Calving and maternal body weight change in the reindeer

Earlier studies in Ungulates have indicated that reproductive success is closely related to the mother's reproductive condition or factors affecting this (Sadleir 1969, Guinness et al. 1978). Calf birth-weight, growth and survival are indicated to be dependent on eg. maternal age and weight as well as nutrition (Bergerud 1975, Albon et al. 1983, Rognmo et al. 1983, Eloranta & Nieminen 1986). Mitchell & Brown (1974) showed that red deer hinds (Cervus elaphus) which had not raised a calf the previous summer were significantly more fertile than hinds that had done so. The fertility of hinds is documented to reduce also with late calving in the spring (Clutton-Brock et al. 1983). One explanation suggested for the higher fertility of hinds with higher body-weight and early calving would be that they are more likely to meet the energy demands of pregnancy and lactation, which becomes pronounced with late calving, and produce a viable calf, without risking their lives. In this paper we test the prediction that calving followed by lactation reduces the mother's condition i.e. the body-weight and future reproductive success. Reproduction was studied in the experimental reindeer herd in Inari, Kaamanen (69°10N') in Northern Finland. The fertility and weight changes of a stock of semi-domesticated reindeer {Rangifer tarandus tarandus L.) over a period of 16 years has been assessed. The reindeer grazed natural vegetation within the enclosed area of about 70 km 2 . Besides this the reindeer were offered supplementary food during the winter months. The reindeer calved yearly in a paddock of 8 ha. During the calving period the animals were fed with lichens, molasses and pelleted concentrates. The data collected consisted of 842 hinds aged 1 to 14 years when giving birht. Fertility seemed to be ageand weight-dependent, as shown in our earlier study, the calving rate clearly increased with age up to 5 years being 87.2% in hinds calving at the age of 3 to 5 years (Eloranta & Nieminen 1987). Also the weight of hinds is known to increase during the first five years (Eloranta & Nieminen 1986). The present observations on the influence of calving and lactation on the mother's condition and fertility show that reproduction stress reduces neither the body-weight nor the fertility in reindeer in conditions with abundant food. The reindeer were divided into four groups: true yeld (hinds which had not given birth the previous summer) ; yeld (hinds which had borne a calf but lost it during the calving season) ; summer yeld (hinds which had lost the calf in sum-

Earlier studies in Ungulates have indicated that reproductive success is closely related to the mother's reproductive condition or factors affecting this (Sadleir 1969, Guinness et al. 1978).Calf birth-weight, growth and survival are indicated to be dependent on eg.maternal age and weight as well as nutrition (Bergerud 1975, Albon et al. 1983, Rognmo et al. 1983, Eloranta & Nieminen 1986).Mitchell & Brown (1974) showed that red deer hinds (Cervus elaphus) which had not raised a calf the previous summer were significantly more fertile than hinds that had done so.The fertility of hinds is documented to reduce also with late calving in the spring (Clutton-Brock et al. 1983).One explanation suggested for the higher fertility of hinds with higher body-weight and early calving would be that they are more likely to meet the energy demands of pregnancy and lactation, which becomes pronounced with late calving, and produce a viable calf, without risking their lives.In this paper we test the prediction that calving followed by lactation reduces the mother's condition i.e. the body-weight and future reproductive success.
Reproduction was studied in the experimental reindeer herd in Inari, Kaamanen (69°10N') in Northern Finland.The fertility and weight changes of a stock of semi-domesticated reindeer {Rangifer tarandus tarandus L.) over a period of 16 years has been assessed.The reindeer grazed natural vegetation within the enclosed area of about 70 km 2 .Besides this the reindeer were offered supplementary food during the winter months.The reindeer calved yearly in a paddock of 8 ha.During the calving period the animals were fed with lichens, molasses and pelleted concentrates.
The data collected consisted of 842 hinds aged 1 to 14 years when giving birht.Fertility seemed to be age-and weight-dependent, as shown in our earlier study, the calving rate clearly increased with age up to 5 years being 87.2% in hinds calving at the age of 3 to 5 years (Eloranta & Nieminen 1987).Also the weight of hinds is known to increase during the first five years (Eloranta & Nieminen 1986).The present observations on the influence of calving and lactation on the mother's condition and fertility show that reproduction stress reduces neither the body-weight nor the fertility in reindeer in conditions with abundant food.
The reindeer were divided into four groups: true yeld (hinds which had not given birth the previous summer) ; yeld (hinds which had borne a calf but lost it during the calving season) ; summer yeld (hinds which had lost the calf in sum-  mer) and milk (hinds which had successfully reared a calf the previous summer).There were no significant differences in the body-weight of yeld, summer yeld and milk hinds (F=0.44;d.f.=2; p<0.7) in autumn.Contrary to belief, the true yeld hinds proved to be slightly leaner in autumn compared to the calved ones.None of the age groups studied showed significant weight differences between true yeld and calved hinds either (Figure 1).
The difference in birth-weight was not due to sex-difference in different cohorts of hinds.Of the total of 676 calves whose sex was identified 344 (53.6%) were males.Although the sex-ratio was slightly male biased, the trend was not, however, significant (G=3.30;d.f.= l; P<0.1).In true yeld and yeld hinds the calf sex-ratio also favoured males (57.9% and 60.0% respectively) but the sex difference was not significant.In summer yeld and milk hinds the amount of male and female progeny was well-balanced (50.6% and 50.8% males respectively).