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Marbling occurs in animal muscle (intramuscular fat) rather than on its perimeter (subcutaneous fat). Beef cattle attain their intense marbling relatively late in life – 28 to 36 months – whereas traditional cattle are typically slaughtered at 12 to 18 months. Weight gain should be less than the normal 1,7 to 2kg/day of feedlot animals. Increasing marbling requires a longer, slower feeding and growth method.
Diets and nutrition
The site of maize digestion may play a role in marbling. Grain that bypasses rumen fermentation is digested and absorbed in the small intestine of cattle, and the starch absorbed there is thought to increase marbling content more efficiently.
The starch in freshly harvested maize is digested mainly in the rumen. As maize matures over time more starch is digested in the small intestine. This ‘maturing’ process in maize and maize silage improves up to 12 months of age. The starch in hominy chop is fine and digested mainly in the rumen, and is therefore not recommended.
Grain processing, whether by grinding or steam-flaking, and the fine starch in chop can also negatively affect marbling, as this type of starch is digested mainly in the rumen. Whole maize contains less available rumen starch. Therefore, more starch bypasses the rumen and is digested and absorbed in the small intestine.
Research at Kansas State University showed that increasing the amount of distiller’s grains (12% fat) in the diet led to reduced marbling. The fat content in hominy chop is around 9%, while maize contains only about 3%, therefore maize will result in improved marbling. Lower daily fat intake has been shown to improve marbling in the meat.
Dietary protein levels may also influence marbling. Increasing the protein content of the diet can enhance starch digestion and absorption in the small intestine. For young calves, increase the dry matter (DM) protein to around 16% on a DM basis after weaning until they weigh at least 300kg. It can then be reduced to 14% protein on a DM basis.
A diet combining higher protein and starch or grain along with around 40% hay or veld grass will increase marbling. The more consistently cattle are managed by minimising stress and standardising nutrition and management, the more likely the local beef industry is to succeed.
Early development
Marbling fat develops at a young age in beef cattle. Feeding higher-energy diets to young calves will help increase the amount of marbling, with creep feeding being the easiest way to achieve this, as demonstrated by research in Georgia.
To increase marbling, creep-fed calves should receive a high-energy maize-based diet, providing around 22% crude protein and 11,5MJ/kg on a DM basis, both before and after weaning. However, research has not yet determined the precise minimum average daily gain (ADG) below which marbling is at risk or being lowered.
A United States study found that calves treated two or more times for bovine respiratory disease in the feedlot experienced a 33% reduction in prime and choice grades (less fat). Ear implants may also have a negative effect on marbling, although some studies show no effect.
Feed efficiency and fatty acids
Marbling also varies between the sexes. In general, heifers tend to have more marbling than steers. The timing of castration in bull calves can also influence marbling. Male calves left intact for longer periods will have more lean growth, while castrated males deposit fat earlier, thus increasing marbling. Intact male calves have a more aggressive disposition, which may reduce marbling.
Residual feed intake (RFI) is a measure of feed efficiency and is defined as the difference between an animal’s actual feed intake and its expected intake based on its size and growth. It is independent of the production level: The lower the value, the more efficient the animal. In a study of 92 yearling beef bulls, their RFI was tested and classified into three groups: efficient (RFI > 0,5 standard deviation [SD] below the mean), marginal (RFI within 0,5 SD of the mean) and inefficient (RFI > 0,5 SD above the mean).
Inefficient bulls consumed more DM than efficient bulls. Observations from the study suggested that beef sires superior in both feed efficiency and marbling, can be identified with the help of RFI analyses.
Studies have quantified the advantages in fat production when feeding cattle a high percentage hay diet over extended periods. The human body can manufacture most of the fat types it needs, except for essential fatty acids (EFAs).
Most positive health benefits are seen in two types of EFAs: linoleic acid (omega-6) and linolenic acid (omega-3). Beef is an excellent source of both. As demand grows for high-quality marbled beef, breeders have a golden opportunity to supply it. – Dr Vlok Ferreira, technical executive, Molatek
For more information, send an email to Vlok.Ferreira@rclfoods.com or phone 082 464 4661.
