Potential of alternative forage plants (herbs and legumes) in terms of secondary plant metabolites and capability of protein precipitation

High contents of rapidly rumen degradable protein in forage plants are associated with metabolic and hepatic stress, disorder of proliferation and poor N utilization. Phytogenic agents, particularly tannins, may favorably modify rumen protein degradation and improve animal health and productivity (Mueller-Harvey 2006).

To identify home-grown forage plants of such properties, freeze-dried and grounded material of six herbs and nine legumes (table 1) harvested in 2010, was analyzed in terms of condensed tannins (CT), total phenolics (TP) and the ability to precipitate the model protein bovine serum albumin (BSA). In addition, crude protein was fractionated according to the Cornell Net Carbohydrate and Protein System. It was assumed that plants with decent CT concentrations are able to form complexes with proteins, which consequently is reflected in protein quality.

As expected, CT and TP concentrations as well as protein precipitation capacities were highest in Onobrychis viciifolia Scop. (Ov) and Lotus corniculatus L. (Lc) (table 1). Sanguisorba minor Scop. (Sm) with negligible CT but highest TP concentration showed above-average protein precipitation capacities (table1).

Tab. 1: CT, TP and capability to precipitate BSA of all evaluated species

Species	Common name	CT2 (% DM)		TP (% DM)		BSA precipitation (mg/g plantDM-1)
Carum carvi L.	Carraway	0.04	-	4.44		1.05	-
Lolium perenne L.	Perennial ryegrass	0.04	-	1.58	-	0.03	-
Galega orientalis L.	Goats rue	0.05	-	3.98	-	1.09	-
Melilotus officinalis L.	Yellow sweet clover	0.06	-	1 59	-	2.15	-
Melilotus alba Medik.	White sweet clover	0.06	-	1.67	-	0.98	-
Taraxacum officinale Wiggers	Dandelion	0.07	-	3.54	-	2.81	-
Achillea millefolium L.	Yarrow	0.07	-	9.45		0.99	-
Medicago sativa L.	Alfalfa	0.08	-	1.37	-	0.41	-
Medicago lupulina L	Black medic	0.09	-	1.62	-	0.57	-
Cichorium intybusL.	Chicory	0.09	-	6.14		0.96	-
Trifolium repens L	White clover	0.11	-	1.80	-	0.31	-
Trifolium pratense L.	Red clover	0.11	-	3.14		0.64	-
Trifolium hybridum L	Alsike clover	0.12	-	2.75	-	2.72	-
Sanguisorba minor Scop.	Salad burnet	0.17	-	18.56	+	28.15	+
Plantago lanceolata L.	Narrowleaf plantain	0.30	-	6.61	+	2.01	-
Lotus comiculatus L.	Birdsfoot trefoil	1.93	+	4.80		18.62	+
Onobrychis viciifolia Scop.	Sainfoin	8.39	+	10.33	+	125.44	+
Total average of all species		0.69		4.90		11.11
+/-= statistical deviations from total average (p < 0.001)

As hypothesized, Ov contained statistically significant (p ≤0.01) below-average amounts of rapidly rumen degradable fractions (A and B1) and high amounts of not degradable fraction C. As to fraction A and B1, Sm showed equal characteristics. Sm contained significant (p ≤0.001) highest amounts of rumen-undegradable but intestinal available fraction B3. No anticipated distribution of protein fractions could be observed in Lc.

Results demonstrate that CT concentration seems to be an insufficient criterion to identify forage plants that potentially effect ruminant's protein metabolism. However, transferability of findings to the animal in-vivo situation has to be examined.

References:

[1] Mueller-Harvey, I. 2006. J.Sci.Food Agric.86:2010 – 2037.