and Their Cure
Herd wastage from disease stems from five major sources. These are sterility and abortion, mastitis, bloat, T.B. and the metbolic diseases. Included under this heading are milk fever, grass staggers and acidosis.
Abortion in cattle is most commonly due to the diseases brucellosis and vibriosis, though leptospirosis and trichomoniosis also occur. Brucellosis is usually the main source of trouble and should the incidence of dead born calves exceed the New Zealand average of 2½%, veterinary diagnosis should be sought. There should be no question as to the advisability of vaccinating calves six to eight months of age with Strain 19, but there are farmers who still neglect this essential safeguard.
As a result of Strain 19 reducing brucellosis to low levels throughout the country, vibriosis is more often found today. The cows may abort at any time during pregnancy. It is a true venereal disease passed from cow to cow by the bull. Veterinary aid is necessary and an effective control is through artificial insemination with bulls free from the disease.
Apart from lowered herd fertility following abortions, by far the greatest problem is getting the herd in calf when required. This is known as the temporary sterility problem, responsible for the spread of calving characteristic of all herds. 80% of the healthy cows in the herd should be in calf after the second round of mating. However, if at the completion of mating 6% of empty cows are still empty it is still probably a healthy herd and if sufficient time was available even the majority of these cows would conceive. There are problem herds, however, where these figures are very different and much research work has failed to diagnose the real source of the trouble. Practical methods in control of mating will do much to ensure a high conception rate. The following points should be noted:—
Before each cow is mated two heat periods or an interval of at least 30 days should be allowed after calving. Earlier mating increases the chances of the bull becoming contaminated, and in addition cows are less likely to get in calf.
Conception is at a maximum a few hours before and a few hours after the end of heat, so that mating too early in heat is undesirable.
The fertility of the bull is important and can be affected by excessive use when young. 15 heifers are sufficient for a yearling bull under natural mating conditions.
Handmating should be practised and records kept. This also ensures that the bull's service is not reduced by too frequent servicing of cows.
Bulls should be kept in good condition as a poorly fed bull will have reduced fertility.
Every farmer is conversant with the use of penicillin in the control of mastitis and the incidence has been considerably reduced. Early detection is the key factor and much can be done to reduce the incidence by hygienic shed routine. The use of clean running water controlled by a valve in a dropper line is recommended, together with inspection of the milk before applying cups.
This is most prevalent in the spring and autumn period of flush clover growth, and the incidence can be reduced if there is mature feed available at these times. If a serious outbreak occurs it is often best to put the herd on supplementary hay and silage, plus limited grass until the pasture matures. This is often not possible and the spraying of pastures with cheap oils is necessary. Penicillin can also be used but this has disadvantages where the incidence is frequent and high. However, proper grazing management and the avoidance of clover dominance in the swards should always be the main consideration.
Occurs in late pregnancy and most commonly within two days after calving in older (five years and over) cows. The cow goes down and appears semi-conscious. Some cows are more susceptible than others, and it is more prevalent in over-fat cows and where there is a high level of feeding prior to calving. It is caused by a fall in the calcium level of the blood. A bottle of calcium borogluconate injected under the skin will result in an immediate recovery unless the disease has reached an advanced stage or is complicated by grass staggers or acidosis. As a prevention, overfeeding should be avoided before calving.