So how is your mating going?

So how is your mating going?
By Katrina Roberts, Herd+Plus Veterinarian

Interpreting your Return Interval Analysis (RIA) and Non-Return Rate (NRR) in combination with your three week submission rates, can give you early information about how mating is going.
Reviewing this data as early as possible (during week four of AB) enables you to make changes in order to improve the rest of the mating period (number of bulls, date the bulls go in, AB changes, total mating length) to minimise the impact of any issues during the early mating period.

Firstly you need to find this information. Here’s how:

Interpreting Non-Return Rate (NRR) and Return Interval Analysis (RIA)
If you are a Minda user, you can find the NRR and RIA reports on MINDAPRO under reproductive analyses, or on Mindaweb on the Reproduction tab.
If you are an Insight user you will also be able to find similar reports on the online version of Insight.

Understanding the terminology:
NRR is a proxy for conception rate. The NRR is influenced by a number of factors, and unfortunately you cannot always get excited about a high NRR.

Reasons for a high (>70%) NRR include:
- A high conception rate i.e. lots of cows holding to the first service.
- Poor heat detection of the returns (heat detection fatigue can kick in at around week four of mating so often the returns are not picked up) and/or there is poor recording of the returns.
- An abnormally high number of early embryonic deaths i.e. cows are pregnant initially but then lose the embryo.
- A high occurrence of phantom cows – non-cycling cows have a higher chance of being phantom cows. Cows that are mated and then don’t return despite not being pregnant i.e. they become anoestrous that is they are pretending to be pregnant (hence phantom).

Your herds’ NRR may be 10-20% higher than your actual first service conception rate due to the above factors.
If your AB period is less than four weeks, or your total number of returns is less than 50, the NRR and RIA is not reliable.

Reasons for short returns include:
• First heat since calving i.e. if there is a high percentage of later calving cows in your herd then you will see a higher percentage of short returns.
• Non-cycling cows - return intervals following a non-cycling programme can be more variable than in cycling cows, therefore if a high percentage of non-cyclers were treated, this will influence the spread of return lengths.
• Enthusiastic heat detection - often cows will partially join with the sexually active group (SAG) a few days before their true heat, which is due to the high concentrations of oestrogen being secreted from the dominant follicle. These cows will exhibit a normal heat when the follicle actually ovulates. Therefore having some of these is normal, and having no short returns suggests that the heat detection is perhaps missing heats.
• Unsure heat detection – if the heat detector is unsure of the true signs of cows being on heat then the RIA pattern is erratic i.e. almost equal numbers of short, normal and long returns.

The RIA is very useful for understanding the heat detection accuracy in your herd. The graph below shows the percentage of returns by interval.

This graph shape will change as the number of returns recorded increases, as mating progresses i.e. there will be fewer long returns, if the report is generated at week four of mating compared to week seven.
The key features of the graph are the peak of returns falling within the ‘normal range’, which is 18-24d, with a smaller peak occurring around 2-7d or 8-12d. A small percentage (target <13%) of short returns are normal.
If you have any questions regarding interpretation of these reports speak to one of our InCalf-trained vets.

Date Added: Tuesday, 3rd November 2015