bearing in mind the Regiment was in existance for about sixty years (7 May 1860 to 1919), probably a couple of hundred plus regulars at least.
Here are the regulars at as 1914. In addition there were a couple of Turkish officers attached and Oberstleutnant Adolf Friedrich Herog zu Mecklenburg was à la suite. The 1914 Rangliste also lists a further 23 Reserve Officers.
The Ehrenrangliste shows a further 19 regular Leutnants were commissioned into the regiment during the course of WW1.