La circonférence scrotale, l'aspect macro- et microscopique des testicules, les concentrations plasmatiques des hormones gonadotropes LH et FSH et celles de la testostérone ont été étudiés lors de deux expériences de castration partielle et totale effectuées sur des béliers Poulfouli du Cameroun, abattus à 15 mois. La mesure de la circonférence scrotale permet de suivre l'involution testiculaire chez les béliers castrés à la pince de Burdizzo. Cette involution ne se stabilise que tardivement. Aucune influence saisonnière n'est observée chez les béliers entiers. La fonction exocrine (spermatogénèse) comme la fonction endocrine (production de testostérone) sont totalement supprimées chez les castrés à la pince. Le poids des testicules des béliers castrés partiellement par la méthode du "short scrotum" est très variable (76,1 + ou - 41,78 g) ainsi que la suppression de la spermatogénèse. En revanche, les taux de testostérone sont proches de ceux des béliers entiers et expliquent vraisemblablement les performances zootechniques observées antérieurement. Les auteurs concluent que, si la castration partielle constitue une alternative intéressante du point de vue zootechnique, il faut rester prudent dans la suppression du pouvoir fécondant chez les castrés par le short scrotum.
Summary Statistical analyses were carried out on the data obtained under strictly controlled conditions in metabolism stalls with 41 different rations fed to 127 adult non-pregnant dry cows, and with 14 other different rations fed to 35 adult non-pregnant lactating cows that had calved 2–6 months earlier and whose daily milk production ranged from 11 to 20 kg. The authors have calculated and studied the correlations between faecal and urinary potassium losses, potassium excretion in the milk, digestible potassium and potassium balance, and the 75 other nutritive factors which were analysed for each of the 55 above mentioned experimental diets. The results show that three nutritional factors, potassium, dry-matter and nitrogen intakes, influence the fate of dietary potassium. The apparent digestibility of potassium is hyperbolically related to potassium content of the diet since the true digestibility of potassium is very high, unrelated to potassium intake and rather constant and since about 2·2 g of endogenous potassium are excreted in the faeces per kg of ingested dry matter. The quantities of digestible potassium strongly influence both the potassium urinary outputs and potassium balance. An increase in digestible dry matter enhances too the urinary potassium excretion as well as faecal output and lower potassium balance twice as much. But the most interesting feature in the potassium metabolism is that at any level, ingestion, digestion, excretion, there is a very close correlation between potassium and nitrogen.
Five Suffolk ewes underwent daily laparoscopy for 18 days at the onset, middle and end of the breeding season (August, November and February, respectively) and during anoestrus (May) to examine their ovaries. Ovarian follicles ≥ 2 mm were measured and their relative locations reported on an ovarian map to follow the sequential development of each individual follicle. Some aspects of follicular growth (mean day of emergence and mean number of small, medium-sized and large follicles, maximum size before regression and ovulation rate) were also studied and compared. Three waves of follicular growth and atresia were observed during the oestrous cycle; two waves occurred during the luteal phase and one during the follicular phase. This cyclic pattern of growth and atresia was not influenced by the stage of the breeding season. A similar turnover of follicles occurred during anoestrus. Features of follicular growth were similar at all stages studied except for the size of the large follicles which were smaller during the two waves of the luteal phase (P < 0.05). The number of growing follicles did not vary and the mean ovulation rate was 1.2 ± 0.4 at all stages of the breeding season.
La production et la composition du lait de 31 chèvres locales burundaises ont été déterminées au cours des 84 premiers jours de lactation. Parallèlement, la croissance de 44 nouveau-nés a été étudiée. Le faible rendement laitier de la chèvre locale (440 g/j) est cependant fort variable d'après les individus (167 à 881 g/j). La production laitière culmine entre la 2è et la 3è semaines de lactation et diminue en pente douce par la suite. Elle s'accroît avec l'augmentation du nombre de jeunes allaités et le poids de la mère (p < 0,05) et non avec la parité. Le lait de la chèvre burundaise est plus pauvre en éléments nutritifs que celui des autres races tropicales notamment en matière grasse (3,1 g %) et en lactose (2,8 ± 1,67 g %). Les poids des chevreaux à la naissance (1,54 ± 0,29 kg) et à 28 jours (3,05 ± 0,70 kg) sont faibles comparés à ceux d'autres races caprines tropicales. En revanche, les jeunes ont une meilleure efficience alimentaire au cours du premier mois post-natal (6,04). Leurs faibles performances pondérales pourraient donc être dues à la faible production laitière des mères et/ou à la déficience énergétique dans le lait. Une amélioration génétique de cette production est possible.
SUMMARY Statistical analyses were carried out on the data obtained under very strict conditions in metabolism stalls with 41 different rations fed to 127 adult non-pregnant dry cows and with 14 other different rations fed to 35 adult non-pregnant lactating cows that had calved 2–6 months earlier and whose daily milk production ranged from 11 to 20 kg. The correlations between faecal and urinary phosphorus losses, phosphorus in milk, digestible phosphorus and phosphorus balance and the other nutritive factors of the 55 above-mentioned experimental diets have been calculated. In dry and lactating cows, with very variable intakes of phosphorus, phosphorus faecal and urinary losses show very wide variations and may be important. They are not influenced by phosphorus intake, and are related, among the many other nutritional factors we analysed only to ingested water and to a lesser extent to the nitrogen of the diet. The phosphorus balance is thus also very much variable and not really related to the composition of the ration. This low influence of the diet on the apparent fate of phosphorus can be explained by the interference of unpredictable but certainly quite variable endogenous phosphorus excretion, which is also probably responsible for the effect we found of individual factors and of the previous nutritional status. In the lactating cows, the phosphorus requirements for milk production influence the utilization of phosphorus since a significant correlation exists between phosphorus secreted in the milk and urinary phosphorus. In our experimental conditions, the Ca: P ratio does not seem to influence the fate of dietary calcium and phosphorus.
