T.T. Dolan* and J.J. Mutugi
National Veterinary Research Centre
Kenya Agricultural Research Institute
P.O. Box 32
Kikuyu, Kenya
*Present address:
International Laboratory for Research on Animal Diseases
P.O. Box 30709
Nairobi, Kenya
Four hundred Boran (Bos indicus) heifers were immunized against Theileria parva by infection and treatment on a large ranch in the Kenya highlands. The immunizing stock was prepared as a stabilate (184) from ticks collected from the ground in the riverine areas of the ranch, where resident and migrant buffalo graze. The immunizing infection was controlled in 300 cattle using long-acting oxytetracycline (Terramycin LA, Pfizer) at the time of infection and in 100 cattle using parvaquone (Clexon, Wellcome) on day 8. The cattle were exposed to tick challenge under four different tick control regimes and monitored for disease and productivity parameters for one year (July 1984-July 1985) (Dolan, 1985). The disease challenge was estimated by exposing groups of 10 heifers to unlimited tick challenge. The group of 10 heifers was replaced when they all became clinically ill with theileriosis or developed antibodies to T. parva The disease challenge was potentially 20% lethal for July to September, 60% for October, 100% for November to May and 60% for June. During the year 17 (3.9%) of the immunized heifers developed clinical theileriosis and 67 (15.6%) had anaplasmosis. The theileriosis challenge was due mainly to buffalo-maintained T. p. lawrencei.
The rains due in September 1983 and March 1984 had failed and the heifers were healthy but thin and on poor grazing when they were immunized and joined with the bulls in May 1984. The heifers were between 26 and 30 months old. The bulls were removed in August and only 63% of the heifers were in-calf in October. The bulls were re-introduced in January 1985 until mid-March, then introduced again in May. Between November 1984 and March 1985 there were 24 abortions, with the majority occurring in January. In addition, a number of very small calves were born and some of the heifers showed poor mothering ability. There was some rain in July and August 1984 and good and consistent rain fell from September to December. There was almost no rain in January 1985, some in February and March and good rains from April to the end of the trial. The land did not recover rapidly in spite of the plentiful rain, and the cattle were moved to better grazing on another part of the ranch in March 1985. By October 1985, 86% of the heifers had either calved or were in-calf.
During the year and particularly at the peak of abortions in January, samples were taken and examined for infectious causes of abortion or infertility. The heifers had been immunized against Brucella abortus and no Brucella were isolated from ten freshly aborted foetuses. Paired serum samples were negative for leptospirosis, Rift Valley fever and bovine virus diarrhoea antibodies. A review of records of the other breeding herds on the ranch during the year showed a pregnancy rate of about 70%.
A question that could not be answered at the end of the trial was what effect the immunization had on the fertility of the heifers. They had come on the trial on a falling plane of nutrition and the grazing did not improve for some months, which might have influenced the low in-calf rate, abortions and weak calves. The land did not recover rapidly, probably because of the extended drought from 1983, and mothering ability may also have been adversely affected. An infectious cause for infertility or abortion was not identified and the overall calving rate for the year on the ranch was low (70%). Thus, nutritional influences probably explain the low in-calf rate at 5 months. Certainly the calving/in-calf rate of 86% by October 1985, once the cattle were back onto a good plane of nutrition, indicated that no long-term adverse effects were suffered.
To test the effects of the immunization procedure on similar heifers 26-30 months old on a good plane of nutrition, a group of 166 were selected in January 1986. Fifty were immunized at random using the same stabilate (184) and all 166 were joined with the bulls immediately. In this immunization, tetracycline alone was used because no differences had been detected between tetracycline and parvaquone in the previous trial and a single manipulation of the cattle was desirable. The herd was subjected to once-a-week dipping and detailed records of disease and breeding history were kept throughout the following year. Six animals in the control group died of theileriosis in March/April 1986, two were stolen (one immune), one died while giving birth, one died of haemorrhage and one died of debility. Seven were culled or transferred to other herds and two were sold. A summary of the breeding history of the immunized and control heifers is shown in Table 1.
Thus on a good plane of nutrition and in the absence of the management interventions and disease challenge related to the earlier trial, immunization did not affect the fertility of these Boran heifers. The heifers from the first trial were distributed among other herds on the farm beginning in October 1985 and it was not possible to obtain accurate records of their subsequent fertility. Available records, however, show that these heifers have had normal calving rates and have demonstrated good mothering ability.
Table 1. Breeding performance of immunized and control cattle (%)
|
|
Immunized |
Control |
|
Calving |
86.0 |
80.0 |
|
Non-breeders |
4.0 |
5.5 |
|
Slow breeders |
4.0 |
5.5 |
|
Abortions |
2.0 |
4.0 |
ACKNOWLEDGEMENT
These trials were conducted with the enthusiastic support of 01 Pejeta Ranching Ltd. and the assistance of Mr. J. W. Poulton and Mr. J. Weller.
REFERENCE
Dolan, T.T. (1985). Immunization against theileriosis on 01 Pejeta Ranch, Laikipia, Kenya. In: Irvin, A.D. Immunization against Theileriosis in Africa: Proceedings of a Joint Workshop Held in Nairobi, 1-5 October 1984. Nairobi: The International Laboratory for Research on Animal Diseases, pp. 73-75.
