Vital statistics for an experimental flock of Merino sheep. I. Death rates in adult sheep, in relation to method of selection, age and sex

Abstract

Estimates of death rates are given for four mating groups in a flock of approximately 1000 Merino ewes, for each year of age from 1½ to 10½. Three of the groups are under selection for clean wool weight and other characters, and the fourth is an unselected control. The flock is run under extensive grazing conditions, and death rates are based on ewes dead or missing between one pen-mating and the next. Between 1951 and 1957, the average death rate for ewes 1½ to 7½ years old was 2.2 per cent. per annum, while at the older ages the average was no higher than 7.3 per cent. During the drought year 1957-58 losses averaged 3.8 per cent. for ewes up to 6½ years old, then rose steeply with age to 45.6 per cent. for ewes 9½ years old. In neither period did the selected groups differ from the unselected control. Starting with the 1953 drop, all rams in the unselected control group have been retained for the study of age effects on them. Average losses to date in each age group have been less than 5 per cent.

Response to selection for multiple births in the Australian Merino: a progress report

“…Cunnamulla lies in the semi-arid region of south-western Queensland and the environment and management of experimental sheep there have been described by Turner, Dolling and Sheaffe (1959). The twinning rate is not high; in the experimental mating groups it ranges, on the average, from approximately 2% for 2-year-old to approximately 16% for 6-year-old ewes (Turner, unpublished).…”

Risk factors for Merino ewe mortality on the Northern Tablelands of New South Wales, Australia

“…Increased risk of postweaning mortality in sheep has been well documented and is most strongly associated with body weight (BW) and current growth rate . In contrast, there is a lack of current published data on the rate and predictive correlates of mortality of mature Merino sheep, with historical studies suggesting mortality of this age group is in the range of 2–7% per annum . Higher mortality rates have been recorded for ewes on the Northern Tablelands, New South Wales (NSW), Australia, with mortality affected by the degree of control of gastrointestinal nematodes (worms) and the highest worm‐related mortality coinciding with seasonal peaks of infection with the haematophagous abomasal parasite Haemonchus contortus …”

Méthodes d'analyse des données démographiques et généalogiques dans les populations d'animaux domestiques

“…La difficulté d'une telle entreprise explique que de nombreux auteurs aient recours à des synthèses transversales : sans l'annoncer explicitement, ils établissent en fait une table de mortalité du moment, c'est-à-dire une table résultant de l'attribution à une cohorte fictive des quotients de mortalité calculés sur les diverses cohortes réelles soumises au risque de mortalité pendant un laps de temps donné (T URNER et al, 1959 ;H ICKEY , 1960 ; M ATASSINO et al, 1. Etude de la carrière reproductive d'une cohorte d'animaux Ce type d'étude est le plus souvent réalisé sur des femelles, mais rien n'empêche d'utiliser les mêmes méthodes sur des mâles (L ANGLOIS , 1976).…”