Effects of rumen protected fat on in vitro dry matter degradability of dairy rations.

Rumen protected fat (PF) was incorporated in 12 concentrate mixtures (CM1-CM12) and total mixed rations (TMR1- TMR12) to study the effect of different levels of PF in dairy rations and the effect of urea in dairy rations containing limited grains and high PF on in vitro dry matter degradability (IVDMD) and in vitro fermentation. The CM1 contained 6% natural fat and no PF whereas, in CM2, CM3, CM4, CM5, CM6 and CM7, the natural fat was replaced @ 30, 40, 50, 60, 70 and 80% by PF, respectively. The CM8-CM12 contained limited cereal grains (5–10%), high deoiled rice polish (50–60%) without (CM8-CM10) or with 1% urea (CM11-CM12), in which 80% natural fat was replaced by PF to increase the fat content. The 12 total mixed rations (TMR1-TMR12) contained respective CMs (CM1-CM12) and green sorghum in 50: 50 ratios on DM basis. Increasing the deoiled ingredients in CM1-CM7 increased the CP and NDF content but, IVDMD remained similar. Limited grain, high PF based CMs (CM8–CM12) with or without urea had comparable chemical composition but, IVDMD was lower in urea containing CMs. The chemical composition of TMR1-TMR7 showed significant variation and lower IVDMD when PF replaced more than 40% natural fat. The IVDMD in TMR8- TMR12 showed inconsistent variations. No difference (P>0.05) in in vitro fermentation (TVFA, TN, TCA-N, NPN and NH3-N) was observed between CM1-CM7, CM8-CM12, TMR1-TMR7 and TMR8-TMR12. It was concluded that the PF can substitute up to 40% of the natural fat of the CMs (6% natural fat) contained in TMRs (50: 50, R: C). In rations with limited grain (5–10%) and high PF, 1% urea can reduce IVDMD.