Do young pigs need more help digesting soy-based feeds?

Supplemental enzymes and multicarbohydrase may improve weaned pigs digestion of crude protein from soy-based feed ingredients, however current digestibility values may be miscalculated, say researchers. 

A team of researchers from several universities in Brazil examined the ability of piglets to digest diets that included either micronized full-fat soybean meal (MFFS) or textured soy flour (TS) with or without adding multicarohydrase and phytases. The group published its results in the journal of Animal Feed Science and Technology​​.

“The objective of the current study was to determine the apparent total tract digestibility (ATTD) of nutrients and energy and the apparent (AID) and standardized (SID) ileal digestibility of AA [amino acids] in MFFS and TS with or without multicarbohydrase (MC) and phytase (Phy) supplementation in weaned pigs using the slaughter technique,”​ said the researchers.

The group found that younger pigs may have increased difficulty using some soy-based feed ingredients, the researchers said. However, more work is needed assess the digestibility of the ingredients for piglets of different ages.

“Most digestibility values for MFFS evidenced a numerical difference compared with previous studies from the literature,” ​they said. “Since most studies have used ileal-cannulated pigs older than six weeks, we suggest that weaned pigs are less able to harness the energy and nutrients from ingredients when compared to growing-finishing pigs.”​

Despite the potential for reduced nutritional intake, the use of enzymes to mitigate anti-nutritional elements may help, they said. “The enzymes phytase and multicarbohydrase may be an alternative way to increase the digestibility of crude protein in both ingredients,”​ they added.

Why enzymes?​

Pigs’ ability to digest amino acids from feed ingredients is often studied using pigs that have been fitted with a T-cannula on the distal ileum, said the researchers. But those pigs tend to be older than six weeks to avoid complications from surgery.

But, that additional development may mean that nutrient digestibility in weaned pigs is overestimated as the feed formulations used stem from digestibility data generated by older animals that have reached a more developed gastrointestinal tract, they said. And, there are some previously reported age and bodyweight related differences for feed use and nutrient digestibility.

“According to Marion et al. (2003), an acute phase of decreased digestive enzyme secretion occurs after weaning,” ​they said. “When pigs are fed a solid diet, the physiological functions of the small intestine increase gradually.”​

Using a different technique to collect samples from the distal ileum may offer an alternative, they said.

Soybean-based feed ingredients may be the main protein source offered to meet the AA needs of pigs during growing phases, the researchers said. But, soybean digestion can be limited by anti-nutritional factors that can cause diarrhea, reduced nutrient uptake and flatulence.

“Heat processing procedures such as micronization have been reported to disrupt cell wall components and increase dry matter and nutrient digestibility in pigs (Lawrence, 1973) and poultry (Igbasan and Guenter, 1997),”​ they said. “However, the use of micronized feedstuffs to reduce nutrient excretion and swine manure output has not been examined extensively and requires further evaluation.”​

Textured soy flour may have reduced amounts of trypsin inhibitors and antigenic properties, making nutrients more available, they said. Energy use may be improved by extruding or pelleting.

Enzyme use also may limit the influence of anti-nutritional factors, they said. Phytse can increase the availability of phosphorus (P).

“However, there are conflicting and inconsistent results in the literature regarding the improvement of nutrient utilization from phytase supplementation in pig and poultry diets,”​ the researchers said.

Additionally, plant-based feed ingredients often contain fiber, which can limit nutrient access, they said. But, adding a carbohydrase to the diet may improve nutritive value and increase energy digestibility and AA availability.

Methods and materials​

In the study, 50 23-day old pigs were split evenly into two feeding experiments, said the researchers. In both experiments – MFFS or experiment 1, and TS or experiment 2 – corn, dry-whey and milk powder-based diets were used to establish ATTD of energy and nutrients and corn starch-based diets with 5% casein were given to quantify the AID and SID of AA.

“The enzymes were a MC blend of α-galactosidase, galactomannanase, β-xylanase and β-glucanase activities,”​ they said. The MC was commercially available.

The Phy used was derived from Saccharomyces cerevisiae ​and included genes of Escherichia coli​ and Citrobacter braakii​, they said.

Each set of feeding trials used five diets, one control and four experimental feeds, they said. In the experimental diets, 30% of the reference diet was replaced with the test ingredient – either MFFS or TS – and given without any supplement, with the multi-carbohydrase at 0.2%, with the phytase at 0.05% or with both enzymes.

Diets were fed for 10 days, and samples of urine and manure were collected during the last four days of the feeding trial, said the researchers. At the end of the period, all piglets were given a corn starch-based diet with experimental variations for 4 days.

On day 45, all piglets were weighed, harvested and the illeal digesta was gathered, they said.  ATTD, AID and SID were calculated.

Results​

The researchers concluded that younger weaned pigs were less able to access the energy and nutrition from soy-based ingredients than older pigs, they said.

“However, since digestibility of raw materials differs from batch to batch and from experiment to experiment, more researches should be conducted to compare the digestibility of ingredients for piglets in different ages,”​ they said.

The group found no influence from the use of MC or Phy supplements on nutrient or energy digestability for MFFS, they said. But, the SID of AA in MFFS without enzymes was lower by about 6% than data published in the literature.

“The amino acid concentration in the experimental diets with 300 g/kg MFFS replacing the reference diet was uniform and homogeneous, as expected,” ​they said. “There were no isolated effects or interaction effects of MC and Phy on nutrient digestibility.”​

Little is known about the nutritive values of textured soy products when fed to growing pigs, said the researchers.

No effect from enzyme use was found on the standardized ileal amino acid digestibility or apparent ileal amino acid digestability for TS, they said. “However, Phy supplementation improved the ATTD of crude protein (CP) and the SID of Arg [arginine], His [histidine], Glu [glutamic acid] and Pro [proline], while MC improved the SID of His, Cys [cysteine], Glu, and Gly [glycine],” ​they added.

“There were no interactions between enzymes on the AID or SID of essential AA,” ​they said. “Interactions from MC and Phy were found only on the AID and SID of Ser [serine] and Tyr. The AID and SID of most AA in TS, with or without enzymes was higher than 90%.”​