Key Findings
Milk urea Nitrogen (N) refers to the amount of urea in milk. Urea is a naturally occurring molecule produced by protein metabolism and often found in urine, as well as blood, bile, milk, and perspiration. Elevated levels of milk urea N generally indicate excess protein consumption and lower milk production.
Cows fed alfalfa-grass produced more 4% fat-corrected milk, energy-corrected milk, and milk fat than cows fed red clover-grass.
Feeding red clover-grass decreased milk urea N, indicating that red clover-based diets may be more environmentally friendly. Red clover-grass also produced milk with a healthier fatty profile for human consumption compared with cows fed alfalfa-grass. Although, red clover-grass decreased enteric methane production, this was not consistent over time.
Partially replacing red clover-grass baleage with alfalfa/white clover-grass reduced dry matter intake, but dry matter digestibility, organic matter, net energy of lactation were lower. Cows fed red clover-grass did not produce more milk or milk fat and protein than those fed an alfalfa/white clover-grass mixture.
About the Co-Author
Andre Brito, Professor of Agriculture, Nutrition, and Food Systems
Contact information: Andre.Brito@unh.edu
603-862-1341, Brito Lab website
This research was published in the INSPIRED: A Publication of the New Hampshire Agricultural Experiment Station (Winter 2021)
Researchers: A.F. Brito et al.
Research has shown that dairy cows fed legume silages consumed more dry matter (DM) and produced more milk than those receiving grass silages. However, across northeastern U.S. dairies, legumes only contributed to 26% of grazed forage. Research to improve legume persistence while closing knowledge gaps about which legume-grass mixtures are best suitable for producing profitable milk (i.e., higher butterfat and protein) is needed to make organic and conventional dairies in New England more competitive in the long run.
Alfalfa has become the “gold standard” for production of silage, baleage, and hay in the United States, but a large proportion of alfalfa protein is broken down to non-protein N (i.e., ammonia, amino acids, and peptides) during ensiling, thus reducing the efficiency of protein utilization when cows are fed alfalfa silage.
In contrast, protein from red clover is protected against degradation in the silo due to the presence of the enzyme polyphenol oxidase in red clover tissues. Previous research demonstrated that red clover silage was comparable to alfalfa silage in terms of DM intake, milk production, and percentage of milk fat (Johansen et al., 2018). Cows fed red clover silage had lower concentrations of milk urea N (MUN) and excreted less N than those fed alfalfa silage (Broderick et al., 2007), thus showing improved use of dietary protein with red clover.
Our research compared the effects of alfalfa- and red clover-grass mixtures on feed intake, milk production and composition, and dietary utilization of N and energy in dairy cows. The work was conducted the UNH Organic Dairy Research Farm, where twenty mid-lactation organic certified Jersey cows were assigned to one of two diets in a randomized complete block design.
Study 1: Full diet adjustment for red clover-grass
M.J. Lange, L.H.P. Silva, M. Ghelichkan, A. Zambom, and A.F. Brito
Two fields were planted with alfalfa- or red clover-grass mixture with a 79:14:7 legume:meadow fescue:timothy seeding rate (% total) in 2017. Second- and third-cut legume-grass mixtures used in this study were harvested as baleage in 2018. The botanical composition (DM basis) of fields from which second cut alfalfa- or red clovergrass averaged: 65 vs. 80% legumes, 17 vs. 15% grasses, and 18 vs. 5% weeds, respectively. Third cut alfalfa- or red clover-grass mixture botanical composition (DM basis) averaged 84 vs. 96.5% legume, 3 vs. 2.3% grasses, and 13 vs. 1.2% weeds, respectively. Diets were fed as total mixed ration and contained (DM basis): 65% second- and third-cut alfalfa or red clover-grass (32.5% of each cut) baleage and 35% of a ground corn-soybean meal-based mash concentrate. The study lasted seven weeks, with sample collection done at weeks four and seven. Diets averaged 18.7 vs. 18% crude protein and 30 vs. 31% neutral detergent fiber for alfalfa- vs. red clover-grass mixtures, respectively. View Table 1
Diets did not affect DM intake, production of milk and milk protein, and percentages of milk fat and protein (Table 1). Production of 4% fat-corrected milk increased in cows fed alfalfa- vs. red clover-grass, while production of energy-corrected milk and milk fat tended to increase with feeding alfalfa-grass. Cows fed red clover-grass had lower MUN than those receiving red alfalfa-grass, indicating improved utilization of dietary protein. Milk proportion of ?-linolenic acid, which is the major omega-3 fatty acid present in milk fat, was greater in cows fed red clover-grass than alfalfa-grass diet. Likewise, milk proportion of total omega-3 fatty acids increased with feeding red clover-grass vs. alfalfa-grass. In addition, the omega-6/omega-3 ratio was lower with feeding red clover-grass compared with alfalfa-grass diet.
Our results showed that plasma methionine, lysine and isoleucine did not differ between diets. However, even though production of milk protein was not affected by diets, red clover-grass appears to be more effective than alfalfa-grass to increase plasma concentration of essential amino acids. We also observed an interaction between diet and sampling week for methane production. Cows fed red clover-grass had lower methane emissions than cows fed the alfalfa-grass in week four of the study, but no difference was observed when measurements were taken on week 7. Methane yield and methane intensity were not affected by diets.
Study 2: Partial replacement of red clover-grass mixture with an alfalfa/white clover-grass mixture
J.P. Sacramento, L.H.P. Silva, D.C. Reyes, Y. Geng, and A.F. Brito
Two fields were planted with alfalfa- or red clover-grass mixture with a 79:14:7 legume:meadow fescue:timothy seeding rate (% total) in 2017. Second- and third-cut legume-grass mixture used in this study were harvested as baleage in 2019. The botanical composition (DM basis) of fields from which the second and third cut red clovergrass averaged: 75 vs. 62% red clover, 4 vs. 11% grasses, and 21 vs. 10% weeds, respectively. Note that 17% (DM basis) of white clover was present in the red clover-grass field from the third cut. The botanical composition of the second cut alfalfa-grass field harvested as baleage averaged (DM basis): 40% alfalfa, 2% red clover, 26% white clover, 9% grass and 23% weeds. View Table 2
Compared with 2018, the botanical composition of the alfalfa-grass field changed, with some alfalfa being replaced by white clover due to alfalfa winter kill. Diets were fed as total mixed ration and contained (DM basis): (1) 60% second and third cut red clover-grass baleage (30% of each cut) and 40% of a ground corn-soybean meal-based mash concentrate (high red clover-grass mixture diet = HRC-M), and (2) 30% second and third cut red clover-grass baleage (15% of each cut), 30% second cut alfalfa/white clover-grass baleage and 40% of a ground corn-soybean meal-based mash concentrate (low red clover-grass mixture diet = LRC-M) Diets averaged 17.8 vs. 17.2% crude protein and 31.7 vs. 31.3% neutral detergent fiber (NDF) for HRC-M vs. LRC-M, respectively.
Cows fed the HRC-M diet had greater DMI than those receiving the LRC-M diet (Table 2). However, milk production did not differ between diets. Likewise, production of 4% fat-corrected milk and energy-corrected milk were not impacted by either feeding HRC-M or LRC-M. Milk fat percentage increased, and milk protein tended to increase in cows fed the LRC-M diet possibly caused by a dilution effect due to a 0.9-lb numerical reduction in milk production. The concentration of plasma urea N was lower with feeding HRC-M, perhaps due to red clover containing the enzyme polyphenol oxidase that acts to reduce the breakdown of protein during ensilage. The observed drop in the plasma concentration of urea N with the HRC-M diet suggests improved N use efficiency, but the fact the MUN concentration was not changed indicates that the response was not consistent.
The apparent total-tract digestibility of DM, organic matter and neutral digestible fiber (NDF) increased, and that of crude protein tended to increase in cows fed HRC-M versus LRC-M. Increased digestibility with the HRC-M resulted in improved intake of net energy of lactation (NEL). However, milk production was not significantly changed, suggesting that additional dietary NEL intake was not used to produce milk. Methane yield was lower in the HRC-M vs. LRC-M diet because of decreased DM intake in cows fed the HRC-M diet. In contrast, methane intensity did not change.
