How long to leave the bulls in for??

Options for joining periods in the face of drought conditions & using early pregnancy diagnosis more effectively as a management tool…

NB: this article is primarily focused on joining cows rather than heifers.

Most producers will be getting towards the end of their Spring joining period and will be weighing up how long to leave the bulls in with the cows (if they haven’t already taken them out). This decision will be affected by a number of variables including:

1. Cow condition – one of the major factors regarding fertility and conception rates is always going to be condition score of the females. From our observations, most producers have managed to maintain reasonable to good condition on their cows in spite of the current conditions (through a combination of decreased stock numbers, improved supplementary feeding, early weaning last year, etc).

If cows are in good condition and not going backwards, there is no reason that they shouldn’t be cycling and able to conceive within your normal joining period. It is important to consider the ramifications of extending your joining period, especially if you have spent years trying to reduce it – it is much harder to get those late calvers back into a tight window.

If you have been unable to maintain reasonable condition on your cows, an extended joining period may be an option to consider to maximise number of cows in calf. In these cases we would strongly recommend early pregnancy diagnosis and identification of those later calvers to give ourselves options down the track (see below for further discussion of this).

2. Feed availability/desired numbers – in herds already greatly reduced in number over the past 2 years, some producers may be keen to hold onto as many cows as possible. This may be reason to extend the joining period but again we would recommend early preg testing to ID any outside of the normal joining.

On the flip side, many producers may be looking to further reduce herd numbers with no positive outlooks in sight. This is an opportunity to at least create one positive from a terrible situation and tighten the joining period – creating more cows to offload. One way we can do this is to leave bulls the bulls in and preg-test early to detect only the first ‘x’ weeks of conceptions (i.e. preg-test at 11 weeks post bulls going in to detect the first 6-7 weeks of conceptions). See more on preg-testing options below.

3. Market prices – this ties in with the above points and may influence whether producers are tempted to sell further cows or hold onto them in the hope of getting another calf.

A couple of key points that we would like to draw to attention are:

• Impacts of an extended joining period – whilst chasing numbers of cows in calf, it is easy to lose sight of the flow on impacts of an increased joining period which include:
  • Reduced selection pressure on fertility – retaining less fertile cows in the herd as well as their female offspring may lead to a reduction in the genetic fertility of your herd over time
  • Longer calving period the following year – means an increase in labour costs required to monitor calving cows and heifers as well as health impacts on calves (later calves are exposed to more pathogens that have built up during the calving period such as salmonella/E coli/etc)
  • Increased range of age/weights at weaning – weaning (especially in early-weaning programs) is one of the key benefits of a tight joining period. Weight at weaning is a critical factor in the likely success of an early weaning program and an extended joining period will result in a large weight range across the calves meaning either many will be underweight if blanket weaned or calves will need to be weaned in batches
  • Increased weight range at point of sale – calves born earlier in the joining period will be older and heavier than calves born later = more $$ at sale time
  • Disease issues – with calving periods running later in the year into late Spring scours, pinkeye and other issues may become more prevalent.

• Impact of early weaning – if weaning calves during the joining period, it is worthwhile to leave the bulls in for at least 3 weeks after weaning as most of these cows that were not already cycling will cycle in 2-3 weeks.

I have opted to extend my joining period – how can I best manage this??

Once all aspects have been considered and an extended joining period has been decided on, a couple of options available to manage these cows going forward include…

1. Use an extended joining period as a risk mitigation tool only:

This is a good option for those producers who would prefer to maintain their current (or shorter) joining period but are concerned by how their cows may join. What we mean by this is to keep the bulls in with the cows for an extended period however preg-test early enough that we will only be detecting what has conceived in your desired window. I.e. if you are aiming for a 9 week joining then leave the bulls in and we would recommend preg-testing at 13-14 weeks POST BULLS GOING IN – that way we would only identify the first 9 weeks of conceptions (detectable from 4-5 weeks of gestation). If results are acceptable those that are not detectably pregnant (NDP) can be sold. If results are lower than expected, we can come back at a later date and re-test those initial NDPs to get a few more pregnant animals to hold onto.

The other way we can achieve this is to preg-test a little later and make a split in the foetal ages to identify those that are in the ideal joining period and those that are later and make the same decisions as above. I.e. if aiming for a 9 week joining, leave the bulls in and preg-test 16-17 weeks POST BULLS IN and split the pregnancies before (earlies) and after (lates) 7-8 weeks of age. The advantage of this method is that a second visit is not required to re-test the empties, HOWEVER the results will not be as accurate as the above method with some overlap in the ageing.

2. Identify later calvers:

If opting to extend your joining period, identifying those cows that have conceived later is key! As above, early pregnancy diagnosis is essential in accurately splitting normal/late pregnancies. Ideally, the required split should be <12 weeks gestation for optimum accuracy.

Once identified, we have options open to us for these late calving cows:

• • If further stock reductions are required, these cows will be amongst the first to go which will have the flow on benefit of tightening the calving period and increasing overall herd fertility.
  • Running these cows separately at calving to then wean these younger calves later than the rest of the mob
  • Treating the progeny of these cows as terminal – I.e. sell all calves including heifers so as to not retain these less fertile genetics in future generations

Summary of key points:

• Consider body condition of cows, available feed, desired numbers & market prices when determining whether to extend your joining period
• Be wary of the flow on effects next year and beyond if opting for a longer than usual joining period
• Use early pregnancy diagnosis as a tool to identify and manage late calvers going forward

Please feel free to call us at the clinic if you would like to further discuss joining periods or any other management issue in your livestock.