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March 19, 2024

In this episode of Head Shepherd… 

Dr Charlotte Westwood, a Veterinary Nutritionist at PGG Wrightston Seeds, joins us to discuss how we can give our livestock the best chance of laying down intramuscular fat (IMF) and successfully carrying it through to processing. Listen to the full interview with Charlotte Westwood on the Head Shepherd podcast here

Genetics, along with specific breeds of cattle, such as Wagyu, tend to spring to mind when the topic of IMF comes up. While genetics is an important factor, Charlotte explains why all aspects of livestock management need to be considered to achieve optimal IMF levels at the point of processing. “It’s like putting a jigsaw puzzle together. If you've got half the jigsaw pieces missing, well, you're not going to get the complete picture and end product,” says Charlotte.  

The marbling window

One aspect we can influence significantly is how well our animals are fed. The key is to remember that setting up the right conditions for laying down IMF is a longer game than people usually realise. While the focus is often on nutrition in the one to two months before animals are processed, Charlotte points out, “A lot of what is happening, when the animal reaches its finished stage for processing, has actually started whilst still inside mum's tum.” 

Charlotte reveals that the nutrition of the cow during late pregnancy affects what happens to stem cells in the unborn calf. “The nutrition of mum in that last trimester can actually influence both the number - but also the potential for the future growth - of fat cells (adipocytes) within the muscle itself. So, if mum has a hard time during the last trimester of pregnancy … that may influence the decision of stem cells; whether they’re going to turn themselves later into muscle, fat or fibre cells,” explains Charlotte. “If we don't get it right inside mum's tum, in a small way that can influence IMF deposition in the progeny.”

Once the calf is born, Charlotte says, “There is some degree of plasticity around continuing to encourage more of those stem cells to end up as fat cells - up to about 250 days of age.” While we often expect our beef cows to work hard, Charlotte’s advice to those who want to improve IMF, and use nutrition to help do that, is to remember that the job starts before the calf is born and needs to remain a focus once they are on the ground. The upside is that maintaining cow condition through late pregnancy and calving will be beneficial for lactation, pre-weaning live weights and other aspects of productivity and profitability.

“It may be a feed deficit, we hit a drought, we don't have a feed budget in place that's adequately conservative, rough weather, transport, mixing mobs or whatever, can be enough for them to go through a short period of negative energy balance. And they'll start to mobilise it out in the same order that it was laid down.”
Laying down the fat 

It can help to think about the sequence for laying down the different types of fat in a growing animal. Charlotte shares that it starts with, “ ... internal fat - your visceral fat - because that's the most important part. It's an energy source and stops internal organs from getting knocked around. Then they'll move on to all of the subcutaneous fat around the body. When that starts to lay down, they'll move on to the fat that's laid down between the muscles. These help with the mobility of muscles so that muscle groups can slide over one another. And then the final stage of fattening is when the animal is through maturity or getting close to its mature live weight - then IMF gets laid down.”

What is frustrating for producers is that while IMF is the last to be laid down, it is also the first to go when an animal needs to mobilise fat as an energy source. Charlotte explains, “It may be a feed deficit, we hit a drought, we don't have a feed budget in place that's adequately conservative, rough weather, transport, mixing mobs or whatever, can be enough for them to go through a short period of negative energy balance. And they'll start to mobilise it out in the same order that it was laid down,” meaning that we need to start over again with putting IMF back in.

Forage options for improving IMF deposition 

To tip the scales in the direction of IMF being laid down, Charlotte highlights that the goal is to increase the amount of a volatile fatty acid (VFA) called propionate. She explains that propionate is used to make blood glucose and, “Intramuscular fat cells love their glucose and love to take that glucose and turn it into fat, versus the subcutaneous fat that tends to prefer making fat directly from some of the VFAs inside the rumen, which is mainly acetate, but also butyrate. When we feed a heap of good quality leafy green feed, what we're trying to do is improve the total amount of VFAs, so we’re getting more of a special one called propionate.”

While propionate (and blood glucose) levels can be driven up by feeding grain, fortunately for New Zealand producers and their pasture-based systems, there are other options. Charlotte highlights several forages that are being looked at for their ability to increase IMF, including chicory-rich pastures (which are gaining traction with lamb producers and are also being studied in cattle) as well as other species, such as brassicas (where trials are ongoing). 

To hear more of this conversation with Charlotte Westwood - from the effect of genetics and nutrition on reproduction to how her work in the rural community is about much more than the nuts and bolts of nutrition, especially in tough times - listen to the full interview on the Head Shepherd podcast. You can also check out Charlotte’s own podcast, The Rumen Room, for more on the nutrition, health, reproductive performance and well-being of ruminant animals. 

Head Shepherd is brought to you by neXtgen Agri International Limited, we help livestock farmers to get the most out of the genetics they farm with. Get in touch with us if you would like to hear more about how we can help you do what you do best -

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