Effect of grazing different forage systems prior to and during mating on the liveweight, condition score, conception and reproductive rate of maternal-composite ewe lambs

Context Economic modelling identified that mating of ewe lambs for lambing at 1 year of age has the potential to increase the profitability of sheep-production systems in south-western Victoria. In order to optimise reproductive rates, ewe lambs should weigh at least 35–40 kg, have a condition score (CS) of 3.0 at mating, and be gaining weight (100–150 g/day) during mating. However, typical perennial ryegrass (Lolium perenne L.) pastures in south-west Victoria do not support the attainment of these targets without additional supplementation. Aim Our research aimed to determine how grazing summer-active pastures or brassica (Brassica napus L.) forages affects the liveweight, CS, conception and reproductive rate of ewe lambs when offered before and during mating compared with a system using perennial ryegrass plus supplement. Methods A field experiment was conducted at Hamilton, Victoria, Australia, in 2014 and 2016 testing seven forage treatments replicated four times in a complete block design. The treatments were: canola (B. napus, two treatments of different cultivars), forage brassica, lucerne (Medicago sativa L.), chicory (Cichorium intybus L.), plantain (Plantago lanceolata L.) and perennial ryegrass. Key results Ewe lambs grazing canola or forage brassica had higher (P < 0.05) liveweight gains during the pre-mating and mating periods than those grazing the perennial ryegrass treatment (148 vs 75 g/day in 2014, s.e.m. 17; 139 vs 54 g/day in 2016, s.e.m. 17). In 2014, spring-sown dual-purpose canola, lucerne and chicory resulted in higher (P < 0.05) reproductive rates (144–151%) than the perennial ryegrass treatment (103%); forage brassica and plantain gave intermediate results (128% and 129%). Conclusion Brassica forages (including spring-sown canola), lucerne and chicory can support the attainment of key liveweight and CS targets for successful mating of ewe lambs in autumn. Implications Spring-sown canola is therefore a viable alternative forage for use by livestock producers in southern Australia and presents an opportunity to incorporate an alternative income stream in mixed-farming systems.

Performance of sheep systems grazing perennial pastures. 3. Fertility, fecundity and lamb survival

Management system has the potential to alter the reproductive output of sheep flocks and thereby farm profit. A study was conducted between 2006 and 2010 to evaluate the reproductive performance of four management systems with differing combinations of time of lambing, stocking rate and ram breed, while grazing at a similar midwinter stocking rate (dry-sheep equivalents per hectare of 8, 10.2, 13, 11.2 and 11.2 in the successive seasons 2006–2010). Three systems, winter lambing Merino (WLM), split lambing (SL) and later lambing (LL), grazed replicated farmlets comprising pastures that were 20% lucerne (Medicago sativa), 20% tall fescue (Festuca arundinacea) and 60% phalaris (Phalaris aquatica). A fourth system (high lucerne (HL)) grazed farmlets of 40% lucerne, 15% tall fescue and 45% phalaris. All systems used Merino ewes: in WLM mated to Merino rams, lambing in July; in SL half of the ewes lambing to terminal-breed rams in July, the other half lambing to Merino rams in September; and in LL and HL lambed in September, half to terminal-breed and half to Merino rams. The number of lambs weaned per ewe joined was 10% higher (P < 0.05) in the WLM system (0.99 ± 0.03) than in the September-lambing systems LL and HL, largely a result of a higher number of fetuses per ewe and despite lower (P < 0.05) lamb survival to marking in some years. The SL system weaned a similar (P > 0.05) number of lambs per ewe (0.95 ± 0.03) to all other systems. However, the number of lambs weaned per hectare was least in WLM (4.6 ± 0.2), lower than in the HL and LL systems by 2.7 lambs/ha because of a lower stocking rate. The ranking of systems for fetal number and lamb survival was not consistent among years. Spring-lambing systems produced more lambs per hectare because of a higher stocking rate but fewer lambs per ewe than the WLM system. System differences in pregnancy rate, fecundity and lamb survival were not consistent between years.

Performance of sheep systems grazing perennial pastures. 4. Simulated seasonal variation and long-term production

Choice of sheep-management system alters both production potential and the production risk due to variability in seasonal conditions. This study quantified production and gross margins from systems based on Merino ewes and varying in stocking rate, time of lambing, and the proportion of ewes joined to terminal-breed or Merino rams. Simulation studies were conducted between 1971 and 2011 using the AusFarm decision-support tool for a grazing property in southern New South Wales. Joining between December and May resulted in higher gross margins than in other months because of higher numbers of lambs sold combined with a lower requirement for supplementary feeding. More ewes could be carried per hectare for April joining than February joining to achieve the same midwinter stocking rate and risk of feeding. Self-replacing systems could produce median gross margins similar to those with replacement ewes purchased, but gross margins were sensitive to the cost of replacement ewes. Of the systems compared, February joining to Merino rams produced the lowest gross margins at all stocking rates, but this system also had the lowest variability among years. The advantage of different systems was dependent on seasonal conditions, which altered lamb production and supplementary feeding. The median ranking of systems for gross margin generally did not alter with changes in feed, sheep or wool values. Large increases in gross margins can be achieved through use of terminal-breed rams, optimal stocking rates and time of lambing, but the superiority of any option depended on production system, price assumptions and seasonal conditions.

Reproductive performance in ewes fed varying levels of cut lucerne pasture around conception

Elevated intakes of protein and energy may increase embryo mortality, but it is not clear whether fresh lucerne (Medicago sativa) pasture poses a risk. A two-year pen study using oestrous synchronised and artificially inseminated Merino ewes (n=175 in 2013 and 215 in 2014) evaluated whether feeding freshly cut lucerne pasture (mean crude protein 19.7%, metabolisable energy 9.4MJ/kg DM) at maintenance or ad libitum during different periods around insemination altered reproductive performance in comparison with ewes fed a Control diet (mean crude protein 7.8%, metabolisable energy 9.0MJ/kg DM) of pelleted faba bean hulls and oat grain hulls at maintenance. The proportion of pregnant ewes carrying multiple fetuses was reduced (P=0.026) when ewes were fed lucerne ad libitum between days 0 and 17 after insemination compared with the Control diet (0.18 and 0.34, respectively), but not when ewes were fed lucerne ad libitum between days 0 and 7 after insemination (0.22). Reproductive performance, including the proportion of ewes pregnant and the proportion with multiple fetuses, was not different (P>0.05) when ewes were fed lucerne at maintenance between days 0 and 7 compared with the Control diet. While reproductive performance was similar when ewes were fed lucerne at maintenance between 0 and 17 days after artificial insemination compared with pellets at maintenance, fetal numbers per pregnant ewe were reduced by feeding lucerne ad libitum after insemination.

Modelling the effect on stocking rate and lamb production of allowing ewes to graze a dual-purpose wheat crop in southern New South Wales

Slow pasture growth rates during winter limit the potential gross margins from autumn and early winter lambing in southern New South Wales (NSW) by limiting stocking rates and/or increasing supplementary feed requirements. Dual-purpose crops can reduce the winter feed gap in mixed-farming systems by increasing the available feed in winter. The simulation software AusFarm was used to model a mixed-farming system at Wagga Wagga with Merino ewes joined to terminal sires and grazing lucerne-subterranean clover pasture over a 41-year period. A paddock of dual-purpose wheat was then added to the system, and ewes were allowed to graze the wheat crop when feed on offer reached 850 kg DM/ha and before GS31. Weaned lambs were sold after late August if lamb growth rates fell below 20 g/head.day, mean lamb weight reached 45 kg or production feeding of lambs was required. Lambing in June resulted in the highest median gross margin whether or not ewes were able to graze the wheat crop during winter. Grazing of a dual-purpose wheat crop resulted in greater proportional increases in gross margins as stocking rate was increased, increased lamb production and reduced supplementary feeding costs, and reduced interannual variability in gross margin returns.