Every veterinarian who conducts regular reproductive visits on a dairy farm needs certain tools in their toolbox to assess the fertility status of the farm they visit. Also, the possibility for feedback on reproductive performance varies enormously per farm.
The relationship between the veterinarian and the farmer is key to the ability to discuss figures and indices in a productive way. There is a lot of variation in how records are kept; some farmers only keep paper records, while others have a sophisticated software management programme that comes out with all sorts of numbers and calculations.
Interpretation of indices
The first step of assessing reproductive data is to be aware of each index’s definition. It is important to realise that definitions vary depending on the country, company, software programme and even personal preference.
Nevertheless, software programmes are a must when analysing large amounts of data quickly, especially for larger herds where the number of animals and, therefore, the amount of data (eg service numbers, service dates and pregnancy tests) increases rapidly over time. There are quite a few software programmes on the market, and many of these calculate the same indices slightly differently, which means figures can vary significantly between programmes. It is important to be aware of these as data can easily be interpreted differently, which changes the figures significantly.
Software programmes are a must when analysing large amounts of data quickly, especially for larger herds where the number of animals and, therefore, the amount of data increases rapidly over time
For a proper assessment, the first hurdle is the assessment of the farm data that has been entered. Is there enough available data, is all the data entered and was it entered fairly accurately and correctly? Secondly, are barren cows included in the calculations? Thirdly, what voluntary waiting period (VWP) is used and does the VWP in the software match up with this? The final two factors that cause the most differences between the values of indices between software programmes are the definition of an index and the eligibility of a cow for a specific index. For example, some programmes include more animals (or for a longer period) than others.
To overcome these variations, it is advised to extract and analyse the data in the software that is catered specifically for veterinarians. By analysing data consistently in the same programme, it is easier and more reliable to compare indices. Independently of the programme used, the quality of the data needs to be assessed before and during analysis.
It might be difficult to believe, but farms with only paper records and limited computer records still exist! If the herd does not have any kind of electronic recording system in place, then it is recommended to enter calving and service dates into a software programme or spreadsheet. If the resources for this are unavailable, then counting pregnant, open and serviced cows can give an indication of the herd’s fertility performance.
If the farmer does not carry out regular pregnancy diagnoses and has only one bull running with the herd, the only index that can be of use is the non-return rate
When interpreting these figures, take into consideration if there are variations in calving patterns (all-year-round calving versus block calving) and how long, on average, open cows are in milk before breeding starts.
If the farmer does not carry out regular pregnancy diagnoses and has only bulls running with the herd, the only index that can be of use is the non-return rate. The non-return rate is the number of cows not seen bulling after a service compared to the number of cows coming in oestrus after a service. This rate is only of use if cows show oestrus clearly and heats are detected and written down. Keep in mind that the non-return rate is often much better than the actual pregnancy rate.
It is important to realise that some indices consider the aspect of time more than others. For a proper assessment, it is important to include performance over a set period, as one week or month can look very different from another.
For most herds, the most useful indices to assess are the 21-day heat detection and 21-day pregnancy rates. Most eligible cows should come in oestrus within 21 days, so the number of animals picked up and serviced compared to the number of eligible cows gives a good indication of heat detection and how well the cows are holding to being bred. These two indices can be used in block-calving herds and all-year-round breeding herds.
It is essential to keep an eye on eligible cow numbers, as rates can look much more favourable with fewer eligible cows.
Oestrus detection can also be assessed in comparison to the cow’s cycle: consider, for example, how many cows have been serviced within the first 80 days in milk. However, this index only works for all-year-round calving herds and often not so much for herds with fixed dates when breeding starts and ends.
Calving to first service and calving to conception intervals can be useful but, again, are often less so in well-managed block-calving herds. Assessing the number of services for each conception and each cow bred (the first index only includes pregnant cows, while the second also includes those not pregnant) are indices that give a good handle on how long it takes for a cow to get pregnant. A large discrepancy between these two figures indicates failure of conception.
For all farming systems, inter-service intervals are a good way to assess the farm’s ability to detect heat. Most repeats (four to six times as many as in the next regular repeat) should take place 18 to 24 days after the first service. An increased percentage in the next regular interval (36 to 48 days) tends to mean that heats are missed. Large amounts of irregular repeats (more than 5 to 10 percent for one interval) need further investigation (Cockcroft, 2015).
It can be useful to assess the calving interval, but be aware that it is a historic figure. It calculates the interval between the last and previous calving, which means it is not up to date. Also, cows that did not achieve a pregnancy are not included.
The accuracy and historic nature of the 21-day pregnancy rate depend on how often the cows are checked for pregnancy and when the data was entered. Bear in mind that a resorption rate of 10 percent is not considered abnormal for up to 42 days in cattle (Thatcher et al., 1993). This means early pregnancy checks (before 42 days) will generate better results than when it is compared to the actual number of cows calving after a full gestation period.
The number of conceptions over a particular time frame is a useful index to assess how well individuals in the herd hold to a service. It is essential to split this index into smaller groups, as it can highlight the strengths and weaknesses of certain groups. Conception rates per parity and bull in a three-month period are fantastic examples of how you might split this index up. Again, always check the number of animals included in the calculation.
If the veterinarian uses hormonal treatments for oestrus synchronisation on-farm, it is essential to assess how good the conception rates are for these treatments compared to normal oestrus detection. When the data derives from a programme, you should investigate how the figures are generated to form an accurate interpretation (for example, sometimes conception rates to a synchronisation are derived from all services of a synchronised cow, not just the synchronised service).
Cost–benefit analyses of the different protocols used after a breeding period are an essential part of assessing the veterinarians’ added value
In many cases, synchronised cows do not conceive as well as cows bred to their naturally occurring heat. Nevertheless, higher submission rates can compensate for lower conception rates. Cost–benefit analyses of the different protocols used after a breeding period are an essential part of assessing the veterinarians’ added value.
With the help of historic information, textbook standards and regional differences, a critical and fair assessment of the current performance can be conducted
There are three ways of comparing and setting targets:
- The first is a comparison of “gold-standard” or “textbook” targets for a specific management system
- The second is to look at national or regional averages. While farmers tend to appreciate how well their neighbours perform, textbook targets can be daunting or un-motivational to some of the best farmers around
- A more sympathetic and constructive way of setting targets is the third option: analysing the farm’s performance over several years and comparing this to the most up-to-date figures
Subsequently, with the help of historic information, textbook standards and regional differences, a critical and fair assessment of the current performance can be conducted. By identifying where the weakest and strongest areas are, improvements to weaker areas can be suggested. It is essential that the new targets are achievable and measurable, and all parties need to agree on the changes in management suggested.
It is important to recognise that the usefulness of feedback sessions is dependent not only on the amount of data and figures available but more so on the ability of the veterinarian to analyse the data and the willingness of the farmer and the veterinarian to sit down together and discuss reproductive performance constructively.
|Voluntary waiting period|
|21-day heat detection rate|
|Percentage of cows served in the first 80 days in milk|
|Calving to first service interval (days)|
|Calving to conception interval (days)|
|Number of services per conception|
|Number of services per cow|
|21-day pregnancy rate|