Comparative studies on dry matter intake, digestibility and nitrogen metabolism between Thai native (TN) and Anglo Nubian × TN bucks

Metabolic experiments were conducted for each Thai native (TN) and Anglo Nubian-TN 50% (AN × TN) bucks, 26.5-38 kg BW and 35-52 months of age, by assigning the following concentrate diets, which had four levels of CP concentrations, T1: 14%, T2: 21%, T3: 28% and T4: 35%, on a DM basis. The animals were fed the concentrates at a rate of 1% of their BW and had ad libitum access to Paspalum plicatulum hay. As the CP level increased, digestibility of CP, N excretion in urine and N retention increased (P < 0.01). No significant differences of DM digestibility among the CP levels of diet and between the breeds of bucks were observed. The AN × TN had higher DM intake than TN (P < 0.05, 40.9 g/(kg BW0.75 day) versus 36.0 g/(kg BW0.75 day)), thus N intake of AN × TN was higher than that of TN (P < 0.01, 0.99 g/(kg BW0.75 day) versus 0.90 g/(kg BW0.75 day)). Digestibility of CP and blood urea N concentrations of TN were higher than those of AN × TN (P < 0.05, 69.8% versus 64.0% and 32.2 mg/dl versus 26.7 mg/dl, respectively). The AN × TN tended to retain more N than TN in the higher CP feeding condition of T3 (0.19 g/(kg BW0.75 day) versus 0.11 g/(kg BW0.75 day)) and T4 (0.25 g/(kg BW0.75 day) versus 0.17 g/(kg BW0.75 day)). Digestibility of NDF and ADF, and TDN of TN were higher than those of AN × TN (P < 0.05, 61.1% versus 55.9%, 49.6% versus 43.5% and 65.8% versus 62.4%, respectively). The overall mean DE was 109 kcal/(kg BW0.75 day), and no significant difference of DE among CP levels nor breeds of bucks was observed. Thai native was superior to AN × TN in digestibility of N and fiber fractions at the maintenance level of DE, which might have overcome inferiority of TN to AN × TN in amount of N and energy intake caused by the lower DMI. It is likely that TN goats are well adapted to fodder shortage condition due to their efficient utilization of nutrients.