The American Dairy Science Association (ADSA) and the American Society of Animal Science (ASAS) organized their 2016 joint annual meeting this past July in Salt Lake City, Utah.
Passionate dairy science students and researchers, along with dairy industry personnel discussed what’s new and relevant on the experiments and best practices involving livestock production during this five-day event. These are some of the highlights of this important conference.
Management advances on dairy cattle reproduction in the past decade
Dr. Jeffrey Stevenson from Kansas State University gave an outstanding presentation on “Physiological and Management Advances on Applied Reproductive Procedures in Dairy Cattle.”
On this topic, he covered key advances applied in the field of reproduction since the first Dairy Cattle Reproduction Council (DCRC) meeting in 2006, in which many of these were refinement strategies to achieve better results than what was obtained with the standard seven-day Ovsynch program developed 20 years ago. Methods of pre-synchronization and the role of progesterone concentration during timed A.I. (TAI) were also discussed.
A protocol largely used to pre-synchronize cows for first A.I. after they are past their voluntary waiting period (VWP) is based on two prostaglandins injections, usually 14 days apart, then followed by an Ovsynch protocol (known as Presynch-Ovsynch).
Cows are stimulated to come into estrus, and some people would take advantage of that behavior and perform A.I. (known as “cherry-picking”) on those animals, letting cows that did not display estrus complete the Ovsynch protocol. These cows that are inseminated on this “backup Ovsynch” normally are not cyclic animals, and are presented to the protocol with low progesterone concentration due to an absence of a corpus luteum.
They have their conception risk performance impaired in comparison to cows that have medium levels of progesterone at this same time (beginning of the Ovsynch).
To solve this issue, in the past few years, injections of gonadotropin-releasing hormone (GnRH) have been incorporated into the program to pre-synchronize cows for first A.I. (i.e., Double Ovsynch and G6G). With this strategy, cows would get to the start of the Ovsynch protocol with a corpus luteum, therefore presenting medium to high progesterone concentrations.
Combining results from different studies, he concluded cows that are pre-synchronized with a protocol that includes GnRH on its design, have a weighted average of 5 percentage points higher on pregnancies per A.I. compared to cows that are pre-synchronized using only prostaglandin F-2 alpha (PGF).
Nonetheless, it is also important to highlight that protocols for pre-synchronization using GnRH injections would “force” cows to ovulate a follicle greater than 10 mm on their ovaries, decreasing the possibility of these cows to display estrus; therefore more cows would complete the timed-A.I. protocol instead of being inseminated after estrus.
Reproductive performance and economic outcome for different durations of the voluntary waiting period
Dr. Julio Giordano and his Ph.D. student, Matias Stangaferro from Cornell University, discussed the reproductive performance of cows submitted to different lengths of the VWP. The objective of their study was to evaluate the impact of three different strategies to manage first A.I., including different hormonal treatments and duration of the VWP.
Cows were submitted to a standard Presynch-Ovsynch (PO) protocol, VWP of 50 days in milk (DIM) and A.I. after estrus expression (cows that did not show estrus received timed A.I. at 75 DIM), Double Ovsynch (DO) with the end of the VWP and 100 percent timed A.I. for cows at 60 DIM (called “short” VWP, DO-short) and Double Ovsynch ending at 88 DIM (called “long” VWP, DO-long).
There were no differences in pregnancies per A.I. for first service among these three strategies, with 38 percent for Presynch-Ovsynch, 41 percent for DO-short and 44 percent for DO-long. Even though there was a normal difference in pregnancy per A.I. between first-lactation animals (primiparous) and older cows (multimaparous), this difference was not presented among the three different treatments.
Also, there were no differences on mean and median days to conception between the lactation groups, but on the multiparous cows, the percentage of cows not pregnant at 350 DIM tended to be higher for cows with DO-long compared to DO-short and PO. Lactation length was shorter for PO and DO-short compared to DO-long, but also the percentage of multiparous animals sold was higher for DO-long (44 percent) compared to PO (36 percent) and DO-short (33 percent).
Cows with shorter VWP (DO-short and PO) became pregnant earlier during lactation than cows with longer VWP (DO-long). Despite differences in reproductive performance and individual factors that affect profitability, there were no differences in profitability during the experimental lactation or an 18-month period after calving.
Addition of a PGF injection within the standard Ovsynch protocol
One of the hot topics being discussed these days is the addition of a PGF injection within the standard Ovsynch protocol (GnRH – 7d – PGF – 56h – GnRH – 16h – TAI) 24 hours after the first PGF injection (GnRH – 7d – PGF – 24h – PGF – 32h – GnRH – 16h – TAI).
In an attempt to answer this question, Dr. Paul Fricke at the University of Wisconsin – Madison performed a trial with 1,438 lactating dairy cows receiving second and subsequent timed A.I. (resynchs), and the results on their reproductive performance in pregnancies per A.I. are as follows: Cows with the second PGF injection tended to have more pregnancies per A.I. (37 percent) than cows with the standard Ovsynch protocol for resynchronization (33 percent).
Pregnancy loss was not different among these two strategies, with an average of 8 percent between pregnancy diagnosis on day 38 after timed A.I. and reconfirmation at day 66.
Another question that usually comes along when an additional PGF is discussed is if there would be a difference in reproductive performance if a double dose of PGF is given on the normal schedule (GnRH – 7d – 2xPGF – 56h – GnRH – 16h – TAI).
This question was also addressed by Fricke and his lab, and no difference in pregnancies per A.I., nor in pregnancy loss, were found when a double dose of PGF was given in comparison to a standard protocol with a single dose (34 percent versus 33 percent, respectively). PD
Gláucio Lopes is a veterinarian graduated from Brazil and received his master’s degree in dairy cow reproduction at the University of Wisconsin – Madison.
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Glaucio Lopes
- Alta University Manager
- Alta Genetics
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