ENC28J60 to sleep

void loop()
{
  //--------------------------------------
  // 1) Measurements and data preparation
  //--------------------------------------
  if ((millis()-lastupdate)>10000)
  {
    Serial.println("Powered up");
    es.ES_enc28j60PowerUp();
    delay(2000);
    lastupdate = millis();

    float temperature = getVoltage(0);  //getting the voltage reading from the temperature sensor
    temperature = (temperature - .5) * 100;          //converting from 10 mv per degree wit 500 mV offset

    // Convert int/double to string, add it to main string, add csv commas
    // dtostrf - converts a double to a string!
    // strcat  - adds a string to another string
    // strcpy  - copies a string
    strcpy(str,"TEMP,");
    dtostrf(temperature,0,1,fstr); strcat(str,fstr);
    dataReady = 1;
  }

  //----------------------------------------
  // 2) Send the data
  //----------------------------------------
  if (ethernet_ready_dhcp_dns() && dataReady==1)
  {
    ethernet_send_post(PSTR(PACHUBEAPIURL),PSTR(PACHUBE_VHOST),PSTR(PACHUBEAPIKEY), PSTR("PUT "),str);
    Serial.println("sent"); dataReady = 0;
  }
    Serial.println("Powered down");
    es.ES_enc28j60PowerDown();
    delay(2000);
}