Epsilon Archive for Student Projects

Abstract

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 sheep
production, producers needs to be successful in the breeding of the animals and achieve
an economic surplus in the end. Lambs that are born healthy and vital have greater
conditions to perform high lamb weight gains and thus a successful production. There
are many factors affect the survival, birth weight and early weight gain of the new born
lamb. The most important factors regarding the maternal influence and the
environmental factors that affect the lambs survival and early life weight gain was
explored 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 by
that 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 it
declines again. The foetus grows rapidly during the last weeks of gestation and the
newborn lamb weight can be affected by feeding. Feeding regime in early gestation does
not affect the growth of the foetus. The milk production of the ewe is of great
significance for the lambs’ early weight gain. Lambs that have restricted access to milk
in 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 weight
gain in post natal lambs. The study included 53 lambs of different breeds. The weights
of the lambs were registered at as close to birth as possible and as close to 120 hours
after the first occasion as possible. An hourly weight gain was calculated in order to
calculate a corrected weight at 120 hours. Litter size, sex of the lamb, age and the
maternal behavior of the ewe and occurrence of complications during parturition were
also registered.
The study showed that birth weight affects the early weight gain. Lambs with higher
birth weights had higher early weight gains than lambs that were smaller at birth. The
results confirmed earlier studies. A likely explanation is that small lambs have a lower
early 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 higher
growth rate than the heavier lambs. The study also showed that male lambs were heavier
and had a higher weight gain than female lambs. Triplets had lower birth weights and
grew less than twins and single born lambs. There was only a marginal difference
between twins and single born lambs. Adult ewes had the heaviest lambs and the highest
weight gains of their lambs. Crossbreeds lambs had higher weights at birth than the
purebreds. The study suffered from the relatively low number of lambs which makes
extensive conclusions difficult to make except for the correlation between birth weight
and early weight gain. It is suggested that birth weight and early weight gain can be used
for selecting ewes in the herd as this parameter may well reflect the ewes’ success
potential, including, foetus growth, maternal instincts and behaviour and milk
production. But this has to be further investigated.