SCANNING ewes around halfway through pregnancy is extremely important as it enables producers to manage feed requirements.
Liz Genever, Eblex livestock scientist, said scanned ewes can be separated according to feed requirement, which can reduce the total feed bill and help avoid metabolic problems around lambing time.
Scanning percentage, which is usually calculated by the scanner, can then also be used as a measure of the overall health of the enterprise. The figure is obtained by calculating the total numbers of lambs scanned and dividing it by the number of ewes put to the tup, then multiplying it by 100 to get a percentage.
She said: “The target scanning percentage will depend on the system and therefore needs to be established for each individual flock. It is worth comparing the scanning percentage year-on-year in order to identify any significant changes.”
Dr Genever said it was worthwhile looking at the barren rate, which is calculated by dividing the number of empty ewes by the number put to the tup and multiplying this by 100.
“If the barren rate is greater than five per cent, seek veterinary advice,” she said, “Making comparisons with results from previous years may also help identify any significant trends.”
“Looking at trace element levels may provide an explanation, but this should only be explored once other possible causes have been ruled out, such as feed quality during flushing, tupping and early pregnancy, body condition and ram fertility.”
She said the implantation of the embryo does not occur until 15 days after ovulation, so changes in condition or diet and stress during this period can affect implantation and reduce conception rates.
Nutrition plays an important role in determining embryo mortality in ewes, with low levels of feeding or body condition before mating increasing embryo loss and barren rate. High feed intake in early pregnancy can also reduce conception rates.
Dr Genever said: “Care should be taken regarding the composition of feed, as selenium deficiency and excessive phosphorus increase embryonic mortality. It is important to avoid grazing ewes in early pregnancy on red clover, kale or rape, as this can increase embryo loss. Mortality rates will also be higher in young or lactating ewes and in ewes subjected to climatic stress.
See the Eblex Better Returns Programme manual, Target Ewe Fertility for Better Returns.