Beyond Weight: The True Measure of Feedlot Productivity

The cost of feed is a major limitation on profitability when feeding livestock to reach slaughter weights in a feedlot. One of the key measures of success is feed conversion efficiency. Monitoring this typically involves regularly weighing animals and intermittently taking stock of stored feed. But weighing animals to analyse growth rates is incredibly unreliable, particularly when a feedlot entry weight is used as a starting point.

Growth rates over short timeframes are heavily influenced by changes in organ mass and the clearance rate of digesta, or gut fill, which both respond rapidly to diet type and feeding level. This means that entry weights are likely impacted by the prior diet and any feed restrictions for yarding and transport. It also means that on any day, liveweight can be impacted by the weather, the time of day or anything else that has affected access to feed.

In sheep, CT scans can be used to calculate rumen volume and estimate the weight of gut fill based on the density of the contents. During experiments I conducted using CT scans, when lambs were weaned onto pasture, over 70% of the liveweight gain over four weeks was due to changes in organ size and gut contents. In another group of lambs weaned into a feedlot, the rumen volume increased from 4.4 litres in 35 kg lambs to 8 litres ten weeks later. The liveweight gain over that period was 8.1 kg, meaning that 44% of the gain was likely a result of the increased weight of stomach contents. The contents of the rumen were estimated to contribute anywhere between 13 and 27% to a lambs liveweight. But this could vary even more with different animals and diets.

Measuring feed intake when feeding in a feedlot is not only more accurate but is probably a more reliable predictor of success. When the key to success is feed conversion efficiency, it may seem somewhat counterintuitive, but animals need to be eating as much, and as quickly, as they possibly can. This is despite the earlier mention of ‘maximal growth for minimal intake’.

There are three reasons for this:

1. Animals eating lots are happy and healthy. The first thing that sick or upset sheep and cattle do is stop eating.
   
2. Animals must meet their maintenance energy requirements before excess energy can be utilised for muscle and fat deposition. Greater intake results in more excess energy above maintenance requirements.
   
3. Faster growth rates reduce the time to slaughter thus reducing the number of days they need feeding to meet those maintenance requirements.

The best method to measure feed intake will depend on feeding strategy. You might have a feeding trailer with scales used to fill self-feeders or troughs. You should be able to find the volume of a self-feeder and calculate the weight per litre of the diet using a bucket. Depending on the shape of the feeder, a measuring tape could be used to work out the disappearance of feed from the top.

Measuring the intake of hay or silage is harder, but if you can track what is being fed and try to minimise wastage there’s potential for a good estimate. Wastage can be minimised by feeding in racks and by only providing a new bale once the previous one has been cleaned up. The only other important details are the number of animals you are feeding and the dry matter percentage of each of the components of the diet (feed test or look up some drying techniques).

In lambs, a good rule of thumb is to target 3.5 to 4% of their liveweight in dry matter intake, anything higher than that is a bonus. For cattle, targets of 2.5% of liveweight in dry matter for heavier cattle and up to 3% for lighter cattle should be achievable.

In lambs, a good rule of thumb is to target 3.5 to 4% of their liveweight in dry matter intake, anything higher than that is a bonus. For cattle, targets of 2.5% of liveweight in dry matter for heavier cattle and up to 3% for lighter cattle should be achievable.

Obviously, measuring intake while livestock are grazing pasture is much more difficult and possibly less reliable than growth rates. The good news is that recording growth rates is not useless, especially when you are aware of how liveweight can be impacted by dietary changes. The best advice I can offer is to weigh less often or only analyse growth rates once you have weights over six to eight weeks. When a diet change occurs, wait 14 days or more before recording an initial liveweight to calculate growth rates from.  Weighing animals at the same time of day may help reduce some of the error due to their regular timing of meals. Locking animals up to ‘empty out’ is probably not that useful considering the retention time of digesta is often days, not hours, and having animals off feed for extended periods of time will definitely slow their growth.

Measuring intake is one thing but increasing intake is the real challenge. It requires attention to detail, minimising livestock stress and a consistent feeding program. Introducing a new and rapidly fermentable diet is the first major hurdle in a feedlot. The incidence of acidosis and presence of shy feeders (which are potentially a direct result of acidosis) can ruin any chances of being profitable.

Research in cattle indicates that it can take four to six weeks for the rumen to adapt to a concentrate rich diet. Contrary to the previous message of ‘maximise intake’, take time adapting livestock slowly and only step up the feeding level when animals are eating all the current provisions. Don’t be afraid to stay on the same feeding level an extra day or even go back to the previous level if concerned, because the likely alternative is starting again. A successful induction to the feedlot will increase overall intake in the long run.

Energy intake can also be increased by increasing the energy density of the diet. Typically, energy density is limited most by the necessary inclusion of a fibre source. Particularly when a low-quality roughage is provided separately and without restriction which is common when feeding lambs. Recommendations are for 20% of the dry matter in the finishing diet to be in the form of roughage and this is essential to maintain rumen health and enable maximal intake. But providing ad-libitum access could mean the roughage proportion of the diet is much greater than 20%, reducing overall energy consumed. The solution could be to restrict the roughage provided or perhaps provide a higher quality roughage source where available.

Higher quality roughages have the added advantage of a reduced filling effect. This can facilitate greater intake but could also increase the risk of acidosis due to a lower content of effective fibre. Higher quality roughages with lower effective fibre (sometimes estimated using neutral detergent fibre) will likely need a higher rate of inclusion and conversely, inclusion rates could be as low as 10% for low-quality roughages. Another potential method to increase intake could involve chopping or grinding roughages to speed up passage through the digestive tract. But providing either high-quality roughages and chopping or grinding will likely be of little benefit if it substantially increases the cost of the diet.

There are many variables that contribute to the profitability of feeding livestock in a feedlot but with the cost of feed being a major limitation, it pays to measure how much is being consumed. Maximising intake will ensure maximal growth and then the only time you need to put them over any scales is right before they walk onto a truck.

Tom Keogh is the author of this article. Tom completed a PhD investigating lamb growth and nutrition with a focus on feeding lambs in feedlots. Tom is currently a postdoctoral research fellow at the CSIRO, spending most of his time modelling livestock farming systems to answer questions in relation to genetic selection, management strategies, climate change, and more. Prior to, and throughout, his university studies he gained experience working on commercial sheep and cattle farms and in his spare time still assists with his parent’s small property in southern NSW.  

We’re delighted to have Tom Keogh contributing a series of articles to our website. As Tom puts it:

“I decided to write articles because I realised that no producer has the time to sit down and read my PhD, or any other scientific literature, and try to make sense of it all. But I knew there was useful information worth sharing, if I just broke it into bite-sized chunks. I’m always looking for ways to connect with farmers and explore new challenges, and writing felt like a simple way to do that.”