So often we can get caught up in the specific traits that we would like to see in our beef cows such as milking ability, growth and eating quality but realistically, none of these traits mean anything if the cow can’t carry out her three main objectives;
- Get in calf
- Have a calf
- Get back in calf
It’s nothing new to anyone that genetics and management are vital for our cows to carry out these three responsibilities, and more. Genetics can’t make up for insufficient management – but good genetics coupled with feeding, ongoing inputs of trace elements, disease protection and good animal handling/management will be key to reproductive success. Here are a few reminders on the genetics of fertility.
Cow fertility is what we call a low heritable trait meaning the variation you see with some cows getting in calf and others not – will be mostly due to management and slightly due to genetics. Unlike traits like double muscling where one gene has a massive phenotypic influence, fertility is a trait where many genes have small influences. As the genetic aspect of variation is small, we want to capture as much of it as possible because small changes can have big impacts, as seen in a couple of example traits below. The way we understand and capture the variation is by recording phenotypes. Recording as many animals as possible, for traits like days to calving and gestation length. The more good recording, the more confidence that can be had in the available breeding values and the more likely the animals will perform as predicted.
As technology is enhanced, there will be no doubt more breeding values, superior and more objective recording methods, and new genotyping strategies for both stud and commercial farmers.
For now as a commercial farmer, along with your own good management, your best tool for influencing your cows genetics is your bull breeder. Be sure to ask their own objectives around fertility. Do they mate their heifers? Do they take the extra effort required to record the fertility traits? Do they invest in technologies like DNA testing (genomics) to add even more confidence to their breeding values? What is their policy for managing cows that do not get in calf? Where your breeder goes – you will go.
Once you’ve selected your breeder, the next thing is selecting your bull. Don’t forget that you select on the bulls own eBVs but you are actually selecting for performance of his progeny and in the case of fertility – for performance of his daughters.
There are 3 traits in the Angus Breed Evaluation that will have an influence on your herds fertility.
- Days to calving
Days to calving (DTC) predicts the number of days between the bull going in and the cow calving. Selecting bulls with a more negative DTC will mean his daughters should get pregnant earlier in the season. Earlier pregnancy means an earlier calving and therefore more recovery time before mating the following year. It also has the positive effect of calves being born earlier in the season and therefore heavier weights earlier.
The Angus Australia Sire Benchmarking Program is a good example of the variation you can see in genetics where the best and worst sire for days to calving had daughters calving 37.1 days earlier – so almost two cycles!
- Gestation Length.
The average gestation length for a beef cow is 283 days but can be shorter or longer depending on the breed or the selection pressure placed within that breed. Genetically influencing gestation length is especially popular in the dairy industry where every day of extra milk and recovery time counts, but the concepts should also apply in beef by applying to calf growth. The variation seen in the Angus sire referencing scheme between the top and bottom sire on gestation length was one week.
Gestation length combined with earlier days to calving means earlier pregnancies, shorter pregnancies and ultimately a longer chance to recover before the bull going back out again.
If we do focus on these two traits, then we need to be prepared for calves to be born earlier and cows requiring that spring flush earlier for peak milk production. High performance cattle are often blamed for not actually performing – but is just because we change genetics and not management?
- Scrotal circumference.
Scrotal size is consistently debated as an indicator of the age of puberty of his daughters, however it is still the best indicator of male fertility. Provided your bull breeder undergoes soundness checks for fertility on all sale bulls, you will make more progress from selecting on days to calving and gestation lengths to influence heifer fertility (and possibly most importantly ensuring she is 67% of her mature cow weight before mating)
So you now have two tools for influencing fertility – your breeder, and then the breeding values of your selected sires. A third tool is cross breeding.
It is well known that the effect of hybrid vigour (which is a result of cross breeding and the combination of genes inherited from each parent) is larger for traits that are less heritable, such as fertility, and can also result in improvements of calf liveability, calf weaning weight and cow longevity. Cross breeding can increase milk yield by up to 14.5%, calf weaning weight per cow by 11%–20%, and overall cow lifetime productivity by 25%–30%.
As technology advances in both understanding fertility at a genomic level, but also in methods for recording performance – there will definitely become more and more ways to influence cow fertility. It might be that a new breeding value pops up for antral follicle counts, reproductive tract scoring or traits specific to heifers such as the time to first detectable heat.
Currently, it is only in sire selection where commercial farmers can effectively genetically select for fertility traits but there are already DNA profiling tools available for commercial farmers, like INHERIT Select or Heifer SELECT that will hopefully eventually include fertility traits as well. We may even see technology not just profiling the heifer’s own DNA but profiling the mRNA of their molecular features like white blood cells which are circulating the body differently with different pregnancy outcomes.
Fertility should be the most important trait for commercial farmers because if your cows aren’t getting in calf then there is no need for that extra growth rate or marbling for eating quality! However, don’t think that you can change your genetics but not your management. They go hand in hand so be sure to utilise your own good farming practices, but also your industry experts to keep your own feedback loop on both management and genetics.
Happy breeding and happy feeding!
Johanna Scott
Independent Consultant at Targeted Breeding LTD.
