Effect of fat supplementation (Ca-salts) in starter diets differed in rumen undegradable protein levels on performance, growth and blood metabolites of Holstein calves

The interaction of fat supplementation (0 and 30 g/kg DM) and by-pass protein level (36 and 40% of dietary CP) was investigated on performance, skeletal measurements and blood metabolites of calf. Forty calves (aging 39 d) were used in a factorial design with four treatments. Experimental diets consisted of; 1) un-supplemented fat with low un-degradable protein (UF-LRUP), 2) supplemented fat with low un-degradable protein (SF-LRUP), 3) un-supplemented fat with high un-degradable protein (UF-HRUP), 4) supplemented fat with high un-degradable protein (SF-HRUP). The results show that supplementing fat in calves increased starter intake, gain as well as feed efficiency (P< 0.01). No performance result was affected with fat-RUP interaction. Considering the growth parameters, fat supplementation improved body length as well as chest width. Greater RUP also increased hip height. The interactions of fat-RUP did affect chest width and wither height as well. However fat supplementation did not affect blood metabolites, greater RUP reduced both glucose and insulin concentrations. In conclusion, fat supplementation may be recommendable after 4 weeks of age in calves and the results would be more favorable if this supplementation would accompanied with greater RUP level.