There have been several reports of wet silages with a high potential acid load (PAL), something causing sheep to eat less at an important time.
John Vipond, senior sheep specialist with the college’s SAC Consulting team, says: “When you are totally reliant on silage for energy supply it is very important you monitor consumption. If your silage analysis shows a PAL figure of more than 1,000 and certainly 1,200, intake will be reduced, putting ewes at risk of pregnancy toxaemia. It is more likely to be a problem with wetter silage, below 20 per cent dry matter.”
In addition to older ewes, Dr Vipond is also concerned about gimmers, lambing for the first time and possibly unused to silage. It is important to introduce them to high PAL silages gradually as a sudden intake might cause a sore stomach, making them avoid the fodder in future.
One way to check if silage is meeting energy requirements is to have a vet blood test six ewes in each management group for betahydroxybutyrate levels, four weeks before lambing.
However, as a rough consumption guide Dr Vipond suggests test weighing bales or a load of pit silage four to six weeks before lambing to work out what ewes are eating.
“An 80kg ewe should eat 1.2kg dry matter, or about 5kg/ewe day of fresh silage with a 250g/kg dry matter content, allowing for a little wastage.” He advises re-testing the silage if it is suspected the dry matter content across the pit varies.
According to Dr Vipond, all pregnant ewes, particularly those with triplets, benefit from more trough space.
“However, as sheep can neutralise high acid silage with saliva allowing the extra trough space, to a maximum of 45cm, also encourages ewes to eat little and often, increasing their saliva production and helping them cope.”