Technical information - selection

Is there a conflict between selecting females for reproduction and carcase traits of the male progeny in the Northern Beef herds?

BRAHMAN NEWS MARCH 2011 Issue #170

by Philip Mann Tropical Beef Technology Services

Improved female reproductive performance of beef herds in Northern Australia is an important means of increasing profitability.

Genetic improvement of this trait in industry has generally been limited due to the late expression of traits and their low heritability. The Beef CRC has conducted extensive research into this area to find early female indicator traits for whole of life female reproductive performance. Age of puberty has been identified as a potentially suitable trait for this purpose. Age of puberty was measured in the research as the age at which a Corpus luteum was detected via ovarian scanning at 4-6 week intervals commencing when the average of 200kg lwt. was achieved.

In Brahmans, the Beef CRC research has found that age of puberty has a heritability of 53% and is highly correlated (0.86) with days to calving measured on the first calf of heifers mated at 25-27 months. The same research has also provided indications that selection on age of puberty in Brahmans will result in reduced time for cows to return to oestrus following calving and have a higher frequency of ovulations prior to weaning (in younger cows at least). While these results are very encouraging for genetic improvement of female fertility we also need to know if selection to improve this trait will have associated trade offs with other economically important traits.

The Beef CRC research has looked at answering this question. This research used a total of 2159 heifers of two genotypes (1027 Brahman and 1132 Tropical Composites) that were bred on co-operator properties in Queensland and Northern Territory and raised on the research properties of "Toorak", "Belmont" and 'Swans Lagoon" (Brahman) and "Toorak", "Belmont" and "Brian Pastures" (Tropical Composites). The Tropical Composite was made up of 50% tropically adapted Bos indicus and Bos taurus e.g. Brahman and Belmont Red and 50% non -tropically adapted Bos Taurus. In addition to the age of puberty, these heifers were measured for a range of adaptive, growth and body composition traits from weaning through to joining at 27 months of age. A further 2216 paternal steer half sibs to these heifers were also used in the research and measured for growth and body composition, on grass and in the feedlot, and slaughtered to determine carcase and meat quality traits. A total of 53 Brahman sires and 50 Tropical Composite sires were represented in the male and female progeny.

A particular focus of this research was to determine genetic correlations between the heifer traits for puberty and adaptation and those of steer performance, carcase and meat quality i.e. can we improve steer performance without compromising female performance and adaptation in the Northern beef industry?

In relation to selection for improved female reproduction using age of puberty and steer carcass and meat quality traits, the initial results of significance are:

  • Large differences exist between genotypes in terms of genetic correlations of female fertility, as measured by age of puberty, and steer carcase traits
  • For Brahmans, reducing the age of puberty in females is genetically correlated to (genetic correlation in parentheses);
  • Increased RBY% in feedlot finished steers (-0.55)
  • Reduced feed efficiency of feedlot steers (-0.60)
  • Reduced (darker) meat colour in feedlot finished steers (0.73)
  • Reduced hip height (frame size) in feedlot finished steers (0.50)

For Tropical Composite, reducing the age of puberty in females is genetically correlated to;

  • Increased marble score of feedlot finished steer carcase (-0.49)
  • Reduced steer carcase rump fat (0.43)
  • Increased serum insulin like growth factor 1 (IGF-1) of feedlot finished steers (-0.58)

While some antagonisms exist between the improvement of female fertility in terms of reduced age of puberty and steer traits (mostly Brahman) many carcase and meat quality traits can be improved through selection without compromising selection efforts to improve female fertility. Of particular importance for Brahman is the ability to select for reduced Shear force for improved meat tenderness.

Further data in relation to a females 'whole of life' reproductive performance and correlation to economically important traits for both sexes will be analysed in the near future. The results from these analyses will confirm if the current correlations remain or if better early indicator traits exist to enable selection for improved female fertility in the Northern beef herd.