Leaf protein concentrate was extracted and measured in a range of commonly grown pasture plants and cereals in Victoria, with the aim of identifying species most suitable for a leaf protein concentrate industry. The effects of sward maturity, nitrogen fertilizer and pH, on protein extractability were examined. Best yields (1100 to 1500 kg ha-1) of extractable protein were obtained from irrigated lucerne and white clover. Extractable protein yield from perennial grass, cereals and lucerne declined rapidly with maturity, whereas lupins, vetch and white clover were much less affected by maturity. Soursob in mixed pasture reduced yields by reducing pH of juice. Nitrogen fertilizer applied in spring on a mixed pasture reduced the clover content and consequently the extractable protein yield.
A series of six experiments compared the production of lactating dairy cows eating either fresh herbage or the pressed herbage remaining after the partial extraction of juice. Irrigated perennial pasture and irrigated lucerne (Medicago sativa) were used in different experiments. With forage-harvested pasture, extraction removed an average of 42.1 g of protein per kg dry matter (DM) of pasture processed. An average of 85% of the DM of the original fresh pasture was left as pressed pasture. The process lowered the in vitro digestibility, total nitrogen, and cell contents of the herbage, and raised the cell wall constituents. It also reduced herbage phosphorus, potassium, magnesium and sodium, but increased herbage calcium slightly. The milk yield of cows fed an equivalent DM intake of pressed residue was, on average, 6% lower than the milk yield of cows fed fresh pasture. The responses shown by the milk constituents were inconsistent. With lucerne, extraction removed an average of 95.9 g of protein from each kg of fresh herbage and an average of 74% of the lucerne was left as pressed lucerne. This reduced the quality of the pressed residue as determined by in vitro digestibility (5%), Kjeldahl nitrogen (19%) and neutral detergent fibre (27%). However, there was no significant loss of production for cows on the pressed herbage, although there were small differences. It is concluded that lucerne would appear to have the greater potential for a leaf protein extraction industry in the irrigated areas of the Goulburn Valley of Victoria.
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