I am going to define failing pastures as those that no longer can meet the nutritional needs of the horse. This can happen a lot sooner than you may think.
Brown, dormant grass is easy to spot but very mature green grass also lacks sufficient nutrients
Grasses stressed by extremes of weather - drought, heat, or cold - will either die or go dormant to protect their carbohydrate reserves until growing conditions improve. They lose their green color because the production of chlorophyll and other pigment ceases.
Another pigment is carotene, the precursor of vitamin A, and vitamin A activity in these grasses is low, as is vitamin E and essential fatty acid level. Calories are lower than young green grasses and fiber much higher. Protein is deficient, typically around 5%. Even mineral levels may be lower.
You may not think of grass and hay as a source of B vitamins but the fact is they are the horse's major source and levels are much higher than in grains. The B vitamins are also in their most bioavailable forms, incorporated into active compounds. When metabolic activity slows (maturity) or stops (dormancy or death), levels naturally fall.
Grass hay is best cur right before it starts to set seed. At this stage, there has been enough growth for a good yield and the nutritional value of the grass portions above ground is good. Once the grass has reached full height, set, and dropped seed, its metabolism slows, fiber fractions rise and protein drops. The other changes described above for dormant hay also begin. Significant loss of nutritional value can occur while the grass is still green.
Supplementing protein is a major consideration in all scenarios late in the grazing season. Begin essential amino acid supplementation of lysine, methionine, and threonine as soon as grasses go to seed. When grasses begin to brown, start 1/4 to. 1/2 lb/day of 40% protein supplement or 1/2 to 1 lb/day of a 20 to 25% protein and mineral supplement.
The mixed protein and mineral supplements have to be fed in higher amounts but they are good insurance against drops in mineral levels that can occur. They will also cover the dropping vitamin A and B vitamin levels.
Maintaining good intakes of omega-3 fatty acids is important for supporting the body's ability for the normal homeostatic balance of inflammatory reactions. Flax and Chia seeds are the ideal way to do this with omega-6:omegs-3 rations which mimic young green growths of grass.
Dead, dormant, and overly mature grasses have a nutritional profile similar to straw. Horses relying on failing pastures for the bulk of their nutrition can still get some caloric value but will encounter significant gaps until they are switched over to their winter rations. By knowing what the issues are you can target them and support the horse in this transitional period.
- Eleanor Kellon, VMD