THREE crucial management decisions impacting on the productivity of replacement heifers in northern breeding systems are bull selection, joining weight and disease prevention, an MLA-funded Producer Demonstration Site has shown.
Producers Doug and Zoe O’Neill were concerned about the performance of their maiden heifers on their property Mt Oweenee, north of Charters Towers.
With a group of like-minded producers, they approached Dave Smith, Queensland Department of Agriculture, and Dr Geoffry Fordyce, University of Queensland’s Queensland Alliance for Agriculture and Food Innovation, to run a Producer Demonstration Site to investigate how to lift heifer reproduction.
Given that reproductive performance is paramount to the success of any breeder herd, getting the management of replacement heifers right is vitally important for two reasons.
Firstly, replacement heifers are the foundation of the future breeder herd and, secondly, this group of females represents the largest age cohort in the herd. The ultimate goal, therefore, is to ensure that they conceive at the right time to have the best chance of getting back in calf the following year.
What tends to happen in many northern enterprises is that bulls are put in with maiden heifers at the beginning of the wet season and pregnancy-tested the following year in the middle of the dry season.
Even if reasonable conceptions rates are achieved, there is a fair chance that they did not actually get into calf until late in the wet season, which means they have a reduced chance of getting back in calf as a first calf breeder.
Even in continuously-mated herds, it is important to get the replacement breeders off to the best possible start.
The Mt Oweenee herd comprises a mixture of Brahman, Charbray and Droughtmaster cross cattle. Doug and Zoe usually mate heifers for about four months starting in January.
“The pregnancy rates in our maiden heifers was quite variable and ranged from 30pc in some years to around 70pc in others, and we needed to improve this,” Mr O’Neill said.
As part of the PDS, the O’Neills monitored the weights, disease status and cycling activity of their maiden heifers for a three year period starting in 2014.
“It was run over three dry and challenging seasons and our heifers had to be sent on agistment for some of that time but we persevered so we could collect the data. The effort was well worth it however and we have learnt some valuable lessons,” he said.
The lessons included:
Less bulls: Dr Geoff Fordyce recommended implementing fertility testing for bulls, which led to a reduction of bulls from 12 to four bulls per 350 heifers.
“It subsequently proved to be the right decision because it did not impact the conception rates and we ended up some $24,000 better-off immediately, as we reduced our bull cost/pregnancy from $21/pregnancy down to $7/head,” Mr O’Neill said.
Focus on health: Fertility diseases were also a major concern so the O’Neills vaccinated their bulls for vibriosis and monitored the herd for Pestivirus. Diseases of fertility were not a factor over the three years of the PDS and the heifers remained free of Pestivirus.
“While disease can causes crashes in some years if not managed properly, in most cases it is nutrition and the body weight of the heifers at joining that is usually the cause of poor performance,” Dr Fordyce said.
Worth the weight
At a recent field day at Mt Oweenee, DoA’s Dave Smith presented the body weight data that was collected at pregnancy testing, captured in the table below.
“It was too hard to differentiate between breeds in this PDS simply on phenotype but the key message is that we need to aim to have a target weight of 400kg in this herd at the time of pregnancy test,” he said.
“The economics and cost benefits of achieving this will vary from year to year but stocking rates and determining the phosphorus (P) status of your heifer paddock are paramount.
“If heifers are being run on P deficient paddocks, then a simple blood test at the end of the growing season will help determine if an extra 30-60kg can be obtained by simply supplementing with P over the wet season.”
Finally, the pre-puberty heifer traits are highly heritable and rapid progress can be achieved by selecting bulls with low age at puberty and good scrotal circumference measurements.
Dr Fordyce suggested that producers should target bulls from cows that produced a weaner and got back in calf as first calf cow.
“The trial was an excellent learning experience. We now know that our target liveweight at joining is around 350 kg and by identifying the non-pregnant heifers early, it has allowed us to make sound decisions going forward,” Mr O’Neill said.
“This year the price of these animals is very good and we will offer them for sale. They won’t be part of our breeder herd going forward.”
Take home messages:-
- Target mob average of 400kg at pregnancy diagnosis or 350kg at start of joining to get high pregnancy rates
- Foetal aging is a valuable tool in managing joining periods and preferably retain those heifers pregnant early in the joining period.
- Use fewer, but better bulls (maximum 2.5pc bulls)
- Though disease can be an issue, body weight at joining is the main problem
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