Why did 60,000 endangered antelopes in Kazakhstan die in 4 days?

In 2014, a country had 257,000 saigas, but now only half remain. Field workers collected samples from the environment to understand the decline. Necropsies showed females and calves were most affected, likely due to toxins from bacteria like pasteurella and clostridia, which caused organ bleeding. Normally harmless, these bacteria became deadly due to weakened immune systems, possibly from a harsh winter and wet spring that facilitated bacterial spread.

What role does the mother's milk play in the health of female saigas and their calves?

What environmental conditions are thought to have contributed to the spread of bacteria affecting the saigas?