Sorry to hear about the pup... we just lost one of our two cats to a fisher a couple of weeks ago; the survivor really misses his brother; sad to watch.
At the risk of sounding like a know-it-all, perhaps you'd like a brief intro to diesel engines..
Remember your physics classes? Charles' Law? Boyle's Law? Diesel engines don't use spark plugs- they rely on a compression ratio that's sufficient to raise the temp of the air in the cylinder, when compressed, to a point where the diesel fuel, sprayed in under high pressure, ignites all by itself.
The glow plugs are little heaters stuck into the air chamber to pre-warm the air; as you only get so much rise in temp (dependent on starting air temp and compression ratio), if the air is cold it requires a lot more work from the starter --remember the high compression in diesels?-- to start the engine.
The glow plugs are there to help that. Some modern diesels don't require glow plugs at all, some benefit from using them all the time, some only need glow plug help when it's really cold out.
My Massey-Ferguson likes some glow plug any time the engine's cold, but my VW Jetta doesn't need them at all unless it's below 5 or 10 degrees out.
Hope this might help clarify things a bit. Welcome to
TBN!