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Comparison of Grass and Legume Silages for Milk Production. 1. Production Responses with Different Levels of Concentrate

R. J. Dewhurst^*, W. J. Fisher, J. K. S. Tweed^* and R. J. Wilkins

^* Institute of Grassland and Environmental Research, Plas Gogerddan, Aberystwyth SY23 3EB, U.K.
Trawsgoed Research Farm, Aberystwyth SY23 4LL, U.K.
North Wyke Research Station, Okehampton EX20 8SB, U.K.

	ABSTRACT

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION CONCLUSIONS ACKNOWLEDGEMENTS REFERENCES

 
Silages prepared from pure stands of ryegrass, alfalfa, white clover, and red clover over two successive year were offered to lactating dairy cows in two feeding experiments. Proportional mixtures of all cuts prepared in a yr were used to ensure that the forage treatments were representative of the crop. Additional treatments involved mixtures of grass silage with either white clover silage or red clover silage (50/50, on a DM basis). Silages were prepared in round bales, using a biological inoculant additive, and wilting for up to 48 h. Although the legumes were less suited to silage-making than grass, because of their higher buffering capacity and lower water-soluble carbohydrate content, all silages were well-fermented. A standard concentrate was offered at a flat-rate (8 kg/d in yr 1, and 4 or 8 kg/d in yr 2). All of the legume silages led to higher DM intake and milk yields than for the grass silage, with little effect on milk composition. Intake and production responses to legumes were similar at the two levels of concentrate feeding and with forage mixtures they were intermediate to those for the separate forages. An additional benefit of the clover silages, particularly red clover silage, was the increase in levels of polyunsaturated fatty acids, particularly ;-linolenic acid, in milk. Legume silages also led to a lower palmitic acid percentage in milk. The efficiency of conversion of feed N into milk N declined with increasing levels of legume silage. White clover silage led to a higher N-use efficiency when the effect of N intake level is taken into account.

Key Words: silage • clover • alfalfa • milk production • fatty acid

Abbreviation key: A = alfalfa silage, FAME = fatty acid methyl esters, G = grass silage, G4 = G with 4 kg/d concentrates, G8 = G with 8 kg/d concentrates, , GRC = mixture of G and RC, GRC4 = GRC with 4 kg/d concentrates, , GRC8 = GRC with 8 kg/d concentrates, , GWC = mixture of G and WC, RC = red clover silage, RC4 = RC with 4 kg/d concentrates, , RC8 = RC with 8 kg/d concentrates, , RIC = roughage intake control, WC = white clover silage, WC8 = WC with 8 kg/d concentrates

	INTRODUCTION

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION CONCLUSIONS ACKNOWLEDGEMENTS REFERENCES

 
Earlier experiments have established the high intake and milk production potential of legume silages. Castle et al. (1983) and Auldist et al. (1999) showed the high feeding value of white clover silage for dairy cows. Other studies (e.g., Thomas et al., 1985 with red clover and Hoffman et al., 1998 with alfalfa) have demonstrated the superiority of legume silages in comparison with grass silages. However, the area of forage legumes has been declining for a number of reasons, including the relatively low cost of N fertilizer, and difficulties with the agronomy and ensiling of legumes.

Further work on legume silages is timely because of growing interest in organic and low-input production systems as we become increasingly aware of the pollution potential from dairy units (Jarvis et al., 1996). Plant breeding has improved the persistency and disease resistance of legumes (Rhodes and Ortega, 1997). Earlier work often used long periods of wilting, precision-chop harvesting and high levels of formic acid and/or formalin as additives. The loss of high-protein leaf material is a particular problem with legumes and is exacerbated by extensive handling of the crop. In this work we have adopted shorter periods of wilting (up to 48 h), baling of silage with minimal handling and chopping, and the use of a biological inoculant silage additive to reduce harvesting losses and avoid the safety and equipment corrosion problems associated with acids. There is limited earlier evidence, with beef cattle, of successful feeding of red clover silages prepared with wilting, but without the use of chemical additives (Thomas et al., 1981).

The objective of this work was to evaluate feed intake and milk production with diets based on legume silages prepared using new technologies of biological inoculants and big bales. A further objective was to investigate effects on N utilization and the fatty acid composition of milk fat.

	MATERIALS AND METHODS

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION CONCLUSIONS ACKNOWLEDGEMENTS REFERENCES

 
Field Management
Pure stands of forage crops were established for this work during the summer and fall of 1997: red clover (Trifolium pratense cv. Milvus), white clover (Trifolium repens cv. Aran), alfalfa (Medicago sativa cv. Vertus) and ryegrass (mixture of Lolium perenne cv. AberElan, Lolium x boucheanum cv. AberComo and Lolium multiflorum cv. Augusta). The forages were grown at Aberystwyth (52°25'N, 4°05'W) and harvested over the following two growing seasons (1998 and 1999).

The legume crops received 85 kg phosphate/ha (as triple superphosphate) and 260 (185 for white clover) kg potash/ha (as muriate of potash) in March of each year. Additional applications were given in mid-season (56 kg potash/ha in 1998; 115 kg phosphate/ha and 150 kg potash/ha in 1999). The ryegrass crop received 320, 47, and 47 kg/ha of N, phosphate, and potash in 1998 and 335, 50, and 50 kg/ha in 1999.

Silage-making
The timing of silage cuts was planned to be optimal for the growth patterns of individual crops, modified according to weather conditions. Cutting dates, approximate growth stages, and the percentage contribution of each cut to annual production for each crop is given in Table 1. Experiences in 1998 suggested that the potential of ryegrass and red clover might further be exploited by cutting these crops on 4 occasions. However, poor ground conditions meant that we were unable to conserve the small fourth growth of red clover.

Feeds
A recurrent difficulty of this type of work has been the need to identify representative material. Consequently, in this work we used all material produced from the fields over the yr in each feeding experiment (see Table 1). Although there were some differences in treatments and objectives between the 2 yr, we maintained several common treatments in order to provide yr replication. Mixtures of silages prepared from each crop over each growing season were used in the feeding experiments in order to ensure that feeds were more representative of the crop type. Bales were chopped and mixed just prior to feeding.

A standard concentrate was used for both years of the experiment, comprising (%): wheat (30.0), palm kernel expeller (15.0), corn gluten feed (14.0), extracted rapeseed meal (double-zero) (11.0), extracted sunflower meal (9.0), molasses (5.0), expeller linseed meal (5.0), groundnut meal (5.0), extracted soybean meal (2.0), vegetable fat (1.5), and minerals/vitamins (2.5). The mineral/vitamin premix supplied (on a concentrate DM basis): 11,600 IU of vitamin A/kg, 2300 IU of vitamin D₃/kg, 29 IU of vitamin E/kg, 35 mg/kg of Cu, 140 mg/kg of Mn, 0.46 mg/kg of Se and 14 mg/kg of Zn.

Animal Measurements
Experiment 1 (silages prepared in 1998).
The first experiment involved 18 Holstein-Friesian cows (mean BW = 579 (40.4) kg; mean initial DIM = 64 (SD = 22.3)), in a 3-period cyclical changeover-design experiment (Davis and Hall, 1969), with 4-wk periods. One block of cows (n = 6) had previously been prepared with simple rumen and duodenal cannulae and additional measurements are reported by Dewhurst et al. (2003).

There were 6 dietary treatments based on 6 different forages: grass silage (G), red clover silage (RC), white clover silage (WC), alfalfa silage (A), and 50/50, (DM basis) mixture of G and RC (GRC) and G and WC (GWC). The cows had ad libitum access to the forages either through roughage intake control (RIC) feeders (Insentec B.V., Marknesse, The Netherlands) in a free-stall barn, or through individual stalls (for the fistulated cows). All cows were given 8 kg/d of the same concentrate, with 3 kg offered at each milking and 2 kg distributed as a mid-day feed (fistulated cows) or through out-of-parlor feeders. The concentrate was designed to balance the protein content of G and so provided excess protein in other diets.

Cows were milked two times each day, at approximately 0600 to 0700 h and 1600 to 1700 h. Feed intake and milk yields were recorded daily throughout the experiment; milk composition was recorded from 4 consecutive milkings each wk. The model of Tolkamp et al. (1998) was used to estimate the number (and, consequently, size) of forage meals for the 12 cows using the RIC feeders. Single blood samples were taken from the jugular veins of each of the 12 non-fistulated cows in the final wk of each period (between 1030 and 1200 h). Blood was held on ice, and spun at 1700 x g for 25 minutes at 4°C to separate plasma, which was decanted and stored at -20°C until analysis using test kits (Moorby et al., 2000).

Diet digestibility was measured with 6-d total collections of feces from the fistulated cows in the third wk of each period, using the equipment described by Aston et al. (1998). An additional experimental period was used for digestibility and milk fatty acid measurements using the fistulated cows. Outputs of urinary N appeared to be erroneous and so are not reported.

Experiment 2 (silages prepared in 1999).
This experiment involved 7 dietary treatments, including some repetition of treatments used in Experiment 1, but also investigating two levels of feeding of the same standard concentrate (4 or 8 kg/d). Concentrates were offered through out-of-parlor feeders in 4 equal allocations that were spaced by 4.5 h. The dietary treatments in this experiment were: grass silage and 4 kg/d concentrates (G4); grass silage and 8 kg/d concentrates (G8); a 50/50 mixture (DM basis) of grass silage and red clover silage and 4 kg/d concentrates (GRC4); a 50/50 mixture of grass silage and red clover silage (DM basis) and 8 kg/d concentrates (GRC8); red clover silage and 4 kg/d concentrates (RC4); red clover silage and 8 kg/d concentrates (RC8); white clover silage and 8 kg/d concentrates (WC8). The forage yields obtained previously led us to concentrate on diets based on RC, though treatment WC8 was retained because this gave the highest milk yields in Experiment 1. The feeds were offered to 21 Holstein-Friesian cows in a 3-period cyclical changeover-design (Davis and Hall, 1969), with 4-wk periods. The mean BW was 609 (SD = 49.6) kg and the mean initial DIM 82 (SD = 15.3) for the 19 cows that completed the experiment. All cows were housed in a free-stall barn with ad libitum access to the forages through RIC feeders. Measurements were as described for Experiment 1, except that diet digestibilities were estimated for two blocks of cows (n = 14) by an indirect method using acid insoluble ash (Ministry of Agriculture, Fisheries and Food, 1986) as an internal marker, with 2 samples of feces taken on 2 consecutive days.

Sampling and Chemical Analysis
At least 3 forage samples were collected from each field immediately prior to harvesting and stored frozen (-20°C), before freeze-drying and analysis for oven-DM (AOAC, 1990), CP (N x 6.25; Leco FP 428 N analyzer), water-soluble carbohydrates (Ministry of Agriculture, Fisheries and Food, 1986), nitrate (Bremner and Keeney, 1965) and buffering capacity (Playne and McDonald, 1966). Lactic acid bacteria counts were conducted according to Merry et al. (1995).

Samples of each silage (composite of 3) and concentrates were taken during each measurement wk, stored frozen and freeze-dried prior to chemical analysis according to the methods described by Dewhurst et al. (2000). Ethanol was determined according to the method of Fussell and McCalley (1987). All intake and chemical composition values for forages have been corrected to a freeze-DM basis.

Milk fat, protein and lactose were determined by infrared milk analyzer (Milkoscan 605, Foss Electric, Denmark). Additional milk samples were collected and stored at -20°C without preservative, prior to freeze-drying and analysis of fatty acids by GC as fatty acid methyl esters (FAME), which were prepared using the one-step extraction and methylation procedure of Sukhija and Palmquist (1988). For Experiment 1, a 30 m ZB-Wax column (Phenomenex, Macclesfield, UK) was used to separate FAME, with nitrogen as carrier gas. The injector was held at 200°C and the detector at 230°C; a temperature gradient (60°C for 3 min, 20°C/min rise to 230°C, and 8.5 min at 230°C) was used to separate the FAME. For Experiment 2, a 100 m CP-Sil Select for FAME CB column (Varian, Walton-on-Thames, UK) was used, with helium as carrier gas. The injector was held at 250°C and the detector at 255°C; a temperature gradient (starting at 70°C, 20°C/min rise to 175°C, hold for 25 min, 2.5°C/min rise to 200°C, hold for 2 min, 20°C/min rise to 230°C, hold for 8.5 min) was used to separate the FAME. Fatty acid methyl esters were identified and quantified by reference to quantitative external standards (Larodan Fine Chemicals AB, Malmö, Sweden). Trans-11 C_18:1 co-eluted with cis-9 C_18:1 on the 30 m column. Neither C_4:0 or CLA were reported from the 30 m column.

Statistical Analysis
Mean values from the final wk of each period were used in the statistical analysis of feed intake, milk production, and milk composition. Analysis of variance was conducted using the restricted maximum likelihood (REML) directive of Genstat 5 for Windows (Lawes Agricultural Trust, 2000). For Experiment 1, the fixed model had 6 treatments with an embedded 2 x 2 factorial (50 or 100% legume silage x red clover or white clover). For Experiment 2, the fixed model was a 3 x 2 factorial (grass/red clover level x concentrate level) with an additional control treatment (WC8). In each case, the analysis adopted a random model of ‘Period’ x ‘Cow’. Measurements were lost from one fistulated cow that was lame at the end of the first period of Experiment 1. One of the fistulated cows became sick (digestive upset) and was not used in the second and third periods. Two cows were lost from the second experiment for reasons unrelated to treatments (failure to use the feeding equipment) and were excluded from the analysis. The Tables show the number of cows for each dietary treatment and measurement.

	RESULTS

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION CONCLUSIONS ACKNOWLEDGEMENTS REFERENCES

 
Crop Composition
The chemical composition and lactic acid bacteria counts of the herbage ‘as ensiled’ are shown in Table 2. The relatively low levels of lactic acid bacteria in many of the crops suggest that the biological inoculant was essential for successful fermentation with many of the materials. The relatively higher buffering capacity and lower content of water-soluble carbohydrates for the legume crops made them more challenging as materials to ensile.

Milk fatty acid profiles are given in Tables 9 and 10 for the two experiments, respectively. White clover silage led to an increase in the proportion of shorter-chain fatty acids (particularly C_10:0 and C_12:0) in milk from both experiments. The most notable effect on milk fatty acid percentages is the increase in levels of ;-linolenic acid (C_18:3) in milk produced from cows consuming clover silage, particularly red clover silage in Experiment 2. A significant reduction in levels of C_16:0 in milk from cows offered red clover silage was also evident in this experiment. Odd-chain fatty acids made up 3 to 5% of milk fatty acids. The effects of diets on odd-chain fatty acids in milk were generally small.

	DISCUSSION

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION CONCLUSIONS ACKNOWLEDGEMENTS REFERENCES

Feed Intake and Meal Patterns
Both experiments (Tables 7 and 8) confirmed the higher levels of voluntary intake of legume silages in comparison with grass silages observed previously (e.g. Thomas et al., 1985; Hoffman et al., 1998). The RIC feeders enabled us to define meals (Tolkamp et al., 1998) and suggest that the increased intakes of legume silages are associated with a similar number of larger meals. The physiological basis of these effects is further discussed, in relation to the kinetics of rumen digestion and passage, in the companion paper (Dewhurst et al., 2003).

The decline in forage DM intake in response to the 4 kg/d increase in concentrate allocation was similar for G, GRC and RC treatments in Experiment 2; substitution rates were -0.41, -0.29, and -0.41 kg/kg, respectively. The additional concentrates led to increases in CP intake of 630, 703, and 597 g/d for G, GRC, and RC, respectively. The fact that similar responses to concentrates occurred despite the widely different CP supply at the lower level of concentrate feeding (2796, 2981, and 3855 g/d for G4, GRC4, and RC4) confirms that protein supply had little part in the responses observed in these studies.

Milk Production and Composition
The higher DM intake of legume silages compared with grass silage was reflected in higher yields of milk, milk fat, milk protein, and milk lactose (Tables 7 and 8), though increases in milk protein yield were quite small, other than for animals receiving white clover silage. The yields of milk obtained from alfalfa silage were low relative to the high DM intake and this may reflect the higher ADF content (Table 5) and lower digestibility (Table 7) of this diet. Previous studies have also highlighted the superiority of red clover silage over alfalfa silage in relation to milk yield relative to intake (Hoffman et al., 1997 (Experiment 2); Broderick et al., 2001). Similarly, Broderick et al. (2000) estimated that red clover silage contained 10% more NE_L than alfalfa silage. The use of mixtures of cuts in each silage treatment, as well as the similarity of responses between year, confirms the reliability of the intake and milk production responses recorded. The additional yield of milk in response to a supplementation of 4 kg/d of concentrates was similar for G, GRC and RC, reflecting the similar substitution rates noted above.

This work provides new information on the effects of legume silages on milk fatty acids (Tables 9 and 10). Milk from cows offered legume silages generally contains higher levels of polyunsaturated fatty acids that are regarded as beneficial for human health (linoleic acid, conjugated linoleic acid, and ;-linolenic acid). These experiments also showed that alfalfa and red clover silage can lead to some improvement in the saturated fatty acid content of milk (Tables 9 and 10). There was no consistent effect on stearic acid (C_18:0), which is regarded as neutral in its effect on plasma cholesterol in humans (Yu et al., 1995), but a significant reduction in palmitic acid (C_16:0) which is known to increase plasma cholesterol in humans (Yu et al., 1995). At the low level of concentrate feeding (4 kg/d), we observed a 3-fold increase in the level of ;-linolenic acid in milk from cows offered red clover silage in comparison with cows offered grass silage. The increase in n-3 fatty acid (;-linolenic acid) content is particularly valuable given the growing perception of the need to reverse the decline in the n-3/n-6 fatty acid ratio in our diet (Simopoulos, 2001). The increase in polyunsaturated fatty acids in milk from cows offered white clover is in line with the higher intakes (Tables 7 and 8) and higher levels of these fatty acids in white clover silage (Table 5). The mechanism is very different with red clover silage, which contained similar levels of ;-linolenic acid to grass silage (Table 5). For Experiment 2, the apparent recovery of ;-linolenic acid from the diet into milk was 9.7% for diet RC8, in comparison with 5.9% for WC8 and 5.1% for G8. The substantial increases in polyunsaturated fatty acids in milk from cows offered red clover silage must reflect reduced rumen biohydrogenation (see Dewhurst et al., 2003). Other studies (Dewhurst and King, 1998) have shown that wilting is an important source of loss of polyunsaturated fatty acids in silage and since the red clover silages in this work were usually subject to 2 d of field wilting, there is clearly potential for further increases in this area. In another aspect of our work with ;-linolenic acid (from linseed oil) we have shown beneficial effects on fertility (Petit et al., 2001, 2002). We hypothesize that these mechanisms could explain the improvements in fertility of cows consuming red clover silage in earlier work (Austin et al., 1982; Thomas et al., 1985), which occurred despite evidence (from sheep) that phytoestrogens from red clover can impair fertility (Austin et al 1982).

Nitrogen Utilization
The primary objective of this work was to evaluate forages against a standard level and type of concentrate allocation, which was designed to balance the protein content of the grass silages. This limits the interpretation of the N utilization results, since N intake varied considerably between treatment groups (Tables 7 and 8). Nonetheless, taking into account these differences there are still clear areas of interest (Figure 1). The results presented in Table 8 suggest that increasing the level of concentrate feeding from 4 kg/d to 8 kg/d had no effect on N efficiency. However, when N intake is taken into account (Figure 1), an increase in efficiency with increased concentrate feeding becomes apparent. Although N intake and urinary N were highest for cows offered white clover silage, these cows exhibited a considerable (25%) increase in milk protein yield, so that N efficiency was not as low as may have been expected. Similarly, there was little loss of N efficiency when changing from grass silage to a mixture of grass silage and red clover silage in both experiments, suggesting a synergistic effect of the forage mixture on efficiency. Changing to diets based exclusively on red clover silage did not lead to a further increase in milk protein yield. In fact N efficiency declined markedly suggesting that balancing red clover N with some other diet component is more important for N efficiency than the inherent attributes of red clover. The dark coloration of red clover silage reflects the action of polyphenol oxidase to oxidize natural phenols which produce quinones that polymerize with proteins (Jones et al., 1995) and reduce proteolysis (Hatfield and Muck, 1999). However, our studies provide no evidence that this mechanism affected overall N utilization—though further studies with low protein supplements are required to clarify this question. Relative to N intake, the efficiency of use of N from alfalfa silage was low, probably reflecting imbalances between rapidly available N and indigestible fiber in the rumen and/or the lower energy supply from alfalfa—this is evident from the high digestible N: digestible DM ratio for this diet (Table 7). The inefficient use of N from alfalfa silage was confirmed by these animals having the highest plasma urea concentrations (Table 11). Broderick et al. (2000) also noted low N utilization efficiency with alfalfa silage. Further work is needed to design forage mixtures, and protein and energy supplements to optimize N efficiency with diets based on high levels of legume silages.

View larger version (16K): [in this window] [in a new window]   Figure 1. Efficiency of conversion of feed N into milk N (%) for the forage treatments in Experiments 1 and 2 (grass silage, red clover silage, white clover silage, alfalfa silage, and 50/50 (DM basis) mixtures of grass silage with red clover silage or white clover silage. Concentrates were offered at 4 or 8 kg/d.

	CONCLUSIONS

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION CONCLUSIONS ACKNOWLEDGEMENTS REFERENCES

These studies confirmed the high intake potential and milk production from legume silages. White clover silage consistently led to a 6 kg/d increase in milk yield in comparison with grass silage. Whilst white clover is probably not a viable monoculture, owing to low yields, it is clearly beneficial to nutritional value in situations (such as organic farming) that encourage higher levels in swards. The increased intake of legume silages was associated with cows consuming a similar number of larger meals.

There was a general decline in N use efficiency associated with increasing legume content in the diet, associated with increasing N intake. Nonetheless, efficiencies for cows offered white clover silage and a mixture of red clover silage and grass silage showed higher N efficiencies than may have been anticipated, probably because of improved rumen function and/or energy supply to the mammary gland. Clover silages led to a reduction in the content of palmitic acid and an increase in the content of polyunsaturated fatty acids, particularly the n-3 ;-linolenic acid, in milk.

	ACKNOWLEDGEMENTS

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION CONCLUSIONS ACKNOWLEDGEMENTS REFERENCES

 
The financial support of the EU (project FAIR-CT96-1832), the Milk Development Council and the Ministry of Agriculture, Fisheries and Food (Department for Environment, Food and Rural Affairs) is gratefully acknowledged. The authors acknowledge the skilled technical assistance of members of the Microbiology, Ruminant Nutrition and Analytical Chemistry laboratories at the Institute.

Corresponding author:
R. J. Dewhurst; e-mail:
Richard.Dewhurst{at}bbsrc.ac.uk.

Received for publication November 28, 2002. Accepted for publication April 1, 2003.

	REFERENCES

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION CONCLUSIONS ACKNOWLEDGEMENTS REFERENCES

 


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