Födelsevikt och tidig tillväxt hos nyfödda lamm
Sheep production is the only animal production in Sweden that is increasing. Therefore,increasing knowledge of the production is of great interest. In order to run a viable sheepproduction, producers needs to be successful in the breeding of the animals and achievean economic surplus in the end. Lambs that are born healthy and vital have greaterconditions to perform high lamb weight gains and thus a successful production. Thereare many factors affect the survival, birth weight and early weight gain of the new bornlamb. The most important factors regarding the maternal influence and theenvironmental factors that affect the lambs survival and early life weight gain wasexplored in this paper. Weight at birth is positively correlated to survival, weight gain,adult weight and maternal traits. Litter size affects the birth weight and is explained bythat the uterus is a limited space. Birth weight of lambs is lower in first parity ewes.Birth weight of lambs increases with the ewe?s age up to the fourth parity when itdeclines again. The foetus grows rapidly during the last weeks of gestation and thenewborn lamb weight can be affected by feeding. Feeding regime in early gestation doesnot affect the growth of the foetus. The milk production of the ewe is of greatsignificance for the lambs? early weight gain. Lambs that have restricted access to milkin early life have a low correlation between birth weight and early life weight gain.A minor investigation was made to study the influence of birth weight on early weightgain in post natal lambs. The study included 53 lambs of different breeds. The weightsof the lambs were registered at as close to birth as possible and as close to 120 hoursafter the first occasion as possible. An hourly weight gain was calculated in order tocalculate a corrected weight at 120 hours. Litter size, sex of the lamb, age and thematernal behavior of the ewe and occurrence of complications during parturition werealso registered.The study showed that birth weight affects the early weight gain. Lambs with higherbirth weights had higher early weight gains than lambs that were smaller at birth. Theresults confirmed earlier studies. A likely explanation is that small lambs have a lowerearly weight gain due to their smaller potential to feed as much as heavier lambs.However, lambs which were smaller at birth had relatively, to the birth weight, a highergrowth rate than the heavier lambs. The study also showed that male lambs were heavierand had a higher weight gain than female lambs. Triplets had lower birth weights andgrew less than twins and single born lambs. There was only a marginal differencebetween twins and single born lambs. Adult ewes had the heaviest lambs and the highestweight gains of their lambs. Crossbreeds lambs had higher weights at birth than thepurebreds. The study suffered from the relatively low number of lambs which makesextensive conclusions difficult to make except for the correlation between birth weightand early weight gain. It is suggested that birth weight and early weight gain can be usedfor selecting ewes in the herd as this parameter may well reflect the ewes? successpotential, including, foetus growth, maternal instincts and behaviour and milkproduction. But this has to be further investigated.