Abortion and Lamb Mortality between Pregnancy Scanning and Lamb Marking for Maiden Ewes in Southern Australia

The contribution of abortions to the overall mortality of lambs born to maiden (primiparous) ewes in Australia remains unclear. This cohort study aimed to quantify abortion and lamb mortality for ewe lambs and maiden Merino two-tooth ewes. Lamb mortality from pregnancy scanning to marking were determined for 19 ewe lamb and 11 Merino two-tooth ewe flocks across southern Australia. Average lamb mortality from scanning to marking was 35.8% (range 14.3–71.1%) for the ewe lambs and 29.4% (range 19.7–52.7%) for the two-tooth ewes. Mid-pregnancy abortion was detected in 5.7% of ewes (range 0–50%) in the ewe lamb flocks and 0.9% of ewes (range 0–4.4%) in the two-tooth ewe flocks. Mid-pregnancy abortion affecting ≥2% of ewes was observed in 6/19 ewe lamb flocks and 2/11 two-tooth ewe flocks. Lamb mortality from birth to marking represented the greatest contributor to foetal and lamb mortality after scanning, but mid-pregnancy abortion was an important contributor to lamb mortality in some ewe lamb flocks. Variability between the flocks indicates scope to improve the overall reproductive performance for maiden ewes by reducing foetal and lamb losses. Addressing mid-pregnancy abortion may improve the reproductive performance in some flocks.

Effect of Breeding Heavier Romney Ewe Lambs at Seven Months of Age on Lamb Production and Efficiency over Their First Three Breeding Seasons

This experiment examined the effect of breeding heavier ewe lambs on lamb production and their efficiency over their first three breeding seasons. Two groups of ewe lambs were bred at seven months of age at an average pre-breeding live weight of either 47.9 ± 0.36 kg (heavy; n = 135) or 44.9 ± 0.49 kg (control; n = 135). Ewe live weight, number of lambs born and weaned, and lamb live weight were recorded until 39 months of age, and efficiency was calculated for each ewe. Although the number and lamb weaning weight did not differ between treatments over three years, when data were pooled, heavier ewe lambs at breeding weaned a greater number of lambs over the three-year period. The total lamb weaning weight over the three-year period increased by 2% for each additional kilogram at ewe lamb breeding. Breeding heavier ewe lambs had no effect on efficiency. These results suggest that although breeding heavier ewe lambs had a positive effect on lamb production over the three-year period, it had no effect on efficiency. Before final recommendations can be made, lifetime performance and longevity to five years of age of heavier ewe lambs at breeding are required.

The Number of Offspring Weaned from Ewe Lambs Is Affected Differently by Liveweight and Age at Breeding

In this paper, we tested the hypothesis that ewe lambs that are heavier and older at breeding will wean more offspring, due to increased reproductive rate and offspring survival and lower maternal mortality. To test this hypothesis, we analyzed data from more than 11,500 maternal composite ewe lambs collected over eight years. The ewe lambs had full pedigree records including birth type, age and liveweight at breeding plus records of the birthweight and survival of their offspring and the dam. The average liveweight and age at breeding was 40.2 kg and 228 days. The reproductive rate and weaning rate responses to liveweight at breeding were curvilinear (p < 0.001), and if ewe lambs achieved 45 kg by the start of breeding, their reproductive rate and weaning rate were within 5% of their maximum. By contrast, the effects of age at breeding on weaning rate was linear and increased by 0.4% per day, despite a quadratic (p < 0.01) effect of age at breeding on reproductive rate which increased only marginally when ewe lambs were older than 8 months at breeding. Increasing liveweight (p < 0.05) or age (p < 0.001) at breeding increased survival of their offspring, however an extra 10 kg of liveweight or 30 days of age at breeding increased offspring survival by less than 5%. Both liveweight (p < 0.001) and age (p < 0.01) at breeding also influenced survival of the ewe lamb dam but survival rates exceeded 95% across the range in liveweights from 30 to 55 kg and ages from 6 to 9 months. This understanding of the trade-off between age and liveweight at breeding will assist farmers to optimize the management of their ewe lambs, given the earlier they can be bred successfully the easier they can be integrated with the breeding of the adult ewe flock the following year.

Ewe-lamb bond of experienced and inexperienced mothers undernourished during gestation

The aims were to compare ewe-lamb behaviours between primiparous (PRI) and multiparous (MUL) undernourished grazing ewes at birth and at 3 months of age, and to determine if mothers’ parity affects milk yield and composition, and lambs’ body weight (BW). Food availability restricted the nutritional requirements from day 30 to day 143 of gestation. The MUL ewes had greater BW than the PRI during gestation, and their lambs tended to vocalize less frequently until their first suckle. PRI ewes both displayed a lower frequency of acceptance behaviours and, a greater number of high-pitched bleats toward the alien lamb than toward that of their own, but MUL did not. PRI ewes produced less milk than the MUL ewes. The heart rate was greater in lambs reared by MUL ewes than by PRI. Although PRI ewes had a lower BW during gestation, this difference was stable throughout and did not affect the establishment of the ewe-lamb bond neither at birth nor at 3 months postpartum. At least under nutritionally restricted conditions during gestation, inexperienced mothers appeared to have had a shorter sensitivity period of maternal responsiveness than that of experienced mothers.

Primiparous and Multiparous Ewes Undernourished During Gestation: A Study on Mother-Lamb Bond at Birth and at 3 Months of Age

The aims were to compare ewe-lamb behaviours between primiparous (PRI) and multiparous (MUL) undernourished grazing ewes at birth and at 3 months of age, and to determine if mothers’ parity affects milk yield and composition, and lambs’ body weight (BW). Food availability restricted the nutritional requirements from day 30 to day 143 of gestation. The PRI ewes had lower BW than MUL during gestation, and their lambs tended to vocalize less times until their first suckle. PRI ewes displayed a lower frequency of acceptance behaviours toward the alien lamb than toward their own lamb, but MUL did not. Whilst PRI ewes emitted a greater number of high-pitched bleats toward the alien lambs than toward their own lamb, MUL did not. PRI ewes produced less milk than the MUL ewes. The heart rate was greater in lambs reared by MUL ewes than by PRI. Although PRI ewes had a lower BW throughout the gestation, this difference was stable and did not affect the establishment of the ewe-lamb bond at birth or at 3 months postpartum. At least under nutritionally restricted conditions during gestation, inexperienced mothers appeared to have a shorter sensitivity period of maternal responsiveness than experienced mothers.

171 The effects of supplementing a chelated mineral containing Ascophyllum nodosum on intake and performance of creep-fed hair lambs

The objective of this study was to determine the effect of two commercial mineral supplements on ewes/lamb pairs DMI and ADG. All ewes prior to lambing were maintained a sheep pellet formulated for no mineral, vitamin, or probiotic content at a rate of 2% body weight, ad libitum Bermuda hay, and ad libitum access to the control mineral supplement. Ewe/lamb pairs were randomly assigned based on twining and parity to study groups four days post-lambing. The treatment (TRT) group had 12 ewes/18 lambs, and a control (CNTRL) group had 11 ewes/17 lambs, and was conducted over 6wks. Lambs in both groups were offered ad libitum alfalfa via a creep feeding gate. The TRT group received a commercial chelated mineral mix that included Ascophyllum nodosum seaweed extract in the blend and the CNTRL received a commercial non-chelated mineral without seaweed extract. Chelated minerals were Cu, Mn, and Zn. Daily feed and ort samples were collected 2x week and dried at 55℃ for analysis. Feed was adjusted daily to maintain a 3–5% refusal rate. Samples were compiled by week and analyzed for DM, Ash, aNDF, aADF, EE, and CP. Blood samples were collected from a subset of 7 ewes per group, 3x during the study (wk1, wk3, wk6) for later trace mineral analysis (Co, Cu, Fe, Mn, Mo, Se). Results indicate a significant difference in mineral DMI between groups (P = 0.03), but no significant impact on DMI of Bermuda or alfalfa. ADG for lambs was numerically increased 0.25±0.01 TRT versus 0.23±0.01 kg CNTRL but was not statistically significant (P = 0.18). No significant differences in trace mineral levels between groups or over time were seen. All mineral levels were in the normal range for both groups. It appears the addition of the chelated mineral with Ascophyllum nodosum seaweed extract did not improve ADG or DMI, but the results of this study were potentially affected by severe weather conditions. Further study is needed under more favorable conditions to confirm product impacts in ewe/lamb pairs.