Genetics

Weekly genetics review: Is navel gazing impacting your herd’s fertility?

Genetics editor Alastair Rayner, 17/10/2023

CATTLE descriptions and terminology in Australia can often vary significantly between regions, market sectors and even between breeds. While there is a national language for livestock description that has been agreed to, and published by Meat & Livestock Australia and AusMeat, there are still many subjective descriptions that are frequently used to describe cattle and traits.

Quite often these subjective descriptions are used in reference to particular traits of an animal.  Occasionally these descriptions reference the trait with an inference that it will have some association or relationship with a production outcome such as growth or fertility.

For many producers, these inferences are often unclear and cause confusion. It may be the inference is that the presence of a trait in the physical appearance of the animal is a positive one and beneficial for production.

However, to another observer the same trait could be seen as a negative and less desirable feature. More importantly for many observers, there is some confusion as to why the trait is even being remarked upon, and what relevance it may have in a breeding program.

In the Bos Indicus breeds, this is particularly true when it comes to observations about the loose skin at the navel. Producers who have watched and listened to comments at shows and sales will often hear comments reflecting on an animal’s loose skin and navel. From these comments it can be difficult sometimes to determine if this is a positive or negative trait, and what relationship it actually has with production.

One source of confusion for many producers is associated with the desirability of looser skin and an animal’s ability to dissipate heat. Tropical adaptability or heat tolerance is a one of the major reasons for many producers to source and use Bos Indicus genetics, and there is often an unwillingness to risk a compromise on this trait. As a result it is possible some producers are prepared to accept and use animals, particularly females that have looser skin, and as a result looser navels.

Lifetime reproduction studies

While there are often anecdotal examples provided by some producers that this approach, or looser navels, are not detrimental to production, there are some useful research results from the Beef CRC and Northern Repronomics projects which may help producers rethink these examples.

In the case of lifetime productivity, CRC research conducted on 2159 Bos Indicus females, published by Dr Matt Wolcott, Dr David Johnston & Steve Barwick found there was no indication that genetic variation in navel scores affected lifetime reproduction.

This research reflected earlier CRC research on the genetics of adaptive traits in heifers. This earlier research found that traits such as tick resistance, temperatures (measured rectally under hot conditions) coat scores and coat colour along with navel scores and flight-time had generally low phenotype correlations with each other, and no genetic correlations, which means these traits are independent of each other.

The practical application of this research is that for producers wanting to address or ensure adaptive traits are not compromised, loose navels do not necessarily represent a useful trait for inclusion in selection decisions.

Also emerging from the research was a better understanding of the heritability of navels.  Every animal in these studies were scored on a 1-9 scale (1 = very pendulous to 9 = extremely tight along the underline).

The data demonstrated a moderate heritability (0.33) for the navel.  This data should be of particular interest to producers as the looseness of navels strongly influences the angle of sheaths and pendulousness of sheaths in Bos Indicus bulls.

During the 1990s, significant research was carried out to investigate the physical traits that producers should consider when selecting bulls for use in Northern Australia. The research was conducted by Mike McGowan and others from the University of Qld and the QDPI using Santa Gertrudis (three-eighth Brahman), Brahman and Belmont Red bulls.

Source: M.R. McGowan et al. / Animal Reproduction Science 71 (2002) 25–37

This work identified that in Brahman bulls there was a positive relationship with umbilical cord thickness and the depth of the sheath. It was also found that these two traits had a negative relationship with the number of mounts and serves in a serving capacity test.

In three-year-old Santa Gertrudis bulls, the navel was negatively related to the number of serves in a serving capacity test. The research suggested that the combination of a thickened umbilical cord remnant and enlarged navel may result in a mechanical interference in serving ability.

While navel score may not impact on lifetime productivity of Bos Indicus females, there are significant implications for breeders seeking to produce bulls.

Given the moderate heritability of the trait, efforts by breeders to improve both the angle and reduce the depth of the sheath in bulls, have to include selection in both the breeder herd and in the use of bulls at joining.

Breeders wanting to make improvements through the use of bulls with tighter sheaths could find their efforts to improve restricted if there is a high number of loose-navel females in the breeding herd.

 

Alastair Rayner is the Principal of RaynerAg, an agricultural advisory service based in NSW.  RaynerAg is affiliated with BJA Stock & Station Agents.  He regularly lists and sell cattle for clients as well attending bull sales to support client purchases.  Alastair provides pre-sale selections and classifications for seedstock producers in NSW, Qld, and Victoria.  He can be contacted here or through his website www.raynerag.com.au

 

 

 

 

 

 

 

 

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  1. Brett McCamley, 18/10/2023

    Unfortunately, whilst thought provoking and backed by some research, the topic of sheaths: looseness(depth), Umbilical cord thickness, and navals, have a high monetary value to the broader beef industry, particularly those that use multiple bulls in a group of females. Firstly calves born with a thick umbilical cord have a predisposition to infection and bleeding out after birth, this can also lead to rosettes in the naval at a later date (there are certain bloodlines that are prone to this). Last, but by no means least, depth of sheath, this is probably the single highest cause for failure/culling of bulls from a breeding program in the north. Depth of sheath can be a huge problem in speargrass/spinifex country, also it is a very big problem with bulls fighting and hence bulls breaking down due to sheath damage. For anyone to say there is no relavence to placing an emphasis on this, has never been outside their own backyard.

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