This experiment was the first of my thesis, which is focused on optimising the rearing of young stock. This experiment investigated the feasibility of rearing the calf with the cow in a pasture-based setting, and the impact that such a system has on cow behaviour at weaning.
Learnings from this work provides options for the industry to pursue an alternative mode of rearing young stock, alongside learnings to help improve conventional practices.
We conducted two experiments. Experiment 1 determined the feasibility of rearing the calf with the cow in a pasture-based system. Experiment 2 determined these cows' response to separation, as compared with cows separated from their calf within 24 hours.}
- Six cow-calf pairs were contained in one paddock with strip grazing as per conventional rotational grazing systems.
- Cows were temporarily separated twice a day for milking, leaving their calves in the paddock.
- Calves were weighed once a week and daily milk yields were recorded.
- Behaviour was recorded for the first seven days and then two times per week thereafter.
- At 100 days calves were removed from the cow and sent to the abattoir to assess rumen development and meat quality.
- The stomach was compartmentalised, emptied, cleaned, and weighed.
- Another six cows were added to the study to compare the behaviour response to full separation of the experimental cows.
- Triaxial accelerometer neck collars (SCR Dairy, Netanya, Israel) were used to monitor rumination and activity of the experimental cows (100 days) and the control cows (~24 hours). }
- The average daily weight gain of calves was 1.42 kilograms/day (+/- 0.62 kg) (see Figure 4).
- Daily milk yield harvested between 10 and 20 litres/day. At weaning, the milk yield doubled, suggesting that the calves were drinking about 20L of milk per day at the time of weaning.
- Cows vocalised between 20-30 per cent of the observed time during the first three weeks. At week six this dropped to below 10pc of the time. Average vocalisations observed for the remainder of the study was 6pc.
- Most of the cow vocalisations were observed during physical separation of the cow and calf, and during the time cows were pushed to the parlour (see Figure 5).
- For all calves, the reticulorumen accounted for over half of the total stomach weight.
- Following full separation of the calf, experimental cows ruminated for 503 minutes/day compared to the control cows that ruminated for 376 minutes/day.
- Following full separation of the calf, activity levels of experimental cows were on average 697 minutes/day compared to the control cows 544 minutes/day during the three-day observation period. Both groups increase activity on the day of separation. However, control cows decreased activity the day after full separation compared to the experimental cows that decreased activity 2 days after separation. }
Discussion and conclusions
Calf weight gain in the experiment was double the industry standard, with an average daily gain of 1.42 kg/day compared with 0.7 kg/day. However, this may be reflected in milk consumption/milk yield.
The financial costs and benefits of this type of rearing system has not been evaluated, but will be an important outcome of further studies.
Vocalisation can be used to determine stress levels in cattle. After six weeks, the cows vocalise 10% of the time. The idea can be proposed that the cows display less stress in leaving their calf because they know their calf will be there upon return.
The industry standard for proportion of the total stomach weight contributed by the reticulorumen is 67pc in calves 12-16 weeks of age. The rumen weight of the calves in this study were smaller than industry standard, therefore future research into cow-calf rearing systems should focus on rumen development. A more objective measurement of rumen development would be useful.
Rumination is a low arousal, routine behaviour that has been used to assess stress, health, and welfare of cattle. Experimental cows spent more time ruminating than the control cows, suggesting they were less affected by calf separation.
However, there was an opposite effect on activity, whereby experimental cows were more active during the observation period than the control cows. Activity is a measure of arousal, and can increase during stressful events, therefore it is possible that the control cows were less stressed than the experimental cows.
That being said, we cannot determine that more activity equates to more stress because it is unclear the types of behaviours that are monitored by the neck collar. Further detailed behavioural evaluation is necessary to gain a greater understanding of the welfare impact of these two contexts.
This study has identified four potential advantages to rearing calves on the cow:
1. Calves doubling weight gain.
2. A more gradual weaning process for calves.
3. Creating new options for the dairy industry.
4. The possibility of a new revenue source from rearing bobby calves.
While we have demonstrated the feasibility of rearing calves on the cow in a pasture setting, the impact of scaling this up to larger herd sizes, loss in milk yield, time of weaning and rumen development still requires evaluation. Long-term studies can provide an understanding of suckling on immediate and future lactations. Furthermore, the impact on replacement heifer lactations is unknown.
I would like to thank my advisers Dr Cameron Clark and Dr Sabrina Lomax, from the University of Sydney, and Dr Dan Weary, Dr Nina Von Keyserlingk and Lara Sirovica, from University of British Columbia, for their support in this project. This project was the beginning of my PhD at the University of Sydney with a focus on optimising the weaning process in cattle.
*Sarah Mac is a PhD student at the University of Sydney, who took part of the Australian Dairy Conference's Young Dairy Scientist Award competition. This is an edited version of the article she submitted as part of that competition.}
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