Holmøy Ingrid Hunter, Waage Steinar
Faculty of Veterinary Medicine and Biosciences, Department of Production Animal Clinical Sciences, Norwegian University of Life Sciences, P.O. Box 8146 Dep., 0033, Oslo, Norway.
Acta Vet Scand. 2015 Sep 30;57:65. doi: 10.1186/s13028-015-0155-6.
Perinatal mortality is a major cause of loss in the sheep industry. Our aim was to explore time trends in crude population stillbirth and neonatal mortality rates in Norway. We used data on 6,435,715 lambs from flocks enrolled in the Norwegian Sheep Recording System (NSRS) from 2000 through 2010 for descriptive analysis of trends. Longitudinal patterns of mortality rates were compared for lambs within different levels of variables suspected to be associated with perinatal loss.
There was an approximately linear increase in the annual proportion of stillborn lambs during the study period, from 3.3 % in 2000 to 4.7 % in 2010. In the same time period, average litter size of ewes in NSRS flocks increased from 2.00 to 2.19. However, a steady rise in stillbirth rate was observed within each litter size group, suggesting a gradually increasing impact on stillbirth risk of other, yet unidentified, factors. Average flock size increased during the study period. The highest stillbirth rates were found in the largest and smallest flocks. Early neonatal mortality rates (0-5 days of life) varied from year to year (minimum 2.2 %, maximum 3.2 %) and were invariably higher among triplets and quadruplets than among singletons and twins. Annual fluctuations were parallel within the various litter sizes. A significant overall decreasing trend was present within all litter sizes with the exception of singletons. Weather data for the prime lambing months (April and May) 2000-2010 indicated a relationship between low temperatures and high neonatal mortality rates. At the flock level, there was a significant positive correlation between stillbirths and early neonatal mortality rates (r = 0.13), between stillbirth rates in two consecutive years (r = 0.43) and between early neonatal mortality rates in two consecutive years (r = 0.40).
The substantial increase in ovine stillbirth rate in recent years in Norway was to some extent related to a corresponding increase in the proportion of lambs in triplet or larger litters; however, other factors apparently have contributed. Early neonatal mortality rate exhibited year-to-year variations, partly following temperature fluctuations, which is somewhat unexpected, considering that lambing mainly occurs indoors in Norway.
围产期死亡率是养羊业损失的主要原因。我们的目的是探究挪威粗出生率和新生儿死亡率的时间趋势。我们使用了2000年至2010年纳入挪威绵羊记录系统（NSRS）的羊群中6,435,715只羔羊的数据，对趋势进行描述性分析。比较了怀疑与围产期损失相关的不同变量水平内羔羊死亡率的纵向模式。
在研究期间，死产羔羊的年度比例呈近似线性增长，从2000年的3.3%增至2010年的4.7%。同一时期，NSRS羊群中母羊的平均产仔数从2.00增至2.19。然而，在每个产仔数组中均观察到死产率稳步上升，这表明其他尚未明确的因素对死产风险的影响逐渐增加。研究期间平均羊群规模有所增加。最大和最小的羊群死产率最高。早期新生儿死亡率（出生后0至5天）逐年变化（最低2.2%，最高3.2%），三胞胎和四胞胎的死亡率始终高于单胞胎和双胞胎。各产仔数内的年度波动情况相似。除单胞胎外，所有产仔数组均呈现显著的总体下降趋势。2000年至2010年主要产羔月份（4月和5月）的天气数据表明低温与高新生儿死亡率之间存在关联。在羊群层面，死产与早期新生儿死亡率之间存在显著正相关（r = 0.13），连续两年的死产率之间存在显著正相关（r = 0.43），连续两年的早期新生儿死亡率之间存在显著正相关（r = 0.40）。
近年来挪威绵羊死产率大幅上升在一定程度上与三胞胎或更大产仔数羔羊比例相应增加有关；然而，其他因素显然也起到了作用。早期新生儿死亡率逐年变化，部分随温度波动而变化，考虑到挪威主要在室内产羔，这有点出乎意料。
