Why do some cows give more milk in the parlour in a cow-with-calf system? Investigating effects of cow age and sex of her calf on behaviour and milk production
SRUC and University of Edinburgh, MSc project
This study took place on Rainton Farm, where cows are milked once per day through the parlour and are housed or at pasture with their calves for the rest of the day. It has been previously noted that there is a large variation between cows in the amount of milk harvested in parlour when cows and calves are kept together, with some cows producing as little as a few litres per day and some as much as 15l. Wider variation between cows with calves, compared to cows solely milked through a milking parlour, has also been noted in other studies.
There could be a number of possible reasons for this:
Range of cow ages at Rainton Farm, which is known to affect milk production
Sex of the calf, which may affect milk production, a phenomenon known as differential ‘maternal investment’
Research in other wild species has shown that mothers may ‘invest’ more in their male or female offspring if this differential investment results in more grand-offspring or better survival. This maternal ‘investment’ can take the form of a higher production of milk (nutritional investment), or more time spent caring for that offspring (behavioural investment).
To investigate whether the variation in milk yield observed is due to age or is related to the sex of the calf, a number of datasets were analysed and observations taken.
RESULTS
To assess effect of age and maternal investment on milk harvested through the parlour, milk yield data from the first month after calving for the 2019 autumn calving group and the 2020 spring calving group (a total of 111 cows) were analysed. The analysis showed:
There was a large variation in yield, with average daily yield recorded in the parlour ranging from 1 to 23 litres of milk for different cows
Cows with a heifer calf at foot gave over 2 litres/day more in the parlour than cows which had a bull calf at foot
Older cows gave more milk, which is widely known
To assess behavioural investment in heifer and bull calves, observations of the cows were made for 3 hours per day, for 5 days per week, for 5 weeks, from the start of calving onwards. The number of suckling bouts between cows and calves, and behaviours directed towards the calf, such as licking and nuzzling, were counted. The results showed:
Cows with bull calves licked their calves more than cows with heifer calves
Bull calves were observed to suckle from their dams slightly more frequently than heifer calves
Discussion
Overall, results suggest that cows show more behavioural ‘investment’ or care for bull calves than for heifer calves. The higher levels of milk yield seen in cows with heifer calves is harder to interpret. The dams of bull calves may have less milk available to be given in the milking parlour because the bull calves are drinking more of their dams’ daily milk production. Alternatively, there is some physiological influence, as yet undiscovered, that induces a higher yield in the dams of heifer calves.
For farmers with a cow-with-calf system, this suggests that more female calves will result in a higher amount of milk for sale. However, bull calves appear to benefit from the opportunity to suckle from their dams. Further work is necessary to fully understand all of the influence on milk yield and to determine the best way to manage cow-with-calf systems to maximise saleable milk, whilst promoting high levels of animal welfare.