Andrew N Thompson

Mating ewes to lamb at 12 months of age can enhance lifetime productivity but is associated with lower reproductive performance and lamb survival compared to mature ewes. Melatonin, an antioxidant, has been shown to improve placental function and lamb health when mature ewes were supplemented during pregnancy. This study investigated the effect of supplementing one-year-old ewes with melatonin during mid-pregnancy on their survival and the live weight and survival of their lambs. Single- (n = 2711) and twin-bearing (n = 2605) ewes were randomly assigned to Melatonin or Control groups at seven farms across southern Australia. The Melatonin group received an 18 mg implant of melatonin at 90–100 days after the introduction of the rams, which releases melatonin for 60–80 days, and the Control group were not supplemented with melatonin. Seven farms recorded paddock level information including fetal number, lambs present 200 days after the introduction of the rams, ewes present pre-lambing and 200 days after the introduction of the rams and ewe pre-lambing live weight. Lamb survival and ewe mortality were analysed with analysis of covariance. Three of the seven farms also collected individual lambs’ information (n = 4303 lambs) including weight at birth and weaning of lambs, date of birth and weaning, lamb sex and birth type. Individual lamb live weights and growth rate to weaning were analysed with linear mixed models. Supplementation with melatonin had no effect (P > 0.05) on ewe or lamb survival. Melatonin supplementation did not impact (P > 0.05) individual lamb birthweight, growth rate, or weaning weight, consistent with the observed results in lamb survival. These findings suggest that maternal supplementation with melatonin mid-pregnancy is not an effective strategy to improve the survival or early growth of lambs, or the survival of one-year-old ewes.

Measuring feed efficiency (FE) in sheep is costly. Reducing the duration of dry matter intake (DMI) tests as a component of FE may lower expenses, while allowing for more animals to be assessed annually. This study analyzed a dataset of 46 016 DMI values from 1064 animals (796 ewes and 268 rams) in nine contemporary groups to explore the feasibility of shortening the DMI measurement periods from the 38-day standard DMI test period to accurately predict FE. We assessed the accuracy and precision of shortened test periods using Pearson and Spearman correlations, standardized regression coefficients (β), coefficient of determination (R2), and concordance correlation coefficients (CCC). Results indicated that DMI test period can be reduced from the 38 days standard test days to 22, 24, and 25 days in ewes, rams and across gender, respectively, while maintaining Pearson and Spearman correlations of 95%. Other statistics revealed that the DMI test period in ewes could be reduced from 38 to 22 days with a β of 0.89, R2 of 0.94, and CCC at 95%, to 24 days for rams with β of 0.96, R2 of 0.94, and CCC at 0.95, and to 25 days across gender with β of 0.97, R2 of 0.96, and CCC at 0.97. In conclusion, DMI test periods can be shortened without compromising data integrity, enhancing phenotypic evaluations in sheep.

Context
In the south-west of Western Australia, weaned lambs typically graze dry annual pastures and crop stubbles during late spring, summer and autumn (October–March). The low energy and protein content of these feeds typically means that lambs are supplemented with concentrates to achieve target growth rates. Fully mature, standing lupin crops that could be harvested may provide higher quality feed than dry pasture and crop stubbles over this period.

Aims
This study tested the hypothesis that the incorporation of standing lupin crops for grazing will increase whole-farm profitability. Furthermore, we aimed to quantify the relative contributions of stocking rate, sale value of lambs, weaner survival rate and ewe lamb reproduction to this increase in farm profit.

Methods
Whole-farm bioeconomic modelling was used to assess the profitability of grazing standing lupin crops in a mixed farming system. An analysis was conducted for a representative mixed farm in south-west Western Australia with a self-replacing Merino flock, and the profitability of grazing a lupin crop was assessed on the basis of whether it was harvested or grazed. A sensitivity analysis was then carried out to test the robustness of the results and understand the role of standing lupin crops in a mixed farming system.

Key results
Grazing lupins grown on 7% of the total farm area increased whole-farm profitability by almost A$30,000 or A$200/ha of standing crop. In this environment, across a range of assumed crop yields and prices, it was always more profitable to graze standing lupins rather than harvest the lupins. The increase in profit was primarily due to an increase in stocking rate of 1.2 dry sheep equivalent per hectare when able to graze the optimum area of standing lupins compared to when there was no standing crop. In addition to the increase in stocking rate, revenue from sheep sales increased, with the Merino wether and mixed sex crossbred weaners sold for an extra A$13 per lamb when stocking rate was constrained to the optimum for when there was no standing lupin crop.

Conclusions
This analysis demonstrated that in the south-west of Western Australia, grazing standing lupin crops was always more profitable than harvesting the grain.

Implications
If lupins are included in crop rotations in this environment, profit will be increased if they are grazed, but it is also clear that stocking rate should be increased to fully capitalise on potential gains in farm profit.

Context
Lambing triplet-bearing ewes in smaller mobs significantly increases lamb survival.

Aims
This paper reports economic analysis to assess the optimum mob size for triplet-bearing ewes during lambing.

Methods
The analyses considered scenarios for Merino and non-Merino (Maternal) flocks where producers subdivided lambing paddocks using permanent fencing or where ewes were re-allocated within existing paddocks on the basis of pregnancy status.

Key results
The optimum mob sizes for triplet-bearing ewes during lambing were affected by ewe breed, stocking rate, lamb price and the target return-on-investment if subdividing paddocks. The optimum mob size for triplet-bearing Maternal and Merino ewes was between 27% and 40% of the optimum for twin-bearing ewes and this was similar for scenarios where paddocks were subdivided, or where ewes were re-allocated within existing paddocks. At the standard lamb price of AUD$7/kg carcass weight, the economic return from adjusting the relative mob size of triplet-bearing ewes was AUD$2.05 per multiple-bearing or AUD$14.20 per triplet-bearing Maternal ewe and AUD$0.54 per multiple-bearing ewe or AUD$5.70 per triplet-bearing Merino ewe.

Conclusions
Overall, these analyses demonstrated that reducing mob size at lambing can be a profitable strategy for improving survival of triplet-born lambs, depending on the current size of lambing mobs.

Implications
As reported previously for single- and twin-bearing ewes, it is difficult to provide generic recommendations to producers for the optimum mob size of triplet-bearing ewes at lambing because optimum mob size was dependent on several enterprise-specific factors.

In research flocks, supplementing pregnant ewes with melatonin has been shown to be a novel approach to ameliorate parturient neurological damage and improve twin lamb survival. This study investigated the commercial applicability of melatonin supplementation for Merino flocks managed under extensive grazing conditions. Multiparous twin-bearing ewes were implanted with one melatonin implant (18 mg, Regulin®) each on two properties in South Australia and one in Western Australia (n = 585) at a median 79 days of gestation, with control ewes not implanted (n = 586). Ewes were managed as per standard protocols for each property. Lambs and ewes were counted at tail docking and weaning, and the lambs were weighed at weaning. Lamb survival was not influenced by melatonin treatment at either tail docking (p = 0.327) or weaning (p = 0.546). Across all sites, lamb survival at weaning for control and melatonin treatments was 74.7% and 74.0%, respectively, with lamb weaning weight of 27.2 ± 0.1 kg and 26.8 ± 0.1 kg (p = 0.020). These results indicate that supplementing twin-bearing Merino ewes with melatonin during mid-gestation was not a practical strategy to increase either lamb survival or weaning weight on commercial farms.

Low survival of triplet-bearing ewes and their lambs represents lost production and a welfare issue. The effects of feed-on-offer (FOO; low: 1205 vs. high: 1980 kg DM/ha) and concentrate supplementation (low: 50 vs. high: 300+ g/ewe/day) levels during late pregnancy and lambing on the survival of triplet-bearing ewes and their lambs were investigated on 10 commercial farms using 1772 triplet-bearing Maternal ewes. Ewe and lamb survival were estimated at marking, and ewe body condition score (BCS) was recorded in late pregnancy and at marking. Although FOO treatment had no effect on triplet-bearing ewe mortality, receiving higher supplementation decreased mortality by 40% and increased BCS at marking by 0.14 compared with a lower supplementation (p < 0.05). Supplementation, FOO treatments, weather conditions during lambing and shelter availability had no effect on triplet-lamb survival. These findings suggest no additional benefit to triplet-bearing ewe survival when FOO levels exceed 1200 kg DM/ha during late pregnancy and lambing, but increased supplementation can reduce ewe mortality. Further research is required to determine the response to the supplementation level at lower FOO levels on triplet-bearing Merino ewes and their lambs and establish whether supplementation of triplet-bearing ewes during late pregnancy and lambing with higher levels of concentrates would be cost-effective.

Variation in feed resource availability within production systems can cause genotype by environment interactions that change the ranking of the best animals to select between environments. Mediterranean environments have high variation in pasture growth between years that could cause genetic by environment interactions for sheep production traits. Therefore, we estimated heritabilities for live weight, fleece weight, fibre diameter and number of lambs weaned in six years from 2000 to 2005 and correlations between years comparing multivariate analysis and random regression analysis. We compared 3 methods: 1 multivariate analysis estimating (co)variances for traits in each year, 2 Random regression estimated (co)variances for intercept and slope for traits as repeated measurements fitted against average pasture growth in each year and 3. Random regression fitted against corrected average performance of animals in each year. Random regression was estimated with an order of polynomial of one for additive genetic variance and zero for permanent environmental effects. This combination of polynomials was the best fit based on Bayesian information criterion. We estimated heritabilities for each year and correlations between years using records from 3299 pedigreed Merino ewes managed at Katanning in Western Australia. There were 4651 records for adult live weight, 6750 for adult clean fleece weight, 6965 for adult fibre diameter, and 7774 for number of lambs weaned across all 6 years. Number of lambs weaned had more genotype by environment interactions than other traits, with fibre diameter and fleece weight having genotype by environment interactions between only a few years. Based on Bayesian information criterion values, multivariate analysis fit the data better for live weight, fleece weight and fibre diameter. Additionally, random regression estimated higher genetic correlations between years than multivariate analysis suggesting there was not enough flexibility in the random regression analysis, which used only first order polynomials, to fit differences between years. Pasture growth across years did not explain differences in performance for traits across years. Therefore, for number of lambs weaned, random regression using corrected average performance was a better fit than average pasture growth. For other traits, more years or a better indicator of variation in performance within and between years are required to use random regression for genotype by environment interactions.
•Sheep breeding programs in environments with variable feed availability are affected by pasture availability across years.•Reproduction was most effected so the best genetically animal in one year may not be the best animal in other years.•This makes selection of animals that will perform well in all years difficult.•Animal performance distinguishes genetic differences between years better than pasture growth.

Ewe lambs that are heavier due to improved nutrition pre- and post-weaning achieve puberty at a younger age, are more fertile, and have a higher reproductive rate. Fatness is intimately linked to reproduction, and we hypothesised that higher body condition scores at breeding would have positive effects on the reproductive rate of ewe lambs over and above liveweight. We also expected that if only a proportion of ewe lambs were presented for breeding, then it would be more effective to select them based on both liveweight and body condition score. To test these hypotheses, we analysed data from over 17,000 records from Merino and non-Merino ewe lambs from 22 different flocks across Australia. Non-Merino ewe lambs were more fertile (69.4% vs. 48.7%) and achieved a higher reproductive rate than Merino ewe lambs (96.9% vs. 60.7%). There were significant curvilinear relationships between liveweight (p < 0.001) or body condition score (p < 0.001) prior to breeding and reproductive rate for both Merino and non-Merino ewe lambs. For both breeds, there was a significant (p < 0.001) quadratic effect of body condition score prior to breeding on reproductive rate, independent of the correlated changes in liveweight, and at the same liveweight, an extra 0.5 of a body condition score up to 3.3 improved reproductive rate by about 20%. Nevertheless, the results indicated that if only a proportion of ewe lambs were selected for breeding, then selection based on both liveweight and body condition scores may only improve the overall reproductive rate by 1 to 2% compared to selection based on liveweight alone. We conclude that liveweight is a more effective method than body condition score for selecting ewe lambs for breeding.

We tested whether utilising the male effect to stimulate ewes before the mating period can reduce the time to conception following the introduction of entire rams, and increase fertility, prolificacy, and reproductive rate (number of fetuses per 100 ewes exposed to fertile rams). A retrospective analysis was used to analyse records from 59,716 ewes collected over 34 years (1986-2020) from seven genotypes: Border Leicester, Composite (crossbred), Dorset, Merino, Dorset x Polypay, Rambouillet, White Suffolk. The dataset also included nulliparous young ewes (mated at age 8 months) and adult parous ewes. Vasectomized rams were used to stimulate 20,632 ewes before a mating period that lasted 2 or 3 estrous cycles, and the outcomes were compared with those from 39,084 ewes that had not been stimulated. Independently of genotype, utilising the male stimulus advanced the average conception date by 8 days for young ewes (P < 0.0001) and by 1 day for adult ewes (P < 0.0001). The male stimulus also increased the proportion of ewes that conceived in their first cycle by 33 % for young ewes and by 6 % for adult ewes (P < 0.0001). For the cycle of conception, there were significant (P < 0.0001) effects of two interactions: male stimulus x age at mating and male stimulus x live weight at mating. The male stimulus improved fertility in both adult ewes (99.8 % vs 89 %; P < 0.001) and young ewes (77.7 % vs 81.3 %; P < 0.001). The male stimulus increased the number of young ewes (41.9 % vs 11.1 %; P < 0.001) and adult ewes (16.6 % vs 2.7 %; P < 0.001) that conceived multiple fetuses in the first 17 days of the mating period. The reproductive rate was improved by the male stimulus in young ewes (129 % vs 135 %; P < 0.001) but not in adult ewes (120 % vs 122 %; P = 0.12). When all animals for all breeds were included in the analyses, there were improvements in fertility, prolificacy, and reproductive rate as age and live weight increased at mating (P < 0.0001). We conclude that, independently of genotype, utilising the male stimulus before the mating period reduces the time to conception and improves reproductive performance in both young and adult ewes.

This study evaluated the impacts of management of body condition score (BCS) between pregnancy scanning and lamb marking on the mortality of triplet-bearing ewes and their lambs at 19 research sites across Southern Australia. Triplet-bearing ewes of Maternal (crossbred or composite) or Merino breed were randomly allocated to treatment at pregnancy scanning at an average of 97 days from the start of joining: High or Low BCS. The BCS of individual ewes was assessed at pregnancy scanning, pre-lambing (average of 137 days from the start of joining) and marking (average of 165 days from the end of joining), and ewe and lamb mortality to marking, recorded for each mob. The average BCS at pregnancy scanning was 3.4 for Maternal ewes and 3.3 for Merino ewes. There were no breed by BCS treatment effects on the BCS of ewes at pregnancy scanning or lamb marking or on the change in BCS between pregnancy scanning and pre-lambing or between pre-lambing and marking. The change in BCS differed between the High and Low BCS treatments, between pregnancy scanning and pre-lambing (0.12 vs. −0.33; p < 0.001) and between pre-lambing and marking (−0.39 vs. 0.07; p < 0.001) but did not differ between breeds. The average BCS at marking for ewes managed at the High and Low BCS treatments was 3.1 and 3.0 for Maternals and 3.0 and 2.8 for Merinos. Survival of triplet-bearing Merino ewes (p < 0.01) and their lambs (p < 0.001) was greater when ewes were managed at the High BCS compared to the Low BCS. The BCS treatment did not impact the survival of Maternal ewes or their lambs. The survival of Merino but not Maternal lambs was higher when ewes were in greater BCS pre-lambing (p < 0.01) and when ewes gained BCS between pregnancy scanning and pre-lambing (p < 0.01). Ewe mortality was lower when ewes gained BCS between pregnancy scanning and pre-lambing (p < 0.05). Merino ewes were more likely to die than Maternal ewes for a given change in BCS between pregnancy scanning and pre-lambing (p = 0.065). Overall, our findings demonstrate that producers should manage the nutrition of triplet-bearing Merino ewes so that ewes are in greater BCS at lambing and/or to gain BCS between pregnancy scanning and lambing to improve ewe and lamb survival. Triplet-bearing Maternal ewes should be managed to gain BCS between pregnancy scanning and lambing to improve ewe survival.