Timed Artificial Insemination in Dairy Heifers29 April 2014
One delayed heifer pregnancy can cost you over two dollars a day in raising cost, which is why timed insemination should be considered to achieve pregnancy at the desired age, say Professor Jose Santos and Dr Fabio Lima, University of Florida.
Timed artificial insemination (AI) is a technology developed in the early and mid-90’s that allowed performing insemination at fixed time without the need of estrous detection, write Dr Lima and Professor Santos.
One of the first programmes of timed AI reported to successfully synchronize ovulation and result in acceptable pregnancy per insemination was named Ovsynch.
Four Steps to Synchronize Ovulation
This pioneer programme consists of 4 key steps.
- First a dose of gonadotropin-releasing hormone (GnRH) is administered to induce ovulation and synchronize follicle growth in the ovary of cows and heifers.
- Second, an injection of prostaglandin (PG) F2α is administered 7 days after the GnRH to regress the corpus luteum (CL) that might have been present in one of the ovaries when the programme started or the newly formed CL after induction of ovulation with GnRH.
- The third step is a final dose of GnRH administered 56 hours after the PGF2α to induce a synchronized ovulation.
- Finally, cows are inseminated 12 to 16 hours later regardless of signs of estrus.
Ovsynch and other deriving programmes soon become very popular and widely used by dairy producers on lactating cows to mitigate problems with low estrous expression and detection, which ultimately reduce reproductive performance of the herd.
On the other hand, the use of timed AI for management of reproduction in dairy heifers is generally very low compared with that of lactating dairy cows based on surveys by the National Animal Health Monitoring System.
The first studies that investigated the use of timed AI in dairy heifers used the Ovsynch protocol or deriving programmes based on GnRH and PGF2α.
These studies failed to result in pregnancy per insemination that resembles those obtained when heifers were inseminated following detected estrus (Table 1). Furthermore, the higher pregnancy per insemination observed in dairy heifers than in lactating cows typically leads to the perception that heifers would not benefit from programmes that synchronize ovulation.
In general, the goal of timed AI programmes have been to result in pregnancy per insemination similar to that obtained when cows are inseminated following detected estrus, but to allow an increased proportion of eligible cows to be bred at the desired time.
Until recently, the same could not be suggested for management of reproduction in dairy heifers. The low fertility resulting from the standard Ovsynch programme never made insemination at fixed time attractive for dairy producers.
However, when fertility to timed AI is high, there are situations in which incorporation of insemination at fixed time might be advantageous to manage reproduction in heifers.
Recent studies conducted at the University of Florida investigated a new programme aiming to adequate the manipulation of the estrous cycle to the needs of dairy heifers. The initial work resulted in pregnancy per insemination for first and second services ranging from 52.2 per cent to 61 per cent. These values are compatible with results reported for AI at detected estrus in dairy heifers.
Optimization of Timed AI Programme for Dairy Heifers
Dairy heifers have important ovarian and endocrine differences during the estrous cycle compared with lactating cows that influence how they respond to the hormonal manipulations to synchronize ovulation for fixed time insemination.
Therefore, it is no surprise that use of the standard timed AI programmes such as Ovsynch resulted in low pregnancy per insemination and discouraged producers and veterinarians from implementing such technologies (Table 1).
Because of the low success with Ovsynch in heifers, it was clear that changes in the programme had to be made to accommodate the distinct ovarian and endocrine aspects of dairy heifers. Work at the University of Florida first demonstrated that it was possible to inseminate dairy heifers at fixed time and achieve pregnancy per AI above 50 per cent.
In fact, more recent research with heifers at first AI demonstrated that the sequence of hormonal treatments described in Figure 1 resulted in pregnancy per AI above 58 per cent.
Why Inseminate Heifers Using Timed AI?
Many producers still think that application of reproductive technologies is not needed for management of reproduction in dairy heifers.
In many cases, the high pregnancy per insemination observed in heifers detracts producers and veterinarians to consider that one of the goals of heifer breeding is to achieve pregnancy at a desired age such that cost of raising heifers and future lactation performance are optimized.
Delaying pregnancy in heifers results in $2.00 to $2.50/day of additional raising cost with current feed prices ($0.08 to $0.09/lb of heifer ration dry matter).
One advantage of implementing timed insemination programmes in heifers is the ability to breed 100 per cent of the animals on the day they are introduced to the breeding group.
A recent survey of large dairy herds in the Western states in the US revealed that most dairy farms have pregnancy rates in heifers below 30 per cent. This means that for every 3 weeks, less than 30 per cent of the eligible heifers become pregnant on a farm. This is critical in farms where insemination rates are low.
Simulations by our group suggested that timed insemination would be economically attractive for management of first breeding in heifers when the detection of estrus in dairy farms is below 70 per cent, which seems to be the case of many farms.
Despite the costs associated with treatments and labor, implementation of these programmes can result in $10 to $20 reduction in cost per pregnancy in heifers. Producers should evaluate and discuss with their veterinarians and consultants the reproductive programme and consider changes if heifers are not becoming pregnant at the desired age.