Summary of Research on Feeding Low Test Weight Corn to Pigs

Research has shown that, 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 illustrates 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.

Table 1. Corn characteristics at different stages of development.

Stage	Moisture (%)	Protein (%)	Test Weight (lbs/bu)
Early milk	75-80	6-13	35
Early dough	60-65	10.5	47
Mid-dent	50-55	7-9	55
Maturity	25-40	7-9	58

Source: Richert, B. 1996.

We encountered similar harvest conditions in the early 70’s. At that time, the University of Guelph conducted several research trials to assess the nutritive value of the resulting corn crop. What they discovered at that time was (on an 85% dry matter basis):

• The moisture content ranged from 31 - 50%.
• Bushel weights ranged from 60 - 46 pounds.
• Crude protein ranged from 4.3 - 7.9%.
• Energy values ranged from 3050 - 3400 kcal ME/kg.

Based on these results, with the hybrids available at the time, the researchers concluded that a good estimate of the energy value of corn could be calculated using the following information (see Table 2):

• Every 1% increase in moisture content = 12 kcal less ME/kg.
• Every 15% increase in sugar content = 64 kcal less ME/kg.
• Every pound change in bushel weight = difference of 13.9 kcal ME/kg.

Table 2. Estimated energy values for corn at various bushel weights.

Bushel Weight (lbs)	Metabolizable Energy (kcal/kg)
56	3325
54	3297
52	3269
50	3241
48	3213
46	3185

Source: Summers, J. 1992.

In 1992, the OMAF (as OMAFRA was referred to then) Feed Quality Laboratory tested the quality of 90 samples of corn (averaging 49 lb/bu test weight) from the 1992 harvest and concluded, based on poultry metabolizable energy values, that the energy level was 5% below the average energy level for corn from previous years. They concluded that there was a very poor relationship between test weight and energy value and suggested that factors such as hybrid differences, maturity at time of killing frost, harvest moisture level, drying temperature, and handling damage may all have contributed significantly to the variability.

Because low test weight corn is assumed to have a lower feed value than normal corn (56 lb/bu), it can be severely docked at the elevator. As a result, producers are inclined to try to find ways of using this low test weight corn in their own feeding programs. Surprisingly, considering the prevalence of this issue in the past, there has not been a lot of research into the feeding value of low test weight corn for pigs. The research that does exist in this area seems to contradict the assumption that low test weight corn is inferior in feed quality to normal test weight corn. Table 3, Table 4, Table 5 and Table 6 summarize some of the research results that have been reported from experiments with the 1992 corn crop.

Table 3. The effect of feeding wheat and corn of various grades* to growing swine** (32-75 kg – Initial 7 weeks).

Parameter	A Wheat	B Kent Corn	C Kent Corn	D Huron Corn	E Huron Corn
Test Weight of Corn		54	52	48	48
Energy Content (kcal ME/kg)		3314	3153	3036	3093
Average Daily Gain (kg)	1.01	0.93		1.04	1.05
Average Daily Intake (kg)***	2.92ab	2.92 ab	2.77 b	2.90 ab	3.13 a
Feed:Gain Ratio	2.91	3.22	2.84	2.79	2.99

Source: Dr. Jim Morris, Ridgetown College

* Explanation of diets:

A – 1992 Wheat from Ridgetown College - Excellent Quality
B – 1992 Corn (Kent County) – Grade 3
C – 1992 Corn (Kent County) – Grade 4
D – 1992 Corn (Huron County) – Grade 5 – Slow-dried (no carmelization)
E – 1992 Corn (Huron County) – Grade 5 – Carmelized
** 18 pigs/treatment housed in 3 pens
*** Numbers in the same row with different superscripts are significantly different (P<0.05)

In this experiment, low test weight corn did not significantly affect average daily gain or feed efficiency (even with some carmelization damage). One thing that is obvious from these results is that high temperature drying is a problem with corn harvested at high moisture levels. Producers should be on the lookout for evidence of carmelization (burnt smell and dark kernels) and be aware that corn that is severely carmelized could be as much as 15% lower in protein and energy.

Table 4. Effect of corn weight on performance of growing-finishing swine (29-68 lb).

Test Weight (lb/bu)	42	47	51	59
Average Daily Gain (kg)	0.65	0.60	0.64	0.64
Average Daily Intake (kg)	1.32	1.22	1.30	1.29
Feed:Gain Ratio	2.04	2.00	2.04	2.04

Source: Iverson, D.M. and Thaler, R.C. 1996.

Table 5. Light test weight corn for growing-finishing pigs (60-200 LB)

Test Weight (LB/bu)	Light Corn 41	Medium Corn 48	Heavy Corn 54
Average Daily Gain (kg)	0.73	0.77	0.79
Average Daily Intake (kg)	2.68	2.93	2.82
Feed:Gain Ratio	3.56	3.82	3.56

Source: Iverson, DM and Thaler, R.C. 1996.

Table 6. Performance of pigs fed 1992 Ontario corn dried at two temperatures.

Corn in Diet	Drying Temp. (° F)	DE (DM basis) (kcal/kg)	Average Daily Gain (kg)	Average Daily Intake (kg)	Gain:Feed Ratio (as fed)
Ontario control	-	3480	0.55	1.32	0.42
Indiana control	-	3364	0.57	1.22	0.40
Funks 201	180	3545	0.59	1.38	0.42
	220	3530	0.45	1.21	0.37
Pioneer 3787	180	3354	0.60	1.41	0.43
	220	3336	0.51	1.27	0.40
Pioneer 3790	180	3118	0.48	1.24	0.39
	220	3311	0.47	1.27	0.37
Funks 4023	180	3251	0.51	1.23	0.42
	220	3187	0.58	1.37	0.42

Source: Patterson, R., Tuitoek, J. and Young, L. 1993.

Based on results like these, researchers to date have concluded that bushel weight is not a reliable indicator of the feeding value of corn.

Some researchers have concluded that corn test weight does not significantly affect pig growth until it drops below 45 lbs/bu, corn that they refer to as very low test weight corn. They suggest that as test weight declines below 45 lbs/bu, digestible energy decreases by 5-6 % and as a result, feed efficiency and growth rate also suffers (3-10%) because of reduced energy intake. Still others suggest that corn with test weight as low as 40 LB/bu can support similar performance to corn with normal test weight. Research at South Dakota State University and elsewhere has shown that adding 2-3% oil or fat to diets made with very low test weight corn helps improve performance, but does not return it to the level achieved with normal test weight corn.

Research has determined that low test weight corn tends to be higher in crude protein, fiber and ash and lower in fat and starch than normal corn. 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 tested. Corn with test weights above 45 lbs/bu, as we saw in the 1992 corn crop (7 – 10.4% protein), may also have variable crude protein content and requires close monitoring. However, normal published averages for lysine (0.25%) in low test weight corn 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. Producers who mix feed on-farm 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.
• Most importantly, remember that if you work in weight of corn, not volume, or adjust accordingly, you shouldn’t have a problem.

Table 7. Feed weight adjustments for low grade corn.

Bushel Weight (lbs)	Kg required to equal 1 kg 56 lbs/bu corn
56	1.000
54	1.009
52	1.017
50	1.026
48	1.035
46	1.044
44	1.053
42	1.063

Source: McBride, G. 1992.

Table 7 provides an estimate of the weight of low grade corn needed to provide the same energy as 1 kg of 56 lbs/bu corn, based on the research carried out at the University of Guelph in the 70’s. 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

References

Iverson, DM and Thaler, R.C. 1996. Low-quality soybeans and corn as feedstuffs for swine. Swine Health and Production, Vol.4, No. 1.

Johnston, L.J. 1995. Use of low-test-weight corn in swine diets and the lysine/protein relationship in corn. Swine Health and Production, Vol. 3 No.4.

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

Patterson, R., Tuitoek, J. and Young, L. 1993. Nutritional value of immature corn of different bulk density for young pigs. 1993 Ontario Swine Research Review.

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

Summers, J. 1992. Feeding value of immature and low bushel weight corn. Poultry Industry Council Factsheet #16.

Vyn, T. 1993. Corn Quality – What to do? 1993 Southwestern Ontario Pork Conference.