What are your PD results telling you? By Andrew Rafferty, Strathspey Vets
The large animal vets in our Highland practice are busy scanning spring calvers just now. We had a reasonable summer which allowed some good silage to be produced, most farms have plenty to see them through to the spring. The good grass growing summer is evident in the condition of the cows and reflected in the scanning results.
Results have been good, with one or two exceptions. We would hope for 95% to be in calf when we scan, usually at 3-5 months in calf. If we find more than 10% barren, we start to worry and investigate. Of course it can be difficult to make a diagnosis of the cause of infertility because we are scanning several months after the event. Also, we may be scanning a difficult bunch, i.e. ones that may have had a difficult calving last spring, old or repeat breeders, so caution must be exercised before jumping to conclusions, a good understanding of the herd history is essential.
The most common cause of poor conception, apart from the bull, is low energy and protein in the ration at key points during bulling and early pregnancy. Spring calvers have the benefit of being bulled at grass, where the diet is usually good, especially late spring. However, this is not necessarily the case throughout summer. Autumn calvers need to be carefully monitored to ensure good conception, as they are being bulled on winter rations. Analysis of the winter diet is a sensible action. Trace elements are important also, but low trace element levels may not be the sole reason for poor conception in a herd, so results need to be treated with caution.
If suspicious of a bull problem, rushing in to check his semen quality may miss a problem of lameness or penis problems such as corkscrew. The semen may be a good quality, but he can’t get it to the place it needs to be, i.e. inside the cow. I usually ask for a video taken on a mobile phone of him serving to be sure he can serve properly. The problem with the modern electro-ejaculator (EEJ) is we are not seeing the bull jump and it can sometimes be difficult to get a representative sample. Caution needs to be exercised when a poor sample is taken with the EEJ, it may not be representative, and a second sample should be taken. The old fashioned Artificial Vagina gave a much more natural sample and a visual appraisal of his ability to serve, but it needed a cow in season, which invariably happened when the vet was busy elsewhere, or the cow was off season by the time the vet arrived. Poor quality sperm can be temporary following a rise in temperature, so take care when consigning the bull to the scrap heap. A good history is essential.
Once content that you have ruled out bull and nutrition issues, infectious causes of infertility need to be investigated. I have often found it to be difficult to be categorical about an infectious cause of the problem, in particular with IBR and Leptospirosis, as we have many farms with one or the other present, but fertility is good. If it is isolated from an abortion it is more helpful, which is a reminder that all abortions should be notified to your vet in order to rule out Brucellosis and help inform future health planning decisions. Neospora is becoming an increasing problem, usually causing abortion in the second trimester of pregnancy, ie after most have been scanned. This is caused by an organism transmitted in dog or fox faeces, contaminating the pasture. Once a cow is infected it is permanently infected and passes the organism across the placenta to the foetus, causing abortion or symptomless carriers to spread to their own offspring. The Cattle Health Schemes now have an option to test for this annually.
Another infectious cause rearing its head again is Vibrio or Campylobacter, a venereally transmitted disease. Symptoms include returning to oestrus at irregular intervals. This is diagnosed by sheath washing the bulls. This is a good reason not to use a hire bull unless it has been tested for the disease.
No matter how successful the PD, it is still crucial to record the results for understanding herd performance, making a note of barren cows and possible reasons – for example difficult calving previous spring, reared twins, ovarian cysts or bull issue. Reasons can be investigated further by your vet and then included in your annual health plan review.