Oestrous Sychronization 

           By      

Dr Dan Ryan, Reprodoc Limited, Cullenagh,Fermoy, Co Cork

 

Poor oestrus detection rate is a primary cause of extend calving to pregnancy interval. Failure to detect oestrus in cattle at an opportune time negates the cost efficient 365 day calving interval. The latter is associated with calving difficulty, restricted or imbalanced diets, multiple births and suckling effect.

In a situation where visual heat detection is used, one would require 5 x 20 minute periods during the day to detect 90% of heats in fit cows. We use the term fit cows because the cows that are debilitated due to lameness, poor nutrition, calving difficulties or metabolic diseases, will be slower to resume normal ovarian activity post calving.

Farmers will not spend this period of time on a daily basis watching cows for signs of heat; therefore tail paint applied to the tail head was introduced as a simple aid in heat detection. This reduces the number of observation periods from 5 down to 3 to achieve a 90% heat detection rate. Daily observation immediately prior to am milking, 3 to 4 hours after the am milking and 3 hours after the evening milking will detect 90% of heats. However, from various survey data, heat detection or submission rates are still the order of 60 to 70%. This apparently results in an increase to calving to pregnancy interval.

The failure to detect heat at an opportune time in fit cows can be conservatively costed at 100 Euros per cow per heat missed. Therefore, it is cost efficient to consider the use of oestrous synchronization when heat detection rates are below the target set.

The objective of oestrous synchronization is to induce oestrus at a fixed period of time in cows fit for AI. The opportunity of detecting oestrus is increased because of the narrow observation period required to detect heats and with an increased number of animals available in that window, it should be easier to detect heats. Individuals become concerned when we use the term oestrous synchronization that we are referring to a system whereby a complete herd is induced into oestrus on a given day of the week. In practical terms, this situation will not arise. We suggest the use of oestrous synchronization where detection of heat in a given group of animals is not feasible or because of management restrictions on time.

In our evaluation of various oestrous synchronization programmes we would suggest the following options:

1. The Rolls Royce regimen to detect oestrus over a short period of time involves intravaginal insertion of progesterone releasing device prid or cidr on a Monday. Instantaneously, administer a gonadotropin releasing hormone (Receptal, Fertagyl) by intramuscular injection. This will remove the dominant follicle and cause induced ovulation or Luteinization of the dominant follicle if present on the ovary. Seven days later, administer prostaglandin by intramuscular injection. On the following day (day 8 from time of onset of treatment) remove the intravaginal device. Animals will show oestrus between 36 and 72 hours later this program will result in excess of 90% heat detection rate. For a complete review of Synchronization programmes, please refer to the experimental work completed and published by Dr. Daniel Ryan (Ryan et al, 1994) or 1995 in J. Animal Science.

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2. An alternative procedure which is used, in particular, for maiden heifers is an observation period beginning on a Monday through to the following Monday, whereby animals detected in heat are AI’d and on the 7th day, the animals not detected in heat are administered a prostglandan. This will result in the remaining animals synchronized in heat between day 7 and 11. This procedure works very effectively in maiden heifers which are close to the main farm centre. However, because of the level of land fragmentation in Ireland, our experience shows us that a lot of heats are missed when heifers are observed for heat detection on land remote to the farm centre. The best approach in this situation would be the use of synchronization involving the intravaginal insertion of a progesterone device and the prostaglandin treatment as described previously.

 

3. In the dairy herd, our experience shows a far better approach in terms of heat detection, is the use of prebreed assessment using ultrasonography of the reproductive tract. In this situation, we can set targets for the clients for cows that are identified at various stages of the oestrous cycle and an action plan for those cows not detected in heat. In practice, therefore, a client can achieve close to 100% submission rate of fit cows. It is more important to identify the reasons why cows are not fir for AI. Oestrous synchronization in unfit cows results in very low pregnancy rates, a monetary loss from the cost of synchronization and an extension in the calving to pregnancy interval.

 

In conclusion, poor oestrous detection rates increase the calving to pregnancy interval. Oestrous synchronization is a cost-efficient approach to increase submission rates where management has not the time to observe cows. Cows need to be fit for oestrous synchronization programmes and only delays the identification of underlying stressors in the herd. Prebreed reproductive assessment enables a high submission rate in fit cows and early identification of underlying stressors impairing fertility.