While visiting the Cornell Valatie (Field Crops) Research Farm (Columbia County, NY), during late July 2012, I learned something interesting about alfalfa (Medicago sativa). Namely that some of the higher protein test values in early cut — properly managed — M. sativa hay crops fell in the category of “less than meets the eye.” I had long known that some of these higher protein figures — say the difference between 20% and 24% tended to be more soluble. That being the case, often this extra protein actually introduced more non-protein-nitrogen (NPN, basically all soluble) to the dairy cow than her rumen can efficiently metabolize. Total protein solubility in the lactating dairy cow’s diet should fall in the 30-33% range.
I already knew that wetter harvested hay crops tend to run higher protein solubilities — for example, an alfalfa hay crop testing 65% moisture normally tests about 50% protein solubility. This happening makes dairy nutritionists prove just how well they can juggle feedstuffs, while trying to balance cattle rations. I learned something else at Valatie, that summer. Specifically, that with higher quality alfalfa often being saddled with some nitrogenous “baggage”, medium red clover testing 20% crude protein often supports milk production as well as (or better than) 24% protein alfalfa.
At that time, I also knew that at some point too much protein (and NPN) actually siphons off energy to dissipate surplus nitrogen (N) through the kidneys (and ultimately into the environment). This lost energy could have supported milk production. As the N is being dissipated (through a process called de-amination), both blood and milk urea nitrogen (MUN) levels usually elevate. It’s easier to measure MUNs than BUNs. Research (California Cooperative Extension) suggests that the most desirable MUNs for Holstein cows range from 10 to 14 milligrams per deciliter (mg/dl). High concentrations of MUN (> 14 mg/dl) indicate an excess in protein feeding, and/or deficiency in rapidly fermentable carbohydrates. Individual MUNs exceeding 20 are often associated with early embryonic mortality.
Despite all this technical stuff just cited, my understanding of alfalfa’s nutritional shortfall for dairy cattle remained somewhat tethered until recently. So, fast-forward to the May 2020 NODPA (Northeast Organic Dairy Producer Alliance) News. There a scientific paper [written by Andre F. Brito et al. at University of New Hampshire (UNH)] was titled “The Key Role of Forage Legumes in Organic Dairy Diets: Effects on Your Bottom Line”.
According to these UNH scientists, a large proportion of alfalfa proteins is broken down to ammonia, amino acids and peptides during ensiling, thus reducing efficiency of protein utilization in cows fed alfalfa. By comparison, protein from red clover is protected from degradation in the silo and rumen by the enzyme polyphenol oxidase. This enzyme is present in red clover tissues and adheres to proteins. Cows fed alfalfa produced more milk than cows fed red clover, but alfalfa-fed cows had higher MUN and N excretion into the environment. Birdsfoot trefoil (b.f.t.) — not as prevalent as alfalfa or red clover in the Northeast — is more effective than the other two legumes in reducing urinary N excretion. This fact is most likely due to the presence of condensed tannins in b.f.t. (These tannins underwrite b.f.t.’s natural deworming properties for horses and cattle.) UNH workers also showed that silages made from clover and b.f.t. were best for milk production. But that white and red clover diets resulted in the greatest digestibility of organic matter in cows consuming high-forage diets.
A winter (2017-2018) feeding trial was conducted at the UNH Dairy Research Farm (Lee, NH) to investigate the effect of different legume-grass mixtures (harvested as balage) on milk production, milk fatty acid profile, serum amino acid levels and N utilization in Jersey cows. Twenty mid-lactation Jersey cows were assigned to one of two diets in randomized complete block design. The study lasted seven weeks, with sample collection done at weeks four and seven. The alfalfa-grass diet averaged 18.8% crude protein (CP) and 30.5% neutral detergent fiber (NDF); the clover-grass diet averaged 18.1% CP and 31% NDF. Workers found that 4%-fat-corrected-milk, energy-corrected milk, and milk fat significantly increased with feeding alfalfa-grass instead of red clover-grass. However, cows fed alfalfa-grass had higher MUNs than those receiving red clover-grass. This indicated poorer utilization of dietary protein in the alfalfa-grass diet. As stated earlier, the enzyme polyphenol oxidase in red clover prevents protein degradation in the rumen, thus supporting improved N utilization in dairy cows. Despite this benefit, cows fed the red clover-grass diet did lose some milk and milk fat.
Another forage factor gaining importance is growing consumer desire for omega-3 fatty acids in dairy products. According to these UNH researchers, it’s been shown that organic dairy products (particularly grass-fed) have a healthier fatty acid profile than conventional milk. The percentage of alpha-linoleic acid was significantly higher in cows fed red clover-grass than in cows fed alfalfa-grass diet. These scientists confidently stated that the red clover-grass diet promoted a healthier fatty acid profile in milk than the alfalfa-grass regimen.
Leaving fatty acids for a discussion of amino acid protein components, Brito’s crew stated that methionine, lysine and histidine are the most limiting amino acids supporting overall lactating cow performance. But almost equally critical are the amino acids leucine and valine, which increased significantly in cows fed red clover-grass vs. alfalfa-grass diet. They state that red clover-grass diet appears more effective than alfalfa-grass “to elevate plasma concentration of essential amino acids.”
In addition to less dietary N being wasted into the environment, the red clover-grass diet boasts less greenhouse gas methane being liberated, compared to what an alfalfa-grass regimen caused. Methane measurement during the mid-point of the UNH study recorded 157 grams/head/day for red clover-grass, compared to 218 grams/head/day for alfalfa-grass diet. Then there’s hardcore agronomic economics: whatever the soil pH, clovers are happier with one ton less of 100% estimated neutralizing value lime than what alfalfa demands. While corn is still king of forages, alfalfa is still queen — maybe.