Risk factors for perinatal and postnatal mortality in lambs

A study was carried out on six hill farms, located in the main hill regions of Northern Ireland, over three breeding seasons to investigate the effect of sire breed on ewe dystocia, lamb survival and weaned lamb output. On each farm, groups of 26 to 40 purebred Scottish Blackface ewes (n 5 3174) were crossed with Blackface, Swaledale, North Country Cheviot, Lleyn and Texel sires by natural service (year 1) and artificial insemination (years 2 and 3). Each of the mating groups was initially balanced for ewe age, live weight and condition score, and a total of 15 sires of each breed were used over the 3 years. In total, 2272 ewes were recorded at lambing, producing 3451 lambs, over the 3 years. Sire breed had a significant effect (P , 0.001) on lamb birth weight with Blackface and Swaledale the lowest and Texel the highest. The proportion of ewes with dystocia was higher with Texel sires compared with Lleyn, Swaledale and Blackface sires (P , 0.05). Ewes mated to Cheviot sires had more dystocia than those mated to Blackface and Swaledale sires (P , 0.05), while ewes mated to Lleyn sire breed had more dystocia (P , 0.05) than those mated to Blackface sire breed. Most of the incidence of dystocia was attributable to increased lamb birth weight (P , 0.001), and some to litter size (P , 0.05). Swaledale, Cheviot, Lleyn and Texel sire breeds increased the incidence of malpresentations (P , 0.05). Lamb live weight at weaning was higher with Texel-and Cheviot-and Lleyn-sired lambs compared with Blackface-and Swaledale-sired lambs (P , 0.01). The level of lamb mortality at birth was not affected by sire breed. However, lamb mortality at weaning was lower for Lleyn-sired lambs compared with the other lamb genotypes (P , 0.05). These results indicate that the use of sires from larger breeds, such as Lleyn and Texel, within the Blackface ewe flocks can increase lamb output, with no apparent detrimental effects on lamb mortality or ewe survival, but increased assistance at lambing will be required.

Section: Discussionsupporting

confidence: 80%

Effects of sire breed on ewe dystocia, lamb survival and weaned lamb output in hill sheep systems

Speijers

Carson

Dawson

et al. 2010

“…Some studies have postulated that increased lamb mortality in males may be due to differences in birth weight (Smith, 1977;Gama et al, 1991;Nash et al, 1996). In the present study, however, greater lambing difficulty and mortality were still evident in male lambs even after adjusting for gender differences in birth weight.…”

Section: Risk Factors Associated With Lambing Gendercontrasting

confidence: 54%

Risk factors associated with lambing traits

McHugh

Berry

Pabiou³

2016

The objective of this study was to establish the risk factors associated with both lambing difficulty and lamb mortality in the Irish sheep multibreed population. A total of 135 470 lambing events from 42 675 ewes in 839 Irish crossbred and purebred flocks were available. Risk factors associated with producer-scored ewe lambing difficulty score (scale of one (no difficulty) to four (severe difficulty)) were determined using linear mixed models. Risk factors associated with the logit of the probability of lamb mortality at birth (i.e. binary trait) were determined using generalised estimating equations. For each dependent variable, a series of simple regression models were developed as well as a multiple regression model. In the simple regression models, greater lambing difficulty was associated with quadruplet bearing, younger ewes, of terminal breed origin, lambing in February; for example, first parity ewes experienced greater (P < 0.001) lambing difficulty (1.56 ± 0.02) than older ewes. The association between lambing difficulty and all factors persisted in the multiple regression model, and the trend in fixed effects level solutions did not differ from the trend observed in the simple regression models. In the simple regression analyses, a greater odds of lamb mortality was associated with male lambs (1.31 times more likely of death than females), lambs of very light (2 to 3 kg) and very heavy (>7.0 kg) birth weights, quadruplet born lambs and lambs that experienced a more difficult lambing (predicted probability of death for lambs that required severe and veterinary assistance of 0.15 and 0.32, respectively); lambs from dual-purpose breeds and born to younger ewes were also at greater risk of mortality. In the multiple regression model, the association between ewe parity, age at first lambing, year of lambing and lamb mortality no longer persisted. The trend in solutions of the levels of each fixed effect that remained associated with lamb mortality in the multiple regression model, did not differ from the trends observed in the simple regression models although the differential in relative risk between the different lambing difficulty scores was greater in the multiple regression model. Results from this study show that many common flock-and animal-level factors are associated with both lambing difficulty and lamb mortality and management of different risk category groups (e.g. scanned litter sizes, ewe age groups) can be used to appropriately manage the flock at lambing to reduce their incidence.

“…Moreover, the proportion of lambs dying from infection was largest in twin and triplet litters. Mastitis, which is associated with reduced milk production and quality, or poor milk production per se, might result in inadequate milk supply to the lambs and increase the risk of lamb mortality, particularly in lambs from litters of multiples (Nash et al, 1996;Arsenault et al, 2008). The sampling performed in the present study was completed before the earliest reports of Schmallenberg virus in central Europe (Hoffmann et al, 2012;van den Brom et al, 2012) and thus this virus is unlikely to have caused congenital malformations detected in this study.…”

Section: Discussionmentioning

confidence: 99%

Early neonatal lamb mortality: postmortem findings

Holmøy

Waage

Granquist

et al. 2017

An investigation of stillbirth and early neonatal lamb mortality was conducted in sheep flocks in Norway. Knowledge of actual causes of death are important to aid the interpretation of results obtained during studies assessing the risk factors for lamb mortality, and when tailoring preventive measures at the flock, ewe and individual lamb level. This paper reports on the postmortem findings in 270 liveborn lambs that died during the first 5 days after birth. The lambs were from 17 flocks in six counties. A total of 27% died within 3 h after birth, 41% within 24 h and 80% within 2 days. Most lambs (62%) were from triplet or higher order litters. In 81% of twin and larger litters, only one lamb died. The most frequently identified cause of neonatal death was infectious disease (n = 97, 36%); 48% (n = 47) of these died from septicaemia, 25% (n = 24) from pneumonia, 22% (n = 21) from gastrointestinal infections and 5% (n = 5) from other infections. Escherichia coli accounted for 65% of the septicaemic cases, and were the most common causal agent obtained from all cases of infection (41%). In total, 14% of neonatal deaths resulted from infection by this bacterium. Traumatic lesions were the primary cause of death in 20% (n = 53) of the lambs. A total of 46% of these died within 3 h after birth and 66% within 24 h. Severe congenital malformations were found in 10% (n = 27) of the lambs, whereas starvation with no concurrent lesions was the cause of death in 6% (n = 17). In 16% (n = 43) of the lambs, no specific cause of death was identified, lambs from triplet and higher order litters being overrepresented among these cases. In this study, the main causes of neonatal lamb mortality were infection and traumatic lesions. Most neonatal deaths occurred shortly after birth, suggesting that events related to lambing and the immediate post-lambing period are critical for lamb survival.