Suckling, weaning, and growth in captive woodland caribou

Abstract

To delimit the different stages of the weaning process and to understand the relationship between suckling and growth, the evolution of suckling performance and mother–young interactions associated with milk transfer was closely monitored in a group of woodland caribou (Rangifer tarandus caribou) from birth up to 160 days. Suckling rate and total suckling time dropped rapidly during the first 20 days and slowly thereafter, while suckle duration remained stable during the first 20 days and decreased gradually thereafter. In the first 20 days of life, suckling success declined from 90 to 50%, the proportion of suckles terminated by the mother increased from 30 to 90%, and the proportion of suckles with bunting increased from 40 to almost 100%. The mother licked the calf in 70% of the suckles from birth to 20 days, 40% from 20 to 40 days, and less than 20% subsequently. Suckles with licking were longer than suckles without licking during the first 30 days of life. Suckling was initiated by the calf in more than 80% of the suckles, even in the first days of life. No sex differences were found at any age for any of the behavioral variables measured. Birth weights and growth rates of males from 0 to 45 days, however, were higher than those of females. Growth rates from birth to 45 days were positively correlated with suckling rate during the first 35 days. From 46 to 100 days, growth rates were positively correlated with time spent feeding on pelleted ration and on hay. We suggest that metabolic weaning could begin at around 15–20 days, when suckling success and the mother's contribution to establishing and maintaining suckling interactions decreased most steeply. The end of metabolic weaning could occur at 40–45 days, when suckling rate, suckling success, and the mother's contribution to suckling reached low values from which they declined very slowly to the end of behavioral weaning. Behavioral weaning was not yet completed at the age of 160 days.