Early Ultrasound Pregnancy Diagnosis

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Early Ultrasound Pregnancy Diagnosis

Postby david » Sun Dec 10, 2006 10:41 pm

Early Ultrasound Pregnancy Diagnosis and Reproductive Efficiency of Dairy Cattle

by

Sarah J. Lien, John R. Wenz, R. Page Dinsmore,
Derek Foster and Franklyn B. Garry
Integrated Livestock Management,
Colorado State University
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The dairy industry suffers significant economic loss due to impaired reproductive efficiency. Failed estrus
detection alone accounts for losses of approximately $300 million per year in the U.S. dairy industry.
Breeding programs have been developed to eliminate the need for heat detection by controlling the timing
of ovulation. Ovsynch and other similar programs, which control the follicular wave, allow for a timed
insemination without the need for heat detection for that particular breeding . However, poor heat detection
following synchronized breeding still result in significant losses if cows are not determined to be open until
pregnancy examination. If these animals are not observed for signs of a return to estrus, and subsequently
not rebred, the potential opportunity cost of those breedings are diminished. It has been estimated that the
cost for every additional day that a cow is open past 100 days in milk is between $2.50-4.00.
The use of portable ultrasound units has made both early pregnancy diagnosis and evaluation of the
reproductive tract of dairy cows more convenient and accurate. Experienced operators can diagnose cows
open as early as 20 days post breeding. Due to the rate of early embryonic death (10-16%) between day 28
to day 56 of pregnancy, cows diagnosed pregnant via ultrasound at an early stage should be scheduled for a
recheck pregnancy exam. This is ideally done at greater than 56 days post-AI, after which time the risk of
fetal loss decreases to 2%. The use of ultrasound to describe ovarian structures has also been shown to be
more reliable than rectal palpation alone allowing practitioners to more accurately determine the stage of
the estrus cycle in non-pregnant animals. This knowledge is useful when synchronizing non-pregnant cows
because it has been shown that there is a significant difference in response, as well as pregnancy rates,
depending on the point of the estrus cycle that Ovsynch is initiated. Accurately determining the
reproductive status of animals earlier in their normal estrus cycle via ultrasound enables veterinarians and
producers to provide beneficial intervention more rapidly. It has also been shown that there is a greater
economic return the earlier non-pregnant animals are identified.
A recent survey of veterinarians estimated that 77% diagnose pregnancy in cows by rectal palpation while
22% also utilize ultrasound. Only 1% of veterinarians that responded used only ultrasound for pregnancy
diagnosis. As portable ultrasound machines continue to become more affordable, the cost benefit and
practical use in dairy cow reproductive management need to be further assessed.
This past June the dairy specialists (Drs Wenz, Dinsmore and Garry) of the ILM at CSU began a study to
compare days open, average times bred, reproductive culling, as well as measures of reproductive
efficiency (PR pregnancy rates, SR service rates, CR conception rates) between cows scanned for
pregnancy by ultrasound 30-36 days post-AI and those examined manually for pregnancy per rectum at 43-
50 days post-AI followed through an entire lactation. It is anticipated the study will be finished early next
year. This study was part of the ILM Food Animal Intern research program in which the interns (Lien and
Foster) take part in clinical research projects pertinent to the livestock industry.
The 348 cows presently enrolled in this study were past their voluntary waiting period and had received
their first postpartum insemination following synchronization of ovulation using both a traditional Presynch
and Ovsynch breeding program. Their days since first breeding were between 30-36 days and they were
paired as closely as possible by parity and predicted 305 milk production. Cows within a pair were then
randomly assigned to the ultrasound treatment group (US) or rectal palpation control group (RP). The
treatment group (US) presently consists of 159 cows (105 multiparous and 54 primiparous) and 189 cows
were enlisted in the rectal palpation control group (RP) (130 multiparous and 59 primiparous).
Animals in the early ultrasound group (US; n=159) were examined via transrectal ultrasound at days 30-36
post-AI using a Sonosite 3-5 MHz sector transducer to determine their pregnancy status. Animals that were
determined to be pregnant based on visualization of uterine fluid, amniotic vesicle, and/or embryo, were
subsequently scheduled for a recheck pregnancy exam at 45+ days post-AI to confirm that diagnosis.
Pregnant cows were then rechecked by palpation alone two more times (days 100+/-5 and 190+/-). Animals
that were found to be open at their initial exam were managed according to their ovarian status. Animals
that had a corpus luteum on either ovary were immediately resynchronized via the Ovsynch program.
Cows that had no evidence of luteal tissue at the time of their initial ultrasound exam, including animals
that were determined to have two inactive ovaries and those with only follicular tissue, were noted and
scheduled to be rechecked by ultrasound the following week during the routine herd check. Cows that
were found to be cystic at the time of pregnancy diagnosis were subsequently treated with GnRH or PGF2
dependent on the presence of luteal tissue. Animals were not reexamined if they were rebred on an
observed heat during the previous week. All subsequent examinations of cows in the treatment group were
performed by ultrasound alone, including the identification of ovarian structures and future pregnancy
exams.
Cows assigned to the rectal palpation group (RP; n=189) were examined 40-46 days post-AI by palpation
alone. Pregnant cows were then rechecked by palpation alone two more times (days 100+/-5 and 190+/-).
Cows that were found to be open were treated in a similar manner as mentioned above for the treatment
cows. All subsequent examinations of control cows were by rectal palpation only, including the
identification of ovarian luteal tissue and future pregnancy exams.
Cows that were enrolled and subsequently not caught during the assigned vet check were removed from the
study. Cows remained in their assigned group for the duration of the study (culling or dryoff).
A decrease in days open between the ultrasound group and the rectal palpation group was expected because
the cows in the ultrasound group would be identified as non-pregnant 7-12 days earlier then rectal
palpation. This early identification along with hormonal intervention would return these animals more
quickly to the breeding herd and subsequent services. The first service conception rate is presumed to be
equivalent between the two treatment groups, and the animals that become pregnant following a single
breeding, therefore have little effect on the results obtained. Animals that are the most important to identify
and continue to provide reproductive management for, and that will have the greatest impact on the average
days open, are those animals that are determined to be open after their initial pregnancy exam. These
animals, characterized as open or bred, are where the biggest potential impact could be made.
This study is still ongoing. Presently, the average days open ranged from 13-19 days and are not
statistically significantly different between the two groups. To date there is also no significant difference in
average times bred between the treatment and control groups. As with average days open, the animals that
will affect these values the most are the cows that require more than one or two breedings to conceive.
These numbers may change as the remaining animals enrolled complete the study.
The largest differences so far pertain to reproductive efficiency (SR, CR, and PR). Service rates by cycle,
as well as overall pregnancy rates between treatment groups in first lactation heifers (US 30%; RP 20%)
were statistically different. Thus, preliminary results indicate that the use of portable ultrasound to view
reproductive tracts of dairy cows coupled with a resynchronization program may lead to an improvement in
reproductive efficiency and subsequent decrease in economic losses.
david
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