The smoke and mirrors of suckler cow fertility

Herd fertility is a key determinant of profitability in suckler beef production.  Few farmers have a clear concept of what herd fertility is, how it should be measured and how their herds measure up.  It is even possible to have poor fertility yet be able to extract some positive aspects from the data – hence the title “smoke and mirrors.”

There are a number of ways to measure fertility in suckler herds and often there may be confusion due to misunderstanding of terms.

Calving interval is the number of days from calf to calf – ideally this should be 365 days.  However, a short average calving interval may be maintained by intense culling resulting in a significantly higher replacement rate.  Therefore calving interval alone is not a completely satisfactory measure of fertility.

Reappearance rate is a measure that takes both calving interval and culling rate into account.  If a cow has a calf in one year, she “reappears” in the herd register when she calves again in the following year.  A time period must be included to make this meaningful and four standard periods have been adopted namely 365 days (one year), 390 days (13 months), 450 days (15 months) and 750 days (two years) (the latter is included as a catch-all for cows that have aborted, produced a stillborn calf etc).  So typical reappearance rates might be 38 percent of cows produce a subsequent calf within 365 days, 57 percent by 390 days, 72 percent by 450 days and 76 percent at 750 days (implying that 24 percent of cows were culled or died and hence never reappear or produce a subsequent calf).

Finally a herd of 104 cows could have an excellent calving interval and reappearance rate but have two cows calving every week of the year probably including one at lunchtime on Christmas Day and one on a significant birthday!  Calving spread is therefore another key measure of fertility.  A 12 week calving period should be more than adequate for all suckler herds.

Many farmers use this figure without considering cows that were culled, cows that did not become pregnant during the bulling season or even bought-in calves.  Many farmers are therefore under the illusion that their cows have at least 0.95 calves per year.  In a herd of 100 cows, if 5 cows are empty at scanning, three calves die at calving and two calves die before weaning, calves weaned per cow per year is only 0.90 at best.  Furthermore, if cows have a calving interval greater than 365 days then they might be calving in each calendar year but the calves will be lighter at weaning time.  A typical progression is shown in Table 1.  

Table 1:  Comparison of the output of two cows with differing calving interval

Assumptions:

Both cows initially calved on 1^st January in year 0.

Calf weighs 45KG at birth, gains 1.0 KG/day on the cow and is sold on 1 October.

Although technically a calf has been produced in every calendar year, the output of weaned calf from cow B is significantly lower every year.  Furthermore, the difficulty of carrying out routine management tasks and the risk of disease spread, particularly pneumonia, when there is a significant range in calf weight/age is increased.  Hence, calves per cow per year is a poor measure of fertility.

Farmers often focus on particular measures of success which may not be very relevant to overall profitability.  These may include price per KG, conformation classification or carcase weight achieved by the “best” calf.  However it is possible to have the best or heaviest animal at a sale and yet have an unprofitable business because there are simply not enough animals sold each year due to infertility and/or calf mortality.  Consider two differing suckler herds each with 100 cows put to the bull annually.  Herd 1 has a calving interval of 365 days respectively and sells 90 beef animals per year with an average sale price of £1000.  The manager of the second herd places more emphasis on conformation than fertility and consistently produces higher “quality” cattle.  The finished animal price required in Herd 2 to match annual output in Herd 1 is shown in Table 2.

Table 2:  Finished animal price required by Herd 2.

To achieve the same output as Herd 1, each beef animal sold from Herd 2 needs to produce 120KG more carcase weight by the same age or achieve a premium of 90p/KG carcase weight.  Some high prices can be impressive but poorer fertility and increased calf mortality can quickly destroy the margins.  Appropriate use of EBVs can combine the benefits of fertility AND superior quality cattle.

In a herd where there are two or three calving seasons or indeed all year round calving, it is easy for a cow to “slip” from one calving pattern to the next (i.e., calving interval more than 365 days) without being noticed.  In a batch calving herd it is much easier to identify cows that have not produced a calf within a fixed time period.  Routine management, vaccinations, grazing management, batch weaning and selling etc are all so much simpler when calves are of a similar age.  It is also easier to hire in labour to help with the peak demands at calving time.

Acheiving batch calving may be a simple process for some and more difficult for others depending on the length of the current calving period and probably more importantly, the willingness to change.  

This will be related to grass growth and availability of labour and facilities.  Identify the period that is best for you and STICK TO IT.

Check when the first and last calves were born in previous years.  It is also useful to calculate how many calves are born in each 3 week period after the start of the desired calving date.  This will indicate how serious the remedial action needs to be.  

Culling 5-10 percent of cows may significantly reduce the calving period and a disproportionate amount of the “hassle.”  Further options include going for two compact periods initially and then only bringing replacements into one of the herds allowing the other to gradually disappear.  On the other hand, cows may be sold in-calf or with a calf at foot and cows with calves bought in (see health risks below).  Additional heifers may be purchased or retained.

On many farms the required number of replacement heifers is selected pre-bulling on the basis of their conformation with little or no consideration given to fertility or EBVs.  These heifers are then AI’d or bulled over a protracted period of time to ensure that these “favourite” heifers become pregnant.  This approach stacks up problems for years to come with lack of milk, poor fertility, calving difficulty and extended calving periods.  At CAFRE, extra heifers are selected based on EBVs of their sires (typically at least top 25 percent of the breed for milk, growth and muscling), date of birth (earlier born are from more fertile mothers), performance on the cow (heavier calves are from more milky cows) and structural soundness.  Synchronisation is employed to minimise labour at AI’ing and calving.  Heifers are only given two opportunities to conceive and calve down two weeks before the main cow herd (that is, just before their second birthday).  Any heifers that have not become pregnant after two services are slaughtered.

At CAFRE heifers have been mated to Aberdeen Angus bulls to calve down at two years of age for a few years.  Veterinary and labour costs to calve heifers and assist calves to suckle are £22.50 higher per heifer when AA bulls with average rather than top 1 percent calving ease EBVs are used.  As a result of this technology investigation only bulls within the top 1 percent of their respective breed for calving ease EBV are now used to mate heifers.

Many farmers appear to have little interest in herd health status until a major incident occurs which costs a significant proportion of their calf crop for at least one year.  “I don’t have a problem,” “It’s just one of those things,” “I’m vaccinating anyway”, “It’s too much hassle,” “It’s too expensive,” “I have a closed herd” are all typical responses.  However, assuming vaccination is covering all risks without testing “sentinel” groups can be an extremely risky policy, especially for BVD.  This is because persistently infected (PI) animals do not respond to vaccination and are virus “factories” which can overwhelm the vaccine in healthy animals due to the sheer numbers of virus excreted.  PI animals may appear to be perfectly healthy and may produce a series of calves which will all be PI as well.  Joining an accredited health scheme or at least performing some routine screening under veterinary advice could pay great dividends.  

All abortions and stillborns must be reported to the relevant authority and all cases of retained placenta, metritis (“whites” or discharges), regular and irregular repeats should be recorded and investigated to determine whether it is an individual animal or a herd issue.  Review your records with your vet after calving and scanning to identify the best course of action for future years.

Although most discussion centres on cow fertility performance, the bull usually warrants more attention than he receives.  Pay attention to EBVs when purchasing – make sure he has the genetics to do what you bought him for!  Don’t implement a sudden change from ad-lib feeding to starvation and over-work and expect a high pregnancy rate.  Pay attention to feet and legs and have any remedial work done well in advance of the mating period.  It is worthwhile noting that a small percentage of bulls are completely infertile but up to 30 percent may be permanently or temporarily sub-fertile so have your vet perform a breeding soundness examination before the bulling period.  Rotate bulls and/or pregnancy diagnose early so that an infertile or sub-fertile bull can be identified early.  Do not borrow or share bulls!

CAFRE Beef and Sheep Development Service staff are now delivering a Fertility Focus programme to farmer groups (with assistance from veterinary practitioners).  Farmers in these groups have access to a full report on herd fertility generated through the APHIS system.  This allows study of the herd situation against the group average and generates discussion on how to remedy particular herd weaknesses.

Dr Norman Weatherup and Willie Warwick, CAFRE Hill Farm Manager, with part of the batch calving suckler herd

CAFRE uses EBVs to benefit from maternal and easy calving traits