Quality and Feeding
	
        Feeding silage
	
        Silage evaluation
	
        Quality of corn silage is determined by energy content and intake 
		potential as well as content of protein and minerals. Methods used to 
		evaluate corn silage quality include chemical methods such as fiber 
		analysis, biological methods such as fermentation with ruminal microbes, 
		and instrumental methods such as near-infrared reflectance spectroscopy 
		(NIRS) which predicts nutrients rather than measuring them directly. 
	
        All methods require that the sample being analyzed is representative of 
		the silage that is being offered to the animal. Therefore, 
		representative samples must be obtained from the silo and the samples 
		must be handled properly prior to analysis. Corn silage samples should 
		be sealed in a plastic bag and sent to a laboratory as soon as possible 
		to reduce spoilage. Care should be taken to avoid exposure of the sample 
		to high temperatures. Samples of fresh forage which are taken when the 
		silo is being filled must be dried immediately to reduce losses due to 
		respiration of sugars, which can dramatically increase the
		concentration of the remaining nutrients. Do not freeze samples as the 
		fiber content becomes artificially increased during thawing due to the 
		condensation of soluble protein with other compounds.
	
        METHODS FOR DETERMINING ENERGY CONTENT
	
        The energy content of corn silage is primarily determined by the amount 
		and digestibility of fiber. Grain content also affects energy content, 
		although it is possible for a corn silage with less than 30% grain to 
		have a higher energy content than a corn silage with more than 50% grain 
		due to differences in stover digestibility. Starch digestibility affects 
		energy content for dry corn silages but is less of a factor for corn 
		silage with greater than 60% moisture. As determining digestibility 
		using animals (in vivo digestibility) is too time consuming and 
		expensive for routine use, several techniques are used to estimate 
		digestibility and energy content.
	
        Total digestible nutrients (TDN) describes the energy 
		content of feeds as the sum of the digestibilities of different 
		nutrients. However, because animals use the available energy differently 
		depending on the
		feed and on the animal's production status, the TDN system overestimates 
		energy derived from forages relative to grain. Appendix table 4 presents 
		commonly used energy estimates. 
	
        The net energy system accounts for the variation in 
		digestible energy usage by assigning feeds three net energy values: net 
		energy for maintenance (NEm)' net energy for gain (NEg), and net energy 
		for lactation (NEL). Digestible energy used for maintenance and for milk 
		production is used more efficiently than digestible energy used for 
		gain. While equations convert TDN energy values to NE values, the same 
		equation is usually used for both forages and grains, which decreases 
		accuracy.
	
        The acid detergent fiber (ADF) content of silage is the 
		most common method used by commercial feed testing laboratories to 
		predict energy content. As ADF decreases, the digestibility and 
		therefore the energy content increases. This method offers low cost and 
		rapid turnaround, which are requirements for balancing animal rations. 
		ADF contains lignin (totally indigestible) as well as cellulose (poorly 
		digestible) and pectin (highly digestible). The relationship between ADF 
		and energy content is not absolute, however, since ADF accounts for less 
		than two-thirds of the variation in energy content in corn silage. The 
		inaccuracy of this method is caused by significant variations in the 
		digestibility of the fiber in corn silage.
	
        In vitro digestibility methods use fermentation by 
		ruminal microbes in test tubes or artificial rumens to determine 
		digestibility. In situ digestibility methods allow forage digestion 
		inside the rumen of a cow or steer. These methods offer greater accuracy 
		of energy prediction because they account for variation in fiber 
		digestibility but are more time consuming and expensive than ADF 
		determination. Due to cost and complicated procedures of in vitro 
		techniques, they are used primarily for research purposes such as hybrid 
		comparison. However, near-infrared reflectance (NIRS) equations 
		accurately estimate in vitro values, allowing ranking of commercially 
		available hybrids.
	
        Table 11. Average composition of poor and well-eared corn silage.
	
		| Component | 
		Well-eared (%) | 
		Poor (%) | 
	
	
		| Crude protein | 
		8.6 | 
		8.4 | 
	
	
		| NDF | 
		46.0 | 
		53.0 | 
	
	
		| ADF | 
		26.0 | 
		30.0 | 
	
	
		| Cellulose | 
		22.0 | 
		23.0 | 
	
	
		| Lignin | 
		4.0 | 
		5.0 | 
	
	
		| Ash | 
		3.0 | 
		7.2 | 
	
	
		| Calcium | 
		0.30 | 
		0.34 | 
	
	
		| Phosphorous | 
		0.28 | 
		0.19 | 
	
	
		| Potassium | 
		1.32 | 
		1.41 | 
	
	
        SILAGE COMPOSITION
	
        FORAGE QUALITY TERMS
	
        NDF (neutral-detergent fiber). A measurement of the 
		total fiber content of a forage. NDF is composed of cellulose, 
		hemicellulose, and lignin. High fiber forages fill the stomach faster, 
		meaning the animal
		eats less and needs more ration supplements. Corn silage NDF 
		concentration ranges from 36 to 50%. A low corn silage NDF is desirable.
	
        ADF (acid-detergent fiber). A measurement of the 
		cellulose, lignin, and pectin fiber fractions of forages. ADF is 
		commonly used to predict energy content of corn silage and other 
		forages. Corn silage ADF concentration ranges from 18 to 26%. Corn 
		silages with lower ADF values have a higher energy content and are 
		desirable. 
	
        Lignin. An indigestible fiber that has no energy value 
		to the animal. In addition, lignin restricts digestibility of other 
		fiber components. The lignin content of corn silage is low and ranges 
		from about 2 to 4%. A low lignin content is desirable.
	
        In vitro dry maHer digestibility (IVDMD). A measure of 
		the apparent digestibility of dry matter. Determined by incubating feed 
		in a flask with ruminal microbes and following this incubation with a
		pepsin and hydrochloric acid incubation to simulate digestion in the 
		true stomach. The amount of dry matter remaining is divided by the 
		original dry matter and subtracted from 1.0.
	
        In vitro NDF digestibility (or cell wall digestibility).
		A measure of ruminal digestibility of NDF. Determined by 
		incubating feed in a flask with ruminal microbes followed by analyzing 
		the fiber content of the residue. The amount of fiber content remaining 
		is divided by the original fiber content and subtracted from 1.0.
	
        In situ dry matter digestibility. A measure of the 
		apparent digestibility of dry matter. Determined by placing the forage 
		sample in a dacron bag within the rumen of a cow or steer. The sample is 
		retrieved, washed, dried, and weighed. The amount of dry matter 
		remaining is divided by original dry matter and subtracted from 1.0. 
	
        In vivo digestibility. A measure of the digestibility 
		of dry matter using animals. Disappearance of dry matter (digestibility) 
		is determined as the difference between the quantity of dry matter 
		consumed
		and the quantity of dry matter excreted in the feces.
	
        Energy content. The results of each method can be used 
		directly to rank: hybrids for digestibility but must be adjusted for 
		specific feeding situations to accurately predict digestibility and 
		energy content. The length of time that feeds reside in the rumen and 
		are fermented varies depending on several factors including animal 
		species and level of intake. Digestibility increases as fermentation 
		time increases. In general, animals with high dry matter intakes such as 
		those that are rapidly growing or producing large quantities of milk, 
		have shorter ruminal retention times and digest food less efficiently 
		than animals with lower dry matter intakes.
	
        Consequently, the energy content of corn silage varies depending on the 
		animal to which it is fed. For instance, a steer at maintenance intake 
		with a ruminal retention time of over 40 hours will obtain more energy 
		from the same feed as a high-producing dairy cow with a ruminal 
		retention time of 30 hours or less. Accuracy of energy prediction also 
		decreases as corn silage dry matter increases because many corn kernels 
		pass through the gastrointestinal tract undigested, reducing starch 
		digestibility. These factors coupled with the environmental effects 
		cause energy content of corn silage to vary from 62 to 74% TDN or 
		approximately 0.64 to 0.75 mcal/lb NEL.
	
        Corn silage in vitro NDF digestibility ranges from 30 to 60%. This 
		variation is primarily due to environmental conditions during crop 
		growth. However, corn hybrids have been found to differ by up to 5 units 
		in NDF digestibility and NDF digestibility has been found to decline 
		with advancing maturity. Variation in NDF digestibility has great 
		consequences to forage utilization in three different areas: it affects 
		the energy density of the ration, dry matter intake, and microbial 
		protein production.
	
        Energy density of the ration is affected because a certain amount of 
		fiber is required in the ration for normal, healthy rumen function. 
		Therefore, less energy from this fiber will reduce energy density and 
		energy intake. Feeds with high fiber digestibility have a lower filling 
		effect and allow greater intake than feeds with low fiber digestibility. 
		Differences in fiber digestibility also affect the amount of protein 
		available to the animal.
	
        Intake potential. High fiber diets fed to ruminants 
		limit intake due to the filling effect of the food. Fiber (ND F) is 
		fermented and passed from the rumen slowly compared to nonfibrous feed 
		components such as sugars and starch. Less digestible fiber is retained 
		in the rumen longer than highly digestible fiber. Therefore, the filling 
		property of a forage is related to its NDF content and NDF 
		digestibility. A low NDF content and high NDF digestibility of corn 
		silage are desirable to maximize forage and dry matter intake.
	
        The NDF content of corn silage varies by hybrid and climate, and 
		decreases with nitrogen fertilization and maturity at harvest. It is a 
		major factor determining corn silage intake for lactating dairy cows in 
		early lactation. To ensure adequate chewing and salivation, 
		nutritionists generally balance rations of high-producing cows for an 
		optimum amount of fiber to maximize energy intake. If too much fiber is 
		in the ration, intake will be limited and more body condition will be 
		lost. If there is too little fiber in the ration there will be excess 
		formation of fermentation acids and inadequate buffering, intake will be 
		limited and again more condition will be lost. Because of this, meeting 
		the animal's fiber requirements takes precedence over attempting to meet 
		the animal's energy requirements. Corn silage with a low NDF content can 
		be included in the ration at higher levels than corn silage with a high 
		ND F content.
	
        Protein. Crude protein is a mixture of true protein and 
		nonprotein nitrogen. Less than 30% of the total protein in corn forage 
		is available to the animal as absorbable true protein as much of it is 
		degraded by
		fermentation in the silo and in the rumen to nonprotein nitrogen. 
		However, much of the ammonia produced in the fermentation process is 
		available to the animal. Some of the crude protein is totally 
		unavailable to the animal. This fraction is called bound protein or 
		heat-damaged protein. Although it is usually negligible, this fraction 
		can be substantial for silages that have heated extensively in the silo 
		and must be adjusted for when balancing rations. Crude protein levels of 
		untreated corn silage range from less than 6% to over 10% of dry matter 
		depending on environmental conditions, fertilization, hybrid, and 
		maturity.
	
        Feeding silage to dairy cattle
	
        Corn silage is used for feeding all dairy cattle on the farm: growing 
		animals, dry cows, and lactating cows. It must be supplemented with 
		protein, minerals, and sometimes energy to meet the animal's nutrient 
		requirements. Although corn silage is occasionally used as the only 
		forage for dairy cattle, it is usually fed with a complimentary forage 
		such as alfalfa which is higher in crude protein but lower in energy. 
		Corn silage feeding strategies vary depending on animal age, level of 
		production, and physiological status as well as the other forages being 
		fed, if any. Because of its high grain content, feeding strategy for 
		corn silage fed to high producing cows differs from most other forages. 
		Corn silage quality factors that are important to consider when 
		balancing rations are energy content, NDF content, NDF digestibility, 
		length of cut, starch content, and starch digestibility.
	
        HEIFERS AND DRY COWS
	
        Corn silage is an excellent dry cow forage as it is palatable and can be 
		limit fed or mixed with lower energy forages. However, the amount of 
		corn silage fed to dry cows and heifers must be restricted due to its 
		high energy content. Dry cows require rations balanced from 0.57 mcal/lb 
		NEL early to over 0.72 mcal/lb NEL depending on their body condition and 
		time until calving. Increase the ration energy density 2 to 3 weeks 
		before calving as fetal energy requirements increase and the cow's dry 
		matter intake decreases. Fat cows should receive rations of lower energy 
		density than thin cows. Feeding unrestricted quantities of corn silage 
		throughout the dry period will result in fat cows which tend to have 
		lower dry matter intakes and higher incidence of metabolic problems such 
		as ketosis and fatty liver following calving. Corn silage contains low 
		calcium compared to other forages. This is an advantage because high 
		calcium intake in the dry period contributes to milk fever following 
		calving.
	
        Corn silage can be fed to replacement heifers beginning at approximately 
		6 months of age. Energy requirements of growing heifers decreases from 
		69% TDN at 3 to 6 months of age to 61%TDN for heifers over 12 months of 
		age. Feeding unrestricted quantities of corn silage to heifers will 
		result in fat animals with lower potential milk production due to fatty 
		infiltration of the udder. Restricting feed intake presents a problem 
		for group-housed heifers because more aggressive animals may receive 
		more than their share, resulting in uneven body condition among the 
		heifers in the group. As protein requirements of growing heifers ranges 
		from over 16% at 3 to 6 months of age to about 14% for heifers over 12 
		months of age, corn silage must be supplemented with protein when fed to 
		heifers. A solution to restricted feeding of corn silage to heifers is 
		to feed a combination of corn silage and a higher protein, lower energy 
		forage such as a legume silage.
	
        LACTATING DAIRY COWS
	
        The high energy requirements of lactating dairy cows increase the 
		difficulty of balancing rations that meet animal needs for both energy 
		and fiber. The effectiveness of corn silage fiber at stimulating rumen
		movements and chewing is primarily determined by its length of cut. 
		Coarsely chopped corn silage will stimulate more chewing and salivation 
		per pound of fiber than feeding the same silage that has been finely 
		chopped. If fiber is more effective at stimulating chewing and 
		salivation, less is needed in the ration to provide the same amount of 
		buffering from saliva. Although coarsely chopped corn silage is more 
		effective at stimulating chewing it will not pack as densely in the 
		silo, will have fewer corn kernel coats broken, and will have larger 
		pieces of cob which will allow sorting and possibly refusal by cows than 
		more finely chopped corn silage. Length of cut should be adjusted to 
		provide larger silage particles while minimizing the number of large cob 
		particles and unbroken corn kernels. Wetter corn forage can be chopped 
		coarser than drier corn forage. Dry corn kernels require a finer chop to 
		break seed coats than wetter corn kernels. Kernel breakage will maximize 
		starch digestibility. In addition, wet corn forage chops more 
		consistently than drier corn forage. The chopper knives shred dry leaves 
		rather than cut, decreasing the uniformity of particle size and allowing 
		animals to sort further.
	
        Corn silage contains up to 35% starch and needs to be supplemented 
		differently than most other Forages to High-producing cows due to this 
		high starch content. Excessive starch can lead to digestive upsets and 
		low energy intakes due to excess accumulation of fermentation acids in 
		the rumen. To optimally supplement forages, one must consider the starch 
		content and ruminal fermentability of grains as well as forages. 
		Low-starch forages such as alfalfa should be supplemented with a grain 
		such as high-moisture corn or barley, which will be highly fermented in 
		the rumen. This will increase the fermented organic matter in the rumen 
		and allow more efficient utilization of degraded forage protein.
	
        Corn silage is high in starch which is usually highly digested in the 
		rumen. Therefore, supplementing corn silage with a starch source such as 
		high-moisture corn that is highly digestible in the rumen is likely to 
		cause digestive upset. To increase energy intake, corn silage should be 
		supplemented with a grain source that partially bypasses ruminal 
		fermentation yet has high whole-tract digestibility such as dried ground 
		corn. When corn silage is fed in combination with alfalfa, less bypass 
		starch is needed as the fraction of alfalfa is increased.
	
        Feeding silage to beef cattle
	
        Energy and protein provision represents the majority of the volume and 
		cost of beef rations. Corn silage may be a logical feed ingredient 
		alternative in providing adequate energy in beef cattle feeding 
		programs.
	
        COW/CALF
	
        The biological cycle of the beef animal results in tremendous diversity 
		in nutrient requirements, particularly energy, among the various classes 
		of beef cattle. The cycle begins with the cow/calf production phase 
		which includes both purebred and commercial production. Within this 
		production phase the nutrient requirements of the cow vary from very low 
		during the mid-gestation dry period to high requirements during early 
		lactation and rebreeding. As calves are weaned at approximately 7 months 
		of age, those entering the reproductive herd are fed at moderate energy 
		levels until near calving. The offspring intended for the slaughter 
		market are typically placed on high-energy, high-grain finishing 
		rations. Table 12 provides the energy requirements of beef cattle at 
		these various production stages with energy content of corn silage for 
		comparison. A ration management strategy that is often utilized to meet 
		the animal's energy requirement is to combine high-energy corn silage 
		with low-quality, low-cost roughages.
	
        Table 12. Energy requirements of beef cattle.
	
		
			 | 
			
			Metabolizable energy | 
		
		
			| Cattle type | 
			Mcal/day | 
			Mcal/lb | 
		
		
			| Dry cow—mid-gestation | 
			  | 
			.80 | 
		
		
			|     1000 lb | 
			
				 14.5 
				 | 
			.80 | 
		
		
			|     1400 lb | 
			18.7 | 
			  | 
		
		
			| Dry cow—late gestation | 
			  | 
			  | 
		
		
			|     1000 lb | 
			17.3 | 
			.88 | 
		
		
			|     1400 lb | 
			21.5 | 
			.86 | 
		
		
			| Cows nursing calves—average milk | 
			  | 
			  | 
		
		
			|     1000 lb | 
			18.8 | 
			.93 | 
		
		
			|     1400 lb | 
			23.0 | 
			.90 | 
		
		
			| Cows nursing calves—superior milk | 
			  | 
			  | 
		
		
			|     1000 lb | 
			22.7 | 
			1.10 | 
		
		
			|     1400 lb | 
			27.1 | 
			1.01 | 
		
		
			| Two-year-old heifers nursing calves | 
			  | 
			  | 
		
		
			|     900 lb | 
			19.8 | 
			
				 1.03 
				 | 
		
		
			| Replacement heifers | 
			  | 
			  | 
		
		
			|     750 lb, 1.4 lb daily gain | 
			16.4 | 
			
				 .98 
				 | 
		
		
			| Steer Calves, medium frame, 600 lb | 
			  | 
			  | 
		
		
			|     1.5 lb daily gain | 
			15.3 | 
			1.04 | 
		
		
			|     3.0 lb daily gain | 
			18.8 | 
			1.39 | 
		
		
			| Corn silage | 
			  | 
			  | 
		
		
			|     Few ears | 
			--- | 
			1.02 | 
		
		
			|     Well eared | 
			--- | 
			1.15 | 
		
	
	
        Cow/calf production in North America typically follows an annual cycle 
		of calving in the spring and weaning the calf crop the following fall. 
		Cows are sustained from calving to weaning on grazable forages, 
		predominantly grass pastures. Following weaning, cows are in 
		midgestation and their energy requirements can be met through the fall 
		and early winter with low-quality roughages such as crop residues. 
		Subsequently, nutrient requirements increase as cows enter late 
		gestation followed by lactation and rebreeding. This period is the 
		logical time for corn silage feeding as energy requirements
		are high and the cows are often in confinement or can otherwise be "bunk 
		fed." Corn silage can be added into rations at this time to obtain 
		suitable cow body condition. Management of body condition via dietary 
		energy levels during late gestation through breeding season is important 
		for successful lactation and rebreeding. Cow body condition management 
		has become especially important in recent
		decades as the beef industry has incorporated larger, European 
		continental breed into herds. These cows require greater levels of 
		metabolizable energy (table 12), which often cannot be provided by 
		conventional wintering forages.
	
        GROWING AND FINISHING RATIONS
	
        Corn silage makes an excellent feed for growing cattle following 
		weaning. Rations are often formulated with sufficient energy to allow 
		1.5 to 2.0 pounds of daily gain. Typical rations may contain 60% corn 
		silage with 30 to 35% hay and 5 to 10% supplement. Addition of grain to 
		corn silage-based rations such as this may reduce fiber digestibility 
		due to sustained lower ruminal pH. Because corn silage is fine chopped 
		and moist, an insufficient amount of saliva may be mixed with the 
		consumed ration. Feeding coarse-chopped or long hay with corn silage 
		will encourage rumination and saliva production for a more healthy 
		ruminal environment. 
		
		Corn silage is also routinely included in beef finishing rations. These 
		rations require only a minimum level of forage to provide ruminal 
		stability. Corn silage is an excellent forage for finishing rations as 
		it is finely chopped and has a high moisture content, making it very 
		mixable with other ration ingredients. Energy is widely considered the 
		limiting nutrient in finishing rations, therefore energy provided by 
		corn silage is of principal importance. The high level of grain in 
		finishing rations results in a very poor ruminal environment for fiber 
		fermentation. The stover fraction of corn silage therefore is probably 
		very poorly digested when fed in finishing rations. Consequently, the 
		grain content of corn silage is an important factor in the nutritive 
		value of silage for finishing rations.
	
        IMPORTANT COMPOSITION CONSIDERATIONS
	
        Energy values of corn silage fed in forage-based rations appear to be 
		reasonably well predicted by fiber (NDF and ADF) content. Research has 
		demonstrated a wide range of differences in fiber content of corn
		silage. These differences are a function of grain content and of the 
		fiber concentration in the stover fraction. Differences in corn silage 
		fiber content affect differences in digestibility. 
	
        Since many beef cattle operators are more accustomed to feeding dry 
		feeds, the dry matter content of silage is often overlooked. Subtle 
		changes in the dry matter content will drastically change the as-fed 
		amounts of silage to be fed. Similarly, changes in dry matter content 
		should be reconciled by changes in the purchase price of the silage if 
		the beef producer is buying the silage. Producers should be aware of 
		changes in dry matter content and implement formulation and price 
		changes accordingly.
	
        MYCOTOXINS IN CORN SILAGE
	
        Mycotoxins are toxic substances produced by molds growing on grain or 
		feed. Mycotoxins can cause illness or death to livestock and humans. 
		While the vast majority of molds that can grow on silage are harmless, a 
		few species produce mycotoxins. The primary mycotoxins found in corn 
		silage are aflatoxin, deoxynivalenol (DON or vomitoxin), zearalenone, 
		T-2 toxin, fumonisin, and ochratoxin. Mycotoxin-contaminated silage fed 
		to cattle is rarely fatal. More commonly, contaminated feed reduces 
		growth rate, lowers feed conversion and reproductive rate, impairs 
		resistance to infectious diseases, and reduces vaccination efficacy.
	
        TOXIC LEVELS
	
        Establishing the toxic level for specific mycotoxins in cattle is 
		difficult and only limited data exists. Various classes of livestock are 
		more susceptible than others. Cattle are generally more tolerant than 
		other livestock species. Mycotoxin-contaminated feed poses a greater 
		health risk to young or pregnant animals and animals that are stressed.
	
        The only regulated toxic feeding level for a specific mycotoxin is for 
		aflatoxin. The maximum dietary level for aflatoxin has been set by the 
		Food and Drug Administration (FDA) for cattle to be no more than 200 
		parts per billion (Ppb) for breeding cattle, 300 ppb for finishing 
		cattle, 20 ppb in feeds for lactating dairy cattle. Never use 
		contaminated feeds that exceed these levels.
	
        The toxic levels for the other primary mycotoxins found in silage are 
		much less defined and significant controversy exists among researchers 
		working in this area. This controversy largely stems from the methods 
		used to determine the toxic effect. The toxic effect of a mycotoxin can 
		be defined in either acute or subacute (chronic) terms. The acute level 
		is the level that will produce a clinical (pathological) illness when 
		the animal is given a single dose over a relatively short period of 
		time. While the subacute or chronic effects have generally been 
		established through field observations of animals receiving contaminated 
		feedstuffs over longer periods of time. The subacute toxic level for a 
		particular mycotoxin is difficult to establish since some mycotoxins are 
		partially degraded by rumen microorganisms. Feeding practices that 
		influence rumen fermentation, such as frequency of feeding, diet 
		composition, level of intake, and duration of feeding, may have an 
		impact on the tolerance level of the animal. Likewise, most cases of 
		mycotoxin contamination involve more than one source of mycotoxin. It 
		has also been suggested that there are associative effects when multiple 
		sources of mycotoxin are fed. Thus, clinical studies which have 
		established the acute toxic level of a purified mycotoxin may actually 
		underestimate the toxic level found in contaminated feedstuffs fed in 
		field situations.
	
        The guidelines in table 13 offer some practical recommendations for 
		establishing the tolerable levels of specific mycotoxins when fed to 
		cattle. The acute levels given are those established by clinical studies 
		which have clearly demonstrated a toxic effect. The subacute (chronic) 
		levels indicate the mycotoxin level in the diet which may reduce 
		performance.
	
        Table 13. Descriptions of mycotoxins and illness symptoms for 
		cattle.
	
		
			| Mycotoxin | 
			Mold | 
			Acute level | 
			Subacute level 
			  | 
			Illness symptoms | 
		
		
			| Aflatoxin | 
			Aspergillus | 
			20 ppm (lactating dairy cattle) 
			200 ppb (breeding cattle) 
			300 ppb (finishing cattle) | 
			Reduced growth and milk production. 
			Increased susceptibility and reduced 
				immunity. 
			Liver damage and increased death losses. 
				Milk residues. | 
		
		
			| Deoxynivalenol (DON or vomitoxin) | 
			Fusarium  | 
			10 ppm | 
			500 ppb | 
			Reduced feed intake and lowered production. 
			Toxicity may increase when other mycotoxins 
				are present. | 
		
		
			| Fumonisin | 
			Fusarium | 
			95 ppm | 
			?? | 
			Not known. | 
		
		
			| Ochratoxin | 
			Penicillium and Apsergillus | 
			5 ppm | 
			1 ppm | 
			Diarrhea, kidney damage and reduced 
				production. | 
		
		
			| T-2 | 
			Fusarium | 
			50 ppm | 
			100 ppm | 
			Intestinal hemorrhages, decreased food 
				intake, unthriftiness, and death. | 
		
		
			| Zearalenone | 
			Fusarium | 
			500 ppm | 
			500 ppb | 
			Decreased fertility, swelling around 
				the vulva, and irregular and prolonged estrus cycles (estrogen). | 
		
		
			Total dietary concentration 
		Ppm = parts per million or mg/kg; ppb = parts per billion or µg/kg. | 
		
	
	
        INCIDENCE OF MYCOTOXINS
	
        It is suggested that the incidence of certain mycotoxins are related to 
		geographical location. Mycotoxins produced by Aspergillus, such as 
		aflatoxin, are more prevalent in the southern United States. 
	
        Mycotoxins produced by Fusarium, such as DON, T-2, and Zearalenone, may 
		be more prevalent in the northern United States and are associated with 
		cool, moist conditions and diseases such as ear or stalk rot in corn. 
		However, aflatoxin contamination has been reported in corn silage in 
		Wisconsin and other northern states and Fusarium mycotoxins have been 
		reported in North Carolina and other southern states.
	
        Since molds are spore-forming organisms, they have the unique ability to 
		survive even the most unfavorable growth conditions. They will grow 
		wherever there is a suitable substrate, pH, and adequate amounts of 
		water, oxygen and heat. Mold growth and potential mycotoxin production 
		can occur on the growing corn plant, during the initial aerobic phase of 
		the ensiling process, on the exposed surfaces of the silo during storage 
		and feedout, and in the bunk once fed.
	
        Certain agronomic practices are associated with higher incidences of 
		mycotoxin-producing fungi. No-till or minimum till cultivation, corn on 
		corn cropping patterns, delayed planting, heavy applications of manure, 
		and fertility imbalances have all been implicated. Likewise, corn plants 
		subjected to insect, wind, or hail damage are more prone to mold growth 
		and potential mycotoxin contamination.
	
        MYCOTOXIN TESTING
	
        Analytical techniques for mycotoxin testing have improved over the past 
		decade. Several commercial laboratories are available and many state 
		universities have diagnostic laboratories which provide screens for a 
		large array of mycotoxins. Cost of analysis has been a constraint, but 
		can be insignificant compared with the economic consequences of 
		production and health losses related to mycotoxin
		contamination.
	
        As with any analytical analysis, the results are only as valid as the 
		sample is representative. Since molds can produce very large amounts of 
		mycotoxin in small non-uniform locations, representative sampling is 
		critical. Samples should be delivered to the lab as quickly as possible 
		since mycotoxins can form in the collected sample if allowed to heat or 
		if exposed to oxygen. Acceptable levels of mycotoxin should be 
		conservatively low due to non-uniform distribution, uncertainties in 
		sampling and analysis, and the potential for more than one source in the 
		diet.
	
        PREVENTION AND TREATMENT
	
        Prevention is the most cost-effective and safest way to avoid problems 
		associated with mycotoxins. Since mold contamination begins with the 
		growing plant, sound agronomic practices which minimize the incidence of 
		insect and disease levels will reduce the potential contamination in the 
		silage. Often environmental factors out of the producer's control such 
		as wind and hail damage, drought, or early frost, will dictate the use 
		of the crop for silage. Under these conditions, the mold level on plants 
		will be elevated and this increases the potential risk for mycotoxin 
		production.
	
        The key to the prevention of mold growth during the ensiling process is 
		the elimination of air as quickly as possible, and managing the silo to 
		minimize air infiltration into the ensiled mass during storage and
		feedout. Employing sound silage management practices including rapid 
		filling, harvesting at the correct moisture level, adequate compaction, 
		covering exposed surfaces, and rapid feedout will go a long way in 
		minimizing mold growth and potential mycotoxin contamination in silages. 
		The use of some silage additives may be beneficial in reducing the risk 
		of potential mycotoxin production if they are shown to reduce mold 
		growth. Ammonia and/or propionic acid appear effective in this regard. 
		Certain bacterial inoculants may also be beneficial since they have been 
		shown to increase the rate of pH decline in the silage and extend 
		aerobic stability of the silage on feedout.
	
        At present there is no practical way to detoxify mycotoxin-contaminated 
		silages. If unacceptably high levels of mycotoxins occur, dilute or 
		eliminate the silage from the diet. The addition of absorbent materials, 
		such as clays (bentonites) or anticaking agents (hydrated sodium calcium 
		aluminosilicate), to contaminated rations has helped in some cases and 
		may warrant consideration. Avoid feeding moldy clumps of silage or 
		visibly moldy silage, particularly to pregnant animals or young stock.
	
        Further Reading
	
        Wisconsin
    
        Note: Web resources for Wisconsin are maintained by
		Mike Rankin and
		Team 
		Forage. Please see
		http://www.uwex.edu/ces/crops/uwforage/Silage.htm 
		for an up-to-date listing.
    
        Impact
            of Feed Prices on Cost of Simulated Average and High Corn Silage Rations
        
        by Paul Dyk, Fond du Lac County Dairy and Livestock Agent, and Dr. Randy Shaver,
        UW Extension Dairy Scientist 
    
    
        Degree of Starch
            Access (DSA): Starch Digestion in Forages and Grains Fed to Dairy  Cattle
        by Pat Hoffman and Randy Shaver, UW Extension Dairy Scientists, A "Focus on
        Forage" Fact Sheet.
    
        Milk2006
        for Corn Silage
        This spreadsheet, developed by Dr. Randy Shaver, Dr. Joe Lauer, Dr. Jim Coors, and
        Pat Hoffman, is the latest version of the "MILK" series spreadsheets. 
        It more accurately estimates the feeding value of corn silage than past versions.
    
        Crop Processing
            and Chop Length of Corn Silage: Effects on Intake, Digestion, and Milk Production
            by Dairy Cows
        
        by Dr. Randy Shaver, UW Extension Dairy Scientist, et al. 
    
    
        Influence of Mechanical
            Processing on Utilization of Corn Silage by Lactating Dairy Cows
        
        by Dr. Randy Shaver, UW Extension Dairy Scientist, et al. 
    
    
        Processing and Chop
            Length Effects in Brown-Midrib Corn Silage on Intake, Digestion, and Milk Production
            by Dairy Cows
        
        by Dr. Randy Shaver, UW Extension Dairy Scientist, et al. 
    
    
        Stage of
            maturity, processing, and hybrid effects on ruminal in situ disappearance of whole-plant
            corn silage
        
    
        Corn Silage Hybrid
            Effects on Intake, Digestion, and Milk Production by Dairy Cows
        
        by Dr. Randy Shaver, UW Extension Dairy Scientist, et al. 
    
    
        Impacts of
            2004 Growing Season on Silage Quality
        
        A presentation given by Joe Lauer, UW Extension Corn Agronomist, at the 2005 Wisconsin
        Fertilizer, Ag Lime, and Pest Management Conference
    
        Can we manage corn silage stover
            quality?
        by Dr. Joe Lauer, UWEX Agronomy Advice, December, 2003
    
        Dairy Cattle
            Feeding Tips for Drought Stressed Corn
        
        by Dr. Randy Shaver and Pat Hoffman, UW Extension Dairy Scientists
    
        The Effect of Maturity
            on NDF Digestibility
        by Pat Hoffman, UW Extension Dairy Scientist, Marshfield Ag Research Station, et
        al.  A "Focus on Forage" Fact Sheet.
    
        Agronomic Considerations
            for Molds and Mycotoxins in Corn Silage
        by Mike Rankin, Crops and Soils Agent, UW-Extension-Fond du Lac County and Craig
        Grau, Extension Plant Pathologist - UW Madison.  A "Focus on Forage"
        fact sheet.  For full length, referenced paper: 
            click here
    
        Understanding NDF Digestibility
            of Forages
        by Pat Hoffman, UW Extension Dairy Scientist, Marshfield Ag Research Station,
        et al.  A "Focus on Forage" Fact Sheet.
    
        Enhanced Forage Evaluation:
            NDF Digestibility
        
        by Scott Reuss, Marinette Co. Agricultural Agent
    
        Interpretation and
            Use of Silage Fermentation Analysis Reports
        by Limin Kung, University of Delaware, and Randy Shaver, UW Extension Dairy
        Scientist.  A "Focus on Forage" fact sheet.
    
        Estimating Silage
            Energy and Milk Yield to Rank Corn Hybrids
        
        by Dr. Randy Shaver, UW Extension Dairy Scientist et al.
    
        Feed Delivery
            and Bunk Management Aspects of Laminitis 
        by Dr. Randy Shaver, UW Extension Dairy Scientist 
    
        Supplementation
            of High Corn Silage Diets for Dairy Cows 
        
        by Dr. Randy Shaver, UW Extension Dairy Scientist
    
        Influence of Corn
            Silage Particle Length on the Performance of Lactating Dairy Cows Fed Supplemental
            Tallow
        
        by Dr. Randy Shaver, UW Extension Dairy Scientist, et al. 
    
    
        Impact of the Maturity
            of Corn for Use as Silage in the Diets of Dairy Cows on Intake, Digestion, and Milk
            Production
        
        by Dr. Randy Shaver, UW Extension Dairy Scientist, et al. 
    
    
        Adding
            Enzymes to Silage
        
        by Pat Hoffman, UW Extension Dairy Scientist, Marshfield Ag Research Station and
        Richard Muck, USDA Dairy Forage Research Center.  A "Focus on Forage"
        fact sheet.
    
        
            Adding Urea to Corn Silage
        
        by Pat Hoffman, UW Extension Dairy Scientist, Marshfield Ag Research Station. 
        A "Focus on Forage" fact sheet.
    
        Corn Silage
            Harvest Management 
        
        by Dr. Randy Shaver, UW Extension Dairy Scientist, Dr. Joe Lauer, UW Extension Agronomist
        and Dr. Kevin Shinners, UW Ag Engineer
    
        Balancing Use of Corn Silage
            and Alfalfa in Dairy Rations
        by Dr. Randy Shaver, UW Extension Dairy Scientist
    
        
            FeedVal
        
        This spreadsheet, developed by Drs. Terry Howard and Randy Shaver, is a program
        to compare values of  different feed sources - Calculated from Crude Protein,
        TDN, Ca, and P (Referee Feeds Used to Calculate Value of Nutrients).
    
        
            FeedVal4
        
        This spreadsheet, developed by Drs. Terry Howard and Randy Shaver, is a program
        to compare values of  different feed sources - Feed Comparative Values Calculated
        from Protein (UIP), TDN, Fat, Calcium, & Phosphorus.
    
        Pricer
        
        This spreadsheet, developed by Drs. Terry Howard and Randy Shaver, is a program
        to calculate MAXIMUM price for forage based on a base forage.