Penny Young, ASAS/ASAP Intern
Despite most producers wanting to maximize their output, calving percentages have not changed dramatically over the past few decades and this trend does not seem set to change into the future. Dr Leo Cummins believes ‘twinner’ cattle could change this trend, and shift producers’ goals from a calving percentage of 90% to 130% or beyond. However, many producers are wary of pursuing twinning in their herd, and despite some benefits, for many the costs and risks seem too great.
In the 1980s, interest in twinning in cattle grew and prompted major research projects in the USA and Australia, with significant research occurring in Hamilton in Victoria and Grafton in NSW. Despite this initial enthusiasm and some long running research, producers have not embraced twinning, with the main proponents still being amongst researchers. While researchers claim the benefits outweigh the negatives, it seems producers still fear the downsides of twinning.
The US-MARC twinning study in Nebraska, USA found that the negative impacts of twinning include decreased neonatal survival, more retained placentas, more dystocia due to malpresentation, more days to oestrus and pregnancy postpartum, lower conception rates, and the risk of freemartin heifers. It is perhaps not surprising then that many producers have avoided selecting for twinning, especially when considering that changes in reproductive traits generally take some time to improve due to low heritability.
Dr Leo Cummins has been one of the few to embrace twinning in his herd, after being involved in twinning research projects at Hamilton, and has seen quite positive results. While he acknowledges that more work needs to be done to make a twinning herd commercially viable on a large scale, he has found, like others, that a twinning herd could result in benefits overall. Aside from potential reductions in greenhouse gas emissions, which will likely become more important into the future as pressure mounts to manage climate change, increased profits are an obvious motivator. Despite the lower individual weights of twin calves, it must be remembered that twins result in a greater total when calf weight is considered per cow. Dr Cummins’ experience has found that in the case of twins, the weaning weight is around 160-170% of a cow with a single calf. This translates into greater profit per pregnancy.
Research has also found that, generally speaking, twinning can be implemented without compromising growth rate or carcass merit, meaning that these calves are normally still graded well, and despite their slightly lower weights at birth (around 80% of a normal cow in Dr Cummins’ herd) they tend to do well throughout life. After the first few days, the twin calf group should be able to be handled as a normal herd, and while neonatal calf mortality is worse for twins, there tends to be no greater mortality amongst twins after those early days. Dr Cummins also reports that there has been little impact on fertility in his herd, despite what research has found. Fertility could perhaps be influenced by environment and feed availability, as animals in a nutrient rich environment may cope with and recover better from the greater demands imposed by a twin pregnancy.
How could twinning be made more viable?
For twinning to be made more attractive to beef producers, the risks associated with it need to be addressed. Thus selection for twinning will be most effective when paired with selection for animals with lower rates of dystocia and improved rebreeding rate (even with twins), although this is likely to be difficult. Management at all stages of reproduction should also aim to mitigate the risks, and is likely to prove more effective at improving outcomes.
Researchers suggest that determining which cows in the herd are carrying twins vs single calves is crucial for improving outcomes. Separating the herd and providing greater nutrition and supervision to the twin-pregnancy cows should help to ensure that all animals receive the nutrition and assistance they require. Supervision prior to calving is also important in order to provide assistance in cases of dystocia, and it must be remembered that cows carrying twins tend to calve roughly a week earlier than cows with single calves.
Managing difficult calvings is important, as it appears that the increased risk of placental retention is linked to the increased risk of malpresentation dystocia and reduced gestation length, as studies have found that even in single calf pregnancies, dystocia and shorter gestation length are associated with increased placental retention. This is significant in terms of reproductive ability, as Echternkamp and Gregory published work in 2002 that indicated that placental retention reduces subsequent conception rates by 7-8%, whether in single or twin birth cases. Dystocia also has a role to pay in the increased calf mortality seen in twins; so good management can help to prevent losses in that regard too.
Management of the calves and cows in the first few hours or days is crucial, as producers must watch for rejection of one of the twins. It is also good practice to provide extra colostrum to ensure both twins receive sufficient protection and nutrition. Efforts should also be made to ensure male-female twin pairs are noted, as the females will most likely be freemartins.
Some research suggests that weaning calves early (between 6-8 weeks of age or even earlier) can help to improve postpartum reproductive performance, and thus early weaning strategies might be implemented for cows with twins in order to reduce the lengthening effect twin births usually has on return to oestrus and interval between conceptions. This may pose a challenge for producers and is quite different to standard practice in southern Australia, but serves as a reminder that some of the potential negative aspects of twinning can be overcome. However, the benefits of early weaning were found to be less significant when cows are well-nourished.
More extensive economic modelling and assessment would also be useful in order to determine if the economic returns from twinning do indeed help to offset the increased costs associated with greater feed requirements, more intensive management and potential impacts to cattle health. The pay-off may vary depending on the environment and production system, so it would be interesting to determine where twinning in beef cattle could be best implemented.
For further information, the following articles and papers are a good start:
Brief summary of US-MARC study: http://www.beefmagazine.com/cowcalfweekly/marc-studies-productivity-twins-triplets
Report by K. A. Nephawe: http://www.bifconference.com/bif2002/Baker_Essay_pdfs/Nephawe_02BIF.pdf
Research from Australia (1990s): http://www.asap.asn.au/livestocklibrary/1992/Cummins92a.PDF
Information about Leo Cummins’ herd: http://www.twinnercattle.com/
(Feature image from http://www.twinnercattle.com/)