Following report from ---

A high oil corn and a conventional hybrid were grown for silage. A portion of each field was harvested with a conventional silage chopper and the other portion with a chopper equipped with a kernel processing unit. The high oil silage had higher concentrations of fatty acids and crude protein than the conventional hybrid. Feed intake was not different among diets, but cows fed high oil silage produced 2.3 lbs./day more milk than cows fed the conventional silage. Processing had little effect on production for cows fed high oil silage but increased milk production 2.2 lbs/day for cows fed the conventional hybrid. High oil corn silage had about 4% more available energy than the conventional hybrid. Processing increased the available energy content of the conventional hybrid by 8% but had no effect on the energy value of the high oil corn silage.

Introduction

Previous research with high oil corn silage generally found no difference in milk production compared with a conventional hybrid but those studies used diets that contained relatively low concentrations of corn silage. Because of the relatively small increase in fat content of high oil corn silage, low inclusion rates limit the ability to detect differences in nutritional value. Kernel processing generally consists of two roller mill rolls in the silage harvester between which the chopped material must pass. The rollers crush and shear the material as it passes through the rollers. Very little published data are available on the effects of kernel processing on the nutritional value of corn silage to dairy cows and results have been inconsistent. The objective of this study was to compare the nutritional value of high oil corn silage to conventional silage with and without kernel processing.

Materials and Methods

In Spring, 1997, a high oil hybrid (Doebler's Hybrid 637T6; Doebler's Hybrids, Inc., Jersey Shore, PA) and a conventional hybrid (Doebler's Hybrids 636XY) of corn were planted in plots at OARDC (Wooster). The high oil variety was produced using the TopCross system in which approximately 90% of the corn plants were the same variety (male sterile) as the conventional corn and 10% of the corn plants were a high oil pollinator. Fields had similar soils and agronomic practices were identical for both varieties. Seeding rate was 29,000 seeds/acre. In early October 1997, approximately one-half of each field was harvested as silage using a silage chopper equipped with a kernel processor. The processor was set at 1 mm and the forage was chopped at a theoretical length of cut of 3/4 inches. The remainder of each field was chopped using a conventional silage chopper set at a theoretical length of cut of 0.4 inches. Both varieties of corn were harvested at the one-half milk line stage of maturity.

Four diets composed of 63% corn silage (high oil or conventional corn with and without kernel processing) and 37% concentrate (dry basis) were fed to 32 midlactation Holstein cows (Table 1) for 12 weeks to measure production responses. Diets were purposely high in corn silage to maximize any potential response to the corn silage treatments. Digestibility of nutrients were measured using 4 cows/treatment. Samples of feed and feces were analyzed for nutrients using standard methods. Particle size of the silage was measured using the Penn State particle size separator. The effects of hybrid, kernel processing, and the interaction between variety and processing on production, digestibility, and composition data were analyzed statistically using acceptable methods.

Nutrient composition

Silages contained about 33% dry matter (DM) (Table 2). Based on manual separation of corn plants, 49% of the whole plant DM was grain for the conventional hybrid and 48% was grain for the high oil silage. The DM concentration of the grain was 59% (SD = 0.9) for high oil silage and 55% (SD = 3.0) for the conventional hybrid. Fiber fractions and ash were higher (P <0.05) in processed silages suggesting greater fermentation losses of readily fermentable substrates. Most of the processing effect appeared to be caused by the high oil processed silage. Overall, numerical differences in fiber and ash contents between processed and unprocessed corn silages were small (<10%). Concentrations of crude protein (8.4 vs. 7.5%) and fatty acids (5.5 vs. 3.4%) were higher (P <0.01) in the high oil corn silage than in the conventional silage.

Particle size

Distribution of DM, NDF, and starch among particle size fractions is shown in Table 3. Hybrid had little effect on particle size distribution. Processed corn silage had more DM in the large and small particle size fraction than did unprocessed silage. Based on the distribution of NDF and starch, the increased proportion of DM in the largest particle size fraction was mainly caused by the longer theoretical length of cut used with processed silage. The change in DM distribution between the middle and small particle size fraction was caused mainly by the kernel processing unit. Although processed silage had more DM in the smallest particle size fraction than unprocessed silage, unprocessed silage had more NDF in that fraction. The smallest particle size fraction had about twice as much starch in processed silage as in unprocessed silage. For processed silage, 33% of the whole plant starch was in the small particle fraction, but only 20% of the DM and about 10% of the NDF was found in that fraction. The general conclusions from these data are: 1) for unprocessed corn silage, distribution of DM mass approximates that of NDF and starch; 2) the size of particles containing starch will be overestimated relative to particle size of DM for processed silage; 3) processing allows increased particle size of DM but reduces the size of particles containing starch.

Production data

Treatment did not affect DM intake, but an interaction between variety and processing was observed (P <0.08) (Table 4). This interaction was probably caused by slight differences in body weight because no interaction was observed for intake as a percent of body weight. Cows fed high oil silage produced 2.2 lbs/d more milk (P <0.08) and 2.9 lbs./day more fat-corrected milk (P <0.05) than cows fed the conventional corn silage. Processing did not statistically affect yields of milk or fat-corrected milk, however, an interaction between processing and variety may have been present (P <0.16). Milk production was similar between processing treatments when high oil corn silage was fed, but processing appeared to increase milk production when conventional corn silage was fed. Hybrid did not affect milk fat percent or yield but cows fed high oil corn silage produced milk with less protein (P <0.02). Milk protein yield was not affected by variety. Processing did not affect yield or percent of milk protein. Cows fed processed corn silage produced milk with a higher (P <0.07) concentration of fat (probably because of increased particle size) but fat yield was not changed.

Digestibility

Hybrid had little influence on the digestibility of nutrients except for lower (P <0.07) fatty acid digestibility for diets with high oil corn silage (Table 5). Processing high oil silage had essentially no affect on starch digestibility but had a large effect on conventional corn silage (hybrid by processing interaction, P <0.05). The interaction suggests that kernel structure or starch chemistry is different between high oil and conventional corn. Particle size of the starch was probably not the reason for the difference because no interaction was observed for particle size of starch. The corn silages provided approximately 68% of the starch in the total diet. Assuming the digestibility of starch provided by the concentrate was the same for cows fed processed and unprocessed silage (the same concentrate mix was fed to both groups), processing increased the digestibility of the starch in the conventional corn silage by about 6 percentage units.

The concentration of TDN (Table 5) was higher (P <0.08) in the diets with high oil silage (71.7 vs. 69.9%) and higher (P <0.07) in the diets with processed silage (71.9 vs. 69.7%) and an interaction between variety and processing may have occurred (P <0.07). Processing had little effect on the TDN of high oil corn silage diet but increased the TDN of conventional corn silage diet by 5%. The higher TDN in high oil silage was caused mainly by the increased fat content and the higher TDN in processed silage was caused mainly by increased starch digestibility. If no associative effects occurred, processing increased the energy value of the silage from the conventional hybrid by about 8%, and the high oil silage had about 4% more energy than the conventional hybrid.

TABLE 1. Ingredient composition of the experimental diets (percent of DM).

	Corn silage variety
Ingredient	High oil	Conventional
High oil corn silage	62.70	. . .
Conventional corn silage	. . .	62.70
Soybean meal, 44% CP	15.77	17.54
Corn grain	8.86	7.09
Oats	5.30	5.30
Alfalfa meal	3.54	3.54
Molasses	0.75	0.75
Urea	0.18	0.18
Mineral supplement	1.94	1.94
Vitamins and trace minerals	0.96	0.96
Nutrient
Crude protein	14.8	14.9
NDF	34.5	34.5
Fatty acids	4.72	3.40
Starch	29.0	28.0

TABLE 2. Nutrient composition of conventional and high oil corn silage with and without kernel processing (percent of DM).

	High oil		Conventional			P <1
Nutrient	Unprocessed	Processed	Unprocessed	Processed	SEM	H	P	H X P
DM	33.3	34.1	34.3	33.6	0.33	NS	NS	NS
Organic matter	96.1	95.7	96.0	95.9	0.11	NS	0.03	NS
Crude protein	8.5	8.3	7.6	7.5	0.22	0.01	NS	NS
Fatty acids	5.6	5.3	3.5	3.3	0.23	0.01	NS	NS
NDF	39.3	43.1	40.1	41.8	0.53	NS	0.02	0.03
ADF	22.5	24.3	22.3	23.4	0.54	NS	0.05	NS
Starch	31.1	30.3	30.2	31.8	2.88	NS	NS	NS

¹ H= effect of hybrid, P = effect of processing, NS = P>0.20.

TABLE 3. Effect of hybrid and processing on particle size distribution of DM, NDF and starch (percent of whole plant).

	High oil		Conventional			P <1
Particle size fraction2	Unprocessed	Processed	Unprocessed	Processed	SEM	H	P	H X P
DM
Top	3.7	17.0	3.0	21.9	0.9	0.02	0.01	0.01
Middle	81.1	61.9	82.0	58.8	1.7	NS	0.01	0.08
Pan	15.2	21.0	15.0	19.2	0.7	NS	0.01	NS
NDF
Top	6.4	25.9	5.8	31.5	1.6	0.13	0.01	0.07
Middle	78.6	64.1	77.9	59.5	1.7	0.13	0.01	NS
Pan	15.0	10.1	16.3	9.0	0.9	NS	0.01	NS
Starch
Top	1.1	4.7	0.8	9.4	1.2	0.10	0.01	0.07
Middle	85.9	61.6	83.5	57.7	2.3	NS	0.01	NS
Pan	13.0	33.7	15.7	32.9	1.8	NS	0.01	NS

¹ H= effect of hybrid, P = effect of processing, NS = P>0.20.

² Particle size distribution determined using a Penn State particle separator. Top = particles greater than 1.9 cm, middle = particle size between 0.8 and 1.9 cm, pan = particle size less than 0.8 cm.

TABLE 4. Effect of hybrid and kernel processing on production.

	High oil		Conventional			P <1
	Unprocessed	Processed	Unprocessed	Processed	SEM	H	P	P XH
DM intake, lbs/d	19.2	18.1	17.7	18.8	0.6	NS	NS	0.08
Milk, lbs./d	28.6	28.1	26.8	27.8	0.6	0.08	NS	0.18
FCM, lbs./d	23.8	23.9	22.1	23.0	0.6	0.05	NS	NS
Milk fat, %	2.81	3.10	2.89	3.06	0.12	NS	0.07	NS
Milk fat, lbs./d	0.81	0.84	0.76	0.80	0.03	0.18	NS	NS
Milk protein, %	3.16	3.16	3.22	3.29	0.04	0.02	NS	NS
Milk protein, lbs./d	0.90	0.88	0.86	0.90	0.02	NS	NS	0.16

¹ H= effect of hybrid, P = effect of processing, NS = P>0.20.

TABLE 5. Effect of hybrid and kernel processing on nutrient digestibility (DM basis).

	High oil		Conventional			P <1
	Unprocessed	Processed	Unprocessed	Processed	SEM	H	P	P X H
Apparent digestibility
DM, %	69.8	68.9	67.6	70.2	1.1	NS	NS	0.18
CP, %	74.2	69.6	69.0	70.9	1.0	0.11	NS	0.07
NDF, %	48.7	50.5	45.8	49.1	2.0	NS	NS	NS
NFC2, %	87.4	89.8	86.6	91.0	0.4	NS	0.01	0.07
Starch, %	95.4	94.5	93.2	97.6	0.5	NS	0.01	0.07
Fatty acids, %	77.6	75.4	78.7	82.4	2.3	0.07	NS	NS
TDN, %	71.3	72.1	68.1	71.7	0.9	0.08	0.07	0.07

¹ H= effect of hybrid, P = effect of processing, NS = P>0.20.

² Nonfiber carbohydrates.