The clocks are back and winter is coming even if the weather hasn’t realised yet! No one likes the end of the summer period, but the worst bit to me is the creep into short days – dark in the morning and evening with sometimes only gloom in between.

Cows don’t like short days either. I am reminded of this when I look at a broad range of production figures every year at this time and see the same seasonal slump. When cows (and any mammals including us) are exposed to longer dark periods there is a rise in melatonin which is an important hormonal messenger. How all the hormone interactions work is complicated and poorly understood, but the important bit for us is ultimately they lead to a fall in IGF (a growth hormone).  IGF is an important driver of growth and production. .

• Studies show an average of 2.5kg increase in milk production from cows in long days versus short days. The average production in these trials was in the high twenties so you can see how significant the effect is – in excess of 10%. Day-length manipulation stands along with 3 times a day milking and bST (artificial growth hormone injection banned in EU) in significance when it comes to stimulation of milk production.
• Fertility – Heifers get to puberty quicker in longer days. Cows also return to oestrous after calving quicker in long days than in the winter.
• Youngstock grow quicker and more efficiently in long days. There is also evidence of post puberty heifers laying down fat more in the short winter days than in long days – think about this and perhaps the effect of heifers at grass may not be all due to the grass!

Very significant benefits then – even better is that these studies showed animals operating at increased efficiency of food utilisation/conversion so the extra production was at lower extra feed cost.