Estimating Degradable Intake Protein in Warm- and Cool-Season Forages Grown on Producer Farms in Northern Arkansas

Abstract

Two case studies were conducted on producer farms in northwest Arkansas to assess degradable intake protein (DIP) and undegradable intake protein (UIP) in forages grown throughout the region. In Case Study 1, DIP was greater (P<0.05) by 11.7 and 4.7 percentage units of CP and DM, respectively, for cool-season pastures compared with pastures dominated by warm-season grasses. For both photosynthetic types, NDF exhibited a strong negative correlation (r ≤ -0.61; P≤0.006) with DIP. Generally, both CP and in vitro OM disappearance (IVOMD) were strongly and positively correlated (r ≥ 0.67; P≤0.002) with DIP, but CP was not correlated with DIP (P>0.05) in warm-season pastures when DIP was expressed as a percentage of CP. In Case Study 2, N fertilization in April and July at two producer sites (Latta and Stephens) increased concentrations of CP for subsequent harvests in primarily linear (P<0.0001) patterns for bermudagrass [Cynodon dactylon (L.) Pers.] forages, but there was no residual effect (P>0.05) for a mid-summer (July 7) harvest that received no fertilization. In harvests immediately following fertilization, DIP increased; the linear term was significant (P≤0.004) in each case, but it was coupled with quadratic or cubic effects in some harvests. For the second harvest at each site, DIP was not affected (P>0.05) by residual effects of the initial application of N fertilizer in April. The size of the UIP pool also increased linearly (P≤0.002) immediately following N fertilization in three of four harvests, but the magnitude of these responses was small compared with those observed for DIP.