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Table 5 The urinary purine derivatives (PD) and estimated MP supply to the dairy cows selected for phenotypic divergence in residual feed intake (RFI)

From: Nitrogen partitioning and microbial protein synthesis in lactating dairy cows with different phenotypic residual feed intake

Items Low
RFI
High
RFI
SEM P valuea
RFI Day RFI × Day
Urine volumeb, L/d 33.6 33.4 2.64 0.96 < 0.01 0.07
Urinary PD, mmol/d
 Allantoin 489 520 33.1 0.51 0.60 0.16
 Uric acid 39.4 51.1 4.80 0.11 0.09 0.40
 Endogenous PD 54.2 49.9 2.87 0.31 0.29 0.23
 Sum 474 484 40.2 0.86 0.70 0.77
MCPc, g/d 2152 2198 183 0.86 0.70 0.78
IADPd, g/d 695.5 760.8 22.5 0.06 0.07 0.80
MPe, g/d 2065 2171 100.2 0.47 0.36 0.58
  1. aP value associated with RFI, time, and the interaction of RFI and time
  2. bUrine volume (L/d) = BW (kg) × 29 (mg/d)/creatinine (mg/L) [24]
  3. cMicrobial protein (MCP) was indirectly estimated by the equation [21]: MCP = (allantoin + uric acid - endogenous PD) × 70 × 6.25/ (0.116 × 0.83 × 1000)
  4. dIntestinally absorbable dietary protein (IADP) = RUP × CP intake × IDP, where IDP is the measured intestinal digestibility of rumen undegraded protein (RUP). The feedstuff incubated in the rumen for 16 h was used to determine the IDP according to a modified 3-step procedure [25]
  5. eMP = IAMCP + IADP; IAMCP = Intestinally absorbable MCP = MCP × 0.64 [13]