Technical information - Reproduction

Variation in Lactation Anoestrus in First Calf Cows in Tropical Cattle



A major research project within the Cooperative Research Centre for Beef Genetic Technologies (Beef CRC) has provided very useful information on the success of lifetime production in Brahmans and Tropical Composites in Northern Australia. One of the primary objectives of the Beef CRC project was to investigate what effect genetics had on the Post-Partum Anoestrus (period between calving and a return cycling) in first calf cows and consequently what opportunities may exist to improve fertility rates in Northern Australia through genetic improvement.

Project Design

A total of 2137 cows were involved in the project (1020 Brahmans and 1117 Tropical Composites (TC)). The cows (also used in the age of puberty studies) were breed on 7 co-operator properties (4 Brahman and 3 TC) and at "Belmont Research Station" which breed both Brahman and TC. Genetic linkage, across properties of origin and year within genotypes was generated by the use of AI. The cows were generated over 4 and 3 years for Brahmans and TC respectively. The cows were allocated according to genotype, property of origin and sire to one of the following four properties "Toorak" Julia Creek, "Belmont" Rockhampton, "Swans Lagoon" Ayr and "Brian Pastures" Gayndah at weaning. Belmont and Toorak ran both Brahman and Tropical Composites while Brian Pastures only had Tropical Composites and Swans Lagoon with the harsher environment only had Brahmans.

The project continued until all the cows were around 8.5 years of age and given the opportunity to have 6 calves and mated for the 7th time. The cows stayed in the project unless they failed to wean a calf in 2 connective years or were culled on management decisions (eg. temperament, udder etc.) Cows were naturally mated for 12 weeks and during this period the cows were ovarian/pregnancy scanned at 4 week intervals from joining by the use of real time ultrasound by an experienced scanner. The cows were also scanned a further 4 times after mating and prior to calving. These were half way between mating and weaning, weaning, half way between weaning and pre calving and around 3 weeks prior to calving. Other data collected at each scan was live weight, condition score and a P8 fat measurement.


Lifetime annual weaning rates

The research showed that lifetime annual weaning rate for Brahmans was 60% for those animals involved in the project (1020 cows) and 72% for those cows present at the end of the project (717 cows)at mating 6. The TC had a 73% lifetime annual weaning rate for animals involved in the project (1117) and 83% for those animals present in the project (898) at mating 6. There was an annual calf loss rate of 10% for both the Brahman and TC between calving and weaning for all animals involved in the project (2137). The calf loss rate for those animals that were retained in the project till the end had an annual calf loss of 5% for both Brahmans and TC. It must be mentioned that about 40% of the Brahmans were run on the harsher conditions at Swans Lagoon.

Genetic Effects

Although results from the Beef CRC research show the heritability estimates for lifetime annual weaning rate were low Brahmans 0.11 and 0.7 for TC. Further analysis revealed that there was a 13% difference due to genetics in lifetime annual weaning rate between the top and bottom Brahman sire daughters included in the research trial as shown in Table 1. The difference in lifetime annual weaning rate in TC was not as large as the Brahmans with a 4% difference between the top and bottom sires daughters. Total calves weaned from mating 1 and 2 were moderatly to highly correlated with both lifetime calving and lifetime weaning rate in both Brahman and TC.

Table 1: Difference in lifetime weaning rate EBV between top and bottom Brahman sires in % more calves per year

Calving Rate Figure 1

Figure 1: Calving Rate and Weaning rates % for all cows and those that remained in the project at mating 6.


The results emphasise the substantial opportunity that exists to improve lifetime annual weaning rates in tropical beef cattle breeds by focusing recording and selection on early in life female reproduction traits. Several Traits recorded at the first two matings with moderate to high genetic correlation with lifetime reproduction. The measurements that are correlated with lifetime reproduction range from ultrasound scanning for conception, to manual palpation for pregnancy to observation of a calf born and the number of days after mating the calf is born. The results also showed the days to calving is highly correlated with these measurements and producers using days to calving in their selection will also improve early and lifetime reproduction program. Opportunities exist to improve lifetime weaning rates by collecting accurate birth and female reproductive performance information with BREEDPLAN for the calculation of Days to calving EBVs (particularly reproductive information for maiden heifers and first calf cows), and careful consideration of Days to Calving EBVs when selecting both sires and dams for use within a breeding program.

For further information contact:

Paul Williams

Tropical Beef Technology Services

Phone 07 4927 6066