STRESSED HEIFERS: LOWER YIELDS?
WHEN and how heifers are introduced to the milking herd may result in different stress levels and milk yields.
Work has just finished on a heifer stress project at ADAS Bridgets, Martyr Worthy, Winchester, Hants. Initial results suggest that introducing heifers to the milking herd five days after calving, rather than within 12 hours of calving may reduce stress and boost milk yield.
However, researchers Richard Laven and Ruth Lawson are anxious to point out that experimental data hasnt yet been analysed, and more detailed information will be available after that.
But Miss Lawson explains that reducing competition stress should help increase heifer milk yields. "Within any herd theres a hierarchy. A newly introduced animal doesnt know where it is in that hierarchy and has to establish its place – placing stress on a heifer."
The trial aimed to find ways of reducing stress on heifers, which are generally submissive, to improve welfare and production.
Five groups were set up, each of 20 animals at all times. While in one group, all 20 animals were heifers, the others contained 10 heifers and 10 cows. One group had access to 25 cubicles while the other groups had 20. Heifers were introduced either five days after calving, or after afternoon or morning milking – in both cases within 12 hours of calving.
Heifer heart rate was examined by fitting them with heart rate monitors which they wore for 48 hours after being introduced to the group. According to Mr Laven, heart rates recorded were about a third higher than the text book rate, and were highest in heifers added to groups within 12 hours of calving.
Cubicle lying times and movements were also assessed. Infra-red beams, video cameras and burglar style movement detectors were installed, but data from this experiment requires detailed analysis, he says.
"An initial assessment of results suggests that introducing heifers five days after calving is the least stressful option, but we need to assess whether reducing stress results in better milk yields and how much this approach would cost producers – it may also be difficult where farms are all-year-round calving."
Milk yield results are still to be fully analysed, but Mr Laven says that there does appear to be a difference, but only statistical analysis will show whether this is significant.
But Miss Lawson has no doubt that anything which can be done to reduce heifer stress must be worth considering. "Its not just stress of introduction to a new group thats a problem for heifers – for instance, they must compete with older, more dominant cows for food and lying area – heifers tend to get the worst of everything in a herd." *
• Herd hierarchy
• Establish position in herd
• May affect milk yield