Admixture and diversity in West African cattle populations

We present a population genetic analysis of microsatellite variation in 16 West African cattle populations. West Africa represents a unique juxtaposition of different climatic and ecological zones in a relatively small geographical area. While more humid coastal regions are inhabited by the tsetse fly, a vector which spreads trypanosomiasis among cattle, the disease is not transmitted in the drier areas outside this zone. This is the most thorough study of genetic diversity in cattle within this area, which contains genetically important trypanotolerant Bos taurus breeds. Genetic relationships among the many breeds are examined and levels of diversity are assessed. Admixture levels were determined using a variety of methods. Ancestry informative or population-associated alleles (PAAs) were selected using populations from India, the Near East and Europe. Multivariate analysis, the admix program and model-based Bayesian admixture analysis approaches were also employed. These analyses reveal the direct impact of ecological factors and the profound effect of admixture on the cattle of this region. They also highlight the importance of efforts to prevent further dilution of African taurine breeds by B. indicus cattle.

The effect of josamycine on the control of ileitis in weaned piglets under field conditions

The aim of this trial was to evaluate the effect of in-feed josamycine on the control of ileitis in weaned piglets. On a farm with a previous history of ileitis outbreaks, 288 piglets at weaning age (25 +/- 2 days old) were allocated into three experimental groups, each group comprising of four pens with 24 piglets in each pen. Group one (T1) served the trial as negative control group (unmedicated), group T2 was administered josamycine at 36 mg/kg of feed and group T3 was administered josamycine at 50 mg/kg of feed. Treatments lasted for 14 days followed by an observation period of 28 days. Administration of josamycine at both inclusion levels tested had a beneficial effect compared with the negative control group, by the reduction of prevalence of diarrhoea, the enhancement of growth performance and the reduction of prevalence of Lawsonia intracellularis in the intestine, as determined either by the PCR method or by specific histopathological examinations. The beneficial effect of josamycine was more pronounced at the inclusion level of 50 mg/kg of feed.

Susceptibility of the Namchi and Kapsiki cattle of Cameroon to trypanosome infection

Two indigenous Cameroonian taurine cattle breeds (Namchi and Kapsiki) were evaluated for trypanosusceptibility following inoculation with Trypanosoma congolense. The degree of zebu ancestry in the experimental animals was assessed using 6 microsatellite markers which are known to have certain unique alleles which are diagnostic of Bos indicus genetic input. Their response to the infection was compared to that of known trypanotolerant (N'Dama) and trypanosusceptible (Ngaoundere Gudali) cattle. The Namchi and the N'Dama controlled the development and severity of anaemia and parasitaemia better than the Kapsiki and the Gudali. For these parameters, there was no significant difference between the N'Dama and Namachi nor between the Kapsiki and Gudali. Similarly, weight loss showed significant breed variation. The N'Dama lost the least weight and the Kapsiki the most. Zebu introgression in the Namchi was comparable to that in the N'Dama while that of the Kapsiki breed was higher, indicating a high level of cross breeding. From the results, the Namchi are considered trypanotolerant while the Kapsiki are trypanosusceptible. The potential exploitation of the indigenous Namchi cattle is discussed.

Measurement of trypanotolerance criteria and their effect on reproductive performance of N'Dama cattle

One thousand and twenty-eight cow-year records were available from 260 N'Dama cows each having at least 2 years of monthly matching health and performance data over a 5-year period under a medium natural tsetse challenge in Gabon. Four hundred and fifty-eight calf/dam pairs were also available where the calf had been reared to weaning, both had monthly matching records and each cow had weaned at least two calves. Evaluations were carried out on effects of, and linkages between, environmental and stress factors, number and species of trypanosome infections, curative drug treatments given, anaemia measured by packed red cell volume (PCV), and performance measured by calf weaning weight, cow calving rate and cow weight change over the lactation period. Major findings were that over the period from calf birth to weaning, while calves and their dams grazing together had similar numbers of trypanosome infections detected, the Trypanosoma vivax: T. congolense ratios were very different: 1:0.7 in calves; 1:2.8 in cows. This indicated that some ability to control the development of parasitaemia following T. vivax infection might be being acquired, from weaning onwards. In cows, relationships between lowest PCV recorded and curative drug treatments given suggested that between 20 and 32% of trypanosome-infected cows were not being identified by the buffy coat parasitological diagnostic technique. The high level of curative treatment given (to 13.7% of cows over the calendar year, and to 40% of calves from birth to weaning) will have tended to reduce the variance and linkages between aspects of infection and PCV values, especially in calves. In calves, the influence of trypanosome infections, in both calf and dam, on their respective PCV values and hence on calf weaning weight was apparent. There was a 0.91 +/- 0.40 kg increase in calf weaning weight for each 1% increase in calf average PCV, and a 0.95 +/- 0.39 kg increase for each 1% increase in cow average PCV. In cows, there was a similar pathway of influence of T. congolense infection through the PCV values to calving rate--not significant with T. vivax infection. There was a 3.3 +/- 0.65% increase in calving rate for each 1% increase in average PCV. Repeatabilities of performance traits were in the normal range. Repeatabilities of numbers of trypanosome infections detected by the buffy coat technique were too low to have any practical significance. Repeatability of average PCV at 0.40 +/- 0.03 could allow PCV when infected to be used as one criterion of trypanotolerance.

Evaluation of a field test for trypanotolerance in young N'Dama cattle

In three separate tests in 1987, 1988 and 1989, a total of 436 one-year-old N'Dama cattle were maintained for 12, 18 and 24 weeks under a medium natural tsetse-trypanosome challenge in Gabon, Central Africa. Matching health and performance data were recorded on 4, 10 and 13 occasions respectively, to allow simultaneous evaluation of the effect of different criteria of trypanotolerance on animal performance. Under trypanosome prevalences of 25, 31 and 9%, respectively, ability to control the development of anaemia had a very major effect on daily weight gain, four times that of the ability to control parasitaemia, while previous exposure to trypanosome infection from birth to one year had no effect. Anaemia control, measured by average packed red cell volume percent (PCV) over the test period or by lowest PCV reached, was more closely associated with animal performance than when measured by average PCV when detected as parasitaemic. Above average PCV values in the first two measures resulted in a 44% to 48% superior daily weight gain over below average PCV values. PCV post-test recovery was shown to be rapid following a single trypanocidal drug treatment. In practice, it appeared that a suitable field test would be where natural infection could be effected as early in the test as possible and anaemia control measurements carried out over 6 weeks of detected parasitaemia. A field test would become even more feasible if satisfactory correlation could be obtained between the results of natural infection and those of an experimental alternative.