Feeding for Controlled Growth Rates

Dr Nerida Richards

Producing young horses that are well developed yet sound is a significant challenge breeders face each year. Buyers want forward horses at the sales, with yearlings that look more like 2 year olds but at the same time look for horses with good legs and clean radiographs. The faster a young horse grows, the more prone it is to developing bone and joint issues, so it is very much a case of trying to have your cake and eat it too. However, with the right management and very close attention to nutrition it can be done. This article looks at ways you can maximise your chances of having the ultimate yearling that is well grown with clean legs through good nutrition.

Control Growth Rate

The one very predictable way to increase a horse’s risk of developmental bone diseases including OCD is to feed too much and make youngsters grow too fast. In this situation the young horse’s bones grow too quickly to be properly mineralised, or problems like contracted tendons and being over at the knees develop and put uneven pressure on growing bones and joints.

To minimise the risk of rapid growth rates causing problems with bone development, feeding regimes need to be closely controlled and adjusted as needed to match changing pasture conditions and an individual horses requirements. Growth rates should be closely monitored through regular weighing where possible. The people responsible for feeding should also be observant, experienced and diligent, checking for signs of overfeeding and rapid rates of growth including excess body condition, physitis or any deviation in leg structure from normal in one or more of the horses in a group on a daily basis. As soon as any signs of overfeeding are noticed, feed regimes should be adjusted immediately to bring growth rates back in check.

Mind your Minerals

It is also well recognised that unbalanced mineral nutrition can lead to developmental issues in growing thoroughbreds. While a growing horse requires an extensive suite of minerals, minerals of particular importance for bone development are calcium, phosphorus, magnesium, copper, zinc and manganese. Not only do these minerals need to be supplied in the diet at correct levels, but they also need to be provided in the right ratios so that one mineral doesn’t block the absorption of the other (for example too much phosphorus will block the absorption of calcium, too much zinc will block the absorption of copper and too much potassium will block the absorption of magnesium).

Balancing the mineral component of growing horse rations is not a super simple task, so to be sure you get it right, have a qualified nutritionist assess your pasture or hay and put together a diet based on the mineral profile of the forages your horses have available. Feeding regimes need to be flexible, allowing you to adjust the amount of feed fed to control growth rates without ever compromising mineral intake. Be sure to have a set of diets designed that you can use to cover you for youngsters that need a lot of feed through to those that only need a very small amount.

Are there problems lurking in your pasture?

It is important to have your pasture or hay tested to assess its mineral status throughout the year. Pastures can have various characteristics that can quite quickly unbalance a diet and bring your entire feeding regime unstuck. Some examples from pastures that I have looked at in the past 12 months include:

  • Unbalanced calcium to phosphorus ratio – Pastures that contain more phosphorus than calcium are more common than you would imagine and if not corrected by careful calcium supplementation can lead to a long term calcium deficiency which will almost certainly disrupt sound bone development.
  • Unbalanced zinc to copper ratio – Pastures that contain more than 5 parts zinc to 3 parts copper put horses at risk of a copper deficiency. While not common, it is critical that this ratio is corrected through calculated supplementation to avoid copper deficiency.
  • Extreme potassium content – Potassium contents upwards of 55 grams per kilogram of pasture dry matter have recently been recorded in horse pastures. While very little work has been done on the impact of this in horses, it is well recognised that potassium at these levels will disrupt the absorption and metabolism of both magnesium and calcium in other animal species and circumstantial evidence suggests this may be the case in horses.
  • Mineral deficiencies – this is perhaps the most common problem seen in pastures. Calcium, copper and zinc are the three most common deficiencies seen, but phosphorus and very occasionally manganese can also be too low to meet a growing horse’s requirements. Luckily this problem is also the easiest to correct through calculated supplementation with good quality feeds or pasture balancer pellets.

Because of all the spanners that pasture can throw into your feeding regime the first step toward putting together a well balanced feeding regime for growing horses should always be pasture analysis.

Provide Good Building Blocks

Bone is built upon protein, both collagen and non-collagenous proteins, so it is reasonable to assume that the protein quality of the diet will have an impact on the quality and soundness of bone in growing horses. Diets based on high quality protein from soybean, canola, lupins and faba beans will better support sound bone development than rations based on low quality sources of protein like cottonseed meal.

What about Fancy Stuff?

There are many supplements and feed additives on the market nowadays that will claim they can help reduce OCD and other bone issues. Some are backed by credible science, others aren’t. The key to using any of these supplements though, if you wish to give them a try, is to make sure you are feeding them with a well balanced diet, as no matter how good they are or claim to be, using them when other problems already exist in the diet is not going to give you better results. For example adding silica to diets that are deficient in copper is not going to solve any problems that may exist due to the copper deficiency.

There is a lot we still don’t know...

While managing growth rates, feeding well balanced diets that are formulated to suit pasture conditions, meeting all mineral requirements and feeding diets with high quality protein will give you the very best chance of producing a sound yearling, horses will still develop bone issues, even under the very best conditions. It is also well recognised that some mares will consistently throw foals that go on to develop OCD or other issues. What we still don’t know is why, what is genetically different about these animals that puts them at much higher risk?

Research currently being conducted by Dr Sarah Ralston of Rutgers, The State University of New Jersey USA and funded by Pryde’s EasiFeed Pty Ltd is hoping to unravel some of the remaining mystery surrounding OCD in thoroughbreds. Twelve Australian thoroughbred breeding farms and over 360 weanlings have taken part in the study that we hope will unravel a bit more of the mystery still surrounding hock and stifle OCDs. Some results should be available to report mid-year.

Pryde’s EasiFeed Growing Horse Diets

Pryde’s EasiFeed makes managing growth rates and the mineral balance in growing horse diets easy. The set of diets below gives you feeding rates suitable for weanlings and yearlings using the ‘150 Pasture Balancer Pellet’ and the fully extruded complete feed ‘BioMare Cubes’. Diet 1 at the top of the table that uses only the 150 Pasture Balancer Pellet should be used when pasture quality is excellent and/or young horses are growing too quickly or are too heavy in condition. Diets 2 and 3 should be used as pasture quality drops and youngsters need more feed to maintain desired growth rates while diets 4 and 5 at the bottom should be used under poor pasture conditions when young horses may start to struggle in maintaining the growth rates you need. Using this set of diets will allow you to control growth rate and body condition while always meeting mineral requirements (provided your pasture isn’t unbalancing things for you).

Weanlings and Yearlings
Pasture Quality
Growth Rate
Diet #
Pryde's 150 Balancer Pellet (g/day)
Pryde's BioMare Cubes (kg/day)
Excellent
Too Fast
Diet 1
600
0
Good
Diet 2
400
1
Average
Diet 3
200
2
Poor
Diet 4
0
3
Very Poor
Too Slow
Diet 5
0
4

For detailed assistance with your growing horse diets including a pasture and hay analysis service, please contact Pryde’s Pty Ltd on 1300 732 267 or email info@prydes.com.au

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