When the swine industry typically thinks about response to pellet quality or percent fines at the feeder, it normally comes down to feed wastage and feed efficiency response. So, when former Kansas State University graduate student Patrick Badger garnered a pretty standard response to blending fines with pellets in the finishing barn, it wasn’t too surprising, says Chad Paulk.

“He saw a very traditional response in that different weight range, with that improvement in pig feed conversion from 4 to 6%, pigs fed pelleted diets compared to mash diets, and for about every 10% of fines we increased at the feeder, our feed conversion was poor, by roughly .7 to 1.4%,” says Paulk.

While this data follows a lot of previous research on the subject, the associate professor of feed science and management in the Department of Grain Science and Industry at Kansas State University says what makes it inconsistent is the average daily gain response observed in late finishing pigs when fed pelleted diets.

Although Badger blended fines at the feeder, in the field pellet fines at the feeder is dictated by the pelleting process, pelleting parameters and feed handling.

“One thing in his experiment was his first two phases, he was making good enough pellets to meet his experimental design needs,” Paulk says. “However, when he moved into the late finisher phase we were feeding pigs up to 320 pounds. Those diets did not make good pellets and we couldn't even get enough pellets to the farm in order to meet his treatment needs. Therefore, we used a thicker die when pelleting in order to get optimal pellet quality.”

When the research team analyzed the early grower phase growth performance data when diets were pelleted with with a thinner die (length: diameter [L:D]7), there was no growth performance response. Average daily gain was similar between pigs fed the pelleted diets and the mash diets, and there was no evidence of difference of pellet quality influencing average daily gain.

As research moved into the late finisher phase, all of the pigs fed the pelleted treatments had approximately a 9% improvement in average daily gain compared to pigs fed the mash diets. However, there was no difference in average daily gain as the percentage of fines was increased at the feeder.

“So, this is telling me, maybe pellet quality is not influencing the gain response, but something’s going on, where in the late finisher when diets where pelleted using a thicker die there was an increase in average daily gain,” Paulk says. “Is it just something to do with these heavyweight pigs and their response to pelleted diets or is it the fact that we pelleted those diets with a thicker die (L:D of 12)?”

Paulk says it’s important to remember when measuring L:D, the higher the number, the thicker the die, and the more compression and time that is occurring in the pellet die.

Is there a growth response to pelleting is a question Paulk and K-State’s swine nutrition team have been tackling for some time. While they might not have direct answers to the question, Paulk says they have gained some insight.  

Badger then designed another experiment to test the average daily gain response, but also to make the design more practical in creating fines at the feeder through processing. A typical mash diet was used in the treatments, and then diets were pelleted using a L:D 8.75 die and fed as-is, a L:D 5.5 die fed as-is, a L:D 5.5 die and pellets screened to remove fines and 100% fines. Percent fines were then measured at the feeder to ensure what pigs were getting.

“Diets pelleted using the thicker die resulted in 28% fines at the feeder, we were actually hoping it would be a little less than that, but this is where we ended up. Diets pelleted using the L:D 5.5 resulted in 42% fines at the feeder and then when those diets were screened those pellets we had roughly 37% fines at the feeder,” Paulk says. “So, we found in the screening  process, we were pulling off about 5 to 10% fines. When moving that feed to the farm we would generate some more fines, and then we ended up with about a 5% difference between those two treatments.”

This time when the research team fed those diets to pigs, they decided to include the whole grow-finish period from 114 to 320 pounds. Pigs fed the pelleted diets on the thicker LD had a 6% increase in average daily gain compared to those fed the mash diets, while pigs fed the diets pelleted using the thinner die did not result in differences in average daily gain compared to pigs fed the mash diets, which matched what the team had seen previously.

“When pigs were fed screened pellets there was an increase in average daily gain compared to those fed the mash diets and the non-screened diets, and there was no evidence of difference compared pigs fed diets pelleted using the thicker die,” Paulk says. “Based on our previous data set, I would have told you pellet quality or percent fines did not influence the average daily gain response because we consistently observed no difference in the previous study. However, something's going on when we screened those pellets, where we observed an increase in average daily gain compared to the unscreened diets. We still observed an increase in average daily gain when pigs were fed diets pelleted using a thicker die. Pigs fed diets pelleted using the thicker die had a 6% improvement in gain compared to those fed mash diets and those fed screened the pellets had a 4% improvement gain compared to those fed mash diets.”

Finally, when the team fed straight fines, pigs performed similar to those fed the mash diets.

“From a feed to gain standpoint, very similar to our previous research, we consistently see a 4 to 7% improvement in feed to gain when pigs are fed pelleted diets with approximately 28% fines at the feeder,” Paulk says. “Pigs fed 37 or 42% fines at the feeder had intermediate feed conversion to those fed pelleted diets with 28% fines and mash diets. Pigs fed 100% fines had similar feed to gain compared to those fed the mash diets.”

With the addition of new research associates joining the team, specifically to work in digestibility, Paulk says the group hopes to soon have some answers to how average daily gain improvements are stemming from feed manufacturing processes.

Paulk presented these findings and more during the recent K-State Swine Day. To view all of the presentations and publications, visit the K-State Swine Day website.