Intake, Duodenal Flow, and Ruminal Characteristics of Long or Short Chopped Alfalfa-Timothy Silage with or without Inoculant1, 2

Intake, Duodenal Flow, and Ruminal Characteristics of Long or Short Chopped Alfalfa-Timothy Silage with or without Inoculant1,2 HELENE V. PETIT and P. M. FLiPOT Agriculture Canada C. P. 90 Lennoxville, PO. J1 M 1Z3, Canada ABSTRACT

Eight crossbred wethers each fitted with reentrant duodenal cannula and rumen fistula were used in a crossover design with a 2 x 2 factorial arrangement in order to measure the effects of inoculation and chop length of silage on intake, rate of flow into the duodenum, and ruminal characteristics. As chop length increased, silage DM decreased Microbial inoculation had no effect on silage composition but increased its intake. Short chop length of silage decreased the amount of total N reaching the duodenum. The rumen acetate:propionate ratio was decreased by feeding the short vs. chopped silage. Rumen acetate concentration was lower when the sheep were fed short chopped silage compared with long chopped silage. Rumen volume and DM content were higher for sheep fed inoculated silages. The pH and NH3 N of the rumen and rumen dilution rate of liquid and solids were similar for all treatments. Data show that microbial inoculation increased silage intake and that silage particle size modified duodenal flow of N and production of rumen VFA, which might alter performance of animals. (Key words: silage, chop length, microbial inoculant) INTRODUCTION

Received February 13, 1990. Accepted July 9, 1990. lContribution Number 288. 20rrade names are used in this paper solely to provide specific information. Mention of a trade name does not constitute a warranty of the product by Agriculture Canada or an endorsement of the product to the exclusion of other products not mentioned. 1990 J Dairy Sci 73:3165-3171

Experiments to investigate the effect of length of cut of silage usually have given inconsistent results. Deswysen et al. (6) observed, with 300-kg capacity silos, an improvement in the fermentation characteristics of short versus long cut silage. Increase in intake of short cut silages was related to silage quality (6) and faster eating and rumination rates (7). Conversely, the length of cut of silage in commercial scale silos had no effect on silage fermentation and DM intake (14). The ensiling procedure might have been responsible for discrepancies among published results. Many products have been studied with the goal of improving silage quality. Silage additives formulated with strong acids have proven to be effective, but associated hazards limit their use. Consequently, additives in the form of inoculants based on cultures of homofermentative lactic acid bacteria recently have appeared on the market. Published results on silage inoculants have been inconsistent. Lactobacillus plantarum, added to grass silage, was responsible for lower pH and NH3 N, expressed as a proportion of total N, and higher lactic acid (22, 31). However, Hooper et al. (19) did not observe any difference in chemical composition between Lactobacillus-inoculated and uninoculated grass silages. Kung et al. (22) reported an improvement in DM consumption when alfalfa silage was inoculated with microbes. Other studies with sheep (11) reported no improvement with Lactobacillus-inoculated silages. Studies on silage additives and length of chop have been limited to the ensiling characteristics of silage and to animal performance. Knowledge is limited on the effects of additives and chop length on nutrients supplied from digestion of silage for absorption from the gut. The objective of our experiment was to determine in sheep the effects of chop length and inoculation of silage on intake, rate of passage into the duodenum, and ruminal characteristics.

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3166 MATERIALS AND METHODS

Animals

Eight crossbred wethers averaging 37.6 kg (SE = 3.6) were fitted with duodenal reentrant (20) and mmen cannulas. Surgery was perfonned 3 mo before initiation of the experiment. During the entire experiment, the sheep were kept in metabolic cages, except for the first 7 d of each experimental period when the animals were kept individually in solid floor pens covered with wood shavings. Experimental Design and Measurements

The eight sheep were assigned to four diets assigned in a crossover design with a 2 x 2 factorial arrangement of treatments and four periods. The experimental diets consisted of alfalfa-timothy grass silage of long or short cut length with or without inoculant. The inoculant supplied by Rosell Institute (Rosell Institute Inc., 8480 Blvd. St-Laurent, Montreal, PQ, H2P 2M6, Canada) was a mixture of Lactobacillus plantarum (40%), Lactobacillus casei var. rhamnosus (20%), Lactobacillus amylovorus (20%), Streptococcus faecium (15%), and Cellulomonas jlavigena (5%) containing 27.5 x 1()9/g of inoculant. The inoculant was applied at a rate of 20 glt of freshly cut forage, which was obtained from a third cut of a1falfa-tirnothy harvested at the vegetative stage and stored in concrete tower silos (4 x 12 m) containing about 12 t of DM. The chop lengths were determined in duplicate by hand separation of a fresh sample of timothy taken just before ensiling. Each individual piece of forage was measured and then regrouped into four fractions according to its length (Table 1). The mean chop length of each treatment was calculated according to the method described by the American Society of Agricultural Engineers (1).

The animals were fed twice daily at 0800 and 1600 h. Fresh water and salt were available at all times. Trace minerals were only offered d 1 to 7 of each 31-d experimental period. Adaptation to the diets occurred during the first 3 wk when the animals were fed for ad libitum intake. Voluntary intake was measured during wk 3 of the experiment. Between d 22 and d 27, each animal was limited to 90% of its vohmtary Journal of Dairy Science Vol. 73,

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intake and total collection of feces was carried out. On d 28, a 24-b continuous collection of duodenal digesta was perfonned. Samples of rumen contents were collected from d 29 to 31 of each experimental period. Ten days prior to the collection of duodenal digesta, chromic oxide was deposited in the rumen through the cannula. The 1.5 g of marker were wrapped in paper and given twice daily prior to each meal. The diets were sampled weekly for the first 3 wk, once daily thereafter, and composited for d 22 to 27. AU samples were frozen at -ISoC for subsequent analyses. The 24-h measurement of duodenal flow was initiated just before the morning meal on d 28. AU digesta flowing from the abomasum were collected in a container kept on ice. Once 400 ml of digesta had been collected, the flask was replaced, and a 10% digesta sample was accumulated on a 24-h basis for analysis. The 10% sample of digesta was replaced by digesta previously collected from sheep given similar silages, and digesta were returned to the animal in the upper part of the cannula. Daily flow of duodenal digesta and its components were corrected for 100% recovery of chromium. On d 29 of each period, prior to the morning feeding, 150 ml of Co-EDTA were infused into the romen after taking a rumen sample. The Co-EDTA was prepared according to Goodall and Kay (13) with Co rather than Cr. The CoEDTA solution contained 16,540 ppm Co and was added as the liquid phase marker. At the same time, 20 g of silage treated with La were fed to the sheep. Lanthanum oxide was added as the solid phase marker according to the procedure described by Hartnell and Satter (18) with a solution twice the La concentration. The 6-ml La solution was sprayed on 20 g of silage to provide a La intake of 400 mg per sheep. After spraying, the silage was air dried overnight and frozen until fed. Rumen contents were sampled (100 ml) at 0, 1,2,3,4.5,6, 7.5,9, 12,24,36, and 48 h after the a.m. feeding on d 29. The pH was determined on the first seven samples immediately after collection. The samples were then strained through two layers of cheesecloth, and 2 ml of 50% HCl were added to lower the pH. Samples were then centrifuged at 26,500 x g for 30 min at 5°C and pooled on a sheep basis within each period for determination of VFA and NH3 N. Samples at 0, 3, 6, 9, 12, 24, 36, and 48 h were

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frozen separately for the analysis of the two markers. The supematant of these samples was used for the analysis of Co, and the solid fraction was dried at 6O·C for 48 h in a vacuum oven and used for La determination. The decline in the log of Co and La concentrations over time was used to estimate ruminal fluid and particulate dilution rates, respectively. The 12-, 24-, 36-, and 48-h Co and La concentrations were the only values used in the regression because Co and La did not appear to be distributed uniformly in the rumen before 12 h as already reported for Yb (5).

TABLE 1. Dry matter distribution in length categories of the long- and sbort-cut silages fed to sheep. Silage cut Lcog1h categories

Long

Short

< 25 mm

65.91 15.3 12.6 6.2 21.1

85.9 8.2 4.6 1.3 15.2

25 - 50 mm 51 - 100 mm > 100 mm Mean length of chop, mm

IPen:entage of DM of the sample in length category.

RESULTS AND DISCUSSION Analytical Methods

Silage OM was detennined by toluene distillation (8), and OM in orts was measured by oven drying at l00·C. Dry matter of duodenal digesta was determined by freeze-drying for 96 h. Silage samples were freeze-dried for chemical analyses. Total nitrogen (TN) was determined according to the procedures of the AOAC (2). Cell wall components were measured according to Goering and Van Soest (12). Analysis of silage pH was performed according to the method described by Playne and McDonald (29). The NPN was analyzed using 15 g of fresh silage homogenized in 150 ml .IN HeI. The NPN was determined on the acidified extract of silage juice, which had been deproteinized with 4N TCA in a proportion of silage juice to TCA of 4:1 (28). The contents of NPN and NH3 N were determined by the Kjeldahl method. The VFA were determined by gas chromatography (Varian model 3400, Varian Can., Inc., Ville St-Laurent, PQ H4M 2V2, Canada) on an aliquot of the deproteinized extract using valeric acid as the internal standard. Soluble N was analyzed according to the method described by Brady (3). Cobalt and La were measured by atomic absorption after nitric-perchloric acid digestion for La. Statistical Analyses

All results were subjected to ANOVA. The main effects were chop length of silage (long cut vs. short cut), inoculant (inoculated vs. uninoculated), and period. The least squares mean test was according to SAS procedure (32) using a probability of 5% unless otherwise noted.

Silage Composition

The chop length was detennined by hand separation of fresh material collected before ensiling. Four categories of length were established (Table 1) with the most important difference being observed for the length less than 25 mm. Long-cut silage contained 65.9% of its weight in the category of less than 25 mm compared with 85.9% for short-cut silage. Only 14.1% of the weight of the short-cut silage was in the categories greater than 25 mm compared with 34.1 % for the long-eut silage. Chemical components generally were similar among all the silages (Table 2). The only differences among silages were for OM, which was significantly lower (35.0 vs. 38.5%) for the short versus the long silages and for TN which was significantly higher (2.56 vs. 2.48%) for short-cut silage with inoculant compared with the average of the three others. Higher OM content for silages of short-chop length already has been reported (27) and might be due to better compaction occurring with short- vs. long-chop length of the forage. Content of soluble N and NPN tended to be lower (P<.10) for inoculated vs. uninoculated silages. Average soluble N, NPN, ADF N as percentages of TN, ADF, and NDF were 62.9,39.0, .19,33.1, and 44.3%, respectively, suggesting that the forages were well preserved in the silos. As reported (30), low ADF N is associated with good quality silages. The contents of ADF and NDF were typical of grass harvested at the vegetative stage. The pH of silages was affected neither by chop length nor inoculation. These findings are in agreement with Gordon (14), who measured Journal of Dairy Science Vol. 13, No. II, 1990

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TABLE 2. Composition of chemical constituents of short- (SS) and long-cut (LS) silage without (NI) or with (l) inoculant. Silages Item

SSNI

SSI

LSNI

LSI

X

SE

DM,l % Total N.2 % of total DM Soluble N, % total N NPN, % total N ADF N. % total N ADF, % total DM NDF, % total DM pH

38.7 2.47 65.1 40.1 .19 33.0 44.2 4.16

38.2 2.56 60.4 37.8 .19 32.0 43.8 4.14

33.2 2.51 65.1 40.4 .18 33.2 43.9 4.16

36.7 2.47 60.6 37.4 .21 34.3 45.3 4.12

36.8 2.51 62.9 39.0 .19 33.1 44.3 4.14

.8 .02 1.4 .8 .01

.s

.6 .02

ISignificant effect of chop length (P<.OS). 2Significant interaction of inoculant x chop length (P<.OS).

the effect of chop length on silage pH, and with Kung et al. (21), who determined the effect of inoculation. The absence of any beneficial effect of inoculation on silage pH might be due to the OM content of the silages. Kung et al. (21) reported a beneficial effect only with silage containing 60% OM and no effect when OM dropped to 40%. Microbial inoculation is not effective in silages containing 40% OM, suggesting that OM permits fennentation to proceed fast enough to metabolize the water-soluble carbohydrates to lactic acid and other end products, thus decreasing silage pH. Our results are in agreement with Gordon (14), in that silage fermentation was not modified by chop length, and contrary to Murdoch et al. (26), who reported an improvement in silage fermentation as chop length increased. Dulphy and Demarquilly (9) have shown that the effects of chop length on fermentation might be decreased or even eliminated when an organic acid was added during the ensiling process. Moreover, Marsh (24) suggested that the effects of chop length on silage fermentation are reduced when large quantities are ensiled rather than small experimental quantities, because compaction is sufficient regardless of chop length. Effects of bacterial inoculation on silage fermentation showed little benefit with farm-scale silages (17), but in laboratory-scale experiments inoculants might improve silage fermentation (31). Therefore, possible beneficial effects of microbial inoculation and chop length might be hidden by the effects of compaction, which are greater in larger tower silos than in laboratory silos. Such improved conditions assure good silage fermentation. Journal of Dairy Science Vol. 73,

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Silage Intake

Intake of all silage components, expressed as weight per day, was higher for inoculated vs. uninoculated silages (Table 3). This agrees with Kung et al. (22) who observed an improvement in OM intake when a microbial inoculant was added to silage containing 56% OM. However, Kung et al. (22) related the increased OM intake to an improved silage fermentation due to inoculation which was not observed in our study. Silage intake was not significantly influenced by chop length (Table 3). The lack of difference in intake might reflect the small difference in chop length of the two silages (15.2 vs. 21.1 mm). Gordon (14) also observed no difference in silage intake for lengths ranging from 14 to 52 mm. However, Castle et al. (4) observed an improvement in daily OM intake and milk production as silage chop length decreased from 72 to 9.4 mm. Differences in silage fermentation seem to be responsible for the differences observed in silage intake. A lack of chop length effect on silage fennentation would give similar silage intake as observed in our study. This agrees with the conclusion of Dulphy (10). Duodenal Dlgesta Flow

Total duodenal digesta flow of OM and TN tended (P<.lO) to be lower for short-cut (822.7 and 34.7 g/d) that for long-cut (971.3 and 42.0 g/d) silages (Table 4). This effect was significant (P<.05) for TN total flow expressed as a

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TABLE 3. Intake (gramslday) by shap of some constituents of short- (SS)and long-cut (LS) silage withoat (NI) or with 0 inoculant. silages

Item

SSNI

SSI

LSNI

LSI

x

SE

DM~ Total N1 ADFl NDFl

1360.6 33.6 450.3 602.7

1567.9 405 4% .8 683.5

1526.7 38.3 507.0 669.2

1610.9 39.6 548.9 728.8

1513.0 37.9 498.9 669.2

67.6 1.8 22.1 30.4

lsiflicmt

effect of

inoculant (P<.os).

percentage of daily intake of TN. The amount of TN flowing into the duodenum, expressed as a percentage of intake, was higher (107.9vs. 95.0%) for the sheep fed the long-cut silage than for those fed the short-cut silage. The difference in TN flow might be explained by more feed protein bypassing the nunen or by greater microbial protein synthesis occurring in the rumen. The lower duodenal flow of TN when sheep were fed shortcut silage suggested that short chop length increased ruminal degradation of silage protein. This agrws with the fact that N

disappearance, measured by the nylon bag technique, is higher with small particles than with

large ones (23). Small particles are more easily fermented in the rumen, thereby allowing more degradation to OCCUT. Nitrogen retention tended (Pc.10)to be higher for short-than for long-cut silage (.27 vs. .22 g N/kg of BW). Duodenal digesta flow of ADF and NDF was not affected by chop length. The duodenal flow of the studied digesta components, expressed either as grams per &y or percentage of intake, was similar for inoculated and u n i n d a t e d silages (Table 4).

Silage3 Item Duodenal flow, g/d DM Total N

ADF NDF Duodenal flow, 46 of intake DM Total N ADP NDF Rumen VFA, mg/100 ml Acetate' Propionate BulyratG Acetate:propionate' N retention, g N/kg B W Liquid dilution rate, 96b solids dilution rate, %/h ~ p m e nvolmne? L

Rumen DM2 ka

SSNI

SSI

LSNI

LSI

X

SE

763.1 31.4 186.4 273.7

882.2 38.0 202.9 309.3

960.1 40.6 228.8 338.7

982.4 43.4 224.1 325.4

883.6 37.7 207.5 307.8

44.8 2.2 11.1 16.3

58.8 42.9 47.5

65.3 109.1 47.2 51.9

59.7 106.6 40.6 44.4

59.6 100.2 42.9 472

2.1 3.4 2.1 2.1

257.5 131.6 52.3 2.00 .27

328.1 140.3 70.7 2.40 .22 10.6

6.7 12.4

4.3 11.8 1.00

278.7 130.0 53.6 2.20 25 10.4 5.1 12.6 1.08

9.8 5.3 3.9 .09 .02

10.8

259.6 111.0 45.0 2.41 22 11.3 4.9 15.4 1.14

56.6 93.4 42.0 46.1 273.3 136.0 47.5 2.04 28 9.3 4.4 10.8 1.M

96.6

1.I4

.a

.6 1.1 .10

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Rumlnal Characteristics

Acetate concentration was increased by longer silage chop length (Table 4). Concentration of propionate was similar for all treatments. Butyrate was affected by both chop length and inoculant. Higher concentrations of butyrate were obtained for LSNI than for the three other silages. Decreasing the chop length decreased the acetate:propionate ratio, which is in agreement with Moore (25). This suggests that the short-cut silages would be better used for growth than for milk production. Greathead and McTaggart (16) reported an increase in total weight gain for beef steers fed short-QIt silages. Gordon (14) noted only minor, nonsignificant effects of chop length on milk production and milk composition. Acetate tended to be lower (P<.IO) for sheep fed silages with inoculant (258.6 mg/dl) than for those fed uninoculated silages (300.7 mg/ dl). Adding a microbial inoculant tended to decrease acetate formation in the romen, which might be undesirable for dairy cows, possibly decreasing milk fat percentage. Kung et al. (22) reported no effect of microbial inoculation on milk composition. The inoculant effect, however, might have been circumvented by the level of concentrate given. Gordon (15) suggested that concentrates might minimize any effect of silage treatment on animal production. Liquid and solids dilution rates (Table 4) were affected neither by chop length, in agreement with Shaver et al. (33) nor by microbial inoculation. Rumen volume and romen DM content were higher for inoculated than uninoculated silages, possibly due to increased DM intake obtained with the former. Shaver et al. (33) did not see any difference in romen fill of liquid and solids when dairy cows ingested similar amounts of DM as long or chopped hay. Rumen pH and NH3 N were similar for all silages, averaging 6.62 and 16.9 mg/dl, respectively (data not shown). CONCLUSION

No beneficial effect of adding a microbial inoculant was observed on silage composition. Nevertheless, intake of silage constituents was higher for inoculated than for uninoculated silages, possibly improving animal performance. Short chop length increased DM content Journal of Dairy Science Vol. 73,

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of silage but had no effect on silage intake. Moreover, short chop length decreased the amount of total N reaching the duodenum and tended to improve N retention, which could result in better growth of animals. Short chop length decreased the acetate:propionate ratio, a potentially important factor to consider with the type of production expected (growth vs. milk proouction). ACKNOWLEDGMENTS

The authors thank M. Pelletier, F. Markwell, and G. Gilbert for their technical assistance; C. Gosselin and D. Thibault for their assistance in the care of the sheep; and L. Boisvert for preparation of the manuscript. They gratefully acknowledge the Animal Research Centre in Ottawa for supplying the sheep and the facilities to perform surgery. REFERENCES

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