There are 3 factors that will both contribute to what ‘Calving Difficulty %’ index figure your bull starts out with and also how it changes over time.1.Back Pedigree, 2.Genotype, 3. Calving Data
The first ‘Calving Difficulty’ index that your bull will receive is called a ‘Parent Average’ index. As the name suggests it is an average figure that is calculated from the index figures that his sire & dam have at the time of his birth. So even if the bull calf himself was born without any assistance, if his parents are rated as being difficult calvers then he will start out with a high figure and vice versa if his back pedigree has lots of animals with easy calving figures.
If the index figure of a close relative of the bull moves up or down significantly then this will also affect the index figure of the young bull. A common example of this is if the sire of your new bull calf is a much hyped new AI bull. Before any of his calves are born, based on his back pedigree and genotype he has an average calving index. However, if he does not breed as expected and his first crop of calves turn out to cause a lot of calving difficulty for farmers and they report this through calving surveys then that AI Bull’s calving index will increase, reflecting those hard calvings. At the next evaluation run, the calving figure of your young bull, his son, will also increase, again reflecting this new data that has been recorded on his bloodline.
When a sample of DNA (e.g. BDGP scheme) is sent off and the genotype comes back this will then alter the figure that the bull got in his first evaluation run which would have been through his ‘parent average’ as explained above. So, a Breeder could notice a difference in a bull’s ‘Calving Difficulty %’ from the calf’s very first evaluation compared to the one after the genotype has been included.
3.Calving Survey Data
When the bull then starts to sire calves and the degree of calving difficulty (if any) is recorded, this will then have an impact on his calving difficulty. The key to how much of an effect this data has depends on a couple of factors:
1.How many of his calves had calving surveys recorded on them.
2.How many calves from other bulls (particularly AI bulls) also had calving surveys recorded on them around the same time.
3.How much variation in calving surveys was recorded.
Basically, if lots of calves of your bull are born alongside calves from other bulls and the full scope of the scale is being used (1=Easy – 4=Vet. Assistance) then the calving data recorded on your bull’s calves will have a significant impact on his calving index. If his calves are born alongside the progeny of AI Sires, then the impact will be greater again as the AI sire calves will provide a great benchmark against which the progeny of your bull can be compared.
Pedigree Bull example:
Following is an example of how the ‘Calving Difficulty %’ figures of a pedigree bull are estimated and also how they change over time.
‘Western Lancelot’ is a pedigree Charolais bull that was born on the 15th of May 2015 in his breeder Joe Clancy’s pedigree Charolais herd in Gortreevagh, Oughterard, Co. Galway. He is sired by ‘Meillard’ and is out of a ‘Major’ cow ‘Western Fatacha’. ‘Meillard’ has a calving difficulty figure of 8.3% and ‘Major is ‘8.9%. So ‘Lancelot’ would have started out with a ‘Calving Difficulty %’ figure of around 8.5%.
Then he was genotyped and when this data was factored in at the next evaluation run then his calving index became a little easier.
Calving Survey Data
He was sold for breeding and his first calves started to be born in 2018. The calving surveys of his calves and of the other calves born alongside them were then factored into his calving index. This data can be seen in the ICBF ‘Animal Search’ facility:
- Go to icbf.com
- Go to the Animal Search facility down the right hand side of the website and enter in ’Western Lancelot’.
- Click on ‘Calving Difficulty (%3&4) which is shaded in blue.
- Scroll down to the section that says, ‘Sire Progeny and Progeny Herdmate Information’.
Date of Evaluation: March 2019 (the most recent ICBF evaluation).
No. of Births: Number of his calves with calving surveys recorded on them
Herd Mate Births: Number of calves sired by other bull(s) that were born alongside his calves (also known as herdmates).
Scored 3 or 4 (%): The % of his calves that got a calving survey score of ‘3 or 4’.
Herdmate scored 3 or 4 (%): The % of the herdmate calves that got a calving survey score of ‘3 or 4’.
Male Births: Number and % of his calves that were males.
1st,2nd and 3rd parity ‘Records’ and ‘Scored 3 or 4 (%): His progeny broken down by whether they are out of 1st, 2nd or 3rd calvers.
The most important columns to look at in the table above are highlighted. They show the % of the bull’s own calves that were scored ‘3 or 4’ versus the % of the herdmate calves that were also scored ‘3 or 4’. What is being assumed here is that the management factors on the farm are the same for all the calves. So, allowing for any biase for a bull only getting heifers etc, the main reason for a difference in the number of ‘3 or 4’s’ recorded is to do with the calving difficulty of the sire.
Of course, the more numbers of calves, the less ‘noise’ there is in the data. For example, with very small numbers a bull could be showing a high number of calving difficulty but this could be due to a lot of his calves being out of heifers or the calving difficulty being the fault of the cow not opening at calving etc. However, numbers of calves always overcomes these issues. Especially when there are AI
‘Western Lancelot’ pictures as a calf and also just before he was sold for breeding.