Problems Associated with All Corn Silage Feeding

Problems Associated with All Corn Silage Feeding

Problems Associated with All Corn Silage Feeding C. E. COPPOCK Department of Animal Science, Cornell University, Ithaca, New York 14850 The subject o...

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Problems Associated with All Corn Silage Feeding C. E. COPPOCK Department of Animal Science, Cornell University, Ithaca, New York 14850

The subject of corn silage in the ration of dairy cattle is again receiving the attention of research efforts after a period of time in which grass legume silage received the predominant emphasis among research workers. Cattle feeders, however, have become increasingly aware of the excellent forage characteristics of corn silage and its value in the rmninant ration. F r o m 1947 to 1967, the corn acreage in the United States utilized for the production of silage nearly doubled; the tons of corn silage produced nearly tripled. 5[any features of corn silage are attractive to dairymen. I n those areas where corn is well adapted, its use as whole plant silage results in an energy yield unsurpassed by any other crop. Perennial forages commonly harvested as hay or hay crop silage, decline in digestibility with advancing maturity and cows voluntarily consume less dry matter from them (60). Conversely, the corn plant harvested for silage over a broad range in matlLrity exhibits little change in dry matter digestibility (36); moreover, an increase in dry matter intake occurs through the range of 25 to 35% dry matter (30). The corn plant requires less water than several other commonly grown forages. The amount of water transpired per kilogram of above-ground dry matter produced has been reported (51) as 858 kg for alfalfa, 635 kg for oats, 372 kg for corn, and 271 kg for sorghum. W i t h increasing herd size, limited land resources, and greater emphasis on mechanization, the trend to increased reliance on corn silage forage is expected to continue. ~arions aspects of corn silage nutrition recently have been discussed (12, 31, 49). Studies of All Corn Silage Feeding

A t the 1933 annual meeting of American Dairy Science Association two brief reports (7, 27) were given describing winter feeding trials in which corn silage was fed as the only forage to lactating cows. Body weight gain, milk, milk fat production, and persistency of production were similar for cows that consumed only corn silage as a winter forage, as compared to cows that received corn silage and alfalfa hay (7). Possible long-term effects of all corn silage feeding were examined in an Iowa study (52) in which 22 heifers were paired at birth and fed

either corn silage or corn silage plus hay as forage from birth through two lactations. Both groups, however, were on pasture during the summer after one year of age. Production of milk, milk fat, and breeding efficiency were similar for both groups during two lactations. I n a concurrent experiment at Beltsville (11), 12 cows were fed corn silage as the sole forage for varying lengths of time up to five lactations. Eight cows were reared from birth. The primary objective was to determine the adequacy of corn silage fed ad libitum with grain (25% crude protein) as the source of minerals, vitamins, and unidentified factors, and its longterm effect on reproduction and lactation. Though it was not a controlled study, results were generally favorable based on comparisons with contemporary herdmates; but corn silage intake was relatively low, ranging from 7.7 to 16.4 kg/day, wet basis, per lactation average. Several investigators (4, 69, 74) have considered the possibility that some specific combination or proportion of corn silage to hay might be superior to either forage fed alone for lactating cows. Waugh et al. (74) fed four groups of lactating cows four levels of hay, 0.0, 0.25, 0.50, and 1.00 kg/100 kg body weight, plus corn silage ad libitum to find the proportion that would result in maximum feed intake and milk production. Fifty-six-day trials were employed in which grain was fed according to production. I t was calculated that maximum dry matter intake occurred when hay was consumed at a level of 0.79 kg/100 kg of body weight. However, fat-corrected milk production was not significantly different among groups. Apparently, the greater energy value of corn silage dry matter relative to hay dry matter served to maintain energy intake, as less hay was consumed. A similar trend can be seen in the recent investigations by Brown et at. (4, 5), in which all corn silage, all hay, and two combinations of corn silage and hay were compared as forages for lactating cows. Data from 280 days of the first lactation showed that a reduction in forage dry matter intake occurred as corn silage consumption increased, but apparently there was no decrease in forage energy intake or energy utilization as suggested by the slightly higher milk production of the all-silagefed group. Cows in the all-silage and all-hay-


sYmPOSIUM fed groups were continued on their respective treatments for a second complete lactation and the results were similar to those obtained in the first lactation (5). Another multilactation experiment in which cows were fed corn silage as the sole forage has been reported from Maryland (28, 69). I n addition to the silage-fed group, a second forage treatment consisted of one-half the forage dry matter as corn silage and one-half as alfalfa hay. Each forage group was divided into three subgroups which received a concentrate milk production allowance of 100, 125, or 140% of the Morrison estimated net energy standard. Two additional forage groups received 1 kg of alfalfa hay/100 kg of body weight or 0.9 kg of corn silage dry matter/100 kg of body weight; both groups received the 140% estimated net energy concentrate allowance for milk production. This study was done for three consecutive lactations. Only small differences in milk production and composition were observed among treatment groups. At parturition following the first lactation, three of the first four cows in the corn silage group which calved had retained placentas and produced calves with goiters (28). Subsequent feeding of iodized salt apparently eliminated the problem, although iodine analysis of the forages did not indicate that a simple deficiency was present, because the iodine content of the corn silage was slightly higher than that of the hay. Only two multilactation studies (5, 69) have been reported during the past 25 years in which corn silage as the sole forage was fed to lactating cows with high producing ability fed relatively high grain levels according to recent recommendations (54). Unfortunately, TABLE ].

Energy and protein requirements:


n e i t h e r of these studies has been published in complete form, but with the exception of the goiter problem referred to, no specific problems associated with feeding all-corn silage to dairy cattle for consecutive lactations have been described experimentally. I t appears that under some conditions corn silage alone is at least equal to hay or combinations of hay and corn silage as forage for lactating cows and that neither a depression in appetite nor production occurs when corn silage is fed for at least three lactations. However, several problems related to feeding and supplementing corn silage as the only forage have been observed under field conditions or have been reported to occur and these obsclwations will be discussed. Problems Associated' with Energy Concentration

Although there are several agronomic and managerial reasons why many dairymen choose to feed a combination of forages, there is interest in the potential problems and risks associated with feeding corn silage as tile only forage to dairy cattle. The high energy content of corn silage has led to problems in housing systems where all cows in a herd are in one group and where all cows are offered corn silage free choice. Data given in Table 1 show that corn silage consumed at the level of 2.25 kg dry matter per 100 kg of body weight with a TDN value of 68% dry basis will provide the maintenance energy requirement for a 600-kg cow, plus enough energy for 16 kg of 4% milk using National Research Council (NRC) requirement values (47). I n addition, excess energy consumption by the low-producing cow is further aggravated with grain feeding in the parlor when every cow gets some grain during milking. I f dry cows are allowed corn silage free Intakes from corn silage. Requirements a

Function Maintenance Milk 4% Maintenance -F pregnancy Growth Growth Growth

Body weight (kg) 600 16 600 200 300 400



3.95 5.28 9.23 7.15 3.15 4.10 4.60

Intakes b TDN


0.340 0.736 1.076



0.640 0.380 0.410 0.420

3.06 4.59 6.12

0.256 0.385 0.513


a National Research Council Publ. 1349 (47). b Assumed 2.25 kg dry matter/100 kg body weight and corn silage total digestible nutrient value of 68%, dry basis; digestible protein value of 5.7%, dry basis. ~. DAIRY SCIENCE VOL. 52, N0. 6




choice, over-consumptlon will also occur (Table 1). Because many high-producing cows cannot consume enough energy in early lactation to meet their energy requirements (54), some replenishment of energy reserves is appropriate after production has decreased to a level where this is possible. However, it has been suggested that over-consumption of energy from mid to late lactation may: 1) depress production in the current lactation, that a fundamental metabolic antagonism may exist between milk production and body fat synthesis and that excess dietary energy in late lactation may tend to divert the cow's use of that energy to body fat deposition instead of milk production (72) ; 2) depress appetite in the following lactation; and 3) result in an animal prone to develop clinical ketosis because of the over-condition. Because of the value corn silage has in beef cattle fattening rations, it seems possible that corn silage rations may present an array of fermentation products to the tissues, i.e., a volatile f a t t y acid pattern, which is not only conducive to fattening but one which induces a fattening type of metabolism, at least in some cows. Experimental data which relate to these suggestions, however, are scarce. Limiting energy intake from forage is easily accomplished in the conventional stanchion barn. Where free-stall housing systems have been built without the provision being made for dividing the herd, the problem of excess

energy consumption by the low producers is not easily resolved. The dry cows, however, can be separately housed from the milking herd in many systems Several studies (13, 53, 61, 63) have shown that over-consumption of energy by growing dairy heifers results in growth rates which may be detrimental to later lactation ability (61), which result in greater cow loss from the herd because of sterility (53), and which have no functional significance in terms of longevity or production (62). Optimum growth patterns for dairy cattle were discussed in depth by Swanson (62) in 1967. Economy growth schedules were proposed for Jersey and Holstein dairy heifers, based on age and weight as shown in Table 2. Recent growth studies (58, 64) show that Holstein dairy heifers will gain about 0.8 to 0.9 k g / d a y when corn silage alone is offered ad libitum (Table 3). Limiting corn silage to heifers is not a simple solution under farm conditions, where groups of heifers are often characterized by wide ranges in age and size. Restricting corn silage intake of heifers weighing less than 300 kg, to maintain gains of 0.6 kg/day, will result in a digestible protein deficiency according to NRC requirements (Table 1). This situation seems a p p r o p r i a t e for the addition of nonprotein nitrogen to the corn at ensiling, to effect an increase in nitrogen without increasing the energy content.

TABLE 2. Suggested growth schedules for growing Jersey and Holstein heifers, a Jerseys Time period

Stage Prebreeding Gestation I Prepartum I

(weeks) 60 32 12

Age (months) 15 21 24



Daily gain

186 278 331

0.39 0.41 0.63


Daily gain

270 402 475

0.54 0.59 0.86


a Swanson (62). TABLE 3. Growth of dairy heifers fed corn silage. Average daily gain Corn Corn Corn Corn

silage silage + urea silage + urea + K~SO~ silage + SBM, 907, g / d a y

a Thomas et al. (64). b Schmutz (58). ,.1". DAIRY SCIE~;CE VOL. 52, NO. 6

- - ( k g ) ~ 0.83 a 0.87 b 0.65 0.91 0.89 0.96 0.83 0.68

Corn silage Corn silage + urea, 0.5% Corn silage + urea, 0.75% Corn silage + CaC03, 0.5%

sY~POSIU~ Problems Associated with Nonprotein Nitrogen and Protein Supplementation Daily gains in growing dairy heifers have recently been reported in which corn silage with and without urea was offered ad libitum as the total ration (Table 3). The addition of urea (0.5%) to corn at ensiling did not improve the daily gain in dai~T heifers, suggesting that corn silage may furnish ample protein for growth. However, it is possible that the composition of the gain differed araong treatment groups. The tendency of some animals to fatten when fed energy-rich protein-deficient rations is generally accepted. On the other hand, the composition of the gain may not have differed, if the urea-corn silage fed heifers did not utilize the urea well. Conrad and Hibbs (9) pointed out that about 1 kg of readily fermentable carbohydrate is required per 100 g of urea for maximum utilization of urea in the adapted dairy cow. I t was further stipulated that at least two-thirds of that fermentable carbohydrate should be in the form of starch. The corn plant has been shown by Johnson et al. (35) to contain between 200 and 300 mg of soluble carbohydrate per gram of dry matter when the plant was harvested in Ohio during September. ]~Iuch less soluble carbohydrate was present in later harvested corn. I t was also shown that from 65 to 70% of the soluble carbohydrate present at harvest in September was fermented during ensiling. I f 5 kg of urea are added p e r metric ton of whole plant corn (33% dry matter) which contains 250 mg of soluble carbohydrate per gram of dry matter and if it is assumed that 90% of the urea is recovered and 65% of the soluble carbohydrate is fermented during ensiling, then the silage would contain about 154 g of urea per kilogram of soluble carbohydrate. This calculation does not consider that ~ about 12% of the nitrogen in untreated corn silage was shown to be present in the ammonia-urea fraction (37). Therefore, after fermentation in the silo, urea-corn silage may not have sufficient available carbohydrate for efficient urea use. The suggestion that urea-corn silage fed as the total ration may result in inefficient use of the urea nitrogen is supported by nitrogen balance studies with lactating cows.. (8). Cows fed only urea-corn silage (0.7%) used 8% of the dietary nitrogen for milk production and retention in body tissue, in comparison to 22.0% for a similar group fed alfalfa hay and grain. The nitrogen balance procedure was also used by t t u b e r et al. (32) to compare the utilization of nitrogen by lactating cows fed


corn silage ad libitum as the only forage which had been ensiled with 0.0, 0.5, or 0.75% urea. A 70-day continuous trial was employed in which concentrates were fed at the rate of t kg per 3 kg of milk and the rations were calculated to be isocaloric and isonitrogenous. The level of urea in the silage did not significantly influence the level of milk production, silage intake, or total feed intake. I n a second trial (32) corn silage which had been ensiled with 0.0, 0.6, or 0.85% urea was fed ad libitnm as the only forage to lactating cows in a 63-day trial. Again, no significant differences were observed in milk production or feed intake. However, in this trial, a digestion-nitrogen balance determination was made during the eighth week of the study. I t was discovered that the cows fed the 0.85% urea-corn silage were in severe negative nitrogen balance because of lowered protein digestibility and larger urinary nitrogen losses. The ability of the modern dairy cow to mobilize both energy and nitrogen (54) for milk secretion without a serious depression in milk production makes it very difficult to interpret short-term feeding trials i n v o l v i n g nonprotein nitrogen unless nitrogen balance data are available. Protein supplementation can be awkward when corn silage is used as the only forage for lactating cows (Fig. 1). A series of protein levels is theoretically required based upon the production level if only corn silage is fed; however, when a combination of colin silage and alfalfa forage is fed, one concentrate mixture results in more efficient use of protein. Mobilization of protein reserves and the opportunity to consume forage and grain beyond immediate reauirements under farm conditions, serve to modify the theoretical relationships shown in Fig. 1. When corn silage is the only forage fed, the addition of urea alleviates the high protein level theoretically required by the low-producing cow, because a larger proportion of the digestible protein requirement can be obtained from forage. The use of urea in corn silage rations for dairy cattle has been recently reviewed (12, 31, 56). A comparison of the cost of energy and nitrogen in corn and urea to that in conventional protein supplements such as soybean meal, shows a cost advantage which favors maximum use of urea in ruminant feeding. However, as illustrated in a recent discussion by Armstrong and Trinder (3), an apparent savings in ration cost through use of urea can be completely negated by a small loss in milk production. The problem of using urea lies not in the question of whether to use J'. D A f f y SCIenCE YOL. 52, NO. 6






z_~, o


at u







Corn Silage



Corn Silage--~~ Corn Silage 1/3

':=::2=:, "


Alfalfa I 10



f I






4% FCM (kg/day)

Fro. 1. Effect of type of forage consumed on~ the crude protein needed in the concentrate mix to exactly meet the energy and protein requirements of the lactating cow. Digestible protein and total digestible nutrient requirement figures used were those proposed by Reid et al. (54). A forage intake of 2.25 kg of dry matter per 100 kg of body weight was assumed at low levels of concentrate intake. it, but rather under what conditions and by what techniques and routes of administration of appropriate levels, can be the most effective. The crude protein content of the corn plant can also be increased by high levels of nitrogen fertilization applied primarily to increase yields (14, 21, 25). I n one study (21), as the nitrogen applied per hectare was increased from 27 to 195 kg, the crude protein content of the whole plant dry matter increased from 7.7 to 11.2%, although a corresponding increase in green weight did not occur. This subject has been reviewed recently by Owen (49). The effect of high-nitrogen fertilization on the nitrate content of the corn plant and the resulting silage is of immediate concern. Cummings et al. (14) found that the application of 0, 225, and 899 kg of nitrogen per hectare produced corn forage at ensiling time containing 0.11, 0.49, and 0.62% nitrate (dry matter basis) and 6.2, 7.3, and 8.6% crude protein, respectively. The silages, however, contained 0.08, 0.26, and 0.49% nitrate, respectively, although the highest of these levels is not considered toxic to animals (76). The problem of toxic levels of nitrate in forage seems to be a regional one (19, 76). As shown with orchardgrass (34), ensiling tends to reduce the level of nitrate in forage, through fermentation processes which occur until the p H is lowered to about 4.0. I t has also been shown (15, 66) that additions of limestone which tend to buffer silage acids, and thus prolong fermentation, J'. DAIRY SCIE~TCE VOL. 52, NO. 6

also reduce the level of nitrate in ensiled forage. When hydrolyzed to ammonia, urea also acts as a buffering agent in silage and thus urea may also reduce the level of nitrate in ensiled corn. Another problem which has been postulated to occur relates to both urea and nitrate in the ration. Upon conversion to ammonia, both urea and nitrate can be used by tureen microbes as sources of nitrogen for protein synthesis. I t has been suggested that adding urea to rations which include nitrate-containing forages, may decrease the utilization of nitrate and thus increase its apparent toxic effects. From data obtained with fattening lambs, Hoar et al. (29) concluded that there was no interrelationship between sodium nitrate included at 2.5% of the total ration and urea at 1% of the ration. I n a small preliminary trial, Elliot and others (18) compared the effect of concentrate mixtures containing no additive, 1.5% urea, urea and sodium nitrate at 1.5% on the appetite and milk production response of lactating cows. These additives did not affect daily feed consumption, milk production, or level of hemoglobin and methemoglobin in the blood. Although very limited data are available, there does not appear to be an interrelationship or an additive effect between these two compounds when each is fed at a subtoxic level. Problems Associated with Supplementation


Greater emphasis on urea use suggests the need for sulfur supplementation. I n early studies (65) with purified diets fed to lambs, it was established that inorganic sulfates can be used by sheep, as shown by gain in body weight, wool growth, and sulfur and nitrogen balance data. Lambs fed sulfur-deficient rations had depressed appetite, became emaciated, and eventually died. Sulfur requirements for ruminants, however, have not been published. Davis et al. (16) examined the value of a sodium-sulfate supplement in the ration of lactating cows fed a multi-ingredient concentrate mix during an eight-week continuous trial; although an attempt was made to select low sulfur ration ingredients, the corn silage and timothy hay fed had relatively high concentrations of sulfur compared to recently published values (46) with nitrogen sulfur ratios in the order of 5:1. The control grain mix had an N : S ratio of 8 : 1 , the experimental mix 10:1. No response in milk production or intake was observed. I t was suggested (16)


that because plant proteins commonly used in ruminant feeding contain an N : S ratio of about 15:1, this is the best guide we have regarding the level of sulfur needed in ruminant feeding. More recent writers (1) suggest a ratio of about 10 N to 1 S as the approximate requirement of rmninants. Using corn silage which contained 0.09% sulfur on a dry basis as the only forage, Jacobson and co-workers (33) fed 12 mature lactating tlolstein cows a low-sulfur concentrate mix (0.10% dry basis) and a comparable group the same mix with a supplement of sodium sulfate which increased the sulfur level to 0.18%. The grain mix contained wheat standard middlings, ground yellow corn, and 1% urea. By the last week of a nine-week continuous trial, the voluntary dry matter consumption and milk production of the sulfursupplemented group were significantly higher than the control group. This demonstrates that a sulfur deficiency can be produced in a relatively short time on a practical diet of ingredients commonly fed. I t was shown, however, that there were no significant differences between treatment groups in the concentration of free amino acids in blood plasma or rumen contents, even though an apparent sulfur deficiency occurred. The concentration of several amino acids in the plasma of both groups decreased from the first to the last week of the trial. Methionine decreased to about one-half the initial level, but cystine decreased to about one-seventh the initial level, which was a greater decrease than that shown by any other amino acid. I t was noted that because persistency of milk production for the supplemented group was below normal and because the sulfur supplement did not mMntahl the plasma-free amino acids at the pre-experimental normal level, that apparently this level of supplementation was insufficient or poorly utilized by microorganisms for synthesis of the sulfur-containing amino acids. I n studies of the nitrogen metabolism of lactating cows fed purified rations, Virtanen (73) noted that plasma levels of both histidine and methionine were relatively low. A similar observation was made by Conrad and Hibbs (9) from estimates of ruminal production of methionine and seven other essential amino acids in a cow producing 40 kg of milk and fed a ration of corn silage, ground corn, ground oats, urea, and minerals. This study also suggested that methionine and histidine may be limiting essential amino acids in the lactating cow. I n further studies of ruminal methionone synthesis, the Ohio group (10) compared sev-


eral parameters of nitrogen utilization from dried alfalfa, ensiled alfalfa, and urea-corn silage based rations fed to milking cows. The fraction of the total nitrogen in the three rations soluble in 5% triehloroaeetic acid was 10.4, 38.5, and 76.5%, respectively. "At approximately equal nitrogen intakes, the feed methionine in grams per day was 27.9, 23.7, and 15.1; the synthesized methionine was 19.3, 16.4, and 14.7 g/day, respectively. I t was concluded that the amount of methionine synthesized by cows was directly related to the amount of intact protein consumed. And because tureen microorganisms are not known to require nitrogen in organic form, it was assumed that the greater methionine synthesis with intact protein consumption was a result of near equality between the rates of ammoniacal nitrogen production and its use by tureen microorganisms. Furthermore, McCarthy et al. (42) and others have recently postulated that a shortage of methionine in early lactation can lead to the development of ketosis and considerable success was achieved by this group in treating ketotic cows by an injection of methionine and orally dosing with an analog of methionine. Thus, an appreciation of the importance of the role of methionine in the metabolism of the lactating cow is gradually evolving. The essentiality of sulfur in the biosynthesis of methionine is obvious, but much remains to be learned regarding the appropriate level and the most usable form of sulfur supplement, as well as other factors which govern methionine synthesis in the lactating cow. For example, washed cell suspensions of rumen microflora were used by Trenkle et al. (68) to determine the value of several sulfur compounds for increasing cellulose digestibility. Sulfur in organic forms such as eysteine and glutathione was available, but a higher level of sulfur was required than when sulfate sulfur was used. But methionine produced an increase in cellulose digestibility greater than any of the other forms tested, which suggested that methiomne supplied something beneficial in addition to sulfur. Recently, Goodrich and co-workers (23) obselwed an increase in feed efficiency when elemental sulfur was added to a urea supplement for growing beef cattle; whereas, no response in gain was observed in a similar study by Tolman and Woods (67). Shively et al. (59) used a basal ration for finishing cattle with an N : S ratio of 17:1, the sulfur supplement was Glauber's salts or elemental sulfur. The sulfur supplement~ produced a response in all trials J. DAIRY SCIENCE VOL. 52, NO. 6



for the first 90 days of 6.5, 4.0, and 2.6% in greater gains, feed consumption, and feed efficiency, respectively. However, during the following 90 days, sulfur supplementation resulted in lowered performance approximately equal to the initial increase. Using published values (46) for nitrogen and sulfur, it can be shown that corn silage has an N : S ratio of about 13 : 1; an addition of urea equal to 0.5% of the silage would further widen the ratio to about 18 : 1. Since it has been sbowH by Van Horn et al. (71) that lactating cows can apparently utilize up to 1% urea in the grain mix concurrent with 0.5% urea in the silage, it is apparent that some very wide N : S ratios can be encountered in practice. The problem of sulfur supplementation arises from the fact that little is known regarding the level of sulfur required in the total ration of ruminant animals, factors which affect this requirement (such as the sulfur level in the water) or the best form of sulfur supplement to use. It may be hazardous to make general recommendations regarding the use of sulfur supplements, because sulfur has been shown (70) to increase molybdenum toxicity and modify copper utilization. I t is recognized that the level of sulfur in the soil has a marked influence on the sulfur content of the plants grown on that soil (2). The sulfur content of the soil in many areas has been influenced by the type of fertilizer used and the proximity to industrial plants which discharge sulfur compounds into the atmosphere (2). With reference to the optinmm N:S ratio for plant growth, Allaway and Thompson (1) state that, "Certain forage plants may be deficient in sulfur for ruminant animals, even though the plants themselves are growing at near maximum rates. At the very best, it seems probable that when the yield of a forage is increased through the use of sulfur fertilization, an improvement in its nutritional quality for ruminants coincides with increased yield." Carotene Value of Corn Silage

I t was shown by Wiseman et al. (75) that the carotene content of corn silage is directly related to the maturity at which the plant is ensiled. When corn was ensiled at the milk stage, the silage contained 140 mg carotene per kilogram of dry nmtter; when ensiled at the dent stage the carotene content had decreased to 32 mgfkg and after a light frost it further decreased to 4 mg/kg of dry matter. Thus, with a maintenance requirement of 64 mg of carotene for a 600-kg cow plus 32 mg ft. ])AIRY SOIENCE YOL. 52, NO. 6

for reproduction, the possibility of meeting the total carotene requirement of the eow from corn silage is related entirely to the condition of tbe plant when it is ensiled. I n addition to the variable amount of carotene in corn silage, the biopotency of corn silage carotene has been questioned. Jordan et al. (39) reported vitamin A deficiency symptoms in steers wintered on corn silage and soybean meal for 224 days, even though the corn silage consumed at a level of 16 kg per day contained 11 mg carotene per kilogram and preformed vitamin A was fed at a level of 7,000 to 8,000 IU per steer per day. Klosterman et al. (40) found that corn silage rations quickly restored the plasma vitamin A and carotene levels in depleted fattening steers. A similar conclusion was reached by Martin et al. (41) with lambs. I n the corn silage experiment of Brown et al. (4) referred to earlier, one-half of the cows in each group received a vitamin A supplement of 30,000 IU daily. This level of supplement did not increase the plasma levels of carotenoids or vitamin A in cows fed corn silage as the only forage. I t has been suggested (19, 22) that the corn silage vitamin A syndrome is related to nitrate present in the silage. I n one report (22) it was found that sheep fed rations containing 3.0% added sodium nitrate for 56 days had liver vitamin A reserves 46% lower than sheep on the control ration. Other experiments, however, have shown no direct relationship between the intake of nitrate and vitamin A nutrition of ruminants. Miller et al. (43) depleted 12 Holstein calves of their vitamin A reserves and fed KNOB at three levels, plus carotene from corn silage at four levels. Cerebrospinal fluid pressure, carotene and vitamin A levels in the plasma and liver were affected by increasing levels of carotene, but there was no adverse effect from nitrate. Oregon workers (38) made an intensive study of the responses of lactating cows fed sublethal levels of 0.75 or 1.25% KNOa added to the ration dry matter, and fed half their daily energy as regular corn silage (0.40% KNO.~, dry basis) or high nitrate corn silage (0.78% KN03, dry basis). There was no detectable effect of nitrate present naturally in the silage or nitrate added as the potassium salt on the response in production of milk, milk protein, milk fat, milk vitamin A content, blood hemoglobin, on plasma carotene and vitamin A or on liver carotene and vitamin A. Loss of both carotene (17) and vitamin A (44) have been found to occur in rumen fer-

sY~Posiu~ mentation, but apparently potassium nitrate does not affect the magnitude of this' breakdown. I t has also been demonstrated that nitrate or more likely its breakdown products increase carotene destruction during the ensiling process (48). I n studies with complete ensiled rations (26), it was shown that the activity of vitamin A palmitate added at the level of 4,400 IU per kilogram of ration was lost during the ensiling process. Mineral Relationships

A comparison of the mineral composition of corn silage and alfalfa (Table 4) reveals that the concentration of ten of the 12 minerals listed is higher in alfalfa than in corn silage. I t is recognized that the increased use of corn silage is not always being made at the expense of alfalfa, but where this substitution is taking place the mineral intake from forage is greatly reduced. I t was pointed out in a preliminary repo~t last year (50) that the conception rate of dairy cows was improved by the inclusion of dehydrated alfalfa in normal and high grain rations fed with corn silage. The grain mixture is often used as the cam'ier for supplementary minerals; however, when an energy-rich forage such as corn silage is fed ad libitum, as shown, no additional energy may be required by low producers and dry cows. Therefore, free choice supplements, body reserves, or both must be relied upon to furnish minerals not provided by forage. Use of urea in corn silage rations tends to further reduce the mineral intake from natural ingredients, because plant proteins commonly used are relatively rich (Table 4) in minerals


compared to the cereal grains which replace them. Although it is relatively easy to make isocaloric, isonitrogenous substitutions in nonprotein nitrogen experiments, it is unusual to find trials in which the rations have also been balanced with equal amounts of the known required minerals. This may be significant, because several mineral mixtures have been shown to stimulate the conversion of urea nitrogen to bacterial protein (6). Because trace-mineralized salt is often included in commercial concentrate mixtures, or is offered free choice or both, potential problems such as the apparent iodine deficiency encountered by the Maryland workers (69) have probably been inadvertently avoided. However, increasing reliance on a single plant to furnish the nutrients previously provided by several forages increases the risk of a clinical manifestation of a mineral deficiency. Greater emphasis on the use of industrial by-products and nonprotein nitrogen in ruminant nutrition makes our knowledge of specific mineral requirements and their interactions imperative. Other Problems

Personal observations have been reported (20) in the popular press in which high levels of corn silage in the diet have been implicated in the occurrence of listeriosis or "circling disease" and left abomasal displacement. Listeriosis has been related to silage feeding (24), but no published evidence was found which showed that corn silage was more involved than other types of silages. In fact, it appears that it is poorly preserved silage with a relatively

TABLE 4. Mineral element composition of feedstuffs. Element

Alfalfa hay a

Corn silage a

Calcium Phosphorus Potassium Magnesium Iron Sulfur Sodium Chlorine Manganese (mg/kg) Copper (mg/kg) Cobalt (mg/kg) Zinc (mg/kg)

1.64 0.26 1.77 0.32 0.02 0.36 0.16 0.28 51.80 13.70 0.13 17.00

0.33 0.23 1.15 0.24 0.02 0.11 0.03 0.18 49.00 10.10 0.09 20.90

Shelled corn b

Soybean meal b

0.02 0.27 0.29 0.10 0.002 0.12 0.01 0.04 5.30 4.00 ---

0.29 0.64 ].92 0.27 0.013 0.43 0.34 -27.5 14.3 ---


a National Research Council Publ. 1232 (46). Dry matter basis. b Morrison, 22nd ed. (45). A i r dry basis. J . D A I R Y SCIENCE VOL. 52, NO. 6



h i g h p H , > 5 . 0 , which h a s been p r i m a r i l y associated w i t h Listeric infections. The p h e n o m e n o n of l e f t a b o m a s a l displacem e n t a p p e a r s to be i n c r e a s i n g in d a i r y cattle (55). W h i l e the etiology of this condition rem a i n s obscure, successful diagnostic a n d surgical techniques have evolved in recent years. I n a s u r v e y of affected a n d nonaffected h e r d s in P e n n s y l v a n i a , R o b e r t s o n (55) f o u n d t h a t affected h e r d s h a d h i g h e r a v e r a g e milk production, were f e d l a r g e r a m o u n t s of grain, a n d the cows in the affected h e r d s were f e d significantly more g r a i n d u r i n g the last m o n t h of p r e g n a n c y (lead f e e d i n g ) . A l t h o u g h the a m o u n t of h a y a n d the a m o u n t of silage f e d was n o t significantly different between affected a n d nonaffected herds, there was v e r y little r a n g e in the m a g n i t u d e o f these two p a r a m e ters in the h e r d s studied. A t this time t h e r e is insufficient evidence to show a n y definite link between l e f t a b o m a s a l d i s p l a c e m e n t a n d corn silage feeding.

Conclusions W i t h one exception, specific n u t r i t i o n a l p r o b lems associated w i t h f e e d i n g all-corn silage to d a i r y cattle have n o t been r e p o r t e d . H o w e v e r , the p r a c t i c e of f e e d i n g only corn silage on a y e a r - r o u n d basis h a s not b e e n a common one except in a few a r e a s in recent years. The p r i m a r y p r o b l e m associated w i t h f e e d i n g allcorn silage lies n o t in the composition of the f o r a g e b u t in our limited knowledge concerning the type, most effective route, a n d economic level of s u p p l e m e n t a t i o n n e c e s s a r y to meet the needs of d a i r y cattle.

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