A while ago I was carrying out a Herd Performance Review on a farm in the Usk valley in SE Wales. The herd is high performing and high yielding (12,000 l/cow/year), fully housed and milked through three robots. To optimise robot workload they strive for a level calving pattern of 15 animals a month – the graph shows what they had achieved from Oct21 to Sept22. Three dips stand out for Mar/April, June and September. When we discussed the problem the farmer said in periods of heat stress nothing came bulling. Cross-referencing with our heat stress data for the Usk valley we saw that 9 months before the Mar-Apr dip we had a heat wave up to 32.2’C (average daily temperature) and 9 months before the June dip a heat wave up to 30.7 ‘C. It is hard to quantify the financial losses of such an uneven calving pattern but there will have been times when the robots were overloaded and milking visits will have fallen. The farmer considered these dips big enough to start installing fans in his sheds.
The Sept22 dip corresponds to a service-window around Christmas. Goes to show that although heat stress can cause fertility problems it is not the only cause!