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Effect of Maturity on Digestibility of Forage Sorghum Silages1
Effect of Maturity on Digestibility of Forage Sorghum Silages ' F. G. O W E N and J. W. K U H L M A N *
Department of Dairy Science, University of Nebraska, Lincoln Abstract
Atlas and Rox sorghum varieties were each harvested at the milk, medium-dough, and hard-dough stages. Digestibilities were determined by the Cr.O~, grab-sample technique, using Holstein heifers. The apparent digestibility of Atlas sorghum silage dry matter was depressed from 55 to 46% by advancing maturity from the milk to the hard-seed stages. Energy and protein digestibility also were decreased. Digestibility of Rox silage was not appreciably affected by maturity. Results suggest that frosting may improve digestibility of Atlas. Grinding had little effect. Delaying harvest of Atlas sorghum until the hard-seed stage resulted in a depression in the efficiency of dry matter conversion to milk (6). ttilston and Gifford (3) reported a higher requirement of dry matter for beef cattle gain when feeding Atlas silage cut at the mature stage compared to the soft-dough stage. The possibility that these differences in feed efficiency may be related to digestibility has not been adequately investigated. The only data on this subject appear to be in the following preliminary reports. Ramsey et al. (7) found that advancing maturity of Tracy sorghum from the flower to the ripe-seed stage depressed dry matter digestibility (50 to 46%) ; whereas, in a second trial, it enhanced digestibility (52 to 56%). Texas workers (2, 5) reported a reduction of about 25 % in the estimated Received for publication October 7, 1966 1 Published with the approval of the Director as paper no. 1988, Journal Series, Nebraska Agricultural Experiment Station, Lincoln. :Present address: Buffalo County Extension Office, I~:earney, Nebraska.
TDN value of Tracy silage, due to postponing harvest from the soft-dough to the mature stage. The objectives of the experiments in this report were a) to gain additional information on the relation of stage of maturity at harvest to the digestibility of forage sorghum silage and b) to examine the effects of grinding and frosting on the digestibility of sorghum silage. Experimental Procedure
Two forage sorghum varieties, Atlas, and a mixture containing mainly Rox, were each harvested with a field chopper at three stages of maturity: a) milk stage, when the seed contents had a white fluid consistency; b) soft-dough stage, when most of the seed had reached a soft pasty consistency; and c) hard-dough stage, when most of the seed was very firm, but before becoming brittle. The forage was preserved in 208-liter metal drums sealed with plastic covers. Dates of harvest and composition are shown in Table 1. The design of the digestibility trials consisted of a balanced pail- of 3 X 3 Latin squares for each of the sorghum varieties, ttolstein and Brown Swiss heifers, six to nine months old, where randomly assigned to treatment sequences. During a 2-wk preliminary period all calves were gradually accustomed to a ration, with silage as the sole roughage. A 3rd wk consisted of ad libitum silage feeding. During the three experimental periods which followed, calves were fed 4.5 kg of silage and .68 kg of a pelleted concentrate twice daily. The concentrate was fed to provide nutrients usually needed to supplem.ent sorghum silage in a growing ration. Composition of the concentrate was corn meal, 1,900 kg; soybean oil meal (44% crude protein),
TABLE 1 Forage harvest date and silage composition Variety and maturity Atlas, milk Atlas, soft-dough Atlas, hard-dough t~ox, milk Rox, soft-dough Rox, hard-dough
Harvest date Sept. 4 Sept. 12 Oct. 10 Sept. 8 Sept. 16 Oct. 3
Dry matter
Crude protein ~
Gross energy ~
(%)
(%)
(Kcal/g)
23.1 25.0 28.2 23.4 27.7 29.9
7.75 9.32 6.63 9.91 8.92 9.26
4.046 4.086 4.191 4.110 4.119 4.118
Values on a dry matter basis. 527
pH 4.5 4.6 4.8 4.5 4.6 4.~
528
OWEN AND KUI-ILMAN
986 kg; steamed bonemeal, 62 kg; iodized salt, 31 kg; and chromic oxide, 20 kg. Chromic oxide in the concentrate served as an indicator of fecal output. The first nine days of each 14-day experimental period served as an adjustment period. On each of the last five days fecal samples were taken from each heifer at 6 A~[ and 4 P•. These samples were composited on an equal weight basis. The validity of these sampling times was confirmed by chromic oxide excretion curves. Silage moisture was determined by oven drying (8). Crude protein determinations were made on undried samples of both silage and feces. Other determinations were made on dried, ground samples. Chromic oxide was determined by the method of Brisson (1). Data for the two varieties were combined for statistical evaluation of the differences among maturities. The varieties were produced on different fields and, therefore, were not comparable. Since late cutting of Atlas resulted in a reduction in digestibility, another trial was run to evaluate the effect of grinding and frosting on digestibility of mature, hard-seed Atlas silage. Comparison was made among sorghums harvested for silage on October 14 by conventional forage chopping (12-cm lengths), the same forage ground through a 2.5-era mesh screen, and sorghum from the same field harvested after a severe frost and ground in the same manner. The frosted sorghum was cut ;13 days following the previous harvest. These forages were stored in approximately ;136-kg lots, using plastic sleeves in the drums described above. Digestion trials were begun after four months of ensiling. Five-month-old Holstein steers were used in a 3 × 3 Latin-square design. During a 1-wk adjustment period, calves were shifted on to a ration of only silage and 1.36 kg daily of the
concentrate mixture used in the first trial. Experimental periods were 14 days. The first four days calves were fed silage ad libitnm twice daily (to allow a 10% excess) ; the ]2 days thereafter, calves were fed a constant intake, equal to 80% of their average four day intake. The last six days of this period grab-sample fecal collections were obtained and digestibility determined as in the first trial. The brief periods of ad libitum feeding in the preceding digestion trials suggested that the frosted silage was more palatable than the nonfrosted silages. A 3 × 3 Latin-square was again utilized, to examine the effect of frosting on dry matter intake. The animals of the preceding trial were utilized to compare the ground-mature Atlas and tile ground-frosted Atlas silages, with corn silage. Calves were fed only silage twice daily at 10% in excess of their previous day's intake. Twelve-day periods were used; the first six days for adjustment, followed by six days for comparison. Results and Discussion
Effects of maturity on digestibility are presented in Table 2. Digestibility of Atlas silage was 18% higher in the milk stage than in the hard-dough stage. The digestibility of Rox silage averaged 66% and was not appreciably different for the maturities tested. The effect of silage maturity on the ration (silage plus concentrate) dry matter digestibility was not statistically significant (at P < . 0 5 ) for the combined data on the two varieties; however, a significant ( P < . 0 5 ) interaction of silage X maturity indicated that there was an effect of maturity on digestibility of Atlas, but not on Rox. When the effect of the concentrate on the digestibility values was computationally re-
TABLE 2 Effect of stage of maturity on silage digestibility Ration
Stage of maturity
Dry matter Atlas
Rox
Energy Atlas
Silage plus concentrate
Crude protein Rox
Atlas ~
Rox
(%) Milk Soft-dough Hard-dough
61.4 55.8 52.1
66.6 67.1 65.8
63.0 57.5 56.0
67.6 68.3 67.4
56.0 56.6 45.1
60.5 58.5 63.3
Milk Soft-dough Hard-dough
54.6 46.4 46.0
62.3 64.2 63.2
43.0 35.9 34.1
52.7 54.6 54.9
11.4 15.7 2.2
22.1 20.8 33.4
Silage b
a Nine of the individual values for silage were negative; these were recorded as zero. b Silage digestibilities were determined by difference. Digestible nutrients in the concentrate were computed from published values. J . DAIRY SCIENCE YOL. 50, NO. 4
SORGHUM DIGESTIBILITY
529
TABLE 3 Effect of grinding and frosting on digestibility of Atlas sorghum silage
Treatment
Harvest date
Silage dry matter cm~tent
Dry matter digestibility Ration (%)
Mature, chopped Mature, ground Frosted, ground Standard error
Oct. 14 Oct. 14 Oct. 27
31.4 25.5 29.7
-
43.3 47.2 61.0 (3.2)
Silage ~ -
25.7 32.8 54.9 (4.7)
Silage digestibilities were determined by difference. Digestible nutrients in the coneentrate were computed from published values. moved, digestibility values were reduced especially for Atlas. These results with Atlas are very similar to those from one trial reported by Ramsey et al. (7) for corresponding stages of Tracy sorghum silage. I n a second trial, the following year, their digestibility values differed little among maturity stages. Energy digestibility generally tended to parallel those for dry matter. The ration containing Atlas at the milk stage had a 12% higher digestibility than the ration containing the silage at the hard-dough stage. The Rox ration was not appreciably different in digestible energy for the three maturity stages. The interaction between variety and maturity approached significance at P < . 0 5 . This suggests that delayed harvest decreased the digestible energy in Atlas but not in Rox silage. The reduced digestibility of the dry matter of Atlas may resuIt from a depression in cellulose digestibility with advancing maturity. Rox is a variety with a higher proportion of grain, therefore the decline in cellulose digestibility may have been neutralized by greater amounts of starch deposited during maturation. Such a difference in low- and high-grain varieties is suggested by the results obtained by Joo (4), using the suspended nylon bag technique to measure rumen digestion. Adjusting the digestibility values for the concentrate consmned reduced considerably the digestible energy values for Atlas. I n both the utilization of dry matter and energy the major difference in maturities was between the milk and soft-dough stages. The principal influence of maturity on the digestibility of ration protein was the reduction, for Atlas, from 56% in the milk stage to 45% in the hard-dough stage. Maturity had no apparent influence on digestibility of the protein in Rox silage. Delayed harvest was detrimental to utilization of protein in Atlas but not in Rox (interaction significant at P < . 0 5 ) . The theoretical digestibility values for silage protein itself were considerably lower than ration protein. Most of the digestibilities for
Atlas silage protein were negative. Ramsey et al. (7) found the digestibility of protein in Tracy silage to be 26, 16, and 26% for the milk, soft-dough, and hard-dough stages, respectively. In a trial the following year the silages were supplemented with soybean oil meal. Digestible protein values for the same maturity stages were 42, 32, and 26%, respectively. Helm at al. (2) found the protein of Tracy completely indigestible. Protein digestibility is influenced by many ration factors, especially level of dietary protein. The latter may be the reason for the higher values for Rox than Atlas and may account for much of the variation in previously reported results. Grinding of mature forage tended to only slightly increase the digestibility of the ration (Table 3). Since dry matter consumption from the ground forage was slightly higher, adjusting the digestibility for the digestible dry matter contributed by the concentrate magnified this difference. Digestibility of the frosted silage averaged 55%, compared to 26% for the mature unfrosted silage. Although this is a striking difference, the scope of this trial was limited by the available silage, and statistical tests of desirable sensitivity could not be made. Therefore, this may be considered preliminary evidence that frosting of sorghum results in changes which may enhance its feeding value via improved digestibility. Dry matter intake was not greatly influenced by frosting and the ground sorghums were not more palatable than corn silage. Average daily dry matter intakes p e r 45.4 kg were .77, .82, and .72 kg for the corn, mature ground, and frosted ground silages, respectively. References (1) Erisson, G. L. 1956. On the Routine Deter-
ruination of Chromic Oxide in Feces. Canadian J. Agr. Sci., 36: 210. (2) Helm, Raymond E., and Leighton, R. E. 1960. Relationship of Stage of Maturity at Harvest to the Feeding Value of Sorghum Silage for Dairy Cows. J. Dairy Sci., 43:868. ft. DAIRYSClEt~eEVOn. 50. NO. 4
530
0WEN
AND
(3) Hilston, N. W., and Gifford, Warren. 1946. Comparative Values of Various Roughages for Wintering Feeder Calves. Arkansas Agr. Expt. Sta., Bull. 463. (4) Joo, Y. D. 1965. Influence of Stage of Maturity on Chemical Composition and Small Sample in Vivo Digestion of Two Sorghum Crops. M. S. thesis, Mississippi State ~niversity, State College. (5) Leighton, 1~. E., and Rupel, L. W. 1959. Value of Tracy Sorghum Silage Cut at Two Stages of Maturity for Feeding Producing Dairy Cows. J. Dairy SoL, 4 2 : 3 9 3
J~ DAIRY SCIENCE VOL. 50, NO. 4
KUHLMAN
(6) Owen, Foster G. 1962. Effect of Stage of Maturity on the Nutritive Value of Atlas Sorghum Silage for Lactating Dairy Cows. J. Dairy Sei., 45: 625. (7) Ramsey, D. S., Lusk, L. W., and Miles, J. T. 1961. Observations on the Digestibility of Sweet Sorghum Silage Ensiled at Four Stages of Maturity. J. DMry Sci., 44: 975. (8) USDA. 1959. Second Silage Conference Proceedings, P a r t I. Procedures and Techniques Used in Silage Studies (memo), Beltsville, Maryland.
Department of Dairy Science, University of Nebraska, Lincoln Abstract
Atlas and Rox sorghum varieties were each harvested at the milk, medium-dough, and hard-dough stages. Digestibilities were determined by the Cr.O~, grab-sample technique, using Holstein heifers. The apparent digestibility of Atlas sorghum silage dry matter was depressed from 55 to 46% by advancing maturity from the milk to the hard-seed stages. Energy and protein digestibility also were decreased. Digestibility of Rox silage was not appreciably affected by maturity. Results suggest that frosting may improve digestibility of Atlas. Grinding had little effect. Delaying harvest of Atlas sorghum until the hard-seed stage resulted in a depression in the efficiency of dry matter conversion to milk (6). ttilston and Gifford (3) reported a higher requirement of dry matter for beef cattle gain when feeding Atlas silage cut at the mature stage compared to the soft-dough stage. The possibility that these differences in feed efficiency may be related to digestibility has not been adequately investigated. The only data on this subject appear to be in the following preliminary reports. Ramsey et al. (7) found that advancing maturity of Tracy sorghum from the flower to the ripe-seed stage depressed dry matter digestibility (50 to 46%) ; whereas, in a second trial, it enhanced digestibility (52 to 56%). Texas workers (2, 5) reported a reduction of about 25 % in the estimated Received for publication October 7, 1966 1 Published with the approval of the Director as paper no. 1988, Journal Series, Nebraska Agricultural Experiment Station, Lincoln. :Present address: Buffalo County Extension Office, I~:earney, Nebraska.
TDN value of Tracy silage, due to postponing harvest from the soft-dough to the mature stage. The objectives of the experiments in this report were a) to gain additional information on the relation of stage of maturity at harvest to the digestibility of forage sorghum silage and b) to examine the effects of grinding and frosting on the digestibility of sorghum silage. Experimental Procedure
Two forage sorghum varieties, Atlas, and a mixture containing mainly Rox, were each harvested with a field chopper at three stages of maturity: a) milk stage, when the seed contents had a white fluid consistency; b) soft-dough stage, when most of the seed had reached a soft pasty consistency; and c) hard-dough stage, when most of the seed was very firm, but before becoming brittle. The forage was preserved in 208-liter metal drums sealed with plastic covers. Dates of harvest and composition are shown in Table 1. The design of the digestibility trials consisted of a balanced pail- of 3 X 3 Latin squares for each of the sorghum varieties, ttolstein and Brown Swiss heifers, six to nine months old, where randomly assigned to treatment sequences. During a 2-wk preliminary period all calves were gradually accustomed to a ration, with silage as the sole roughage. A 3rd wk consisted of ad libitum silage feeding. During the three experimental periods which followed, calves were fed 4.5 kg of silage and .68 kg of a pelleted concentrate twice daily. The concentrate was fed to provide nutrients usually needed to supplem.ent sorghum silage in a growing ration. Composition of the concentrate was corn meal, 1,900 kg; soybean oil meal (44% crude protein),
TABLE 1 Forage harvest date and silage composition Variety and maturity Atlas, milk Atlas, soft-dough Atlas, hard-dough t~ox, milk Rox, soft-dough Rox, hard-dough
Harvest date Sept. 4 Sept. 12 Oct. 10 Sept. 8 Sept. 16 Oct. 3
Dry matter
Crude protein ~
Gross energy ~
(%)
(%)
(Kcal/g)
23.1 25.0 28.2 23.4 27.7 29.9
7.75 9.32 6.63 9.91 8.92 9.26
4.046 4.086 4.191 4.110 4.119 4.118
Values on a dry matter basis. 527
pH 4.5 4.6 4.8 4.5 4.6 4.~
528
OWEN AND KUI-ILMAN
986 kg; steamed bonemeal, 62 kg; iodized salt, 31 kg; and chromic oxide, 20 kg. Chromic oxide in the concentrate served as an indicator of fecal output. The first nine days of each 14-day experimental period served as an adjustment period. On each of the last five days fecal samples were taken from each heifer at 6 A~[ and 4 P•. These samples were composited on an equal weight basis. The validity of these sampling times was confirmed by chromic oxide excretion curves. Silage moisture was determined by oven drying (8). Crude protein determinations were made on undried samples of both silage and feces. Other determinations were made on dried, ground samples. Chromic oxide was determined by the method of Brisson (1). Data for the two varieties were combined for statistical evaluation of the differences among maturities. The varieties were produced on different fields and, therefore, were not comparable. Since late cutting of Atlas resulted in a reduction in digestibility, another trial was run to evaluate the effect of grinding and frosting on digestibility of mature, hard-seed Atlas silage. Comparison was made among sorghums harvested for silage on October 14 by conventional forage chopping (12-cm lengths), the same forage ground through a 2.5-era mesh screen, and sorghum from the same field harvested after a severe frost and ground in the same manner. The frosted sorghum was cut ;13 days following the previous harvest. These forages were stored in approximately ;136-kg lots, using plastic sleeves in the drums described above. Digestion trials were begun after four months of ensiling. Five-month-old Holstein steers were used in a 3 × 3 Latin-square design. During a 1-wk adjustment period, calves were shifted on to a ration of only silage and 1.36 kg daily of the
concentrate mixture used in the first trial. Experimental periods were 14 days. The first four days calves were fed silage ad libitnm twice daily (to allow a 10% excess) ; the ]2 days thereafter, calves were fed a constant intake, equal to 80% of their average four day intake. The last six days of this period grab-sample fecal collections were obtained and digestibility determined as in the first trial. The brief periods of ad libitum feeding in the preceding digestion trials suggested that the frosted silage was more palatable than the nonfrosted silages. A 3 × 3 Latin-square was again utilized, to examine the effect of frosting on dry matter intake. The animals of the preceding trial were utilized to compare the ground-mature Atlas and tile ground-frosted Atlas silages, with corn silage. Calves were fed only silage twice daily at 10% in excess of their previous day's intake. Twelve-day periods were used; the first six days for adjustment, followed by six days for comparison. Results and Discussion
Effects of maturity on digestibility are presented in Table 2. Digestibility of Atlas silage was 18% higher in the milk stage than in the hard-dough stage. The digestibility of Rox silage averaged 66% and was not appreciably different for the maturities tested. The effect of silage maturity on the ration (silage plus concentrate) dry matter digestibility was not statistically significant (at P < . 0 5 ) for the combined data on the two varieties; however, a significant ( P < . 0 5 ) interaction of silage X maturity indicated that there was an effect of maturity on digestibility of Atlas, but not on Rox. When the effect of the concentrate on the digestibility values was computationally re-
TABLE 2 Effect of stage of maturity on silage digestibility Ration
Stage of maturity
Dry matter Atlas
Rox
Energy Atlas
Silage plus concentrate
Crude protein Rox
Atlas ~
Rox
(%) Milk Soft-dough Hard-dough
61.4 55.8 52.1
66.6 67.1 65.8
63.0 57.5 56.0
67.6 68.3 67.4
56.0 56.6 45.1
60.5 58.5 63.3
Milk Soft-dough Hard-dough
54.6 46.4 46.0
62.3 64.2 63.2
43.0 35.9 34.1
52.7 54.6 54.9
11.4 15.7 2.2
22.1 20.8 33.4
Silage b
a Nine of the individual values for silage were negative; these were recorded as zero. b Silage digestibilities were determined by difference. Digestible nutrients in the concentrate were computed from published values. J . DAIRY SCIENCE YOL. 50, NO. 4
SORGHUM DIGESTIBILITY
529
TABLE 3 Effect of grinding and frosting on digestibility of Atlas sorghum silage
Treatment
Harvest date
Silage dry matter cm~tent
Dry matter digestibility Ration (%)
Mature, chopped Mature, ground Frosted, ground Standard error
Oct. 14 Oct. 14 Oct. 27
31.4 25.5 29.7
-
43.3 47.2 61.0 (3.2)
Silage ~ -
25.7 32.8 54.9 (4.7)
Silage digestibilities were determined by difference. Digestible nutrients in the coneentrate were computed from published values. moved, digestibility values were reduced especially for Atlas. These results with Atlas are very similar to those from one trial reported by Ramsey et al. (7) for corresponding stages of Tracy sorghum silage. I n a second trial, the following year, their digestibility values differed little among maturity stages. Energy digestibility generally tended to parallel those for dry matter. The ration containing Atlas at the milk stage had a 12% higher digestibility than the ration containing the silage at the hard-dough stage. The Rox ration was not appreciably different in digestible energy for the three maturity stages. The interaction between variety and maturity approached significance at P < . 0 5 . This suggests that delayed harvest decreased the digestible energy in Atlas but not in Rox silage. The reduced digestibility of the dry matter of Atlas may resuIt from a depression in cellulose digestibility with advancing maturity. Rox is a variety with a higher proportion of grain, therefore the decline in cellulose digestibility may have been neutralized by greater amounts of starch deposited during maturation. Such a difference in low- and high-grain varieties is suggested by the results obtained by Joo (4), using the suspended nylon bag technique to measure rumen digestion. Adjusting the digestibility values for the concentrate consmned reduced considerably the digestible energy values for Atlas. I n both the utilization of dry matter and energy the major difference in maturities was between the milk and soft-dough stages. The principal influence of maturity on the digestibility of ration protein was the reduction, for Atlas, from 56% in the milk stage to 45% in the hard-dough stage. Maturity had no apparent influence on digestibility of the protein in Rox silage. Delayed harvest was detrimental to utilization of protein in Atlas but not in Rox (interaction significant at P < . 0 5 ) . The theoretical digestibility values for silage protein itself were considerably lower than ration protein. Most of the digestibilities for
Atlas silage protein were negative. Ramsey et al. (7) found the digestibility of protein in Tracy silage to be 26, 16, and 26% for the milk, soft-dough, and hard-dough stages, respectively. In a trial the following year the silages were supplemented with soybean oil meal. Digestible protein values for the same maturity stages were 42, 32, and 26%, respectively. Helm at al. (2) found the protein of Tracy completely indigestible. Protein digestibility is influenced by many ration factors, especially level of dietary protein. The latter may be the reason for the higher values for Rox than Atlas and may account for much of the variation in previously reported results. Grinding of mature forage tended to only slightly increase the digestibility of the ration (Table 3). Since dry matter consumption from the ground forage was slightly higher, adjusting the digestibility for the digestible dry matter contributed by the concentrate magnified this difference. Digestibility of the frosted silage averaged 55%, compared to 26% for the mature unfrosted silage. Although this is a striking difference, the scope of this trial was limited by the available silage, and statistical tests of desirable sensitivity could not be made. Therefore, this may be considered preliminary evidence that frosting of sorghum results in changes which may enhance its feeding value via improved digestibility. Dry matter intake was not greatly influenced by frosting and the ground sorghums were not more palatable than corn silage. Average daily dry matter intakes p e r 45.4 kg were .77, .82, and .72 kg for the corn, mature ground, and frosted ground silages, respectively. References (1) Erisson, G. L. 1956. On the Routine Deter-
ruination of Chromic Oxide in Feces. Canadian J. Agr. Sci., 36: 210. (2) Helm, Raymond E., and Leighton, R. E. 1960. Relationship of Stage of Maturity at Harvest to the Feeding Value of Sorghum Silage for Dairy Cows. J. Dairy Sci., 43:868. ft. DAIRYSClEt~eEVOn. 50. NO. 4
530
0WEN
AND
(3) Hilston, N. W., and Gifford, Warren. 1946. Comparative Values of Various Roughages for Wintering Feeder Calves. Arkansas Agr. Expt. Sta., Bull. 463. (4) Joo, Y. D. 1965. Influence of Stage of Maturity on Chemical Composition and Small Sample in Vivo Digestion of Two Sorghum Crops. M. S. thesis, Mississippi State ~niversity, State College. (5) Leighton, 1~. E., and Rupel, L. W. 1959. Value of Tracy Sorghum Silage Cut at Two Stages of Maturity for Feeding Producing Dairy Cows. J. Dairy SoL, 4 2 : 3 9 3
J~ DAIRY SCIENCE VOL. 50, NO. 4
KUHLMAN
(6) Owen, Foster G. 1962. Effect of Stage of Maturity on the Nutritive Value of Atlas Sorghum Silage for Lactating Dairy Cows. J. Dairy Sei., 45: 625. (7) Ramsey, D. S., Lusk, L. W., and Miles, J. T. 1961. Observations on the Digestibility of Sweet Sorghum Silage Ensiled at Four Stages of Maturity. J. DMry Sci., 44: 975. (8) USDA. 1959. Second Silage Conference Proceedings, P a r t I. Procedures and Techniques Used in Silage Studies (memo), Beltsville, Maryland.