). This is a concern because F/G was highly variable among the studies, and any negative change in feed conversion would eliminate any economic advantage.

Feeder adjustment and stocking rate are reportedly important variables in influencing F/G of pigs fed with WD feeders. The difference in water usage was not included in this economic analysis; however, the smaller volume of water usage with WD feeders may provide an economic benefit by reducing waste water and volume of slurry.

While the analysis accounted for meal and pellet feed forms, the limited data on pelleted feed (three experiments) showed no interaction between diet type and feeder design. Some data suggest interaction between diet type and feeder design is possible. Researchers have speculated that with CD feeders, pigs fed a pelleted diet have improved F/G compared with those fed a meal diet, but no differences in F/G between diet types when fed with WD feeders. Providing both wet feed and pelleted feed decreases eating time, but it is speculated that the interaction occurs because these two factors are not additive.

Meta-analysis is a great method to provide quantification of biological difference among different feeder types and allow economic analysis in different circumstances. Pigs fed with WD feeders consistently had increased growth rate, feed intake, final BW and HCW, but deposited more fat as indicated by greater backfat and lower percentage of lean. The economic return of WD feeders depends on the feed efficiency response with an economic advantage when F/G is similar among feeder types. However, the F/G response was highly variable; hence, if feed efficiency were poorer due to stocking density or feeder adjustment, any economic advantage to using WD feeders would be lost.

Researchers: Sureemas Nitikanchana, Steve S. Dritz, Mike D. Tokach, Joel M. DeRouchey, Robert D. Goodband and Jim L. Nelssen, Kansas State University. Contact Nitikanchana by phone (785) 323-7603) or e-mail sureemas@ksu.edu.