Scientists are also working to develop chemicals to control the birthrate in deer populations.
科学家们也在努力研制化学物质来控制鹿群的出生率。
2
The newly domesticated animals behaved better, were easier to control, and may have enjoyed a higher birthrate, which in turn yielded greater milk supplies.
新驯养的动物表现更好，它们更容易控制，出生率也更高，且反过来也会提供更多奶源。
3
The Centers for Disease Control and Prevention released data recently showing that in 2009 the preterm birthrate declined, for the third year in a row, to 12.18 percent of all births.