Can Grazing Selectivity Reduce Fatty Acid Intake Declines in Maturing Annual Forages?.

Maximizing grazing availability is important to all organic dairy farmers, and particularly for grain-free “grassmilk” producers. Many producers are utilizing annual forage crops to provide supplemental grazing when perennial pasture is less productive. Annual forages are known to quickly diminish in nutritive quality as they mature however. We posit that grazing selectivity may ameliorate some of the quality decline of maturing annual forages, including the content and profile of fatty acids (FA) which are a key marketing component of grassmilk. Whole plant analysis may underestimate the quality of a selectively grazed forage, thus our study utilizes differences of weighted means of lamina and pseudostem components. Species investigated include an overwintered small grain (cereal rye) and a warm season summer annual (pearl millet).  Preliminary data from cereal rye shows that the polyunsaturated FA alpha-linolenic acid (ALA) - the primary FA in vegetative forages - is present in similar proportions in late vegetative and early head emergence stage laminae (70.9 and 73.2 g 100g^‑1  total FA, respectively, p=0.1052) and pseudostem (46.3 and 45.1 g 100g^‑1 total FA, p=0.2013). While decreases in ALA content occur with increasing maturity on a forage dry weight basis, the decline in lamina content is insignificant (29.5 to 27.1 mg g^-1 forage, p=0.5785) and pseudostem content decline (8.8 to 6.5 mg g^-1 forage, p=0.0045) is less than the overall decline on a whole plant basis (16.4 to 9.8 mg g^-1 forage, p=0.0008) due to the increased proportion of pseudostem relative to laminae in boot stage annual forages. As such, the ingested dry weight ratio of laminae relative to pseudostem in annual forages has a greater impact upon the overall FA profile than maturity stage, and therefore FA intake from annual forages is potentially manipulable through changes in grazing pressures. Millet data will also be presented.