Response of Varying Energy and Rumen Undegradable Protein on Growth, Feed Utilization and Blood Biochemical Profile of Crossbred Heifers

To evaluate the energy and UDP needs for optimum growth performance of crossbred heifers, three oat hay based complete rations of low ((L)) and high ((H)) energy and UDP i.e. (TMRLE/LUDP, TMRHE/LUDP and TMRLE/HUDP) were formulated having 2.3, 2.5 and 2.5 Mcal ME/kg and UDP content of 26.6, 27.0 and 34.8% of total CP with CP ranging from 15.5-16.5% respectively. Fifteen crossbred heifers (average age 4 months) were grouped on average BW and randomly assigned to one of the three dietary treatments. Monthly BW changes were noted and blood samples were collected at 0 d and 120 d of experiment. According to the formulations the fiber was higher in TMRLE/LUDP and EE was higher in TMRHE/LUDP and TMRHE/HUDP. The CP: ME ratio was highest in TMRLE/LUDP (67.9) and lowest in TMRHE/HUDP(62.0). Results from the in sacco degradability study indicated that the soluble fraction 'a' was lowest and potentially fermentable OM 'b' highest in TMRHE/HUCP but comparable in TMRLE/LUDP and TMRHE/LUDP. The rate of degradation and effective degradability remained similar in all the TMRs. There was no significant (P>0.05) difference in ADG due to varying energy and UDP content of diet although the DM intake as % of BW was (P<0.05) different (2.12, 2.95 and 2.55%) in TMRLE/LUDP, TMRHE/LUDP and TMRHE/HUDP groups, respectively. Digestibility of DM was 69.86, 75.96 and 64.76% for TMRLE/LUDP, TMRHE/LUDP and TMRHE/LUDP respectively, and varied significantly (P<0.05). The digestibility of ADF was lowest in TMRHE/LUDP (P<0.05) and highest in TMRHE/LUDP. The EE digestibility was similar between TMRLE/LUDP and TMRHE/LUDP (82.62 and 82.74%) but higher in TMRHE/LUDP (87.08%). The digestibility of CP and NDF remained unaffected by the energy and UDP levels. The blood concentration of serum total proteins and globulins in TMRHE/HUDP increased (P<0.05) due to higher UDP content. It was concluded that TMR containing 15.5% CP with a CP:ME of 62.0g CP per Mcal of ME may be optimum for rapidly growing heifers. Besides, the CP: ME ratio can be a reliable indicator of energy protein needs of growing heifers.