As with any feed item, it is not the item itself that is the problem – the overriding issues with lucerne/alfalfa stem from the fact that:
1. It is recommended WITHOUT taking into account the horse’s pasture. This is how it frequently becomes ‘the straw that breaks the camel's back’.
2. There seems to be little or NO awareness of the potential DISADVANTAGES of feeding lucerne
Because of its low sugar content it is widely recommended. But Lucerne actually has a very similar nutrient profile to short, green grass (high potassium, high Crude Protein, low sugars).
The ‘true protein’ component of the Crude Protein is a good source of protein for some horses but the NPN (Non-Protein Nitrogen) component does have an undesirable feature – nitrates accumulate in the leaves rather than the stems. In grass the nitrates are mainly located in the lower regions of the plant.
The horse’s mono-gastric digestive system is NOT equipped to process nitrates. When feeding horses, nitrate ingestion needs to be MINIMISED to lessen the possibility of serious digestive and other issues developing.
When the already high crude protein and potassium intake from cool season pasture (rye-grass, cocksfoot/orchard, timothy, bromes/prairie, clovers) is further elevated by adding lucerne, depending on the horse’s metabolic capacity at the time, it can ‘tip him over’ into a wide variety of issues including:
1. Head-flicking, laminitis 2. edemas 3. digestive upsets 4. sub-cutaneous ‘protein lumps’ 5. Frequent urination 6. tight muscles, stiffness, tying up 7. Spooky, explosive, dangerous to handle 8. Staggers, recumbency (inability to stand)
Feedback regarding the improvements horse owners observe after removing lucerne from the horse's diet is overwhelmingly positive. Doing so eliminates the unnecessary stress of having to process and excrete both potassium and nitrate over-load, rendering the horse less susceptible to weather and seasonal spikes of these two items in the grass.
Hence if you are in a grazing situation where your horse is consuming cool season pasture which you cannot control it is BEST NOT to add lucerne to his diet. This is something you CAN control. Oil-seeds (eg linseed, sunflower, chia) are better protein sources being very low in nitrates.
Lucerne can work as part of the horses total daily forage (best kept around 10%) especially when fed in regions of warm season grasses.
I recall being informed when in the US that ‘first cut’ alfalfa shouldn’t be fed to horses because of it’s high CP content. Avoid that emerald green Prime lucerne!