The effect of different cereal grains on marbling and soft fat

Summary

This study compared the marbling response and fat texture of steers fed 6 diets based on dry rolled (D/R) and steam flaked (S/F) maize and sorghum and D/R barley a chromium supplement. The conclusions of the study were similar for both visual marbling score and intramuscular fat. Diet had a significant effect on marbling with diets based on maize and steam flaking of maize and sorghum giving the highest marbling scores.

An organic chromium supplement (chelavite (TM)) resulted in increased insulin action but also a trend for increased muscle growth and reduced fatness with no stimulation of marbling. Thus even in relatively heavy steers chromium tends to stimulate the growth of muscle rather than fat. Only the activity of the glucose pathway for fattening (i.e the enzyme ATP citrate lyase in fat) and total body fatness were correlated with marbling. The activity of the glucose pathway for fattening was best correlated with marbling after 97 days of feeding. This suggests that starter diets should optimise the activity of ATP citrate lyase in adipose tissue. A model was constructed for explaining the marbling response using the activity of the glucose pathway for fattening (i.e the enzyme ATP citrate lyase in fat), total body fatness and dry matter intake and this model explained some 40% of the variation in intramuscular fat. This compares to the known genetic effect which also explains about 40% of the variation.

The fat texture in this study was relatively soft for all of the treatments. The feeding of D/R maize and D/R sorghum resulted in softer fat than the steam flaked equivalent suggesting that some of the fat in maize and sorghum was escaping fermentation in the rumen when the grains were fed dry rolled. An additional mechanism was that steam flaking reduced the activity of the enzyme responsible for making soft fat within the animal (?9 desaturase).