Department of Agricultural, Food and Nutritional Science,
4-10 Agriculture/Forestry Centre,University of Alberta,
Edmonton, AB, T6G 2P5, Canada
Take Home Messages
Cereal Grain Silage Production
In Alberta dairy cows are fed conserved forage for six to eight months of the year. Indeed, many producers feed conserved forages throughout the year. Nutrient losses are inevitable during the conservation process. Losses must be minimized, if not, both nutrient concentration and total feed intakes are reduced.
The major forages fed in Alberta are alfalfa and cereal grain silages. Although alfalfa is an excellent forage, environmental conditions do not always favour its growth. Small grain cereals can be grown in a wide range of climatic and soil conditions, are annual crops, and are not subject to winter kill. These spring cereals include barley, wheat, rye, triticale, and oats, either alone or as mixtures. Sometimes legumes or peas are included in the cereal mixtures to enhance the protein content and fiber quality of the forage mix. Improvements in forage yields and in the efficiency of utilization of forage are a result of varietal selection and improved forage conservation techniques. The yield potential of many cereal grain varieties has been determined (Table 1), but their ability to sustain milk production has not been well documented.
Table 1. Mean barley silage yield (kg/ha) with different fertilizer treatment in Central Alberta in 1995.
|Bow Island||Lethbridge||Coaldale||Barons||Pincher Creek||High River||Strathmore|
Source: McKenzie et al. (24).
Factors Influencing the Nutritional Quality of Forages
Forage can make up 35 to 80% of diets for lactating dairy cows; therefore, forage quality can have a major influence on milk production. A number of biological and chemical procedures can be used to determine forage quality. Chemical analyses currently used to predict quality of silages include CP, NDF, ADF, and ADL. The chemical composition of forages is affected by species, varieties within species, stage of growth, and environmental conditions.
It is well established that there is a tremendous difference in the feeding value of alfalfa harvested at an immature stage compared with a more mature stage (e.g., bud-stage compared with mid- or full-bloom alfalfa; 30). Increased digestibility, faster weight gains, and higher milk production from cattle fed alfalfa harvested at an immature stage has been reported (23, 30). Are the same principals true for cereal silages? As the cereal grain plant matures, the proportion of stem and thus the digestibility of the whole plant decreases. The stem is of lower digestibility because it contains a higher proportion of the plants structural components, cellulose and hemicellulose, which are slowly digested and lignin, which is indigestible. Helsel and Thomas (17) observed that in vitro DM digestibility of cereal grain crops is reduced as the stage of vegetation progressed (Figure 1).
Fearon et al. (14) reported that after tillering, the digestibility of triticale decreased with advancing maturity. Baron et al. (2) reported that in vitro digestibility of organic matter (IVDOM) of barley crop remained constant over a 7 week period after heading, and that maximum whole-plant yield is achieved when whole-plant barley is harvested at 42% DM; harvesting at 30% DM reduced yield about 17%. Cherney and Marten (11) and Brignall et al. (6) have reported that DM yields usually increase up to the soft dough stage of maturity. Acid detergent fiber (ADF), cell wall constituents (CWC), and lignin concentrations of cereals increase with pre-heading maturation, but remain constant after heading (11). However, after a certain stage of maturity, the fiber content of cereals may not be a good predictor of maturity. As the fiber content of the stem increases with maturity and becomes less digestible, the cereal grain kernels are developing at the same time. The grain, primarily starch, dilutes the fiber content of the stem and thus modulates changes in ADF content as the cereal plant matures (Figure 2). Therefore, ADF may not be a good indicator of the energy value of cereal silages (Figure 3).
Figure 2. Changes in ADF concentration of crops with advancing maturity.
The equations used to predict the energy content of forages (4) are as follows:
Cereal grain silage NEL = 2.5 - .0287 x ADF
Alfalfa silage NEL = 1.827 - .0137 x ADF
As alfalfa silage became more mature predicted energy content of silage declined (Figure 3). The predicted energy content of cereal grain silages declined with advancing maturity followed by a plateau and then increased (Figure 3). Plant environment also modifies the impact of forage maturity resulting in year- to-year, seasonal and geographical effects on forage quality, even when harvested at the same stage of maturity (7). Thus, the growth phase of the plant must be considered when equations are developed to predict energy content of cereal forages from ADF.
In general, the maximum DM and protein yield is obtained by harvesting at or before the soft dough stage, depending on the species. However, digestibility of DM, OM, energy, ADF, and NDF decline with advancing maturity of the forage. If a single variety of forage is planted it is difficult to harvest at the optimal stage of maturity. Thus, it is recommended to use a number of varieties which differ in their dates of maturity so that you increase your window of opportunity for harvesting high quality forage. Using one variety seeded at various dates will result in a lower overall yield. However, optimizing cereal forage quality will require more information on the individual species before accurate recommendations can be provided.
Figure 3. Changes in NELconcentration of crops with advancing maturity.
The differences between similar crops are less than those between very different crops such as cereal vs. legumes. Is this statement really true?
Mono-crops. A number of feeding trials have been conducted at the University of Alberta to evaluate cereal grain silage quality and to determine the feeding value of cereal silages compared to alfalfa silage. In a review presented in 1995, we reported the performance of early- and mid-lactation dairy cows fed alfalfa and barley, oat, and triticale silages (19). In general, dry matter intake (DMI) of cows fed alfalfa and barley silage were higher than for cows fed oat and triticale silages with no differences between alfalfa and barley silage or between oat and triticale silage. However, there were no differences among diets in milk yield, 4% fat corrected milk (FCM), milk energy output, and milk fat percentage. The lower DMI for cows fed oat and triticale silages was less pronounced in mid-lactation cows than in early lactation cows, and a negative correlation was found between dietary NDF concentration and DMI. We hypothesized that differences in DMI among cows fed alfalfa and other cereal silages was a reflection of the NDF content of these diets. This was supported by the data obtained from rumen evacuation of animals fed these silages (Table 2).
Table 2. Influence of forage source on rumen fill and turnover rates, and rate of degradation and rate of passage of silage NDF in the rumen.
|NDF content of the silage, %||45.6||50.6||60.8||54.3|
|Dry matter intake, kg||19.6a||18.6a||16.7b||17.2b||0.42|
|Total rumen fill, kg||72.6||76.5||78.8||72.3||1.95|
|Turnover time, 1 h||12.9b||13.7b||17.1a||14.3b||0.69|
|Ruminal fill, kg||6.8b||7.3ab||8.0a||6.8b||0.37|
|Rate of intake||4.0a||4.0a||3.3a||3.9a||0.16|
|Rate of passage, %/h||2.4||2.2||2.2||2.3||0.15|
|Rate of digestion, %/h||4.1a||3.9a||2.4b||2.7b||0.3|
a,b Means in the same row with different superscripts differ (P<.05).
1 Turnover time = [ruminal DM (kilograms)/intake (kilograms per day)] x 24.
The rumen evacuation data showed that there were no significant treatment differences in total rumen fill. However, ruminal fill as a percentage of DMI was higher for cows fed oat silage, and no significant differences were observed among the other diets. Relative to other treatments, cows fed oat silage had a longer ruminal residence time, which resulted in greater ruminal NDF fill than cows fed triticale or alfalfa diets. This higher ruminal NDF content reflected the higher NDF content of oat silage and also the lower rate of degradation and rate of passage of oat silage NDF in the rumen. These differences in chemical composition and the rate of digestion were reflected in lower DMI for cows fed oat and triticale silages.
Mix-crops. Little information is available on the quality of mixtures of annual crops, although agronomic information is available (3, 18, 20, 39). Wolfe (39) suggested that mixtures may have better yield than monocrops. Baron et al. (3) found that although spring-winter cereal mixtures had lower yields than spring monocrops the improved forage quality of the mixture, indicated by lower NDF, ADF, and lignin content, would compensate for the reduction in DM yields. Thompson et al. (35) reported that barley-annual ryegrass mixtures outyield barley monocrops and had higher digestibility and crude protein (CP) content.
In an experiment at the University of Alberta we compared alfalfa to mixtures of a) barley (Hordeum vulgare L.) and triticale (Triticosecale rimpani witt), and b) field peas (Pisum sativum) and triticale. At harvest, peas were in the flower stage, and triticale and barley were in the late boot stage. All forages were wilted for 24 to 36 h and then ensiled in silo bags with a Model XP2 forage press (Silopress, Sioux City, IA). Chemical compositions of the silages are presented in Table 3.
Table 3. Chemical composition of silages.
|High protein||Low protein|
|CP, % of DM||17.5||16.1||15.6||12.7|
|NDF, % of DM||49||54||50||50|
Twenty Holstein dairy cows in early-lactation and 24 in mid-lactation were assigned to four diets. Diets were formulated to contain 60% concentrate and 40% forage on a DM basis. The forage components of the rations were 25% alfalfa hay and 75% of one of the following silages: alfalfa, barley/triticale, high protein peas/triticale, and low protein peas/triticale. The high and low protein peas/triticale silages were from two different fields. Cows were assigned to treatments following a two week covariate period and were fed the test diets for seven weeks.
Dry matter intake (DMI) averaged 21.4 kg/d and was highest for cows fed low protein peas/triticale silage, intermediate for alfalfa silage, and lowest for cows fed barley/triticale and high protein peas/triticale silage (Table 4). When the DMI was expressed on a BW basis, dietary treatment had no effect on the DMI. Dry matter intake was similar between early- and mid-lactation cows. Yield of milk, 4% FCM, and milk protein and lactose were not affected by dietary treatment. Milk fat percentage was highest (P<.05) for cows fed the high protein peas/triticale silage, intermediate for cows fed alfalfa and barley/triticale silage, and lowest for cows fed the low protein peas/triticale silage. Messman et al. (28) also reported that the milk production of cows fed peas/triticale silage was not different from cows fed alfalfa plus corn silage. However, they also observed a higher concentration of milk fat for cows fed peas/triticale silage compared to cows fed alfalfa plus corn silage.
Table 4. Least square means of feed intake, milk production, and milk composition for all cows.
|High protein||Low protein|
|Number of cows||11||11||11||10||13||30||19||24|
|% of BW||3.29||3.15||3.12||3.49||0.07||3.33||3.22||3.29||3.23|
|Milk composition, %|
a,bMeans in a row within category with different superscripts differ (P<.05).
New varieties are introduced each year with much promise (Table 1), yet few studies have been conducted on the nutritional quality of these varieties for ruminants. Although, variation in cell wall concentration among cultivars of orchardgrass and smooth bromegrass were reported by Buxton (8) and Buxton and Russell (9), little is known about the genetic variability of whole-plant cereal grain silages. At the University of Alberta we have evaluated the nutritive value of whole-crop barley varieties as a silage source for dairy cattle and the results are presented in this paper.
Ensiling Process. Silage is the end product of preservation of material by acidification. Acidification primarily results from anaerobic fermentation of plant sugars to acids. Fermentation products and pH can be used as indicators of silage quality. During fermentation, sugars are replaced by fermentation products, mostly lactic and acetic acids with variable, but usually small amounts of ethanol. Good quality silage has the characteristics of low pH and over 60% of total acids as lactic acid. The critical pH that affects growth of bacteria in ensiled forage depends on the water activity of the fermentation medium; with decreasing water activity the sensitivity of these bacteria to acidity increases (37). Therefore, the DM of the ensiled forage affects the required pH for a quality silage. Daynard (12) and Oltjen and Bolson (31) have reported that when the whole-plant DM content of cereal grain and corn is below 30%, nutritive losses occur in silage because of seepage from the silo. They also reported that if the whole-plant DM is above 40%, oxidative losses occur. Therefore, the ideal DM content of the whole-plant appears to be between 30 to 40% (12, 31). Baron et al. (2) predicted that in this range of plant moisture, the relative whole-plant yield would vary between 83 to 97% of the maximum yield for barley silage in central Alberta. Thus, it would be advisable to harvest when DM is about 35% so that the whole-plant DM does not exceed 40% DM after wilting. Although, this early harvesting would result in somewhat lower yields, the quality of ensiled forage would not be sacrificed. Wilting can play an important role in ensuring optimum conditions for the ensiling process. As DM content increases nitrogen solubility and ammonia nitrogen concentrations in silage increase. At high DM concentrations the extent of aerobic fermentation can also increase. The resultant heat production can result in increased concentrations of acid detergent insoluble nitrogen (ADIN) and thus lower availability of nitrogen (16). Acid detergent insoluble N values of less than 10% of the total N is desirable.
Degradation of Plant Protein. After the crop has been cut, and during subsequent storage in the silo, proteolysis due to plant and microbial proteases increases the non-protein nitrogen (NPN) content such that it can eventually constitute as much as 40 to 70% of the total nitrogen. Silage NPN and soluble protein are rapidly degraded to ammonia in the rumen (33) and thus the availability of amino acids and peptides could limit protein synthesis. The rapid release of ammonia means that, for efficient fixation into bacteria protein, a readily fermentable source of energy is needed (10). Silage-based diets containing a combination of high ruminal concentrations of ammonia and a low availability of readily fermentable substrates results in low rates of microbial growth and substantial losses of N before the small intestine (32). Thus cows fed these silages are likely to be responsive to protein and energy supplementation (34). The supplement should aim to provide substrates that encourage efficient microbial utilization of silage nitrogen in the rumen as well as ruminal escape protein.
Factors Affecting the Voluntary Intake of Silage
Intake is the key biological constraint which limits the productivity which can be achieved from forages. The economic value of a silage depends upon the level of animal production it will support which is largely dependent on the amount of feed consumed and the efficiency with which it is digested and metabolized. Therefore, an understanding of the factors that control voluntary feed intake in dairy cows would enhance our ability to predict forage quality.
Effect of Method of Conservation of Forage on Feed Intake
Silage is sometimes consumed to a lesser extent than hay of similar quality. The end products of silage fermentation have been implicated in causing this depression (5). The composition of silage differs from hay in a number of ways including decreased water soluble carbohydrate concentrations, increased NPN and organic acid concentrations and higher moisture content (25). These differences are reflected in changes in eating behaviour and ruminal fermentation characteristics of cattle (Table 5). Cattle spend less time eating and chewing silage than hay (25) which in turn influences saliva production of the rumen.
Table 5. Influence of method of conservation on digestion characteristics of forage1.
|Dry matter, %||Silage||Hay|
|Ruminal NH3-N mg/dl||21.3a||22.7a||10.1c||15.2b|
|Eating Time, min/d||279b||272b||268b||429a|
|Total chewing time, min/d||784b||855b||781b||950a|
|Organic matter intake, kg/d||16.4b||18.5a||17.1b||16.5b|
|Digestible OM disappearing in the rumen, %||70||69.7||58.9||64.3|
|Digestible N disappearing in the rumen, %||35.1a||32.4a||9.5b||26.3a|
|Apparent N digestibility, %||72.0a||42.4a||67.6b||70.7ab|
|Bacterial N at duodenum, g/d||265||314||276||238|
|Dietary N at duodenum, g/d||72||80||163||97|
1 From Merchen and Satter (25).
Wilkins et al. (38) analyzed data from a number of trials in which 70 untreated grasses, legume, maize, and sorghum silages were fed to growing and mature wether sheep. They found that DM and total N content and lactic acid as proportion of total acids were all positively correlated with silage DM intake, while ammonia N as a proportion of total N, acetic acid, and total acid contents were all negatively correlated with DMI. Dry matter digestibility, pH, and lactic acid as proportion of DM were not significantly correlated with intake. There are not many studies on the effect of silage fermentation products on voluntary intakes of lactating dairy cows. Gill et al. (15) collected data over a 7-year period and included 206 lactation records with dairy cows at Hurley, England to evaluate the effect of silage components on voluntary intakes. Linear regression of intakes on the various silage characteristics showed significant positive correlation with DM, digestible organic matter in the dry matter (DOMD), pH, lactic acid as proportion of total acid, and total N. Significant negative correlation with lactic, acetic, and butyric acid, total acid content, and ammonia N were observed.
Effect of Physical Fill on Feed Intake
It is well known that physical distension of the reticulorumen limits the intake of low quality forages. Feed residue must escape the rumen by either digestion or passage for further intake to occur. Thus, rate of passage, rate and extent of digestion, rate of comminution, and specific gravity changes are considered of primary importance in determining gastrointestinal fill and intake of high forage diets (27). There are numerous reports (1, 40) on the relationships between dietary NDF concentrations and characteristics of diets that limit intakes, such as bulk density, rumen fill, particle distribution, digestibility, time spent eating and ruminating, rate of digestion, and passage rates of digesta from the reticulorumen. Mertens (26) reported that dietary NDF is highly correlated with digestibility and may be correlated with feed intake depression at higher feed intakes. Mertens (27) proposed that NDF can be utilized for prediction of feed intake and optimal performance of dairy cows. Khorasani et al. (22) reported that cows fed oat or triticale silage with higher NDF content had lower DMI than did cows fed alfalfa or barley silage with low NDF. Khorasani et al. (21, 22) also reported that dietary NDF was closely correlated with feed intake depression; for each percentage unit of NDF, the DMI was reduced by 0.95 kg/d in early lactation and by 0.38 kg/d in mid lactation dairy cows. Khorasani et al. (21) have also observed that in addition to NDF concentration, rate of NDF digestion was also an important contributor to DMI. Thus, advanced forage maturity may limit fiber utilization by affecting the chemical composition as well as the physical breakdown and removal of forage from the rumen. Although, the effectiveness of forage fiber is influenced by factors such as particle size, it is still possible to obtain a reasonable prediction of DMI based on the NDF concentration of the cereal grain silage.
Barley Silage Quality Research at the University of
Over the past three years the University of Alberta in conjunction with the Alberta Agriculture, Food and Rural Development (Edmonton) and Alberta Agriculture Field Crop Centre (AC-Lacombe) have studied the feeding value of three varieties of barley as a forage source for cattle.
Nutritive Values and Fermentation Characteristics of Barley
The influence of barley varieties on the chemical composition and post-ensiling fermentation characteristics of whole plant forage were evaluated. Barley varieties were: Duke, AC-Lacombe, and Seebe. The Duke variety was seeded on May 12 and 13 and harvested on July 26, 1994. The AC-Lacombe variety was seeded on May 10 and 11, 1994 and harvested on July 26, 1994. The Seebe variety was seeded on May 13 and harvested on August 2, 1994. Crops were harvested at the soft-dough stage. Harvested crops were ensiled in six separate silo bags (two for each variety), each containing 40 to 80 tonnes. Before ensiling, representative samples of each barley cultivar were taken, mixed throughly, and analyzed for pH and chemical analysis. The ensiled forages were sampled at two weeks intervals for a further eight weeks. Table 6 summarizes the results for each variety before and eight weeks after ensiling. Table 7 provides details of the fermentation characteristics of the silages.
Table 6. Composition of barley forages before and after ensiling.
|Insoluble CP, %||7.15||6.7||6.75|
Dry matter content of the fresh forage was within the 30 to 40% range recommended for ensiling. The pH of the crop before ensiling averaged 6.48 (± 0.13) with no significant differences among varieties. Over the sampling period Duke silage had a higher pH (4.38, P<.o5) compared to the AC-Lacombe (4.20) and Seebe (4.08) varieties. Period of ensiling had no effect on silage pH. The pH of silage was below 4.4 which is considered to indicate good quality (36). At harvesting, Duke had the highest CP concentration, AC-Lacombe was intermediate, and Seebe the lowest (Table 6). However, the CP concentration of ensiled material was similar for the three varieties and at eight weeks after ensiling the average CP concentration of all silages was lower than the CP concentration of silages at two-, four-, and six-weeks after ensiling. Insoluble CP in fresh forages ranged between 50 to 60% which is slightly higher than 37% reported by Acosta et al. (1) for barley silage. The NDF concentration of AC-Lacombe (fresh and silage) was higher than the NDF concentration of the Duke and Seebe. The Duke silage contained a higher acetate concentration than the other two silages, whereas, Seebe silage contained the lowest propionate concentration (Table 7). Lactate concentration was similar among the three cultivars. It is generally agreed that we want a silage with little or no butyric acid and an ammonia level of less than 10% of the total N. Butyric acid was not detected in any of these silages, which along with low ammonia N concentrations indicates the absence of clostridial fermentation. The low ADIN indicated that no heat damage occurred. It was concluded that differences in nutritive value and ensiling characteristics of silage prepared from these three barley varieties were minor and the effect of ensiling period on the silage fermentation characteristics was minimal.
Table 7. Fermentation characteristics of barley silages.
a,b Means in the same row with different superscripts differ (P<.05).
In Situ DM Degradation Characteristics of Whole Crop
The rate and extent of digestion and rate of passage are considered of primary importance in determining gastrointestinal fill and intake. Thus, DMI may be limited by both the amount of fiber in the diet and the rate at which the fiber is digested in the rumen. Silages prepared from whole crop barley varieties (Duke, AC-Lacombe, and Seebe) were evaluated for rumen DM degradation kinetics. High and medium quality alfalfa silages were included for comparison purposes. Three ruminal cannulated, non-lactation Holstein cows were utilized. Fresh silages were incubated in situ for 0, 1, 2, 4, 8, 16, 24, 48, 72, 96, and 144 h. Table 8 summarizes composition of barley and alfalfa silages used for the rumen degradation study.
Table 8. Chemical composition of silages.
|Duke||AC-Lacombe||Seebe||High quality||Low quality|
|% of DM|
When the silages were incubated in the rumen for 8, 16, and 24 h (Figure 4), the AC-Lacombe silage had the lowest DM disappearance at all incubation times.
Although, high-quality alfalfa silage had the highest DM disappearance at 8 h of rumen incubation, the DM disappearance was similar for the Duke, Seebe, and the low-, and high-quality alfalfa silages incubated at 16 h. Rate of DM degradation was similar among the barley silages and medium quality alfalfa silage. However, high quality alfalfa silage showed a higher (P<.05) rate of DM degradation than barley or medium quality alfalfa silage (Table 9).
Figure 4. Dry matter disappearance for barley and alfalfa silages.
Table 9. Dry matter degradability of barley varieties and alfalfa silages.
a,b,c Mean in the same row with different superscripts differ (P.05).
1 Effective degradability of DM at assumed ruminal turnover rate of 5%.
Silage protein was highly soluble (78.3%) and degradable (87.1%). The rate of CP degradation of alfalfa silages was more than twice that observed for barley silages. The CP disappearance was different among silages up to 16 h of rumen incubation, but after 16 h of rumen incubation, no statistically significant differences were observed (Figure 5).
Figure 5. Crude protein disappearance for barley and alfalfa silages.
The higher soluble fraction and extent of degradation of Duke and Seebe silages indicated that these silages would undergo relatively rapid digestion in the rumen and thus would promote relatively high levels of feed intake. Based on estimated DM degradation parameters, the quality of barley silages was equal or superior to the medium quality alfalfa silage. Because the protein in these silages was highly soluble and degradable, supplementation with a protein source with a high ruminal escape value would be recommended.
Effect of Barley Silage Varieties on Feed Intake, Rumen Fill,
Rumen Fermentation Characteristics, and Performance of
Dry matter intake of dairy cows is positively correlated to the rate of ruminal NDF degradation. Feeds similar in NDF can promote different DMI. The results of the nylon bag study demonstrated that the extent of ruminal digestion of whole crop barley DM is influenced by barley variety. Thus, varietal differences will influence both the end products of ruminal fermentation as well as the nutrient supply to the animal. The overall objective of this study was to evaluate varieties of whole crop barley silage as replacements for alfalfa silage. Specific objectives were to determine the relationship among chemical (e.g., NDF content), rumen fill characteristics, ruminal digestion, and DMI potential of the three barley silages (Duke, AC-Lacombe, and Seebe). The effect of barley silage variety on milk yield and milk composition were also evaluated.
Duke was seeded on May 24, and harvested on July 20, 1995. AC-Lacombe was seeded on May 25, and harvested on July 20, 1995. Seebe was seeded on May 24 and 25, and harvested on August 4, 1995. Cereal crops were harvested at the soft dough stage. Alfalfa silage was harvested as second cut, in mid-bloom, on September 1, 1995. Forages were cut, allowed to field wilt for several hours, chopped with a forage harvester, hauled, and packed in silo bags with a silopress model XP2 forage press (Silopress Inc. 1915 Floyd Blvd., Sioux city, Iowa 51104, USA). The harvested crops were ensiled in 4 separate silo bags each containing 80 tonnes, 1 bag from each crop. Table 10 summarizes analysis results for each silage before and after ensiling.
Table 10. Composition of barley forages before and after ensiling.
|Insoluble CP, %||51||27.8||50||25.8||54||36||56||35.5|
The chemical composition of the cereal grain crops (Table 10) was influenced by variety which in turn probably reflected varietal differences in the rate at which the plant matured. Protein content of the barley silages was relatively high, which reflects their early stage of maturity at harvesting. Based on NDF and ADF content, Seebe cultivars were the highest quality silage, Duke was intermediate, and AC-Lacombe was of the lowest quality. However, the protein content of the silages showed a different ranking (Table 10). Duke silage had the highest CP content, AC-Lacombe was intermediate, and Seebe silage was lowest. Seebe crop was harvested two weeks later than Duke and AC-Lacombe and thus later harvesting may have contributed to the lower protein content of Seebe compared to Duke and AC-Lacombe silage. As the time of seeding and harvesting were similar for Duke and AC-Lacombe, the observed differences in fiber and protein content of these two barley varieties may represent genetic variation. All three barley silages were well-preserved silage as reflected in lactic acid and pH levels. However, AC-Lacombe variety contained a higher level of lactic (126.5 g/kg of DM) and lower level of acetic acid (18.7 g/kg of DM) than Duke (107.8 and 26.0, g/kg DM, lactic and acetic acid respectively) and Seebe varieties (108.6 and 32.9, g/kg DM, lactic and acetic acid respectively).
Effect of Barley Silage Varieties on Dry Matter Intake and Rumen Fill. Four rumen and duodenal cannulated animals were fed a diet containing 20% concentrate and 80% of each of the test silages. The concentrate portion of the TMR was based on rolled-barley, trace-mineralized salts, and vitamins. Four cows were utilized in a 4 x 4 Latin square design experiment and each experimental period was three weeks. Rumen fermentation characteristics including pH, VFA, lactic acid, ammonia N, microbial protein production, intestinal and whole tract digestibility of nutrients, and feed intake were measured. Rumen liquid volume, solids mass, and solid component pool sizes were estimated by complete evacuation procedures. Rumen evacuation was done on four separate occasions during the last three days of each period. Time of evacuation varied in relation to feeding to obtain representative samples of digesta for a 24 hour period. Rumen turnover rates of liquids, solids, or solids component were then estimated.
Dry matter intake was higher for cows fed alfalfa silages compared to cows fed AC-Lacombe silage, but did not differ for other dietary treatments (Table 11).
Table 11. Influence of forage source on feed intake and rumen fill of heifers.
|Body weight (BW), kg||557a||527b||547ab||551ab||7.07|
|Body condition score||3.41||3.38||3.28||3.35||0.07|
|Dry matter intake (DMI), kg||6.98ab||6.39b||8.83ab||9.63a||0.69|
|DMI, % of BW||1.24b||1.19b||1.62ab||1.74a||0.12|
|Solid, % of total||85.9a||82.1ab||76.0bc||74.1c||3.11|
|Liquid, % of total||14.1c||17.9bc||24.0ab||25.9a||3.1|
|Turnover time, h||21.5||21.9||17.3||16||2.24|
a,b,c Means in the same row with different superscripts differ (P<.05).
Cows fed Seebe had a numerically higher DMI than cows fed Duke and AC-Lacombe silages. The DMI reflected the NDF content of silages. Because DMI was lowest with AC-Lacombe and Duke silage diets, these results indicate that the DMI of cows fed AC-Lacombe and Duke silages may have been limited by ruminal fill. This is in agreement with results of Khorasani et al. (21) and Miller et al. (29). Khorasani et al. (21, 22) have reported a negative correlation between DMI and NDF content of cereal grain silages. This is also supported by the rumen volume data. Although, the ruminal evacuation data (Table 11) showed that there were no significant differences in the total ruminal fill among cows fed different barley silages, cows fed alfalfa silage had a lower total rumen fill than cows fed barley silage. Rumen turnover time [(rumen DM/DMI) x 24] was also numerically higher for cows fed Duke and AC-Lacombe silage than cows fed Seebe and alfalfa silage which in turn would influence DMI (21).
Mean pH of ruminal fluid was higher for cows fed AC-Lacombe silage than for cows fed Seebe silage, and no differences were observed for the other dietary treatments (Table 12). The higher rumen pH of cows fed AC-Lacombe may be related to the lower DMI and the lower ruminal DM disappearance of AC-Lacombe silage. Khorasani et al. (21) observed a negative linear correlation between DMI and rumen pH as well as a negative correlation between the rate of ruminal digestion and rumen pH.
Table 12. Influence of forage source on ruminal fermentation characteristics of heifers.
|Ammonia N, mg/dl||10.1||11.0||8.2||15.9||2.32|
|Total VFA, mM||99.3ab||89.9b||102.8ab||119.6a||6.22|
|VFA, mol/100 ml|
a,b,cMeans in the same row with different superscripts differ (P<.05).
Mean ruminal concentration of ammonia N was not affected by dietary treatment. Total ruminal VFA concentrations were higher for cows fed alfalfa silage than for cows fed AC-Lacombe silage, and no differences were observed among other treatments. The contribution of individual VFA to the total VFA concentration was influenced by silage source. Rumen acetate concentration was highest for cows fed AC-Lacombe, intermediate for cows fed alfalfa, and lowest for cows fed Duke and Seebe silage. Rumen propionate concentration was higher for cows fed Duke silage than for cows fed alfalfa and AC-Lacombe, while rumen propionate concentration was intermediate for cows fed Seebe silage. Acetate:propionate ratio was significantly lower for cows fed Duke silage than for cows fed AC-Lacombe, with no differences observed among other dietary treatments. The changes in rumen fermentation characteristics indicate that barley silage variety can influence the rumen fermentation pattern and concentration of individual VFA. The whole crop barley silage variety can influence the DMI and rumen fermentation possibly by its NDF content and digestion characteristics of the fiber. However, other factors such as silage fermentation characteristics and starch content of barley silage variety may also affect rumen fermentation characteristics of cows fed barley silage. Khorasani et al. (22) have reported that barley silage contained twice as much starch as oat or triticale silage. This higher starch content of the barley was related to a greater head to whole plant ratio in barley than in oat and triticale (20).
Effects of Barley Silage Varieties on Milk Yield and Milk Composition of Dairy Cows. Twenty-four lactating dairy cows were blocked according to parity, date of calving, and milk yield, using a covariate design study. The covariate (control) period consisted of two weeks followed by a 12-week test period. The model includes parity, diet, parity by diet, block(parity), and covariate. A control diet was formulated based on 50% concentrate and 50% silage on a DM basis. Barley silage and alfalfa silage contributed to the silage portion of the control ration in a 50:50 ratio. The concentrate portion of the TMR was based on rolled-barley, ground corn, canola meal, soybean meal, fish meal, corn gluten meal, meat and bone meal, trace mineralized salts, and vitamins. A total mixed ration (TMR) was fed to all cows at 0800 h. In the test diets, 50% of the forage was supplied by one of the test silages (Duke, AC-Lacombe, Seebe, and alfalfa silage). Milk yield was recorded daily for the duration of the study. Samples of milk for determination of protein, fat, and lactose were taken weekly (AM and PM). The effect of dietary treatments on performance of animals is shown in Table 13.
The DMI of cows fed AC-Lacombe silage was lower than for cows fed Duke and Seebe silage and did not differ among other dietary treatments. Although, the DMI of cows averaged 22.2 kg/d (±0.6) and 3.03% (±0.08) of body weight, this intake was not as high as expected (3.5% of body weight). This lower DMI of cows may have resulted from the higher forage:concentrate (50:50) ratio used in this study.
Although, milk yield, 4% FCM, and milk components were not affected by silage type, there was a trend for lower milk and FCM yield of cows fed the AC-Lacombe silage. Production responses were also greater for cows with a parity greater than two than for cows with a parity of two (37.5 vs. 33.7 kg/d), which was expected. Milk fat and lactose were not affected by diet, but milk protein content was lower for cows fed Duke silage than for cows fed Seebe and AC-Lacombe silage. Erdman (13) reported that a ruminal acetate:propionate ratio greater than three probably would elicit little change in milk fat percentage.
Table 13. Influence of treatment on feed intake and milk production (LS means).
|DM intake, kg/d||22.7a||20.6b||21.9a||20.7ab||0.52|
|Milk protein, %||3.06b||3.28a||3.32a||3.21ab||0.06|
|Body weight, kg||727||754||736||743||12.1|
|DMI % of BWT||3.00ab||2.86b||3.12a||3.11a||0.08|
a,b,c Means in the same row with different superscripts differ (P<.05).
Performance of dairy cows was similar to that observed for heifers when these silages were fed in the metabolic study. The source of silage did not significantly influence the performance of animals, although treatment differences in DMI and rumen fermentation were observed. Alfalfa silage fed in comparison to barley silage varieties did not significantly affect the performance of animals. Therefore, good quality barley silages can replace alfalfa silage at 50% of dietary DM in early lactation cows.
Increasing the amount of forage in early-lactation diets can help reduce the cost of milk production as well as reducing health problems such as acidosis and laminitis. Results from this study support those of the previous studies showing that varietal differences exist for both chemical composition and digestion characteristics of barley silage. In addition, a comparison of these cereal grain silages to alfalfa silage indicated that cereal silages, like Seebe, can be similar in quality to medium quality alfalfa silage. A negative relationship between silage NDF concentration, rate of NDF digestion, and DMI was observed.
The recommended time for harvesting whole-plant forages range from milk through the dough stage. This corresponds to a range of 24 to 49% DM in the whole-plant. Since whole-plant cereal grain should contain 30 to 40% DM for optimal preservation, harvesting should occur at the late milk to early dough stage. Since the milk or dough stage are subjective visual observations, the actual measurement of the whole-plant DM is recommended. If the silage is being fed to low-producing cows, dry cows, or growing heifers, the production of low quality forage is justifiable. However, if the silage is used as a major part of ration for high-producing cows, the economics definitely favour cereal grain silage harvested at the highest quality.