Metabolic Characteristics and Truly Metabolizable Protein Supply to Dairy Cattle from New Cool-Season Forage Corn Varieties in Western Canada
The objectives of the present study were to quantitatively evaluate the metabolic characteristics of protein in the rumen and intestine of dairy cattle and to estimate the content of truly metabolizable protein (MP) in newly developed cool-season forage corn varieties. Six new corn cultivars, including 3 Pioneer (PNR) and 3 Hyland (HL), coded as PNR-7443R, PNR-P7213R, PNR-7535R, HL-SR06, HL-SR22, HL-BAXXOS-RR, were evaluated in the present study. The metabolic characteristics, MP supply to dairy cattle, and energy synchronization properties were modeled by the DVE/OEB system and the NRC-2001 model. The parameters evaluated were (1) potential microbial protein (MCP) synthesis in the rumen from available degraded protein and energy (2) truly absorbable rumen synthesized microbial protein (AMCP) (3) truly absorbable rumen undegraded feed protein (ARUP) (4) truly absorbed rumen endogenous protein and (5) total truly MP (6) the degraded protein balance (DPB). Both models estimated significant (P < 0.05) differences in contents of MCP synthesized from rumen degraded protein (RDP) and ARUP among the cultivars. The NRC-2001 model estimated significant (P < 0.05) differences in total truly MP and DPB among the cultivars. According to NRC-2001 model, the contents AMCP, ARUP and total truly MP contents were higher (P < 0.05) for cultivar HL-SR06, resulting in the lowest (P < 0.05) DPB. Cultivar, HL-SR06 also had the highest rumen available N/kg of organic matter (OM) and high hourly effective degradability ratios among the corn cultivars. However, none of the cultivars reached the optimal target hourly effective degradability ratio (25 g N g/kg OM), demonstrating N deficiency in the rumen. Hyland-SR06 had the highest contents of MCP synthesized from RDP, ARUP and total truly MP. However, regardless of the differences among cultivars, forage corn based rations of dairy cows needs to be balanced with a high protein containing concentrate to improve the rumen degradable protein deficit.
Keywords: Corn, protein metabolic characteristics, protein evaluation system