This is an entry in the 2019 Australian Dairy Conference's Young Dairy Scientist Award.
The use of sex-sorted semen is regarded as a necessary step forward for the dairy industry in order to be efficient while maintaining good welfare, though many farmers are wary of implementing it due to low conception rates.
A key part of using sexed semen is knowing which animals to use it on and when. This study was developed to help in this decision and using this technology in conjunction with other management practices.
Sex-sorted semen allows a farmer more control of the direction of their business. It can mean more replacement heifers and faster herd genetic gain.
This can help maintain a good level of biosecurity on farm by not adding new animals. Not only that, it also can mean easier calving, given heifer calves are smaller for first-time calvers. If a farm is looking for a timelier return on investment, surplus animals can be sold.
Lower conception rates (33-72 per cent) are expected with the use of sex-sorted semen due to the amount of damage that is done to the sample during the sorting process. In order for sorting to be done at an 80pc accuracy, as is common with this product, more than 75pc of each sample is wasted. This means that money has to be regained for the technology as well as the loss of saleable product, resulting in a higher price tag.
In order to maximise the number of calves born when using sexed semen, it is imperative to use it at the right time. There are many synchronisation protocols around the globe with differing levels of effectiveness, dependent on a farm’s management practices.
Oestrus detection is a common and valuable tool in order to find the optimum time to inseminate cows and heifers. The problem is that it may take 2-3 checks a day by an experienced employee in order to find a percentage of which animals are ready to breed. This is time that most farmers want to spend doing something else.
Synchronisation is advantageous due to the ability to bring a group of animals into heat together. A five-day co-synch protocol has been shown in other studies to provide higher pregnancy rates than its seven-day counterpart, hypothesised by Colazo to be because it better matches the oestrus cycle of a cow.
On day 0, the animal is given a CIDR device, which is then removed on day 5. A scratcher sticker is placed above the animal’s tail at this point and it is given an injection of prostaglandin. Animals are then inseminated on day 8 and given a gonadotrophin-releasing hormone injection. This means that only three handlings are necessary for this protocol, with two pregnancy checks afterwards.
In the study, there were 199 heifers from two farms in South Western Australia included with a median weight of 314 kilograms, ranging from 248-405kgs. All heifers were a mix of Holstein Friesian, Jersey and Angus breeds and aged between 12-18 months of age.
Animals were sorted based on the detection of heat, half of each group were treated with conventional semen and the other half with sexed. In total, 76 animals were treated with sex-sorted semen and 78 were treated with conventional semen.
Two pregnancy detections were done 30-90 days after insemination by ultrasound. Due to lack of random selection, 45 animals were removed from the study.
There were 154 matings in total with 74 resulting in pregnancy (48pc). 115 animals showed heat (75pc) and of those, 55 resulted in pregnancy (48pc). Of the animals treated with conventional semen, animals that displayed no heat had a higher rate of pregnancy although there were fewer animals than in the heat group (19 vs 59). Within the sexed semen category, 6pc more pregnancies were produced with expression of heat than with no expression.
Overall, conventional semen had a conception rate of 62pc whereas sexed semen had a rate of 34pc.
The overall pregnancy results were lower than expected (50pc vs 55-65pc) this is believed to be due to 95pc of animals being below adequate weight for breeding. One farm repeated the program later in the season and received much more favourable results (62pc, 31/50 pregnant).
There are two hypotheses why this was. One is that the animals gained more weight due to improving feed and the other is that the first round forced the animals to ovulate and start cycling, resulting in a later pregnancy.
This program works but only if everything else on farm is running the way it should be. It won’t work unless the management program works.
There has been research to show that optimum profit occurs when conception rates between conventional and sexed matings are within 10pc of each other. This is what our industry should be working towards and potentially, the way of the future.
This project was undertaken at Murdoch University with supervisors Dr Herbert Rovay and Dr Joshua Aleri. Many thanks go to Western Dairy for funding and Dr Shane Ashworth for his participation in the initial stages.
The six finalists were: Caelie Richardson, Latrobe University (Vic).
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