Just checked it out on MW online, and the little guy who pronounces words pronouned it like this:

shuh-VALL-skeez horse

Here's the paste from that webpage:

Pronunciation: psh&-'väl-skEz-, sh&-, "p&r-zh&-'väl-
Function: noun
Etymology: Nikolai M. Przhevalskii died 1888 Russian soldier & explorer
Date: 1881
: a small stocky bay- or dun-colored wild horse (Equus caballus przewalskii syn. E. przewalskii) of central Asia having a large head and short erect mane -- called also Prze·wal·ski horse \-skE-\

[MW online]