Teneral Glossina morsitans centralis were fed on the flanks of African buffalo, N'Dama or Boran cattle infected with Trypanosoma vivax IL 2337. The infected tsetse were maintained on goats and on day 25 after the infected feed, the surviving tsetse were dissected to determine the infection rates. The mean mature infection rates (% ± S.E.) in the tsetse fed on buffalo, N'Dama and Boran cattle were 34·3 ± 9·9, 33·7 ± 13·4 and 58·9 ± 7·1, respectively. Logistic regression analysis indicated that infection rates in the labrum and hypopharynx of the tsetse were significantly lower when fed on the infected buffalo or N'Dama than Boran cattle. Similarly, the risk of infection was significantly lower in male than female tsetse. When teneral G. m. centralis, G. pallidipes, G. p. gambiensis, G. brevipalpis and G. longipennis were fed simultaneously on either the buffalo cow, the N'Dama bull or the Boran steer infected with T. vivax IL 2337, the mature infection rates were higher in the two morsitans group than the two fusca group tsetse, whilst G. p. gambiensis was relatively refractory to the infection, irrespective of the host species on which they fed. Logistic regression analysis indicated that the infection rates in the labrum and hypopharynx were significantly different amongst the five tsetse species for each of the three infected host animals. Nevertheless, the trypanotolerant African buffalo and N'Dama cattle may serve as reservoirs of T. vivax infection as can trypanosusceptible Boran cattle.

This paper reviews the successful N'Dama cattle genetic improvement programme implemented in a low input production system at the International Trypanotolerance Centre (ITC) in 1994, in The Gambia. The first part of the paper presents the genetic improvement programme. The second part deals with the analysis of the genetic improvement programme. The success of the genetic improvement programme expressed through genetic progress and the benefits for the farmers is encouraging. Recommendations to strengthen the implementation process in the field are made.

Les performances zootechniques de la race N'Dama ont été déterminées de 1994 à 1997 à partir du noyau reconstitué en 1993 dans le cadre de l'amélioration génétique des races locales à la Ferme Elevage de l'Okpara au Bénin. Les poids moyens à la naissance, à 6, 12 et 24 mois sont respectivement 17.4, 55.6, 95.9 et 158 kg. La vitesse de croissance de la naissance à 12 mois est de 215 g/j. Excepté le poids à la naissance, le poids et les mensurations corporelles sont largement en dessous de ceux obtenus chez la race dans son berceau. L'intervalle de vêlage a été de 413±54 jours, l'âge moyen au premier vêlage a été situé à 48 mois ± 33 jours, et le taux moyen de fécondité à 84.3%. Les naissances s'observent d'octobre à janvier avec une mortalité variant selon les années de 0 à 8.1% chez les jeunes. Aucun cas de mortalité n'a été enregistré chez les adultes. En somme, il est remarqué que l'expression phénotypique des caractères de productions de la N'Dama est limitée dans le ranch de l'Okpara.

L'article présente une révision intéressante de l'état actuel des ressources génétiques animales en Cóte d'Ivoire. Les cinq espéces principales (bovins, ovins, caprins, porcins et volailles) sont présentées. I1 existe trois groupe de bovins autochtones: le Baoulé, le N'Dama et le Lagune; les deux derniers sont considérés trypanotolérants. Le Baoulé posséde une population de presque 500 000 animaux et le N'Dama quelques 100 000, tandis que la population de Lagune de petite taille est de moins de 1000. I1 existe également u.ne population transhumante formée de zébus croisés (Baoulé x zébu) ainsi que de N'Dama croisés avec des German Fleckvieh ou des French Abondance. La race d'ovin plus répandue est la fameuse Djallonké (environ 1200 000 animaux) que l'on rencontre aussi bien dans les foréts que dans les savannes. L'Institut des Sciences a initié un programme de sélection en 1980 qui se poursuit actuellement. Dans le cas des chévres la seule race présente est la naine de l'Afrique de l'ouest, appelée aussi Djallonké, avec une population de un peu moins de 1 000 000. Les secteurs porcins et de volailles sont dominés par la présence de races locales et de quelques croisements avec des races importées. L'article présente une description approfondie des systémes de production traditionnels et de leur évolution; il donne également des indications sur les normes de conservations existantes pour les races N'Dama, Baoulé et Djallonké.

Two groups of eight N'Dama calves were fed different quantities of milk from birth to 10 months of age to compare efficiencies of converting milk to live-weight gain, and to assess the economic efficiencies of the two feeding regimes. Group 1 received an average of 347 (s.e. 2·4) kg per calf, with a daily and seasonal pattern of feeding designed to simulate a village production system where calves have access to only part of the milk produced by their dams, the rest being extracted for human consumption. Group 2 received an average of 617 (s.e. 5·1) kg per calf, and simulated situations where no milk is extracted such as in a ranch or station-type of operation.

During the first 6 months, when growth was certainly mediated only by milk, and live-weight gains were consistently positive at 151 and 262 g/day in groups 1 and 2 respectively, the biological conversion of milk to live weight did not differ between groups (8·7 v. 8·8 kg milk per kg live-weight gain). When the two groups were compared over the same weight range to remove possible effects of variable maintenance requirements, the conversion efficiencies again did not differ significantly. Over the whole 10-month period the biological conversion factors were slightly less favourable but still not different between groups (9·5 v. 9·4 kg/kg). When monetary values of milk and live weight at farmgate prices were applied to quantities of milk consumed and calf live-weight increases, the cost efficiency of group 1 was superior to that of group 2.

Based on these findings and results from other on-farm experiments in The Gambia, it was concluded that the current practice of partial milk extraction as occurs in the village production system is a logical approach for profit maximization.

Birth-weight data recorded between 1986 and 1991 on 3453 N'Dama calves from the village production systems of The Gambia were analysed to identify major factors influencing this trait and to quantify the relationship between birth weight and early calf mortality. Birth weights were measured over a range of time, from a few hours to 14 days after birth. Least-squares analysis of the fixed effects of site, year and season of birth, parity of dam, sex, age in days at which birth weight was recorded and random effects of herd and cow nested within site showed that all these factors significantly influenced this trait.

A subset of these data (no. = 2452) was used to derive adjustment factors which were applied to the larger data set to standardize birth weights to a common age measurement. Results from these adjustments showed that birth weights recorded between the 7th and 14th day after birth should be decreased by proportionately 0·12 to 0·14 to be comparable with those measured on day of birth.

Maximum likelihood analyis of cumulative calf mortality to 30, 60, 90 and 120 days of age using age-standardized data (no. = 3156), which excluded deaths of traumatic origin, showed that mortality was highly influenced by birth weight. Calves were grouped into three classes, namely below-average, average and above-average of sitemates' values. Mortality rates among the three groups during the first 30 days of life were 3·6, 0·9 and 0·3%. The corresponding values at day 120 were 13·8, 6·3 and 5·0%. The average age at death during the first 120 days in the three groups were 51, 58 and 73 days. Mortality rates among calves born in the wet season were higher than those born in the dry season (e.g. 9·9 v. 5·9% for mortality to day 120).

Examination of data on calving distribution and milk production patterns of the dams of the calves used in this study as well as the causes of deaths among the calves indicated that although dam effect was an important determinant of calf survival other factors such as the vigour of the calf at birth, weather conditions and disease environment at the tethering and grazing areas were important as well.

The effects of milking on the overall productivity of N'Dama cattle kept under village conditions were studied using three groups of cows during a 27-month period. One group of 46 cows in 16 herds in Nioro Jattaba village was not milked for human consumption and their calves had access to all of their milk (group 1). Another group of 46 cows in the same herds was partially milked for human use once a day while the calves had access to the residual milk (group 2), the normal husbandry practice in this village. A third group of 70 cows in six herds, managed similarly in a similar production environment in the nearby village of Keneba, was milked twice daily with the residual milk for their calves, the normal husbandry in this village. A mean extraction of 296 (s.d. 110·7) kg milk per cow occurred in group 2 during a lactation period of 517 days while the figure for group 3 was 450 (s.d. 177·7) kg per cow over 430 days. At the end of the observation period, calf mortality to 12 months averaged 6% and was similar in all groups. Calf weights at 12 months in group 1 (98·1 kg) exceeded that of groups 2 and 3 by proportionately 0·26 and 0·38 (P < 0·001) respectively. Mean calving rate was 53% in groups 1 and 2, and 72% in group 3. Post-partum body-weight losses were most severe in group 1, followed in order by groups 2 and 3. A herd productivity index (incorporating calf weight, live weight equivalent of milk extracted for human use, cow and calf viability and calving rate) was 100·7 kg calf weight per 100 kg metabolic weight of cow per year for group 1, 110·2 for group 2 and 166·1 kg for group 3. These values suggest that recommendations to small-holder farmers for enhancing livestock productivity should include strategies to improve milk yields in general rather than advocating no milk extraction or changing the milking regime currently practised.

Over a 3-year period, productivity characteristics and criteria of trypanosomiasis incidence and severity have been monitored by monthly examination of individual N'Dama cattle in villages in The Gambia. From this database, 60 lactating cows in which Trypanosoma congolense or T. vivax had been detected on blood examination (group 1) were compared with 50 cows which had not been found infected with trypanosomes during the monitoring period (group 2). The latter were selected on the basis of comparability of age and stage of lactation to those of group 1 for examining the effect of trypanosome infections on the quantity of milk extracted for human consumption, and on the growth of their sucking calves. Data from a 6- to 7-month period were examined in the analysis.

The quantity of daily milk extracted during the 1st month ot intection (group 1) decreased by proportionately 0·25 in comparison to the amount extracted during the preceding month when parasites were not detected. The corresponding figure in the uninfected controls (group 2) was 0·02. The mean daily milk extracted for human consumption from uninfected cows during a 6-month period was proportionately 0·26 higher than the mean for the infected cows. Growth rates of calves sucking infected and uninfected dams were similar.

These observations indicate that infection with pathogenic trypanosomes of lactating N'Dama cattle causes a reduction in milk production.

In economic terms, it was estimated that the decline in milk extracted for human consumption due to trypanosome infections amounted to an average of £1 per month per cow.