Genetics

Weekly genetics review: Exploring reproductive traits in temperate beef breeds

Genetics editor Alastair Rayner 15/10/2024

REPRODUCTIVE performance is a crucial factor in the beef industry, significantly impacting profitability and herd efficiency. In southern Australia there can often be an impression that fertility traits are well understood with clear benchmarks established for producers to consider in their selection decisions.

However this impression is open to challenge, with results from research projects such as the Southern Multi-Breed project developing new insights that can assist producers looking to increase their reproductive performance.

In work published in 2021 by Dr Kath Donoghue and a team from the Animal Genetics and Breeding Unit, NSW DPI and UNE, results from work focussed on fertility traits in several Australian temperate beef breeds.

The study examined how traits such as age at puberty (AP), days to calving (DC), and return to oestrus (RO) are influenced by genetic and environmental factors, with the aim of improving reproductive efficiency in the beef industry.

Across production systems, key traits such as early age at puberty, short calving intervals, and faster return to oestrus after calving are highly desirable. Collectively these traits can contribute to greater efficiencies in herd management, increase the number of calves produced over a cow’s lifetime, and improve overall profitability.

Moreover, the ability to identify sires that transmit favourable reproductive traits is essential for genetic improvement in beef herds. Studies in both tropical and temperate environments have shown that fertility traits are heritable, providing a solid foundation for genetic selection programs.

The study involved 571 females from six beef breeds: Angus, Brahman, Charolais, Hereford, Shorthorn, and Wagyu. These females were monitored for fertility traits from weaning through to their second mating.

The research forms part of the Southern Multibreed (SMB) project, which is being conducted across several research facilities in New South Wales. The key traits evaluated were age at puberty (AP), days to calving (DC), and return to oestrus (RO) following the birth of their first calf. These traits provide insight into the reproductive potential of the animals and are critical for improving the efficiency of breeding programs.

Age at Puberty

Age at puberty is a fundamental fertility trait that indicates when a heifer becomes reproductively mature. In this study, serial ultrasound scanning was used to detect the first corpus luteum (CL), a sign of puberty.

AP was found to vary significantly across the six breeds, ranging from 7 to 27 months, with an average of 12 months. This variation highlights the influence of both genetic and environmental factors on the onset of puberty.

Of the 571 heifers studied, 72pc were pubertal by the time of joining at 15 months of age, though this percentage varied between breeds and sites.

The study found a strong positive relationship between AP and DC, suggesting that heifers that reached puberty at a later age also calved later. This finding aligns with previous research, which has shown that delayed puberty is often associated with delayed conception and calving.

Heifers that reach puberty earlier are more likely to conceive earlier in the breeding season, resulting in shorter calving intervals and greater reproductive efficiency.

Days to Calving

Days to calving (DC) is another critical fertility trait, reflecting the interval between the start of the mating period and the birth of the calf. The study recorded 542 DC values, with a range of 273 to 386 days and an average of 316 days.

Females that failed to conceive within the mating period were assigned a penalty value, which extended their DC record. Like AP, DC is an important measure of reproductive performance, as cows that calve earlier in the season have more time to recover and cycle before the next mating period, increasing their chances of conceiving again.

Return to Oestrus

The return to oestrus (RO) after calving is a key indicator of a cow’s ability to resume reproductive activity. Cows that return to oestrus sooner after calving are more likely to conceive in the next breeding season, reducing the interval between calves.

In the study, RO ranged from 1-6 months post-calving, with an average of 3 months. Only lactating females were included in this analysis, as RO is influenced by both the cow’s recovery post-calving and her ability to produce milk.

Interestingly, the study found a weaker positive relationship between AP and RO, indicating that heifers that reached puberty at a later age also took longer to return to oestrus after calving.

However a weak negative relationship was observed between DC and RO, suggesting that sires whose progeny calved later in the calving season exhibited a quicker return to oestrus. This finding contrasts with previous research in tropical breeds, where a positive relationship was found between DC and lactation anoestrus interval.

The relationships between these traits provide valuable insight into the genetic factors influencing reproductive performance in temperate beef breeds.

By identifying sires whose progeny reach puberty earlier and return to oestrus more quickly after calving, beef producers can make more informed breeding decisions to improve reproductive efficiency.

The study’s findings suggest that selecting for earlier puberty and shorter intervals to oestrus can enhance the overall reproductive performance of the herd, leading to higher lifetime productivity.

 

Next week: Genetics editor Alastair Rayner examines progress in polled breeding among popular beef breeds – a core objective in the Australian Beef Sustainability Framework measurables.

 

Alastair Rayner is the General Manager of Extension & Operations with Cibo Labs and Principal of RaynerAg.  Alastair has over 28 years’ experience advising beef producers & graziers across Australia.   He can be contacted here or through his website www.raynerag.com.au

 

 

 

 

 

 

 

 

 

 

 

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