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The Key Role of Forage Legumes in Organic Dairy Diets: Effects on Your Bottom Line

By Andre F. Brito, Maichel J. Lange, and Luiz H. P. Silva; University of New Hampshire, Department of Agriculture, Nutrition, and Food Systems 

Why are legumes important in organic dairy diets? Organic dairy is undergoing a transition. After a decade-long “boom” cycle, where demand outpaced supply and organic dairies could not be transitioned at a fast-enough pace to keep product on grocery store shelves, the direction has dramatically turned.

Now, with reduced demand for fluid milk and lower pay prices aggravated by COVID-19 as the potential new reality for organic dairies, the need to enhance production efficiency, feed quality, and milk components becomes even more critical to ensure organic dairy remains profitable. Legumes are key to addressing several critical challenges facing the organic dairy industry today, including (1) maximizing forage yield, (2) successfully implementing high-forage diets to capitalize on “grass-fed” and other specialty milk markets, and (3) optimizing forage quality and energy:protein balance to improve production of milk and milk fat and protein.

Legume persistence and proper energy:protein balance in forages are the primary challenges impacting pasture quality and productivity, thus limiting farmers’ ability to successfully implement forage-based diets. Perennial legumes provide a crucial, low cost nitrogen (N) source in diverse pastures and are critical to the energy:protein balance of forages, which ultimately affects milk productivity, quality, and animal health. However, a University of New Hampshire (UNH)-led research conducted with 14 organic dairies across the Northeast revealed that grasses made up most of the species (67%) used for grazing, whereas legumes only contributed 26% (Hafla et al., 2016). Note that maintaining legumes in pastures or hayfields is not simply an agronomic management issue; climate, soil fertility, herd management, and grazing practices interact to impact the longevity and maintenance of the legume composition of fields as well. While managing N for productive pastures or hayfields is paramount, this must be balanced with the need to maintain high-energy forages, as forage-based diets can decrease N utilization in dairy cows due to excess N intake and consequent excretion of N to the environment leading to water and air pollution. Another tradeoff of feeding high-legume rations is that increased fiber intake can elevate enteric methane (CH4) emissions, which not only represent an environmental concern, but also energy losses that otherwise would be available for producing milk protein and fat.

Importance of legumes to improving forage quality and milk production

Legume-grass mixtures generally provide more consistent and higher forage yields across a range of environments than grass or legume monocultures. Research done at the University of Vermont showed positive correlations between legume inclusion in pastures and forage quality traits like crude protein and net energy of lactation, and negative relationship with fibrous compounds. As shown in Figure 1, (at the end of the article), approximately 30% legumes in pasture was needed to promote desirable forage quality characteristics including increased protein content and less neutral and acid detergent fiber. Data from a recent meta-analysis, which combined results from studies conducted in Europe and US, revealed that that dry matter intake (+7%) and production of milk (+6.5%) and energy-corrected milk (+4%) were all higher in dairy cows fed high-forage diets containing legume than grass silages (Table 1-at the end of the article). Despite organic matter digestibility being lower in legume vs. grass silages (Table 1), rumen passage rate of fibrous materials is faster when feeding legumes compared with grasses. This stimulates feed intake and more milk production in cows fed legume-based diets.

Effect of different legume sources on milk production and composition

Alfalfa has become the “gold standard” for production of silage, baleage, and hay in the US. Both alfalfa and red clover are commonly used in northeastern organic dairies. It should be noted that a large proportion of alfalfa protein is broken down to ammonia, amino acids, and peptides during ensiling, thus reducing efficiency of protein utilization in cows fed alfalfa. In contrast, protein from red clover is protected against degradation in the silo and rumen due to the enzyme polyphenol oxidase present in red clover tissues that binds to proteins. However, several studies showed that cows fed alfalfa produced more milk than those fed red clover, but alfalfa-fed cows also had higher MUN and N excretion to the environment. Birdsfoot trefoil, which is not as prevalent as alfalfa or red clover in the Northeast, has been shown to be more effective than alfalfa and red clover to milk production and reduce urinary N excretion in dairy cows likely modulated by condensed tannins present in birdsfoot trefoil. Based on a recent meta-analysis, silages made from white clover and birdsfoot trefoil were best for milk production, while white and red clover resulted in the greatest digestibility of organic matter in cows fed high-forage diets (Table 2-at the end of the article). Despite numerous studies done with alfalfa and red clover in the past as the sole forage source in the diet, there is scarce information looking at baleage made from mixtures of alfalfa or red clover with grasses made to balance the energy:protein supply in organic dairy diets. Results from a feeding trial conducted at UNH are presented next.

Results from the UNH winter feeding trial

A winter feeding trial was conducted at the UNH Burley-Demeritt Organic Dairy Research Farm (Lee, NH) to investigate the effect of different legume-grass mixtures harvested as baleage on milk production, milk fatty acid profile, plasma concentration of essential amino acids, and N utilization in Jersey cows. This project was funded by USDA NIFA Organic Transitions Program. Twenty mid-lactation Jersey cows were assigned to 1 of 2 diets in a randomized complete block design. Two fields were planted with alfalfa- or red clover-grass mixture with a 79:14:7 legume:meadow fescue:timothy seeding rate (% total). Second- and third-cut legume-grass mixtures were used in the study. The botanical composition (dry matter basis) of second-cut alfalfa- or red clover-grass fields averaged 65 vs. 80% legume, 17 vs. 15% grasses, and 18 vs. 5% weeds, respectively. Third-cut alfalfa- or red clover-grass mixture botanical composition (dry matter basis) averaged 84 vs. 96.5% legume, 3 vs. 2.3% grasses, and 13 vs. 1.2% weeds, respectively. Diets contained 65% second- and third-cut alfalfa or red clover-grass (32.5% of each cut) and 35% concentrate. The study lasted 7 weeks with sample collection done at weeks 4 and 7. Diets averaged 18.8 vs. 18.1% crude protein and 30.5 vs. 31% neutral detergent fiber for alfalfa-grass vs. red clover-grass, respectively.

No statistical differences between diets were observed for dry matter intake, production of milk and milk protein, and percentages of milk fat and protein (Table 3). In contrast, production of 4% fat-corrected milk, energy-corrected milk, and milk fat significantly increased with feeding alfalfa-grass vs. red clover-grass (Table 3-at the end of the article). However, cows fed alfalfa-grass had higher MUN than those receiving red clover-grass, indicating poorer utilization of dietary protein in the alfalfa-grass diet (Table 3). As mentioned above, the presence of the enzyme polyphenol oxidase in red clover prevents protein degradation in the rumen, thus contributing to improved N utilization in dairy cows. Despite improved N utilization, cows fed the red clover-grass diet decreased production of milk and milk fat, which agree with previous research.

We were also interested in better understand the effects of legume-grass mixtures on milk fatty acid profile. There is a growing consumer interest in purchasing products rich in omega-3 fatty acids and organic milk is known to have a healthier fatty acid profile than conventional milk. The percentage of milk α-linolenic acid, which is the major omega-3 fatty acid present in milk fat, was significantly higher in cows fed red clover-grass than alfalfa-grass diet (Table 3). Likewise, total percentage of omega-6 and omega-3 fatty acids increased significantly with feeding red clover-grass vs. alfalfa-grass (Table 3). In addition, the omega-6/omega-3 ratio was lower in the red clover-grass compared with the alfalfa-grass diet (Table 3). These results confirm that the red clover-grass diet promoted a healthier fatty acid profile in milk fat than the alfalfa-grass diet. Note, however, that the percentage of CLA in milk fat did not differ between alfalfa-grass and red clover-grass diets.

We also looked whether feeding alfalfa-grass or red clover-grass diet would change the blood plasma concentration of essential amino acids. It is well known that the essential amino acids methionine, lysine, and histidine are the most limiting amino acids for production of milk protein in dairy cows. Moreover, the branched-chain amino acids leucine, isoleucine, and valine can be also limiting for milk protein synthesis in dairy diets. Therefore, it is important to understand how methionine, lysine, and histidine and branched-chain amino acids are affected by feeding alfalfa-grass or red clover-grass diet. Our results showed that plasma methionine, lysine, and isoleucine were statistically similar between diets (Table 4-at the end of the article). In contrast, plasma histidine, leucine, and valine acids either increased or tended to increase significantly in cows fed red clover-grass vs. alfalfa-grass diet. Even though production of milk protein was not affected by diets (Table 3), red clover-grass appears to be more effective than alfalfa-grass to elevate plasma concentration of essential amino acids.

Dairy accounts for about 4% of total greenhouse gas emissions and 25% of enteric CH4 emissions in the US. The global warming potential of CH4 is over 30 times higher than that of carbon dioxide, and CH4 production represents 2 to 12% dietary energy losses, justifying the need to better understand how different legume-grass mixtures impact enteric CH4 emissions. Methane emissions in the UNH winter feeding trial was measured using the GreenFeed system (C-Lock Inc., Rapid City, SD; Figure 2-at the end of the article). The GreenFeed unit operates by automatically releasing a pellet feed every 30 seconds for a total of 5-min measurements several times throughout the day triggered by a RFID ear tag worn by each cow and equipped with built-in sensors to measure CH4 fluxes near real-time. Our results revealed a statistically significant interaction between diet and sampling week for CH4 production; cows fed the red clover-grass diet had lower enteric CH4 emissions than cows fed the alfalfa-grass diet in week 4 of the study (157 vs. 218 grams/day, respectively), but no statistical difference was observed when measurements were taken on week 7 of the experiment (182 vs. 200 grams/day, respectively). We also measured urinary N excretion to gain insights on N use efficiency in our cows. A statistically significant interaction was also observed for urinary N excretion expressed in grams/day and as percentage of N intake. Compared with cows fed alfalfa-grass, feeding red clover-grass significantly decreased both the output of urinary N (218 vs. 157 grams/day) and urinary N as a percentage of N intake (27.5 vs. 33.8%, respectively) during week 4, but not in week 7 of the trial for these 2 variable responses. Together with MUN, decreased urinary N excretion suggests improved N use efficiency in cows receiving the red clover-grass diet likely mediated by the presence of the enzyme polyphenol oxidase as discussed earlier.

Take home message

Results from several studies summarized in a recent published meta-analysis revealed that silage made from legumes such as alfalfa, red and white clover, and birdsfoot trefoil resulted in more production of milk and milk components compared with grass silages. Data from UNH confirmed previous results that alfalfa appears to be more effective than red clover to promote production of milk and milk fat, but less environmentally friendly due to increased urinary N excretion, which can pollute water and air. Interestingly, feeding the red clover-grass diet decreased enteric CH4 production even though this response was not consistent over time. Cows receiving red clover-grass also produced milk with a healthier fatty profile (i.e., more omega-3 and lower omega-6/omega-3 ratio) vs. cows fed alfalfa-grass. Agronomic and soil research is needed to better understand decreased persistence of legume forages in pastures and hayfields in the Northeast. Research is also needed to gain knowledge about the tradeoffs between increased legume intake and reproductive performance of organic herds as legume forages, particularly red clover, are rich in phytoestrogens that may negatively affect fertility of dairy cows.



Table 1. Effect of grass vs. legume silages on production and digestibility in dairy cows fed high-forage diets

Silage type

Item

Grass

Legume

P-value

Dry matter intake, lb/day

40.3

43.2

<0.01

Milk production, lb/day

54.0

57.5

<0.01

Energy-corrected milk, lb/day

53.6

55.8

<0.01

Organic matter digestibility, %

70.4

67.9

0.01

Adapted from Johansen et al. (2018).



Table 2. Effect of grass vs. legume silage types on production and digestibility in dairy cows fed high-forage diets

Silage type

Item

Grass

White clover

Red clover

Alfalfa

Birdsfoot

P-value

Dry matter intake, lb/day

41.7b

44.1ab

44.1a

46.3a

48.1ab

<0.01

Milk production, lb/day

57.8c

65.3a

60.2b

61.1b

69.2a

<0.01

Energy-corrected milk, lb/day

56.7d

61.9ab

57.5cd

59.5bc

67.0a

<0.01

Organic matter digestibility, %

71.5ab

73.6a

69.4b

66.0c

67.2abc

<0.01

Adapted from Johansen et al. (2018).

abcdValues in the same row with different superscripts differ statistically at P < 0.05.



Table 3. Effect of feeding diets containing alfalfa-grass or red clover-grass baleage on milk production and composition and milk fatty acids (% total fatty acids) in organic Jersey cows (UNH winter feeding trial)

Baleage type

Item

Alfalfa-grass

Red clover-grass

P-value

Dry matter intake, lb/day

43.7

47.8

0.18

Milk production, lb/day

47.8

45.9

0.11

4% fat-corrected milk, lb/day

58.9

54.5

0.05

Energy-corrected milk, lb/day

62.6

58.0

0.06

Milk fat, %

5.48

5.30

0.18

Milk fat, lb/day

2.65

2.40

0.05

Milk protein, %

3.68

3.59

0.50

Milk protein, lb/day

1.74

1.65

0.21

MUN, mg/dL

13.0

10.3

<0.01

Milk α-linolenic acid, %

0.64

0.86

<0.01

Milk omega-6 fatty acids, %

2.17

2.46

0.02

Milk omega-3 fatty acids, %

0.70

0.94

<0.01

Milk omega-6/omega-3 ratio

3.13

2.62

<0.01

Milk CLA, %

0.44

0.40

0.37



Table 4. Effect of feeding diets containing alfalfa-grass or red clover-grass baleage on blood plasma essential amino acids in organic Jersey cows (UNH winter feeding trial)

Baleage type

Essential amino acids

Alfalfa-grass

Red clover-grass

P-value

Plasma methionine, µM

23.7

22.2

0.47

Plasma lysine, µM

93.1

95.1

0.76

Plasma histidine, µM

36.8

55.1

<0.01

Plasma leucine, µM

142

178

0.03

Plasma isoleucine, µM

144

154

0.37

Plasma valine, µM

253

295

0.06

Figure 1 Brito article for website_thumb

Figure 1. Relationship between legume content in pasture and forage quality traits [DM = dry matter; Source: Bosworth and Cannella (2007)].

Figure 2 Brito article for website_thumb

Figure 2. The GreenFeed system being used at the UNH Organic Dairy Research Farm for methane measurements.

Bibliography cited

Bosworth, S.C. and Cannella, M.P. 2007. Assessing on-farm pasture availability and forage quality for dairy feed planning. USDA-SARE Final Report. https://pss.uvm.edu/vtcrops/articles/SAREPartner_Pasture_Summary_Report.pdf.

Johansen, M., Lund, P., and Weisbjerg, M.R. 2018. Feed intake and milk production in dairy cows fed different grass and legume species: a meta-analysis. Animal 12: 66–75.

Andre F. Brito, Veterinarian, M.Sc., Ph.D., is Associate Professor of Dairy Cattle Nutrition & Management, Keener Dairy Research Building, Department of Agriculture, Nutrition, and Food Systems, University of New Hampshire, 30 O’Kane Road; Durham, NH 03824. He can be reached at: office phone: (603) 862-1341; email: andre.brito@unh.edu.