8 August 1997

CATTLE SCANS TO TAKE OFF

Scanning cattle offers more benefits than just early pregnancy diagnosis. Cheshire vet John Dawson reports

MOST sheep producers scan their flocks routinely, recognising the huge benefits in terms of improved feeding management. But it has taken over 10 years for pregnancy scanning of sheep to become the norm. Scanning of cattle is at the start of that 10-year period, with farmers and vets now awakening to the benefits which go far beyond the pregnancy scanning.

&#8226 Pregnancy diagnosis.

This has always been an important task carried out on many farms during the routine vet visit. Identifying the positive cow allows us to monitor foetal loss as we know the cow was in calf; identifying the negative cow allows us to get her in-calf, limiting lost time. The ultrasound scanner now allows us to pregnancy scan at 28 days, 14 days earlier, on average, than manual diagnosis. If we are finding 10% of cows examined are not in calf then we are, on average, gaining 14 days open on 10 cows in a herd of 100. This is a total gain of 140 days which amounts to £420 (costed at £3 a day) for no extra cost. The only change is that cows must be presented for pregnancy diagnosis during a routine visit two weeks earlier than before. If there are worries about the possibilities of early embryonic death then cows can be re-scanned at the next routine visit.

&#8226 Better diagnosis and treatment of the cows diagnosed as not in calf.

Cystic cows can be picked up earlier and treated. The longer a cyst remains on an ovary the more likely the cow will respond poorly to treatment and thus have to be culled.

Some reports suggest that as the scanner needs less manipulation of the uterus this reduces foetal loss due to manual palpation. But studies show that there is no difference and that the loss by manual PDing is negligible when carried out by experienced vets.

Pregnancy diagnosis in the extremely fat cow or heifer is difficult and sometimes impossible but it can usually be done with the use of the scanner.

Twin pregnancies can also be picked up and then managed to reduce problems during the pregnancy. There is a higher degree of embryonic loss in twin pregnancies which can probably be reduced with improvements to management and feeding.

Foetal abnormalities can also be identified. The scanner can show problems with the pregnancy such as no heart beat or insufficient foetal fluid which would cause embryonic death. These can be monitored, identified earlier, and if a number are seen, identify a herd abortion problem early. With manual PDing these would be found later or just identified as non-pregnant and presumed to never have been in-calf.

&#8226 Infertility problems: The non-buller.

The full benefit of the scanner can be used here. In an ideal world every cow would be scanned daily which would allow us to assess its length of cycle, stage of cycle, whether it was a biphasic or triphasic follicular wave cow, if it was cycling normally, and identify the bulling date accurately. All this information is useful for managing cow fertility. Daily examinations are of course unthinkable but much of this information can be gleaned from the use of the scanner on a routine basis, ideally every two weeks.

Good diagnosis of the stage of the oestrus cycle is possible with manual palpation but accuracy is improved with an ultrasound examination. Bulling cows can be picked up during a routine visit and inseminated immediately when a follicle is on the point of ovulation. When a large dominant follicle is present in the absence of a corpus luteum, the cow can be inseminated within the next two days or information on return to oestrus can be gleaned so that the herdsman can watch closely and apply a kamar or tail paint at the appropriate time.

The scanner allows accurate assessment of the stage of the cycle by visualising the uterus and ovary. This allows very specific treatments and advice on individual cows, producing better conception rates. Bulling cows can be identified, and their follicular picture seen. When they are on the point of ovulation they can be served immediately; if the follicle is about 10mm in diameter then it can be predicted that the cow will ovulate within two days so she can be watched closely for bulling signs. The scanner also allows accurate assessment of cows which have ovulated in the previous five days, or those with an immature corpus luteum, the absence of a mature corpus luteum or follicles of 5mm or more in diameter. Assessment to within two days can be made for the period from minus three to plus four days of bulling. This allows precise information to be used for the non-buller. During the period of the cycle which has the corpus luteum respondent to prostaglandins, dioestrus, the follicular state of the ovary can be assessed accurately by the presence of a corpus luteum.

&#8226 The stage of the follicular waves can be assessed.

A poor conception rate to a prostaglandin induced oestrus can be experienced and recent work suggests that this is because the prostaglandin is given at the wrong stage of the follicular wave. The ultrasound can assess the size of the follicles. If they are 7-10mm in diameter or less then prostaglandin treatment alone should be effective. But if theyre outside this size then better conception rates may be achieved with the use of a hormonal treatment such as Receptal to remove existing follicles and produce a new crop. This is followed by prostaglandin treatment five days later.

Prostaglandin treatment is often used to induce a cow to cycle. A poor response can be due to injection at the wrong time of the cycle. Manual palpation will identify the presence of a corpus luteum but it is not very accurate to determine the precise age of the corpus luteum. Scanning allows more accurate assessment of the age of the corpus luteum and identified the early ones which will be refractory to treatment. Alter-native treatments or delay of the prostaglandin treatment can save time getting the cow to cycle and subsequently in calf.

&#8226 Cystic ovarian disease.

Accurate diagnosis of cystic ovarian disease and definition of the type involved can lead to more specific treatments. This can gain time returning the cow to normal oestrus cycling and conception. Prostaglandin hormonal therapy, the treatment for luteal cysts can gain 10 days over progesterone hormonal treatment which is the treatment for follicular cysts. Accurate diagnosis of the type will save £30 for some cows treated during a routine visit.n

Benefits of scanning go beyond pregnancy diagnosis, says vet John Dawson.

Scanning dairy cows picks up twin pregnancies – this allows the cow to be managed to minimise potential difficulties during the pregnancy.

SCANNING BENEFITS

&#8226 Pregnancy diagnosis 14 days earlier.

&#8226 Cystic cows identified earlier.

&#8226 Non-bullers picked up.