The Effect of Presynchronization and Bovine Somatotropin on Timed AI in Lactating Dairy Cattle
by Teresa L. Steckler and Darrel J. Kesler
TAKE HOME MESSAGES
- Pregnancy rates for cows treated
with bST were greater when the cows were presynchronizationed
- bST increased pregnancy rates in estrus-cycling cows regardless if cows
- Presynchronization increased pregnancy rates in estrus-cycling cows regardless
if cows were administered bST
Bovine somatotropin (bST) results in increased milk yields and improvement
in efficiency in dairy cattle. bST is involved in orchestrating many physiological
processes, including metabolism of carbohydrates, lipids, proteins, and minerals
and alterations in key enzymes. Commercial use began in 1994 in the U.S. and
has been extensively adopted. Since 1994 several synchronization programs utilizing
gonadotropin releasing hormone (GnRH) and prostaglandin F2"
(PGF) have been introduced and discussed for use in dairy cattle. The purpose
of this article is to report research conducted that describes the effects of
presynchronization and bST on pregnancy rates to a timed artificial insemination
protocol in lactating dairy cattle (Moreira et al., 2001).
This experiment included 543 lactating dairy cows from a commercial dairy farm
in Florida kept in free-stall facilities and milked three times daily. The
experiment was designed as a 2X3 factorial experiment (6 treatment groups) with
2 main effects: presence or absence of presynchronization and the day that bST
treatment was begun. Cows were assigned to treatment when they were 37±3 days
post partum (PP).
Presynchronization consisted of 2 injections of PGF (25 mg), given 14 d apart
(Figure 1), then 12 days later a modified OvSynch protocol was begun. The modified
Ovsynch protocol consisted of an initial injection of 100 :g of GnRH, followed 7 days later by
40 mg of PGF, then 2 days later a second 100 :g
injection of GnRH. (The original Ovsynch protocol required a 25 mg injection
of PGF versus the 40 mg employed in this trial). Cows were bred 16 to 20 hours
after the last GnRH injection. All cows received their first service insemination
73±3 days post partum. BST injections were begun either on 63±3, 73±3 or 147±3
days postpartum and injections were administered every 14 days until 30 d before
the dry period. Pregnancy was determined 32 days after AI by ultrasonography
and by rectal palpation 74 days after AI.
Table 1 shows pregnancy rates (PR) for all treatment groups for All cows or
Cycling cows. Cows were considered to be cycling if one or both blood samples
collected 51 and 63 d PP had >1.0 ng/mL of plasma progesterone.
The administration of bST during synchronization with Ovsynch did not decrease
pregnancy rates in All cows. However, presynchronization and the administration
of bST improved PR over the Control/bST-treated cows in All cows.
Cycling cows also shows similar trends. Those cows that had been treated with
presynch had greater PR at both 32 and 74 days after AI. Again bST did not
negatively affect PR in Ovsynch-treated cows.
Pregnancy rates in cycling cows were greater when treated with bST than for
Pregnancy loss overall was 14.6% between 32 and 74 days after AI. A trend
(P<0.01) was observed between presynchronized and cows not presynchronized.
Pregnancy loss was less for those cows presynchronized.
Table 1. First service pregnancy rates at 32 and 74 days after timed
AI for all cows and cycling cows (least square means).
|| All Cows
|| Cycling Cows
|| PR (%) 32d after AI
|| PR (%) 74d
|| PR (%) 32d
|| PR (%) 74d
a,bDifferent superscripts within columns of all cows indicate presynch
by bST interaction (P<0.01).
c,dDifferent superscripts within columns of cycling cows indicate
presynch effect (P<0.01).
x,yDifferent superscripts within columns of cycling cows indicate
bST effect (P<0.01).
w,zDifferent superscripts within columns of cycling cows indicate
bST effect (P<0.04).
Moreira, F., C. Orlandi, C.A. Risco, R. Mattos, F. Lopes, and W.W. Thatcher.
2001. Effects of presynchronization and bovine somatotropin on pregnancy rates
to a timed artificial insemination protocol in lactating dairy cattle. J. Dairy