Reproduction, hormonal treatments and artificial insemination
Updated: Apr 11
I had the opportunity to attend one of the three days of the Dairy Cattle Veterinary Conference in Queenstown June 2019.
There were so many interesting and informative talks so I have attempted to best summarise a handful of the talks over a couple of research summaries.
Part One was about mastitis, Part Two is all about reproduction! With 4 papers summarised below.
As these talks are very heavy on abbreviations, here is a handy cheat table.
Attitudes and beliefs of farmers and veterinarians in relation to hormonal treatment for noncycling cows
Presenter: Emma Cuttance
For most NZ dairy farms, the hormonal treatment of non-cycling cattle is expected to have a positive return on investment. This treatment has been demonstrated to reduce the time to conception and increase days in milk.
Despite this information being available for nearly a decade there are still:
A substantial proportion of farms that do not use any non-cycling treatment
Large variability in the timing of use of reproductive interventions among vets and among farmers.
This is the first NZ study that has attempted to understand the clinical and ethical beliefs around reproductive interventions by farmers and vets using online surveys.
40% of those surveyed never use hormonal treatments for non-cycling cows.
The most common reason for not using hormonal treatments was that it is “not natural and perpetuated poor fertility in the herd” - This point is very interesting and I will do some reading up on it for a future post.
The second most common reason was that they did not feel they needed them as they were happy with their current performance - a fair point!
Of those 60% (263 herds) that do use hormonal treatments of non-cycling cows:
60.5% use it before Mating Start Date (MSD) and
39.5% of herds use hormonal treatment after MSD.
When asked for a reason to not start hormonal treatments until after MSD; the most common response was that they "wanted to give their cows a chance to do it themselves first".
In terms of where farmers are sourcing their information about hormonal treatments for non-cycling cows from; vets were the most utilised source for information, with journal articles being the least utilised - there was no mention of online summaries though!
In summary, many farmers felt that hormonal treatment of non-cycling cows is unnatural and allows for the retention of inferior fertility genetics the herd. A proportion also felt that hormonal intervention is ineffective or unprofitable. These are topics that will most definitely be addressed in a future summary post.
Effect of a second treatment of Prostaglandin F2α (PG) during the Ovsynch program on fixed-time artificial insemination conception rates in split calving, pasture-fed dairy cows
Presenter: Johanna Rheinberger
This study compared fixed time artificial insemination (FTAI) conception rates and progesterone (P4) concentrations for dairy cows treated with the original Ovsynch program (single PG) vs cows receiving a modification of the Ovsynch program (double PG) that involved a second injection of prostaglandin F2α (PG). This study was completed in Australia (Victoria).
The single PG group received the original Ovsynch program:
Day 0 GnRH,
Day 7 PG,
Day 9 GnRH, and
Day 10 FTAI, approximately 13 to 16 hours after the second GnRH injection.
The double PG group received the same Ovsynch program with an additional PG injection on Day 8.
A second injection of PG 24 hours after the first PG injection of the Ovsynch program is designed to provide a second opportunity for the regression of the corpus luteum (CL) in order to stimulate ovulation in cows that had a poor response to the first injection.
Overall, there was a 7% difference in conception rates (CR) between the two groups.
The double PG group had a 49% CR compared with a 42% CR for the single PG programme.
More cows in the single PG group (51% vs 37%) had a P4 concentration at fixed-time AI that indicated that the CL had not fully regressed yet. This meant that more cows in the double PG programme had responded to the PG compared with the single PG group.
Although these are positive results, there needs to be some economic analyses to determine the cost-benefit of the double PG program before considering this programme for a herd.
If you are enjoying this summary, you may like one of these:
Increasing conception rate by addition of a second prostaglandin in an Ovsynch and progesterone non-cycler treatment programme
Presenter: Scott McDougall
This next presentation is similar to the previous presentation, however, includes:
the use of progesterone (P4) administered in CIDRs
only included non-cycling cows
based in NZ.
Between 10% and 15% of cows don't respond properly to one injection of prostaglandin F2α (PG) during synchrony programmes. As mentioned before, 2 injections of PG can be better than 1 injection to stimulate ovulation.
The first group (single PG+P4) received the Ovsynch+P4 program:
Day 0 GnRH + P4 device,
Day 7 PG + P4 removal
Day 9 GnRH, and
Day 10 FTAI, approximately 12 to 24 hours after the second GnRH injection.
The second group (double PG+P4) received the same Ovsynch+P4 program with an additional PG injection on Day 8.
After the FTAI, cows were bred by AI when detected in oestrus for 4-6 weeks followed by the introduction of bulls for 6-8 weeks.
As seen in the figure below, double PG+P4 treatment (blue bars) increased first service conception rate, three-week in-calf rate, and six-week in-calf rate compared with single PG+P4 treatment.
However, there was no difference in final pregnancy rates 84.4% vs 85.6%.
The authors simulated the expected net return for a 500-cow herd using the double PG+P4 treatment and found that it resulted in an economically positive outcome 8 times out of 10.
The average return was $1,719, but it ranged from -$3,158 to $19,271.
To summarise, using a double PG+P4 resulted in positive outcomes in terms of conception rate and 3 and 6-week pregnancy rates compared with a single PG. It was simulated that for the majority of cases it would also result in a positive return on investment.
Mating heifers without bulls in an extensive grazing system: a case study
Presenters: Kristen Baxter, Luke Smyth
This last presentation was a case study and not an experiment. This means that it was an observation style study, as in "we mated heifers with only AI... and this is what happened" whereas, an experimental style study would be "we compared all AI of heifers with using all bulls and we found that one was better than the other...".
The reason for doing case studies is to provide information of what might happen when there is not much research available on the topic.
The case study presented was of a farm of 140 replacement heifers where the farmer was interested in doing only AI of their heifers out of fear of introducing M. bovis to their herd from bulls purchased off-farm.
This table below provides a nice description of the synchrony and re-synchrony methods. It started with a GPG+CIDR programme before MSD (day 0 in table).
There were 3 rounds of AI:
Round 1: at MSD,
Round 2: days 22-26 and,
Round 3: days 43-46
A very important step in this re-synchrony programme was to pregnancy test all heifers 35 days after the fixed-time AI. This was for a few reasons; 1) to provide an out if it was going badly! and 2) to treat the non-pregnant heifers appropriately for round 3 of AI.
Following the pregnancy test, heifers could be grouped into 3 categories:
Group A: heifers the were pregnant to FTAI
Group B: Heifers not pregnant but were mated in round 2
Group C: Heifers not pregnant and not mated in round 2
As illustrated in the above table, Groups B and C were treated either with a CIDR or with another round of GPG+CIDR.
The round 1 conception rate (CR) was 64% (86 pregnant heifers), the round 2 CR was 52% (23 pregnant heifers) and the round 3 CR was 67% (14 heifers).
The higher CR in round 3 is due to having such small numbers of heifers by this point.
The final pregnancy rate at the end of the programme was 91%, so a 9% not-in-calf rate.
Below is a graph of the cumulative pregnancy rate for the heifers (blue) compared with the industry target (red).
As can be seen in the figure, this programme resulted in a very condensed calving of only 46 days, additionally, there would be more high value AI heifer calves produced compared with using only bulls.
However, this programme required a very high level of organisation from all involved (farmer, vet, and grazier).
The authors would not recommended this for farmers with poorly grown heifers or poor facilities for yarding/AI. Additionally, if the CR to each service was only 50%, then there would be a much higher not-in-calf rate. This is a large risk if the not-in-calf rate is higher than usual.
Their suggestion would be to only use this system with prior experience with synchrony programmes and are able to deal with a potentially higher than normal not-in-calf rate in their heifers.
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Effect of a second treatment of Prostaglandin F2α during the Ovsynch program on fixed-time artificial insemination conception rates in split calving, pasture-fed dairy cows - JM Rheinberger, DD Colson, DS Beggs, PD Mansell, MA Stevenson, RJ Rheinberger, MF Pyman