Protein degradability of grassland forage under simulated rotational spring grazing

Abstract

A cutting experiment was conducted to analyze the changes in the crude protein (CP) fraction content and in the estimated ruminal protein degradability of forage, obtained in conditions of simulated rotational spring grazing on permanent grassland. The field trial was conducted on permanent pasture during 2015 and included three cuttings as a simulated rotational spring grazing. For determination of protein degradability of pasture forage, the fractionation of the CP according to Cornell Net Carbohydrate and Protein System (CNCPS v6.5) and the Streptomyces griseus protease assay were used. Relative to CP, no significant differences were found among cuts for ammonia N content (A1 fraction) and for protein fraction C which is completely unavailable to the animals. Values for soluble true protein (A2 fraction) and cell wall-associated protein, which is acid detergent soluble (B2), were significantly increased (p lt 0.05) while a significant reduction (p lt 0.05) of the moderately degradable protein (B1) content was determined during the growing season. The lower rumen degradable protein (RDP) content of grassland herbage was obtained in the second cut which was significant (p lt 0.05) according to the CNCPS procedure. Obtained high solubility and degradability of CP in pasture require adequate content of readily available carbohydrates in rations for grazing ruminants to provide efficient utilization of consumed protein.

Istraživanje je obavljeno u cilju utvrđivanja promena u sadržaju frakcija sirovog proteina (SP) i ruminalne razgradivosti proteina zelene mase dobijene košenjem prirodnog travnjaka u uslovima koji su odgovarali rotacijskoj pregonskoj ispaši tokom prolećne sezone. Poljski ogled je izveden na permanentnom pašnjaku tokom proleća 2015. godine i uključivao je tri otkosa koji su odgovarali ciklusima ispaše. Za determinisanje razgradivosti proteina zelene mase, frakcionisanje sirovog proteina je obavljeno prema proceduri Cornell Net Carbohydrate and Protein System (CNCPS v6.5), kao i primenom in vitro metode korišćenjem Streptomyces griseus proteaze. U odnosu na SP, nisu utvrđene značajne razlike između otkosa - ciklusa ispaše u pogledu sadržaja amonijačnog N (frakcija A1), kao i u pogledu sadržaja proteinske frakcije C, koja je potpuno nedostupna životinjama. Sadržaj rastvorljivog pravog proteina (frakcija A2) i proteina vezanog za ćelijski zid, koji je rastvorljiv u kiselom deterdžentu (frakcija B2) se značajno povećavao (p lt 0,05), dok se sadržaj umereno razgradive frakcije proteina (B1) značajno smanjivao (p lt 0,05) tokom prolećne sezone vegetacije. Najmanja vrednost za ruminalnu razgradivost i učešće RDP (protein razgradiv u rumenu) u SP zelene mase sa pašnjaka utvrđena je u drugom otkosu, a ova razlika je bila značajna (p lt 0,05) kada je ruminalna razgradivost proteina determinisana korišćenjem procedure CNCPS. Utvrđeno visoko učešće rastvorljive frakcije SP i visoka ruminalna razgradivost SP zelene mase sa pašnjaka ukazuju na potrebu podrobnijeg balansiranja obroka za preživare na paši u pogledu sadržaja lako razgradivih ugljenih hidrata, a u cilju obezbeđenja efikasnog iskorišćavanja konzumiranog proteina.