There is recurring discussion in the Speckle Park world about the benefits or vices of the nt821 myostatin gene. The myostatin nt821 gene, when present in heterozygous form, increases eye muscle area as well as yield. It is however not just a simple win – it’s more complicated than that and it’s no free lunch. Yes, it increases muscle but there are drawbacks that may indeed outweigh any benefit gained. And then there are a few other questions that need to be answered: Is the nt821 gene manageable in a commercial situation? Is it profitable? And are there alternate ways to increase muscle and yield?

There have been significant studies into the impact of nt821 and there is some consistency among the research that can be broken down as follows:

  1. There are differences between breeds as to the extent of the influence of nt821
  2. There is an increase in EMA and yield
  3. It reduces IMF%, growth rate, carcase weight and organ size
  4. It increases birth weight, calving difficulty and perinatal mortality
  5. It decreases pelvic area and increases age at fertility
  6. It reduces the eating quality of meat produced

The indirect and anecdotal evidence is also interesting. Greenhams new Dairy Beef program do not accept steers by nt821 carrier bulls. A South Deven stud in the UK reports a significant reduction in calving difficulties once they exclusively used non-carriers bulls. Another study in Red Poll cattle found carriers had increased birth weights, and increased yield but there was a significant reduction in marbling and carcase quality.

As we measure birth weights, scan for EMA and IMF% in Speckle Park and all that data is analysied by Breedplan, we have a valuable natural experiment. When looking at all 2021 registered bulls, nt821 carriers had higher birth weight and EMA EBV’s, and lower IMF% EBV’s than non-carriers. The differences increase if you look at those animals with more data in the system signified by greater accuracies. Birth weight goes up, and IMF% goes down in carriers, and non-carriers see a reduction in EMA. These results align with the published research on the effects of the nt821 gene.

Blue Spark Rogue. Non carrier, low birth weight, high EMA.

At Te Mooi we scan for EMA and also have our animals independently muscle scored. We also benchmark ourselves against some leading seedstock producers of other breeds. What we find with our muscle score is that we have a higher incidence of B- muscle scores and a lower incidence of C muscle scores. This poses the question: do Speckle have enough muscle already? Should our focus be on ensuring growth rates are there to meet market specifications quickly and ensure our meat quality is good enough to supply the premium markets?

A study done in NSW in 2009 on a self-replacing herd model found a $2 per hectare benefit of producing heterozygous nt821 animals. This was before MSA-grading was implemented. Given that premium prices are now being paid for quality carcase, the reduction in carcse quality of nt821 carriers would now see a negative financial impact.

Minnamurra Questacon. Non carrier with plenty of muscle

The overarching breeding objective at Te Mooi is to produce high-quality carcase animals with enough growth to meet market specifications efficiently. Our goal is also to produce moderately framed fertile females that calve easily and get back in calf. We feel Speckle Park is well suited to the self-replacing herd model, not just for use as a terminal sire. To that end, our approach is balanced and holistic. The nt821 gene therefore has more negatives than positives for our program.

Wellerlou Moby T61

Our approach to the nt821 gene here at Te Mooi is that we don’t seek it out, but we don’t avoid it either. Several nt821 carrier bulls are in use this season including Minnamurra Plunderer P216, Minnamurra Nestor N73 and our latest acquisition, Wellerlou Moby T61. Over time our goal is to reduce its incidence in our herd. The main reasons for this are that the combination of reduced carcase quality and the difficulty in managing the nt821 in a commercial setting is offputting to many producers. A commercial producer would need to test retained females to determine their status and then manage those females differently from the non-carriers. The added costs, labour and complexity leads us to believe that the difficulty of managing the nt821 gene is a real negative. The reduction in meat quality in nt821 carriers also outweighs any increase in yield and muscle.