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Lambing percentage is the main contributor to higher profit on New Zealand sheep farms and has increased from 98% in 1960 to 124% in 2006. As ewe litter size increases so does the proportion of triplet-born lambs and consequently preweaning mortality rate. The purpose of this study was to investigate the effect of birthweight (BWT) on survival in triplet-born lambs within and among litters. Data from a total of 594 triplet crossbreed lambs born to mixed-age ewes was analysed. For the statistical analysis, the lambs were allocated according to their BWT, and within the litter were then allocated to three BWT groups (light, medium and heavy). The following parameters were calculated: total litter BWT (TBWT), percentage of TBWT for each lamb (PBWT = BWT/TBWT), coefficient of variation for BWT within litter and lamb average daily gain from birth to weaning. The mortality rate for the light, medium and heavy lambs was 56, 40 and 28%, respectively, and consequently the lightest lamb in a litter was 3.2 times more likely to die than the heaviest lamb. In the light lamb group, as BWT increased mortality decreased (P = 0.006), for medium lambs BWT did not influence mortality (P = 0.88) and in the heavy group there was a trend of increased BWT associated with increased mortality (P = 0.10). The negative relationship between lamb mortality and PBWT was identical in the three BWT groups (P

Perinatal lamb mortality is a serious issue for the sheep industries. Starvation is implicated in many of these lamb deaths. Ewes with a calm temperament lose significantly fewer lambs than ewes with nervous temperament, particularly in the critical first 3 days after birth. Colostrum provides essential nutrition to neonatal lambs. This research set out to determine whether ewe temperament affects the quantity and quality of colostrum that ewes produce. Calm temperament was found to have an influence on the viscosity of colostrum 6 h after birth. High variability in all aspects of colostrum production were found in the study and may be a limiting factor in lamb survival in certain circumstances. There is little evidence, however, to suggest a strong association with ewe temperament and is therefore unlikely to explain the lower lamb mortality that is reported to occur among calm ewes.

Lambs and ewes from 2 Merino lines that had been selected divergently from the same base population for (High line) or against (Low line) multiple rearing success, were assessed for their ability to reunite after temporary separation. Selection in the lines began in 1986, and data for this study were obtained from 1998 to 2002. Postnatal lamb mortality for lambs born during 1998–2002 were generally lower (P0.05). When released from the pens, the dams of 95% of single lambs returned for their lambs, the proportion tending (P

Behavioural factors associated with lamb mortality were examined in regard to the relative effects of age and parity in single-bearing Merino ewes. Primiparas tended to have longer labour and higher lamb mortality than multiparous ewes. Maternal behaviour in primiparas was characterised by more desertions, a smaller proportion that stood and started to groom their lambs immediately after birth, and a larger proportion with non-cooperative behaviour during the initial sucking attempts of the lamb. These traits, and a high incidence of malpresentations, were particularly marked in 5-year-old primiparas deliberately denied access to rams in previous seasons. There was no evidence of improved maternal behavioural attributes associated with increasing age of ewe that were independent of previous experience in giving birth and rearing lambs.

This paper reports on birth-site distribution of Merinos and some British breeds in 34 lambing paddocks in a major study over 5 lambing seasons at Armidale New South Wales, and in minor studies during single lambing seasons, 2 in New South Wales and 3 in the United Kingdom. The observed distribution of birth-sites is related to topographic and other environmental features of the paddocks. In level, or nearly level paddocks, Merinos tended to lamb in a random pattern, but in sloping paddocks their birth-sites were consistently aggregated in the areas of greatest elevation. British breeds (Suffolks and Cheviots in New South Wales, and Welsh Mountain, Scottish Blackface, North Country Cheviots and Greyface in the United Kingdom) showed a pronounced tendency to lamb near the margins of paddocks, and a less marked preference for an elevated site. It is suggested that lamb mortality could be significantly reduced by the use of paddocks that provide shelter at preferred elevated positions, or along and within the paddock margins.

An outbreak of congenital goitre associated with minimal thyroid enlargement resulted in a high level of lamb mortality (36.1 per cent) in a flock in northern Tasmania. Palpation was shown to be a valid means of assessing thyroid gland size and a significant linear relationship between thyroid size and lamb mortality was demonstrated (P < 0.01). Although the overall difference in mortality rate between normal and goitrous lambs was significant this was confined to the middle of the birth weight range; at either end of the range the normal and goitrous lambs experienced similar levels of mortality. Goitrous lambs died earlier and had less chance of walking or metabolising their fat reserves than their normal counterparts. There was no effect of sex or type of birth (single or multiple) on incidence of goitre. In most of the goitrous lambs that survived, thyroid size had regressed to normal in about six weeks.

Three systems of lambing management were compared at Trangie in Central Western New South Wales. A supervised system involving daily drifting of ewes through a series of small paddocks was first compared with an unsupervised system in which ewes were set-stocked in a single large paddock (A) and later, an unsupervised system in which ewes were set-stocked in sub-flocks according to their expected date of lambing (B). Lamb loss associated with the management of marking and mulesing proved to be an important factor in the comparison. The introduction of unsupervised system (B) was associated with a reduction in losses after marking compared with the supervised system. Lamb loss prior to marking was lowest in the supervised system. Of the three systems, unsupervised system (B) is considered the most suitable for areas in which environmental conditions during lambing are not harsh.

Merino flocks lambing in either autumn or winter in south-eastern South Australia showed no consistent differences in reproductive performance over a five-year period. The percentage of ewes that lambed, the level of twin births, and the lamb mortality rates varied in their relative contribution to the final result in any one season. For each reproductive factor measured the difference between the flocks varied from year to year in magnitude and sign. Lambs born in the winter had higher birth weights and better early growth rates, but liveweight during their first summer period was generally less than that of autumn born lambs. Survival rates in both groups were similar.

Statistics are presented from a Peppin Merino parent stud on seasonal variation in flock fertility, differences in fertility between rams of various ages, lamb mortality, age composition of the ram pool, and the differential we of rams of various ages. Variation of the percentage of lambs born to ewes served was largely due to seasonal differences in the proportion of ewes (2.5 per cent to 26.5 per cent) with twins. The majority (about 7 per cent) of lamb deaths up to 24 hours after birth was due to natural causes. Total lamb mortality up to 21 days of age was 13 per cent of the number of lambs born. Male lamb mortality up to 24 hours, including lambs born dead, was higher than female mortality (17 per cent u. 6 per cent). Age composition of the ram pool and ram wastage indicated a replacement rate of about 25 per cent. Average age of rams was 4.4 years at the time of birth of their offspring. Ram fertility, assessed as the percentage of ewes lambing to ewes mated, was 55 per cent for two year old, 70 per cent for five year old, and 59 per cent for nine year old rams. From a total of 27 to 37 rams in we each year, 10 favoured rams sired 52 per cent to 70 per cent of lambs alive at 24 hours. These favoured rams were also above average age (5.1 years v. 4.4 years). Thus, favoured sires contribute more heavily to the future flock genotype than other sires; firstly because they have more offspring, and secondly, became pedigree records provide the basis for additional favouritism towards their offspring, especially in the choice of stud ram replacements. This operational pattern has the two-fold disadvantage of increasing the generation intervals relevant to flock replacements and of inefficient exploitation of genetic gains already, made. If, as we believe, this operational pattern is currently typical of the foremost studs of the Merino industry, if is a matter of some concern with respect to the implementation of genetic improvement programmes and the progress expected from them.Where present procedures follow such a pattern thy should be largely reversed so as to use a higher proportion of young rams and to mate them to a much larger proportion of the ewe flock.