The objective of this experiment was to
determine if pregnancy rates following first
services would be improved by supplementing
lactating dairy cows with progesterone during two
phases after insemination. Cows were inseminated
at estrus (day 0), and progesterone was administered
via a progesterone-releasing intravaginal
device (PRID) from days 5 to 13 or days 13 to 21
after first service with untreated cows serving as
controls. Pregnancy rates at first services were
unaffected by the progesterone treatments whether
the cows received a PRID from days 5 to 13
(13/36 or 36%), a PRID from days 13 to 21
(18/36 or 50%), or no PRID (39/92 or 42%).
Fewer nonpregnant cows receiving the PRID returned
to estrus 17 to 27 days after the first service
compared to the controls (27 vs. 49%).
However, this apparently was not associated with
improved embryonic survival in the cows receiving
progesterone because the pattern of cows
returning to estrus after first service was similar,
except for 17 to 27-day period cited above. Supplementing
progesterone to lactating dairy cows
after first services did not seem to improve fertility.
