2011 (SBTE) 25th Annual Meeting Proceedings - International ...

R.C. Cheb
hebel.
el. 2011. Use of Applied Reproductive Technologies (FTAI, FTET) to Improve the Reproductive Efficiency in
Dairy Cattle. Acta Scientiae Veterinariae. 39(Suppl 1): s183 - s202.
non-treated cows. The increases in P4 concentration
after GnRH treatment are smaller and less consistent
compared with those observed after hCG treatment
because hCG has a longer half-life than GnRH (30
vs. 5 h) and, consequently, a more potent LH-like
activity that not only causes new ovulations but
extends the functional life of CL already present in
the ovaries [18]. Lactating dairy cows treated with
GnRH had higher pregnancy outcomes according to
some [30,81] but not all studies [24,46]. In a metaanalysis
conducted by Peters et al. [53], the effects of
GnRH treatment 11 to 14 d after presumptive
ovulation on pregnancy outcomes was evaluated
based on 16 studies and 8,535 inseminations.
According to this meta-analysis, the interaction
between study and treatment affected the pregnancy
outcomes, which deems this meta-analysis quite
inconclusive [86]. When the authors included in the
logistic regression important independent variables
that could affect the pregnancy outcomes (e.g. OVP
to which cows were submitted, cattle breed), however,
GnRH treatment did not affect pregnancy outcomes
[86]. In recent studies we conducted in dairies in CA,
MN, and TX, we demonstrated that GnRH treatment
at 17 or 31 d after presumptive ovulation did not
reduce pregnancy losses from 31 to 66 d after AI
[87], but cows treated with GnRH at 17 and 24 d
after AI had greater P4 concentration at 31 d after AI
and reduced pregnancy losses from 31 to 66 d after
AI (7.5 vs. 11.9%) [88]. It is interesting to point out
that according to this later study [88] there was a
strong correlation between P4 concentration at 31 d
after AI and incidence of pregnancy loss from 31 to
66 d after AI (Figure 11).
Treatment of cows and heifers with equine
chorionic gonadotropin (eCG) during OVP has
garnered interest for its potential to increase P4
concentration after ovulation and increase pregnancy
per AI or ET. In general, the studies that evaluated
the effects of eCG treatment on P4 concentration and
pregnancy outcomes attempted to promote hastened
growth and ovulation of dominant follicles and,
N
Figure 11. Correlation between progesterone concentration 31 d after AI (P4) and pregnancy loss from 31
to 66 d after AI. Pregnancy loss = 87.41 – (26.5 x P4) + (2.1 x P4 2 ); r 2 (Adj.) = 99.7%. Adapted from
Scanavez et al. [88].
consequently, increased P4 concentration after AI or
ET by treating animals with eCG close to the expected
time of ovulation [32,36,47,56,90]. Although these
studies do not promote consensus regarding the
effects of eCG treatment on pregnancy outcomes, it
appears that anovular cows and cows with low body
condition score would benefit the most from eCG
treatment. On the other hand, treatment of embryo
recipient lactating dairy cows with eCG around the
time of follicular wave emergence to promote
superstimulation and higher P4 concentration at the
time of ET does not seem to improve P/ET (control =
s197