Heifer Management Pre-Joining
With the year quickly slipping by as we approach calving, it is important that we do not ignore our heifers as most producers are only about 3-4 months away from joining. With herd numbers diminished after years of drought and the current positive seasonal outlook, most producers will be looking to build their herd numbers as quickly as possible. As such, it is vital that we manage our heifers carefully to get as many in calf as possible later in the year.
Critical mating weights
The most important factor governing the onset of puberty in heifers is weight rather than age. Therefore, it is vital to ensure that our heifers are provided with adequate nutrition to maintain the necessary growth rates for joining at 15 months of age.
The Critical Mating Weight (CMW) is the heifer weight required at the beginning of joining to achieve an 85% conception rate in a 6 week joining period. To simplify this, as a rule of thumb we work on a CMW of 60% of the mature cow weight of your herd (weight of an average cow in body condition score of 3-3.5/5). E.g. for a herd with an average mature cow weight of 550kg, the CMW for heifers will be 330kg.
It is important to remember that this weight is the minimum weight that you want your heifers to reach prior to mating and as such the average weight should be higher. Ideally, we would like the average weight at joining to be closer to 380-400kg if possible.
The most accurate way to ensure that we are on the right track to reach these weights is by weighing the heifers periodically. This is an ideal point of time to weigh heifers (3-4 months out from joining) which allows us to calculate an average daily weight gain required to meet the desired mating weight. If needed, nutrition can then be adjusted to meet these targets. With the current season, we may even be able to reduce nutritional requirements for the next 1-2 months if the heifers are well ahead of target weights in order to preserve some feed for later in the season. Re-weighing our heifers in 2 months would allow us to ensure that we are still on the right track and allows us to further adjust nutritional intake as required in the lead up to joining.
Remember – we cannot manage what we cannot measure. Weighing the heifers takes the guess work out of the equation and allows us to know exactly what is required and what we are achieving rather than relying on a visual appraisal.
Body Condition Score
Body condition score (BCS) is obviously closely tied in with body weight. At the start of joining we want heifers to be in a minimum of BCS of 3/5 and ideally 3.5/5 or higher. Additionally, in the last 1-2 months leading up to joining, being on a rising plane of nutrition regardless of body weight will help ensure that as many as possible are cycling and ready for the bull.
Trace Element Status
Trace elements are minerals found in the body in very small amounts. There are many different trace elements, some of which are considered essential and some non-essential. Trace elements likely play many differing roles in the normal functioning of the body however our current understanding of many of these roles is limited.
Some of the trace elements considered to be amongst the most important in cattle are copper (Cu), selenium (Se) and cobalt (Co). These three elements have been shown to have a marked effect on the health and fertility of individual animals.
Over the past 12-24 months we have undertaken an increasing number of trace element investigations which have returned a wide variation in results. Several copper and selenium deficiencies have been diagnosed along with Vitamin A & E deficiencies (unlikely to be a problem with the current abundance of green feed). Additionally, in recent years new research has indicated that previously used copper and selenium reference ranges were too low. As such many results obtained in the past that were considered normal would now be considered deficient.
Whilst we may not always know exactly how these elements play their roles in the body, it has been repeatedly demonstrated that deficiencies of copper and selenium especially can have a marked impact on growth and reproductive performance even in animals that are not clinically ill.
Supplementation of these trace elements is available in several forms:
- Injectable (MultiminÓ, CoppernateÓ, etc) – are often the simplest to administer however effects are generally short lived. Can be used to supply a targeted dose for certain time periods such as joining and calving
- Slow release rumen boluses – more difficult to administer however provide a much longer and more reliable duration of action
- Lick blocks & loose licks – whilst easy to provide it is impossible to ensure that all animals are receiving the required amounts
- Pasture top dressing – in cases of confirmed, consistent deficiencies, pasture top dressing with fertilisers often provide the most cost-effective method of supplementation in the long term
There is a considerable cost involved with the long-term use of any of the above methods of supplementation. Therefore, it is recommended that some trace element testing be carried out to determine whether they are necessary prior to embarking on a supplementation program. If trace element levels are shown to be adequate, then that money may be better invested elsewhere.
The importance of internal parasites and the impacts they can have on production have long been recognised in the sheep industry where clinical signs are typically more overt and can often lead to death. In cattle, signs of internal parasite burdens are generally more subtle and tend to involve lost production through reduced weight gains rather than death of individual cases.
Compared with sheep, worm burdens are significant at much lower levels in cattle. Whilst counts of 200 or more eggs per gram (epg) for scour worms and in the thousands for Barbers Pole Worm are considered significant in sheep, any detectable count in cattle is likely to be causing an economically significant reduction in weight gain. This is particularly important in growing cattle such as heifers who we are trying to get to target mating weights.
Previously, limitations with Faecal Egg Counts (FEC) have hampered the ability to accurately detect worm burdens at these low levels thus hindering our ability to properly manage internal parasitism in our cattle herds. With the development of new technology, we can now quickly and accurately detect faecal egg counts as low as 20 eggs per gram. This allows producers to collect a sample, drop it off and receive a result on the same day, allowing them to make informed decisions on whether drenching is required.
In the past month we have had several FECs in weaner cattle above 500 which have likely been causing marked reductions in potential weight gain of our heifers leading up to joining. Post drenching it is also important to perform a follow up FEC to confirm the efficacy of the drench.
Pestivirus, or Bovine Viral Diarrhoea Virus (BVD), is one of the leading causes of lost production within the beef industry. It can cause a wide variety of different diseases which we will not go into in this article.
In relation to heifer breeding and fertility, the greatest concern regarding Pestivirus is as a cause of reduced conception rates and increased embryonic death in females that are infected prior to or during pregnancy. This is of most concern in animals that have not previously been exposed to the virus (are naïve) and as such have not developed any immunity prior to infection. Herds with a high proportion of naïve animals are at risk of significant breakdowns if the virus is introduced at joining time.
In endemically infected herds, relying on exposure of our replacement females as calves or weaners (autovaccination) is an unreliable method of protection as the disease prevalence will wax and wane over time. As such, in some years groups of heifers will reach joining time without being exposed and will be susceptible to a breakdown. Additionally, it has been shown that after natural infection with the virus it can remain in the ovarian tissue for some time which may lead to reduced fertility levels.
Prior to joining, it is recommended to bleed a small sample of heifers and test for previous exposure to Pestivirus. From this we can determine the percentage of naïve animals in the mob. If there are more than 20-30% of animals that are still at risk prior to joining, it would be worthwhile considering a vaccination program.
Most heifers will have had a course of 5 in 1 vaccinations for Clostridial diseases as calves. For heifers prior to joining it is important that they are fully protected from Leptospirosis for both production and human safety reasons. This means TWO doses of either 7 in 1 vaccination or Leptoshield pre-joining are required. If they received 7 in 1 vaccinations as calves, they would only require a single booster to remain protected.
Vibriosis has been implicated in several cases of poor conception rates over the past couple of seasons even in herds with fully vaccinated bulls. As such, some producers are opting to vaccinate their heifers prior to joining as well to provide greater protection against the disease.
It is important to remember that many vaccination protocols require two priming doses four weeks apart before adequate immunity is gained. It is important to start the program at least six weeks prior to the start of joining.
Bull Selection & AI
When joining heifers, especially at 15 months of age, bull selection is a critical consideration. Most producers are aware of importance of birthweights when it comes to selecting heifer bulls to reduce the incidence of calving difficulties. However, if this is the only figure we are focusing on when it comes to choosing the bull, we are often sacrificing other facets such as growth rates, eye muscle area, etc. As such, many of the female progeny from our heifers will end up being culled rather than retained in the breeding herd which can significantly slow our rate of genetic improvement.
The ideal bull to join to our heifers will have good figures for birthweight, ease of calving and gestation length AS WELL AS good growth rates post calving represented by above average 200 & 400 day weights and other carcass traits. Unfortunately, these bulls may be hard to find and are highly sought-after pushing prices above what many can justify paying.
This is where an AI program can be beneficial, gaining access to superior genetics without the outlay for the bull whilst also providing many other benefits (see information on our website coolahvet.com.au > Information > AI in Cattle).
Given the current season and the reduced herd sizes in the area, producers may be tempted to extend the joining period for their heifers to get a few more calves next year. When making this decision it is important to consider some of the flow on effects of a prolonged joining period:
- Reduced selection pressure on fertility
- Longer calving period the following year
- Increased range of age/weights at marking, weaning and point of sale
- Disease issues in calves born later in the year
- Reduced time for 1st calvers to start cycling again before joining
A tight joining period for heifers helps to select for the most fertile individuals and will set them up to remain in the breeding herd for a longer period of time.
One option for those trying to rebuild herd numbers whilst maintaining tight joining and calving periods is to retain a larger number of heifers than usual for joining and let the bull do the classing for you.
If you have any further questions about any of the above topics regarding managing your heifers this year, please do not hesitate to give us a call. If interested, we can organise a visit to examine the heifers, discuss nutritional requirements and collect samples for faecal egg counts and any Pestivirus or trace element testing.