Feeding Value of Low Test Weight Corn for Pigs

As we move into November and continue to see corn standing in the fields waiting for harvest, concern grows for the quality and quantity of our Ontario corn crop. What will this mean for swine producers?

Depending on the corn’s maturity at the time of the first frost and the intensity of the freeze, the impact on the quality and quantity of the corn will vary. Table 1 demonstrates the relative maturity of corn, the estimated percent moisture and crude protein of the grain at each stage, as well as an estimate of the test weight of the grain if a killing frost occurred at various points in the crop’s maturity.

Based on current knowledge, corn test weight does not significantly affect pig growth until it drops below 45 lbs/bu. As test weight declines below 45 lbs/bu, digestible energy decreases by 5-6 % and as a result, feed efficiency and growth rate will also suffer (3-10%) because of reduced energy intake. Research has shown that adding 2-3% oil or fat to diets made with very low test weight corn (below 45 lbs/bu) will help improve performance, but it will not return it to the level achieved with normal test weight corn (56 lbs/bu).

Besides energy, the level of lysine and crude protein is likely to be lower in very low test weight corn because the corn has not had the chance to completely assimilate amino acids. In addition, the crude protein value in very low test weight corn is extremely variable and should be determined. Corn with test weights above 45 lbs/bu may also have variable crude protein content; however, normal published averages for lysine (0.25%) should be relatively constant. Another concern with frost damaged corn is the potential for mycotoxins, specifically vomitoxin and zearalenone, to develop. When immature grain is frozen, the grain moisture is extremely high and if the killing frost is followed by several days of warm summer-type weather (21 °C), the conditions in the field would be perfect for molds to grow.

Feed companies adjust their product ingredient formulas to compensate in bad years when corn has a lower nutritive value. On farm feed mixers must adjust their own rations to compensate as well.

To deal with low test weight corn, producers should:

• Test corn for moisture and protein.
• Determine bushel weight of corn at 15% moisture.
• Balance rations to account for differences in protein, energy and moisture.
• Recalibrate volumetric mix mills to compensate for lower bushel weights.

Table 2 provides an estimate of the weight of low grade corn needed to provide the same energy as 1 kg of 56 lbs/bu corn. These guidelines can be used to reformulate rations.

Example calculation

Reformulate mix of 800 kg corn (56 lbs/bu) + 200 kg soybean meal (SBM) with 50 lbs/bu corn.

Calculate amount of corn needed to provide identical amount of energy:

800 kg x 1.026 = 820.8 kg

Reformulate mix = 820.8 kg corn + 200 kg SBM = 1020.8 kg mix

On a 1000 kg basis, new mix would contain:

820.8/1020.8 x 1000 = 804 kg corn

200/1020.8 x 1000 = 196 kg SBM

Sources

McBride, G. 1992. Feeding value of low bushel weight corn. OMAF Adverse Weather File.

Richert, B. 1996. Feeding value of immature, low-test weight corn and soybeans for swine.

Purdue Crop and Livestock Update.

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