A critical way to reduce the spread of disease from one season to the next is by removal of soiled bedding and thorough cleaning of the calf shed. Ideally this should be done as soon as possible after the last calf leaves the shed.
Calf hood morbidity (“sickness”) appears to have lasting effects on growth, age at first calving, milk production and longevity.
Research has shown that calves have the highest risk of scours in the first and second weeks of life and this risk declines to a low level by four to six weeks of age.
The risk of respiratory disease does not decline as rapidly as that of scours and remains at a reasonably consistent level until 12 weeks of age.
The presence of respiratory disease at two to four months of age negatively affects average daily gain (ADG), body weight and height.
Research suggests that the presence of septicaemia and/or pneumonia during the first six months of life reduced growth by 13-15 days.
This means it took affected calves 13-15 days longer to achieve the same weight as healthy calves.
The effects of calf hood morbidity on age at first calving (AFC) have also been described. One study demonstrated that heifers which were treated for scours in the first three months of life were nearly three times more likely to calve after 30 months than those not treated for scours.
Additionally, the negative effect of calf hood morbidity on lactation performance indicators such as 305-day milk, fat and protein production suggests that health status early in life can affect production up to two years later.
Research from the United States suggests that calf hood morbidity impacts long term herd survival.
Calves treated for pneumonia in the first three months of life were two and a half times more likely to die between three months and two and a half years, when compared to calves that had not been treated for pneumonia. A similar effect was seen for calves treated for scours less than three months of age, in that they were two and a half times more likely to be sold compared to those not treated for scours.
Thus, the long term effects of calf hood morbidity are multi-dimensional.
Every effort should be made to reduce morbidity rates by provision of pro-active, holistic veterinary advice.
Key performance targets and benchmarks play a role in setting defined goals in an outbreak situation along with routine monitoring of dairy calf rearing performance.
Why do we need benchmarks?
Contrary to the resources available in the dairy reproduction and milk quality fields, performance benchmarks for dairy calf rearing have not been established in Australia.
The Fertility Focus Report (InCalf) and Mastitis Focus Report (Countdown Downunder) have enabled advisors and farmers to identify key areas within their system, allowing strategic advice for improvement.
Key performance indicators such a six-week in calf rate, not-in calf rate, total clinical case rate and new infection rate allow proactive decisions to be made and clear goals to be defined.
In some cases there is a general acceptance of high morbidity (sickness) in dairy calves, with such farms relying heavily on mass antibiotic usage.
However, high levels of mortality (death) are less well tolerated and it is usually at this point that veterinary intervention is sought.
An outbreak situation is likely to be fairly dramatic, requiring strong, yet not always sustainable recommendations in an attempt to reduce the inevitable high morbidity and mortality rates.
This raises the question: “If the farmer had been aware that they were achieving a suboptimal level of care in their calf rearing, could earlier veterinary intervention prevented the outbreak?”
This proactive approach is synonymous with that of Countdown Downunder and InCalf, yet it seems to have been omitted from the dairy calf rearing field.
Development of performance targets
Data from Australian research has allowed development of preliminary benchmarks for passive transfer of immunity from colostrum, morbidity rate and mortality rate.
Based on this research, the performance targets within a given calf rearing period are:
• Failure of passive transfer: Less than 20% of calves in a group (minimum of 12) with serum protein <5.0g/dL
• Pre-weaning morbidity rate: Less than 10% of calves should be treated with antibiotics and/or electrolytes
• Pre-weaning mortality rate: Less than 3% of calves should die during this period, regardless of the cause of death.
Your vet can discuss with you the requirements for passive transfer testing.
Passive transfer of immunity allows an early indicator of whether calves are receiving sufficient colostrum to combat disease.
Calculation of morbidity and mortality rates rely on accurate records of any sick or treated calves and any deaths that occur during the calf rearing period.
The main thing to remember when referring to these benchmarks is that they are achievable.
Scope for the future
Australian dairy calf rearing systems are very different to those in the United States.
These preliminary performance targets have been developed from data collected on commercial dairy farms in south west Victoria, Australia.
They require further validation in the broader industry in order to become absolute.
However, in the author’s opinion they are a useful objective guide for farmers and veterinarians, providing early indication for improvement.