The project explores how ewe nutrition may be optimized through the annual cycle to ensure ewes with optimal weight and body condition at mating, and optimal nutrition through gestation and early lactation, aiming to minimize perinatal lamb mortality, and increase viability at birth and early growth rate.
In the first experiment, we studied three energy levels during the last 7 weeks of gestation for adult ewes carrying three fetuses. Nine ewes were allocated to each of three groups. Energy intake in group 1, 2 and 3 equaled 85, 100 and 120% of INRA (1989) recommendations. The study could not detect any significant relationship between late gestational energy level and lamb viability measured as stillbirths, neonatal death, or lambs that were strongly weakened, or died, on pasture. On the other hand, we can neither exclude a causal connection between lambs that deserted from the experiment and poor milk production of the ewe, further caused by low late gestational energy intake and thereby lack of body fat stores for mobilization during lactation.
There were only 3, 5 and 7 ewes in group 1, 2 and 3, respectively, that still had three suckling lambs at weaning. Average live weight for these were 35.6, 32.5 and 38.3 kg in group 1, 2 and 3, respectively, and daily weight gain per lamb from birth was 266, 240 and 284 g. Lambs in group 3 was significantly heavier, and had higher daily gains than lambs in group 2. Lambs in group 1 was intermediate, which could be due to the low number of complete triplet litters in that group. A strong positive correlation existed between a ewe?s daily energy intake in late gestation and litter weight of her triplets in autumn (R=0.70, P< 0.01). An equal correlation was found between a ewe?s body fat mobilization between delivery and the start of the grazing period 4 weeks later, and litter weight of her triplets in autumn (R=0.70, P< 0.01). These correlations suggest that a high feed level in late gestation that causes a high milk production that is maintained during summer, likely may result in high autumn weights of all three lambs.
The second experiment explored the effect of energy level for recruit ewes before and during puberty, and in early-to-mid gestation, on milk yield measured as daily weight gain of suckling lambs. From housing and until mating, two ?puberty?-groups with recruit lambs, 42 lambs per group, were nourished for high (H) and low (L) growth rates, and obtained 182 and 105 g/day, respectively. After mating, the lambs within each group were further allocated to two subgroups, H and L growth rates, from gestation day 20 to 96. Obtained growth rates in this period were 196, 203, 125 and 148 g/d, for groups HH, LH, HL and LL, respectively. Forty eight pregnant recruit ewes carrying 2 fetuses were moved to individual pens at gestation day 96. Recruit ewes with the highest energy feeding in puberty (HH and HL) increased body weight more during late gestation, when all ewes were offered the same high energy diet, than ewes on weaker feeding during puberty (LH and LL). The ewe group on the weakest feeding (LL) was the only one that did not obtain 75% of normal adult weight at their first delivery, with 8 kg lower body weight than the heaviest group. These low weight yearlings delivered in average the lightest lambs (4.3 kg). These birthweights, all twins, were, however, not significantly different from those of ewes from the other feeding groups, 4.7, 4.7 and 4.5 kg, for HH, LH and HL, respectively. No differences in daily lamb weight gain were found during the first 4 weeks, with 302, 291, 300, and 282 g for groups HH, LH, HL and LL, respectively.
Individual body condition (BC) and daily changes in BC scores (BCS) in 111 ewes (1.5 years old and adults) were studied in the third experiment. From housing and until obtained pregnancy, ewes were offered one of three diets that differed considerably in energy concentration. Body mass index (BMI), that is an objective measure of BC in ewes, was calculated as: Body weight (kg)/(length (m) × height (m)). Results showed that the ewes? absolute BMI, and not nutritional status at mating, i.e. increasing or decreasing BMI, is the main determining factor for ovulation rate, and thereby litter size. This implies that if a ewe is in good BC, for example has a BCS of 3.5 at breeding, it does not matter whether this BC is gained long ago og recently, and it is of minor importance whether the ewe currently is in positive or negative energy balance. In that sense, the word ?flushing? is not suitable to describe nutrition that increases litter size. Calculated BMI and the subjectively measured BCS correlated highly, such that both measures may be used to determine expected litter size. Each ewe?s number of fin genes (0, 1 or 2) also influenced litter size considerably, in line with current knowledge.
Prosjektet har medført økt fokus på, og kunnskap innen ernæring og helse hos søyer og lam både ved Institutt for husdyr- og akvakulturvitenskap og ved Institutt for produksjonsdyrmedisin, NMBU. Også hos prosjektets mange samarbeidspartnere, bl.a. ved Sveriges Landbruksuniversitet og København Universitet har prosjektet bidratt med økt fokus og kunnskap om ernæring og helse hos søyer og lam. Fagartikler og foredrag på fagmøter har bidratt til økt kunnskap også hos saueholdere og rådgivningstjenesten innen sau og helse.
Ved at kunnskapen om ernæring av søyer blir bedre vil en overordnet effekt, som vi håper vil vise seg i årene som kommer, være at lammedødeligheten om våren (sum for dødfødte, døde lam inne og på vårbeite) vil reduseres med ett prosentpoeng, og at lam som sendes på utmarksbeite om sommeren er mer robuste, slik at lammedødeligheten også gjennom sommeren reduseres med ett prosentpoeng.
The Norwegian White Sheep is a productive and prolific sheep breed for meat production and constitutes 80% of the Norwegian sheep. Stillbirths and postnatal lamb mortality have shown an increasing trend over the last years, and triplet and higher order li tters are associated with increased risk. Average litter size per mated ewe has increased from 1.9 to 2.1 from 2000 to 2012. Recent research has shown that ewes with stillborn lambs exhibit marked pathophysiological changes as compared with ewes without s tillborn lambs. Failure in ewe nutrition during pregnancy might contribute to unsatisfactory provision of nutrients or oxygen to the foetuses, and contribute to the birth of weak neonates with little brown fat, and supplied with insufficient amounts immun e globulin G or vitamin E from colostrum. The project aims to explore how ewe nutrition could be optimized during the annual cycle, to ensure ewes of optimal weight and body condition score at mating, and with optimal feeding during pregnancy and early la ctation, aiming to significantly reduce perinatal lamb mortality.
The project consists of three experiments exploring impacts of different feed energy levels, offered to multiple-bearing mature and adolescent ewes, before and during gestation. Ewes and n ewborn lambs will be followed closely with measurements of body weight, body condition, ultrasound measurements, blood samples, neonatal viability and lamb growth rate. Stillborn lambs will be necropsied and placentas subjected to histological examination in comparison with placentas from ewes with live-born lambs. The new knowledge developed by the project is expected to reduce total spring lamb mortality (stillborns plus neonatal mortality) by one percentage. In addition, summer lamb mortality is expect ed to decrease since lambs will be more robust during travel to summer pasture. In total, this will increase total incomes for the Norwegian sheep holders with 35 million NOK annually.