Is bigger always better?

Brian Cumming, a More Beef from Pastures deliverer based in NSW, considers the implications of cow size and profitability as discussed in a recent More Beef from Pastures webinar. As Brian relates, the size of the cows in the herd has far reaching implications and should be a fundamental consideration in establishing or maintaining a breeding objective.

As a general trend, cow size has been increasing over the past twenty five years or so. Textbooks from the 1990s and before used a cow weight of 500kg as the base for most British breed herds; today that figure is more likely to be 550 to 600kg.

Why has cow size changed so much and will it now stop?

If we only select for growth rate, cow size will increase. There is such a strong genetic correlation between the two traits that this is almost a given. Large cows do, however, eat substantially more feed to maintain their bigger mass of tissue and heavier cows are more likely to be bigger framed and hence leaner. Leaner cows take longer to re-cycle after calving and may have lower reproductive rates over time if feed is limiting.

The argument that bigger cows are worth more as culls is true, but it’s a misleading argument. Cull cows are just a bi-product of a breeding herd; they are not the main item of interest to select for. Large cull cows might be worth more individually but the profitability of the business would reduce rapidly if all we selected for was the dollar return on cull cows.

Since stocking rate, fertility and the number of progeny for sale can be related to the size of the cow, there must be a point at which an optimum cow weight and frame is achieved. Biologically, we would expect this to be lighter in British cattle than European breeds.

In the recent MBfP webinar, Dr John Webb-Ware looked at the economics of cow size, taking into account that larger cows consume more feed. Using robust statistical modelling, John ran small, medium, large and extra-large cows in a pasture under different stocking rates. At low stocking rates, gross margins per hectare increased as cows size increased; however, at high or even moderate stocking rates, an optimum was achieved after which larger cows under these stocking rates did not further increase profits. This point of diminishing returns appeared to be reached at 550kg for British breed cows in fat score three condition under many grazing systems. European breed cows will be bigger.

As cow weight is related to so many economic contributors to a beef business, maintaining a cow weight around 550kg makes a lot of sense.

One of the many benefits of BREEDPLAN is that it allows breeders to select for growth rate whilst attempting to maintain a particular cow weight by prioritising trait selection.

Many breeds now publish Mature Cow Weight estimated breeding values to assist with this task.

View the webinar

The webinar discussed in this article can be viewed online. The monitoring and evaluation of producer feedback on More Beef from Pastures events and resources plays an important role in helping direct the investment of producer levies to maximise the return to producers. Before and after viewing the cow size webinar, we would appreciate it if you could take a few minutes to complete a brief survey to assist with this task. The survey and webinar can be viewed here: https://www.surveymonkey.com/r/7PLRTSQ

For more information regarding BREEDPLAN visit: http://breedplan.une.edu.au