Factors affecting dressing percentage in feedlot animals

Theoretically, dressing percentage is calculated by dividing the warm carcass weight by the shrunk live weight of the animal and expressing the result as a percentage. In practice, farmers use different weights to determine dressing percentage. The live weight is either measured at the feedlot before loading the animals to the abattoir or at the abattoir just before slaughter. The carcass weight used is mostly the cold carcass weight, as that is what the farmer is paid for. When comparing dressing percentages between different groups, it is essential to use consistent weight measurements.

It is very seldom to get the dressing percentages of individual animals; we mostly calculate the dressing percentage of a group of animals slaughtered. We then compare the group average to other groups; however forget that the variance between groups is much lower than the variance between individual animals. In 594 lambs that were slaughtered, the average dressing percentage calculated from the cold carcass weight (warm carcass weight minus 3%) divided by the final weight at the farm was 47.0%. In this group, we also calculated individual dressing percentages; the dressing percentages varied between a minimum dressing percentage of 37.7% and a maximum dressing percentage of 64.2%.

In the graph 1, we can see how dressing percentages in individual animals vary, these differences in many cases have a large effect on the average dressing percentage calculated.
 
Graph 1: Distribution of Dressing Percentage

To improve feedlot profitability, it is important to evaluate the key factors that influence dressing percentage and to manage them to ensure optimal results.

1. Live weight
The size and weight of an animal are directly linked to dressing percentage. Generally, dressing percentage increases as live weight or fat depth increases in feedlot animals. As animals approach finishing weights, muscle and fat growth outpace the development of other body components such as bone, hide, and viscera. Consequently, heavier animals tend to have higher dressing percentages. Managing animal growth to achieve optimal weight without excessive fat is crucial for maximizing dressing percentage.

2. Fat
Body fat is deposited in various locations, including the body cavity (visceral fat), within muscles (intramuscular fat or marbling), and beneath the skin (subcutaneous fat). Since much of this fat remains with the carcass, increased body fat generally leads to higher dressing percentages. However, excessive fat can result in trimming by the abattoir, reducing the dressing percentage.

3. Age at slaughter
The age at which an animal is slaughtered also impacts dressing percentage. As cattle age, they tend to deposit more fat, which can lead to a higher carcass weight but may not necessarily improve the dressing percentage. In some cases, older cattle may have a higher proportion of bone relative to muscle, which can reduce dressing percentage.

In contrast, younger cattle that have not yet reached full maturity may have a higher proportion of muscle and a lower proportion of fat, leading to more efficient meat recovery and a higher dressing percentage. Therefore, producers often aim to slaughter cattle at an optimal age that balances muscle development with minimal fat deposition.

4. Genetics and breed
Genetic factors play a major role in determining the dressing percentage of cattle and sheep. Different breeds have inherent physical traits that affect how efficiently they convert feed into lean muscle and how much fat they store. For example, beef breeds are typically known for their higher dressing percentages due to their ability to put on muscle more efficiently than dairy breeds, which are often leaner.

The carcass composition of different breeds also varies. Some breeds tend to deposit more fat than lean muscle, which can impact the final carcass weight and, consequently, the dressing percentage. Additionally, animals that are genetically predisposed to higher muscling, such as those from terminal breeding lines, generally exhibit higher dressing percentages.

While dressing percentage differences can be related to mature size, there are other factors such as the weight of the hide, head, feet and viscera, which all have an impact. Polled animals and animals with a smaller hide will have a better dressing percentage, as the additional weight from the horns and hide negatively affects the ratio between the carcass weight and the fifth quarter. Breeds with a heavier hide, head, feet and viscera will have a lower dressing percentage since these body parts are excluded from the carcass weight.

5. Gender effects
Gender is another significant factor that impacts dressing percentage, with differences observed between male and female animals. In beef cattle, heifers usually have a 1.5 to 2.0 per cent lower dressing percentage than steers at a similar fat level. As a whole, heifers tend to carry more waste fat in the udder, around the internal organs and on the carcass than steers.
 
The difference in dressing percentage narrows as heifers become fatter than steers. Since heifers mature earlier, they are usually marketed as lighter than steers.

In sheep, we tend to see that rams have a lower dressing percentage than ewes at the same slaughter weight. In a trial done on merino crossbred lambs that were 5 months of age, on average, the ewes had a 3% better dressing percentage than rams. The main contributing factor to the lower dressing percentage in the rams was the higher frequency of animals with horns.

6. Diet effects
Nutrition is one of the most influential factors in dressing percentage. A well-balanced diet that promotes muscle growth rather than excessive fat deposition will result in a higher dressing percentage. The density of the ration can have a large effect on the dressing percentage. Cattle on a high roughage diet, such as hay, silage or pasture, have a lower dressing percentage than cattle on a high proportion of grain diet, even if the cattle are marketed at very similar fat levels. In a trial done by the Lethbridge Research Station in Canada, the entire digestive tract of slaughtered steers was weighed. Gut fill, as a percentage of live weight, was higher in steers on a roughage diet than in steers on a grain diet. In this trial, steers on the grain diet had an 8% higher dressing percentage than steers on the roughage diet.

Cattle in feedlots are often fed a high-energy diet rich in grains, which encourages muscle growth and fat deposition. The balance of proteins, carbohydrates, fats, and fibre in the diet, as well as the timing of the feeding program, can have a significant impact on how efficiently the animal gains weight. Animals with higher muscle mass and appropriate fat cover (not excessive) tend to have higher dressing percentages. Additionally, animals that have been fed a consistent and high-quality diet throughout the finishing period will typically have better dressing outcomes than those that experience feed fluctuations or poor-quality rations.

The use of Beta Antagonists as a feed additive, such as Zilmax or Growfactor, in the finishing phase of the feedlot can improve the dressing percentage. In both lambs and calves, we expect an improvement in dressing percentage on average of 2% on average. The benefit of the improved dressing percentage outweighs the cost of adding a beta antagonist to the ration.

7. Distance and time from the feedlot to the abattoir
The distance and time from loading animals on the farm to the abattoir play an important role in maximising dressing percentage. This effect of a lower dressing percentage is primarily related to stress, dehydration, and weight loss during transportation, all of which can alter the final yield of meat. It is therefore important to shorten the time from the feedlot to the abattoir as much as possible and reduce stress on the animals.

Transporting animals from the feedlot to the abattoir is a stressful process that can result in weight loss and reduced dressing percentage. Stress can cause several physiological changes in animals, such as an increase in heart rate, muscle tension, and the release of stress hormones like cortisol and adrenaline. The time and distance involved in transportation can lead to weight loss, particularly from dehydration, sweating, and exhaustion. The further the distance from the feedlot to the abattoir, the more pronounced this effect can be.

A trial done on the effect of time without feed and water on the carcass weight of bull calves showed that the animals slaughtered 24 hours later had a 2.91% reduction in warm carcass weight, and the animals slaughtered after 48 hours had a 6.10% reduction in warm carcass weight.

Stress furthermore leads to poor muscle quality. In cases of extreme stress, muscle glycogen is depleted, and the pH of the muscle rises abnormally post-slaughter. This can cause the meat to be classified as PSE (pale, soft, and exudative) or DFD (dark, firm, and dry), both of which can reduce overall carcass quality and yield. Additionally, muscle breakdown can negatively affect the carcass yield, lowering the dressing percentage.
 
If animals are transported a short distance and for a minimal period, they are less likely to experience extreme stress or significant weight loss. These animals are typically in better condition when they arrive at the abattoir, leading to minimal loss of live weight and a higher dressing percentage. Additionally, animals that are transported for short distances can generally be handled more efficiently, reducing the risk of injury and stress during unloading, which can also preserve their dressing percentage.

In addition to time and distance, how animals are handled during transportation can play a significant role in minimizing stress and its negative impact on dressing percentage.

To mitigate the negative impact of transport time and distance on dressing percentage, feedlot managers and transporters can implement several best practices:

•    Shorten travel time: Whenever possible, reducing the time animals spend in transit can significantly reduce stress and dehydration. Local slaughterhouses or feedlots that are located closer to abattoirs will have an inherent advantage in terms of preserving dressing percentage.
•    Pre-transportation management: Before transport, animals should be without stress and must have access
•    to feed and water. This practice helps to minimize weight loss and stress during transit.
•    Improved transport conditions: Ensuring that vehicles are designed to reduce overcrowding, provide ventilation, and maintain a comfortable temperature can minimize the negative effects of long journeys on animal welfare. Using trucks with good air circulation and proper space can prevent excessive sweating, fatigue, and muscle damage, all of which contribute to a reduced dressing percentage.
•    Rest and recovery: For long-distance transportation, rest periods with access to water and feed should be scheduled to allow the animals to recover from the stress of transit. This allows the animals to rehydrate, rest, and regain weight, improving their condition upon arrival at the abattoir and increasing the likelihood of maintaining a higher dressing percentage.

8. Seasonal effects & environmental conditions
Environmental factors such as climate, temperature, and housing conditions can indirectly influence dressing percentage. Animals under heat stress may eat less or metabolize food less efficiently, leading to slower growth and lower dressing percentages. Conversely, in cooler climates, animals may consume more feed and grow at a faster rate, potentially improving the dressing percentage.

Housing and management practices also play a role in minimizing stress. Cattle that are housed in clean, spacious, and well-managed facilities are less likely to experience disease or stress, which can have positive effects on both growth and dressing percentage.

Dressing percentages can vary by 1.5 to 3 percent throughout the year. The period of highest dressing percentages occurs in the winter when feedlot conditions are dry. Other factors that can affect dressing percentages are the thickening of the hair coat during the colder months, and when it is wet, mud can accumulate on the hide, negatively affecting dressing percentage.

9. Health status
Health problems can significantly impact dressing percentage. Sick or stressed animals often experience poor feed conversion, slower growth, and increased fat deposition. Conditions such as lameness, respiratory infections, or digestive disorders can cause animals to lose weight or fail to gain weight efficiently, thus reducing the dressing percentage.
 
In extreme cases, these conditions can lead to animals having a higher proportion of non-carcass components, like organs and bones, relative to their live weight. Furthermore, stress, whether from handling or transportation, can result in decreased carcass yield due to the breakdown of muscle tissue.
Proper veterinary care, disease prevention programs, and stress-reduction strategies are essential in maintaining
high dressing percentages.

10. Feedlot management practices
Effective feedlot management plays a critical role in influencing the dressing percentage. Properly managing the transition from growth to finishing phases, monitoring feed intake, and ensuring animals are free from stress are all essential practices. Managing the timing of the finishing diet, ensuring cattle are not overfed or underfed, and avoiding sudden changes in the diet are all strategies that contribute to optimizing dressing percentages.

11. Carcass handling and slaughter procedures
After an animal is slaughtered, the handling and processing techniques can also impact the dressing percentage. For example, improper or inefficient evisceration (removal of internal organs) or trimming of fat may result in the loss of valuable meat, which can lower the dressing percentage. Similarly, contamination during slaughter or processing can result in parts of the carcass being discarded, further lowering the yield.

The skill and efficiency of the abattoir personnel, as well as the equipment used, can influence the accuracy and overall yield of the carcass. Adherence to proper handling and processing protocols is crucial to achieving the highest possible dressing percentage.

Dressing percentage is a multifactorial trait influenced by genetics, diet, management, health, and other factors. For feedlot producers, understanding and managing these factors is key to maximizing yield and profitability. By focusing on breed selection, nutrition, health, and effective management practices, producers can improve dressing percentages and enhance meat production efficiency.

If you want to learn more about factors affecting dressing percentage in feedlot animals, please contact a De Heus technical advisor for expert guidance - https://www.deheus.co.za/meet-our-team/.