Effect of supplementing finger millet straw with two concentrates differing in their partitioning factor on dry matter intake, organic matter digestibility and nitrogen metabolism in Karan Friesian crossbred heifers

Effects of supplementing finger millet straw (FMS) with concentrates differing in partitioning factor (PF) on dry matter (DM) intake, nutrient digestibility and N metabolism were studied in crossbred heifers. The two concentrates, a high PF concentrate (HPFC) and low PF concentrate (LPFC), were formulated to be iso-metabolizable energetic and iso-N, but differ in PF. Eight crossbred heifers were divided into two groups of four based on body weight. Diets consisted of ad libitum FMS and concentrate supplements at the rate of 1 kg/heifer/day as fed. The feeding experiment was completed in two periods in a switchover design, with each period lasting for 10 weeks with a 6-day metabolism study at the end of each period. The ME (MJ/kg DM) and CP content (g/kg DM) of HPFC and LPFC were 12.3, 161 and 13.1 and 149, respectively. The PF of the corresponding concentrates was 4.16 and 3.73. The intake (kg/day) of DM, organic matter (OM) and CP for the HPFC and LPFC groups were 4.37, 4.07, 0.27 and 4.35, 4.07, 0.26, respectively, but there were no differences between them. The digestibility (g/kg DM consumed) of OM for the two groups was similar (630.3 versus 650.7), whereas the digestibility of CP in HPFC (450.8) was higher (P=0.015) than in LPFC (396.1). The N retained in HPFC was higher than in LPFC (10.74 g/day versus 8.80 g/day, P=0.014), and urinary allantoin excretion (UAe, mmol/day) in HPFC was 54.88 versus 47.67 in LPFC (P=0.085). The calculated microbial N supply to the duodenum (g/day) was higher (P=0.098) in HPFC (38.09) versus LPFC (31.37). The microbial N (g/kg of digestible OM intake) for HPFC and LPFC was 14.7 and 11.8, respectively (P=0.023). Body weight gain (g/day) for the corresponding groups was 349 and 311 (P=0.003). The high PF concentrate supplement tended to result in higher efficiency of microbial biomass synthesis with an FMS-based high forage diet.