Tightening Calving Blocks

The industry target for mating period in beef herds is 9 weeks resulting in 95 calves born to 100 cows put to the bull, 60% of which calve in the first three weeks.  The reality is that many herds are struggling to meet this target. Those herds may be running bulls for a 12 to 16 week period in order to get enough cows in calf at the end of the mating period. 

Why is a tight calving block and therefore a short mating period so important?

As can be seen in Table 1, a calf born at the start of the season is heavier at weaning and therefore worth more when it comes to selling.  The more calves born at the beginning of the calving period, the better, a group uniform in size will sell far better than a group of calves that vary in age and size.

Weight at birth (kg)Weight at weaning (kg)Value at weaning (using average £2.00p/kg live weight)
Calf born on day 1 of 120 day calving period45270£540
Calf born on day 120 of 120 day calving period 45174£348

Table 1. effect of increased number of days to weaning

It is not only the increased number of days of Daily live weight gain that is beneficial to a tight calving block but also it reduces the pathogen load in the calving yard which reduces the likelihood of disease in the calves.  Having calves of a similar age prevents competition and bullying at the creep feeder from older calves.  By having a shorter calving block labour can be directed elsewhere.

Why is this not being achieved in many herds?

There are many reasons that can be involved in a herd not achieving maximum fertility.  The two main reasons seen across the board are an extended anoestrus period.  Once a cow has calved, she has a period of time in which she is not able to conceive a pregnancy; during this period the uterus needs time to return to its original pre-breeding state and the ovaries need to return to normal cyclicity. In a healthy cow this post-partum anoestrus period normally lasts a maximum of 50 days.  This, however, is extended in certain situations; The Body Condition Score (BCS) of a cow at calving and shortly after has the biggest effect on the length of the anoestrus period.  A cow that is in poor body condition at calving or who loses a large amount of weight immediately after calving is far more likely to take longer to return to normal cyclicity and therefore the 50 days can become drawn out.  Heifers are most at risk of this because as well as nursing a calf, returning to normal cyclicity they are having to put energy in to growing themselves.   It has also been shown that the act of suckling by a calf has a negative impact on a cow’s anoestrus period; suckling inhibits the hormone which is responsible for ovulation and therefore the cow is less likely to come bulling.  Twin-bearing cows, therefore, are at even more risk due to having two calves suckling from her. 

This issue is further perpetuated in a late calving cow; she needs the 50 or more days to return to cyclicity but when the bull has already been out with the earlier calving cows for six weeks or so this leaves her either only one cycle to get in calf or in some cases no chance at all, resulting in either being forced to leave the bull with them longer or having a barren cow. 

The second main reason involved in a herd not reaching their target, is bull subfertility.  Unfortunately, one in every five bulls tested are sub fertile.  A fertile bull should be able to achieve a 60% pregnancy rate to each service when running with 40-50 cycling females, however, a sub fertile bull will not be able to reach this target which can lead to the bull running with the cows for longer in order to have enough cows in calf by the end of the season.  This, however, results in a drawn out calving period.  Having a Bull Fertility test carried out on every breeding bull at least six weeks prior to the mating season will ensure any bulls that are not up to the job can be replaced before they are turned out with the cows.

What can be done to tighten a herd’s calving block?

Improving fertility requires a planned approach and should firstly include a discussion with your vet.  There are several areas that can be focused on when trying to reduce the anoestrus period:

  • Monitoring BCS – Body condition scoring is a practical tool for managing the nutrition and fertility of a suckler herd.  Scoring should be carried and assessed at key times during the year; calving, mating and weaning.  A cow calving down in optimum condition is likely to have a shorter post-partum anoestrus period than a thin or fat cow.  (Table 2) Once a cow is heavily in calf it is not advisable to try and alter her condition, therefore monitoring at different stages throughout the year allows changes to be made when it is safe to do so.
Spring calving herdAutumn calving herd
Calving2.5 – 3.03.0
Mating2.52.5
Housing/
Weaning
3.0 – 3.52.5 – 3.0

Table 2. Optimum Body Condition Score

  • Temporary weaning – Improvements in fertility have been demonstrated in herds using restricted suckling and temporary weaning.  Restricted sucking involves dictating how many times a day a calf is able to suck the cow, a twice a day method is most often used. Temporary weaning removes the calves from the cows, to varying degrees, for a period of time from 12 hours to 96 hours at a time between 25 and 90 days after calving.  There are different methods of doing this which should be discussed with a vet before putting this into place. 
  • Hormone Synchronisation – Synchronising late calving cows is an effective method of stimulating cyclicty and so bringing them back into the main calving block. A hormone synchronisation programme can be started as early as 30 days post calving resulting in the cow being artificially inseminated at 40 days post-partum. This programme removes the need for the cow to display bulling behaviour as it is a ‘fixed time’ service.  An added benefit of the use of artificial insemination is the ability to choose bulls with good Estimated breeding values (EBV) for weight parameters leading to heavier calves at weaning.

There are a variety of reasons that having a compact calving block is beneficial in a beef enterprise; if you think this is something you would like to work towards, I would advise consulting your vet on how to best achieve this.

Written by Laura Gibson BSc BVetMed MRCVS. Article first published in Farmers Guardian.