WHAT CAUSES THE ENGINE TO TURN OVER SLOW IN COLD WEATHER

Have the battery tested (high rate discharge test and hydrometer test where applicable),perhaps check starter draw should initially take about 100 amps then drop to 80 amps as the engine is being rotated. Check that the battery connections are clean tight and secure the next thing to do is a voltage drop test, look on You tube "voltage drop test", it checks for high resistance in connections.