It’s well known that a heavier animal is not always more profitable, because the saleable meat yield can vary, with the proportion of fat in the body increasing as the animal matures. A recent review commissioned by EBLEX has looked at how to maximise carcase value and avoid the inefficiencies of too much fat in cattle.
Fat trim increases as the animal ages and gains weight. Fat is a late-maturing tissue and most of its development happens after bone and muscle. According to the findings of the review, this can be influenced by breed, sex, diet and age.
Breed can influence fat weight, location and rate of deposition. For example, dairy breeds have a greater proportion of internal fat than beef breeds. Recent work has found differences between breeds, with Aberdeen Angus crosses having 25% fat tissue compared with 19% for Limousin crosses.
Sex also has a significant impact. In one study, Shorthorns heifers typically had 5.6kg (18%) more fat in the carcase than steers and 13.7kg (45%) more than bulls when slaughtered, with heifers having more fat relative to muscle and an earlier onset of the fattening phase.
Diet impacts include a lower proportion of subcutaneous fat for cattle fed on a mixed grass and cereal diet than the same breeds on a cereal-based diet, with the level of fat trim increasing as the proportion of cereals fed increases.
The work by Scotland’s Rural College (SRUC) suggests that as an animal ages there is a greater increase in fat trim compared with saleable meat. It can be seen from the example below that at 450 days the fat trim was 140g/kg of saleable meat yield, but at 600 days the fat trim equates to 240g/kg.
Change in the ratio of fat trim to saleable meat yield for medium-sized breed steers fed intensively
Lean tissue is comprised of about 74% water, 20% protein and 6% lipid, whereas fat tissue is comprised of about 24% water, 9% protein and 67% lipid. This helps explain why the energy required for liveweight gain increases as the animal ages, as fat deposition requires four times more energy than lean tissue.
There appears to be a 1.5 to 2% fat trim increase as animals move from R4L and R4H. It is predicted that moving from R4L to R4H will take about 39 days for a steer or 37 days for heifers of a medium-sized breed, on an intensive-feeding regime. On an extensive-feeding regime, the time would be about 53 and 51 days, respectively.
For the full final report go to www.eblex.org.uk/research/animal-nutrition/animal-nutrition-generic.
