Barley grain supplementation in late gestation to twin-bearing Merino ewes grazing high-biomass and high-quality pasture does not increase lamb survival

Survival of lambs affects the profitability of Merino enterprises, with mortality from birth to marking the most prominent factor leading to poor reproductive performance. Survival of lambs following parturition is dependent on the ability to access colostrum and milk, which can be altered by the provision of barley grain to promote lactogenesis and colostrum production when feed availability is suboptimal. The present study evaluated whether the survival of lambs could be improved by supplementing ewes grazing abundant quality pasture with barley grain. Naturally joined Merino ewes (n = 240, 65.5 kg, body condition score (CS) 3) bearing twin fetuses grazing spring pastures (1712 kg DM/ha green, 12.3 MJ ME/kgDM, and 18.5% crude protein at the commencement of the experiment) were allocated to a supplemented or a control diet, with two replicates of each. Ewes were supplemented with 550 g/ewe.day barley grain (12.6 MJ ME/kgDM, 10% crude protein) for 20 days before and 2 weeks following the commencement of lambing (supplemented), or were unsupplemented (control). Ewes gained 0.5 CS and 10.6 kg liveweight from pre-lambing to lamb marking age in both treatments, indicating that their energy intake was high. The proportion of lambs surviving from birth to marking was 0.79 for control and supplemented treatments. Lamb survival was affected by the interaction (P = 0.039) between treatment and sex, with control female lambs having a significantly higher survival than control male lambs. Supplemented lambs reared as singles (17.1 ± 0.95 kg) had significantly (P < 0.05) heavier marking weights thanthe control lambs reared as singles (14.8 ± 1.1 kg), supplemented lambs reared as twins (14.7 ± 0.71 kg) and control lambs reared as twins (15.5 ± 0.70 kg). Lamb survival was not increased by provision of barley grain in the final weeks before lambing and the first 2 weeks of lambing when ewes were in good CS and grazed ample high-quality pastures.

Lamb survival in Australian flocks: a review

Lamb survival is known to be a key component of reproductive efficiency in sheep flocks. It has been the subject of a large number of studies over the decades and this review provides an update and insights into the latest understanding of the extent and variability of lamb losses across Australia. The pattern of causes of lamb losses, including dystocia, starvation/exposure, mismothering and predation, are examined. Likewise the importance of birthweight in contributing to such losses is discussed as are strategies for improving lamb survival. The strategies examined include improved ewe nutrition, shelter provision and selection for cold resistance and improved maternal behaviour.

Seasonal reproductive performance of crossbred ewes in intensive lamb-production systems

The lambing performance of 1179 crossbred ewes with 5540 joining records in three seasons (autumn, winter and spring) at two sites (Cowra and Wagga Wagga) was evaluated in three lamb-production systems (spring joining with autumn backup matings at both locations, with accelerated lambing at Cowra or annual autumn joining at Wagga Wagga) over 4 years. Two genotypes of ewes, Border Leicester × Merino (BLM) and Hyfer (Dorset × Merino composite), were used at both sites, with natural matings to Dorset, Suffolk or Hyfer rams. The following five traits were analysed separately at each site to evaluate ewe lambing performance: fertility, litter size, lambs born (per ewe joined), lambs weaned (per ewe joined) and weight of lamb weaned (per ewe joined). The mixed model included fixed effects for season of joining, ewe breed, ram group, ewe prejoining weight (spline) and their interactions, with ewe fitted as a random effect. The autumn (February) joinings had higher ewe fertility, litter size and overall lamb production than did joinings in spring (October and November), with winter (June) being intermediate. At the autumn joinings, the BLM ewes had higher fertility, lambs weaned and weight of lamb weaned than did the Hyfer ewes, although this was reversed at the spring joinings, causing significant season × ewe breed interactions. While litter size was larger in the autumn than in the spring for both breeds there was a much smaller seasonal effect among the Hyfer than BLM ewes. Prejoining ewe weight had a significant effect on all reproduction traits, with generally a curvilinear response with increasing weight. The interactions of weight with season × ewe breed were significant (P < 0.001) for all traits at Cowra and most traits at Wagga Wagga. Ram group was significant (P < 0.05) for most traits, with ewes joined to Hyfer rams having higher fertility than those joined to Suffolk. and with Dorset rams being intermediate. At Wagga Wagga, this was the case for spring joinings, but there was no difference between the ram groups in autumn, causing a significant ram × season interaction (P < 0.001). Ewe repeatability ranged from 0.15 to 0.25 for all traits. Using suitable breeds or genotypes, together with optimising management, could improve out-of-season lamb production.

Effect of nutrition from mid to late pregnancy on the performance of twin- and triplet-bearing ewes and their lambs

This experiment was conducted to determine the effect of two different feeding levels on ewes during mid and late pregnancy on lamb birthweight and growth to weaning. Twin- and triplet-bearing Romney ewes (n = 80 and 56, respectively) were allocated to one of two feeding regimes and provided pastures with an average sward height of less than 2 cm (~700 kg dry matter/ha) or greater than 4 cm (~1300 kg dry matter/ha). Ewes were allocated to these feeding regimes during mid pregnancy (day 70–107 of pregnancy; P70–P107) and were reallocated in late pregnancy (P108–P147). This resulted in four sward height treatments: 2–2, 2–4, 4–2 and 4–4. During mid pregnancy, ewes provided with >4-cm-high swards had liveweight gains of 262–290 g/day compared with 12–31 g/day for ewes provided with <2-cm-high swards. In late pregnancy, ewe liveweight gains were influenced by the ewes’ previous nutritional treatment. Ewes in the 2–4 treatment had higher daily gains (538 g/day) than 4–4 ewes (343 g/day). In addition, 4–2 ewes gained 90 g/day compared with 247 g/day for 2–2 ewes. Throughout pregnancy, triplet-bearing ewes were heavier (P < 0.05) than twin-bearing ewes, but during lactation ewe weights were similar. On P130, ewes provided with <2-cm-high swards (4–2 and 2–2) had greater β-hydroxybutyrate (P < 0.05) and lower glucose (P < 0.05) plasma concentrations than ewes provided with >4-cm-high swards (2–4 and 4–4). On P139, however, ewes provided with 4–4 swards had higher plasma non-esterified fatty acid and β-hydroxybutyrate concentrations than ewes in all other treatments. Lambs born to ewes in the 4–4 treatment had the greatest birthweights (P < 0.05), whereas lambs born to 2–2 ewes had the lowest birthweights. The birthweight of lambs born to 2–4 ewes was similar to that of lambs born to ewes provided with 4–2 and 4–4 swards. At weaning, ewe weights were similar between ewe nutritional treatments and ewes bearing twin or triplet fetuses. These findings suggest that when pasture growth is inadequate to provide pasture sward heights of 4 cm throughout pregnancy, restricted intake in mid-pregnancy may be partially compensated by providing additional pasture in late pregnancy.

Fertility in South Australian commercial Merino flocks: relationships between reproductive traits and environmental cues

High levels of reproductive loss have been reported in commercial Merino flocks (n=68) from the cereal/livestock and high rainfall zones in South Australia (Kleemann DO, Walker SK. Fertility in South Australian commercial Merino flocks: sources of reproductive wastage. Theriogenology 2005;63:2075-88). Relationships between reproductive traits (estrus, ovulation, fertility, fecundity, lamb survival) and environmental end points (liveweight, condition score, temperature at mating, chill index at lambing) are reported in this paper. They were analysed within season of mating (October to December; January to March) and age of ewe (maiden as 1.5-year-old, mature as older). Incidence of estrus was positively related (P<0.05) to condition score in the October to November interval. Return rate to service was positively (P<0.05) influenced and fertility was negatively (P<0.05) influenced by the number of days ambient temperatures were > or =32.0 degrees C during mating, indicating that high ambient temperatures may reduce embryo survival. Liveweight and, to a lesser extent, condition score, accounted for significant proportions of variation associated with ovulation rate (39.3 and 12.7%, respectively). Ovulations per 100 ewes increased by 1.8 per kg increase in liveweight over all flocks. Ovulatory response to liveweight increased (P<0.01) from the October to December to the January to March period of mating (1.5 versus 3.4 ovulations per kg, respectively). Overall, a flock's fertility and fecundity increased by 0.27 and 1.42% per kg increase in liveweight, respectively. Reproductive wastage from partial failure of multiple ovulations (PFMO) was positively related to liveweight (P<0.01) and ovulation rate (P<0.001). Survival of single lambs was positively and curvilinearly related to maternal liveweight and condition score measured in late pregnancy (P<0.05). Linear relationship of these variables for twin lamb survival was significant for condition score only. Single and twin lamb survival were also positively related to liveweight and condition score at mating (P<0.05). We concluded that nutritional cues have a major impact on reproductive traits in commercial Merino flocks in South Australia; it sets the potential number of lambs (ovulation rate) and influences survival of lambs as early as at mating. Indications are that high ambient temperatures may influence embryo survival. It is recommended that future research efforts focus on: (a) prenatal nutritional influences on the physiology of mother-offspring behaviours at birth; and (b) possible peri-conceptional dietary factors controlling embryo loss resulting from partial failure of twin ovulations, to improve reproductive efficiency in the Merino.

Production responses of two genetic different types of Merino sheep subjected to different nutritional levels

The primary selection objective in the South African Mutton Merino is meat production, while wool plays a secondary role. The Merino, on the other hand is selected for wool production. Respectively 20 and 23 of each genetic different type of ewes were used in a 15-week indoor study to quantify the influence of nutrient intake on certain production traits when fed at different levels of their respective requirements during late pregnancy (last 6 weeks) and lactation (first 6 weeks). Results were used to provide production parameters for the two types of ewes and their lambs at different levels of nutrition. Lambing percentage (per ewe lambed) of SA Mutton Merino ewes was 171% compared to 135% for Merino ewes. Live weight gains for meat-wool and wool-type ewes during late pregnancy amounted to 15.9 and 21.9%, with corresponding live weight losses of -8.3 and -1.1% during the first 6 weeks of lactation. Greasy wool production during the last 9 weeks of pregnancy and the first 6 weeks of lactation amounted to 1.57kgewe(-1) (meat-wool type ewes) and 2.84kgewe(-1) (wool-type ewes). Milk production 17 days post partum was 2.33kg/day and 1.84kg/day for the two types of sheep. Lambs of the meat-wool type ewes had a mean birth weight of 4.1kg and an average daily gain (ADG) of 270g/day to 42 days of age. Lambs of the wool-type ewes had a mean birth weight of 4.9kg and a 42-day ADG of 192g/day. There were clear differences in production traits of the two types of Merino sheep, which were in accordance with their genetic differences. The study gave practical production norms for meat-wool and wool-type Merino ewes and their lambs when subjected to different nutritional levels.

Maternal undernutrition during mid-pregnancy in sheep. Placental size and its relationship to calcium transfer during late pregnancy

The aim of the present experiment was to determine the relationship between placental and fetal weight after placental growth had been retarded by maternal undernutrition. Placental weight and fetal weight were measured in single-lamb-bearing ewes which were well-fed throughout pregnancy, or severely undernourished between the 30th and 96th day of pregnancy. Placental transfer of calcium and whole-body metabolism of both glucose and Ca were measured during late pregnancy. The change in fleece-adjusted live weight between the 30th and 96th day of pregnancy was 99 (SE 9.8) and -146 (SE 9.6) g/d for the well-fed and undernourished ewes respectively. The condition score of well-fed ewes did not significantly change between the 96th (2.9 (SE 0.08)) and 140th (3.0(SE 0.13)) day of pregnancy, while it increased from 1.6 (SE 0.15) to 2.3 (SE 0.11) for the previously undernourished group. Undernutrition caused an increase (P less than 0.01) in placental weight measured on the 96th (21%) and 140th (30%) day of pregnancy. In contrast fetal growth was not significantly affected by maternal undernutrition. While the voluntary dry matter intakes (g/d) of previously undernourished ewes after the 97th day of pregnancy were higher than for their well-fed counterparts, there was no significant difference between whole-body glucose or Ca metabolism, or the placental transfer of Ca measured during late pregnancy. This experiment confirms earlier reports of an increase in placental weight as a result of maternal undernutrition during mid-pregnancy; but the factors causing and the functional significance of this response have not been identified. Contrary to earlier proposals, placental weight per se did not limit fetal growth during late pregnancy. It is hypothesized that a combination of factors originating from maternal, placental and fetal sources act together to regulate growth of the fetus.