Specialist Forages Lamb Finishing Guidelines
Opportunities exist for producers to enhance the growth and potential value of lamb through on farm finishing systems based on fresh or conserved forages. These forages may provide a healthier lamb meat product that has a higher value, as well as mitigate against the risks associated with climate variability and market volatility.
Forage options to finish lambs include lucerne, perennial and annual ryegrass with clovers, and specialist forages such as sulla, lotus, chicory and plantain. Whilst fresh forage grown on farm is the most efficient for finishing lambs, conserved silage and hay still remain important and species such as saltbush may play a critical role in filling feed gaps. This information note is applicable to Victorian lamb producers and provides general guidelines for lamb finishing using fresh or conserved forages.
Finishing lambs for market
Finishing lambs is a term used by industry to refer to the time between weaning and when a lamb has reached marketable weight (40-50 kg live weight). A finishing system is defined as a method of feeding lambs that delivers specific protein and energy requirements for optimum daily live weight gain that in turn delivers carcass weights suitable to domestic or export markets. A finishing system can include fresh pasture or forage, grain feeding, or conserved forage.
Lamb growth rates during the finishing phase can vary depending on the quality, quantity and palatability of the feed, ranging from 50g/hd/day to 450 g/hd/day. A 30 kg lamb growing at 200 g/day will require 1.3 kg dry matter (DM) intake per day (Jolly 2006). The pasture or forage will ideally have crude protein (CP) and estimated metabolisable energy (ME) of 14-16% and 10.5-11MJ/kg dry matter respectively. As a general rule, the pasture or forage that is optimal for finishing weaned lambs should have a DM digestibility of about 70% and have more than 50% green matter. The guidelines presented here are based on achieving an average growth rate of 200 g/hd/day based on a 25 - 30 kg crossbred lamb consuming at least 1.3 – 1.4 kg DM per day.
On farm factors that affect growth and quality of lamb meat
There are factors that affect lamb growth and the quality of the meat and most are within the control of the producer. The age and weight of the lamb, breed, lamb sex, the level of stress and the finishing environment all have effects on growth and lamb meat. However, the most significant factor affecting growth and lamb meat is the forage/feeding system. The feeding system can affect the daily liveweight gain, the colour, quantity and distribution of fat in the lamb carcass, the yield of lean meat, as well as the flavour/odour, tenderness and juiciness of the lamb meat. So getting an appropriate feeding system to finish lambs is important for optimising the growth rate, the lamb carcass and the potential return to the producer.
Finishing lambs on pasture
In Victoria, the majority of prime lambs are finished on extensive pasture systems consisting of annual or perennial pastures, including lucerne. The quantity, quality and botanical composition of the pasture system, the time spent on the pasture, and the interactions between the animal and the nutrient supply all contribute to lamb growth rate and the final quality of lamb meat.
There are significant advantages to the health of the lamb, the nutritive value of the lamb carcase and consequently, a quality product for the consumer, in finishing lambs on fresh green pasture. Primarily, lamb finished on extensive pasture systems provides a leaner lamb carcase in comparison to lambs finished on grain or concentrate diets in a feedlot situation. This is because lambs are able to exercise freely which leads to muscle development rather than fat deposition.
Secondly, pasture grasses and legumes are rich sources of alpha-linolenic acid (ALA), which is the pre-cursor fatty acid required for the production of the long chain fatty acids (omega 3 EPA (eicosapentaenoic acid) and DHA (docosahexaenoic acid)) that are essential in the human diet. It is widely recognised that the western diet is deficient in omega 3 fats so meat products that contain these essential fatty acids may contribute to better human health. Finishing lambs on green pasture or forages may increase these fatty acids and provide a healthier lamb meat product.
Thirdly, fresh pasture has high levels of Vitamin E which is important in preventing pigment oxidation and maintaining the colour of lamb meat and retail shelf life. Vitamin E levels in the pasture and the resultant Vitamin E content in the meat are dependent on the nutritive characteristics and growth stage of the pasture. For example, Vitamin E content in lucerne changes depending on its growth stage. It can be higher before flowering than at flowering and it can decrease significantly in the process of hay making. Once forage or pasture has been cut for silage or hay, Vitamin E and essential fatty acids decrease as the forage wilts and is exposed to oxygen and sunlight.
1. Mixed ryegrass and clover
These pastures comprise species such as perennial ryegrass (Lolium perenne), white clover (Trifolium repens) annual ryegrass (Lolium rigidum) and subterranean clover (Trifolium subterranean). Typically they have their main growth period in winter/spring from August through to December with CP and DM digestibility (DMD) declining as the season progresses. White clover is suited to areas that receive greater than 700 mm rainfall, has CP of 12-27 % and dry matter digestibility (DMD) of 64-82 %. Subterranean clover is suited to areas that receive 375-600 mm, has CP of 15-30 % and DMD of 55-75 %. Perennial ryegrass is suited to areas receiving more than 600 mm rainfall, has CP of 8 – 27 % and DMD of 56-85 %. Annual ryegrass is suited to areas receiving 200-600 mm, has CP of 7 – 15 % and DMD of 40-60 %. Growth rates of the mixed pasture will vary according to the species present, soil fertility, available moisture and seasonal conditions.
- Graze pastures to 10-15 cm in height to optimise the supply of green leaf on both legumes and grasses;
- Ensure rotational grazing practices so that species have the opportunity to recover from grazing;
- Ensure sufficient stocking rates to maximise pasture utilisation. For example in north east Victoria where the growing season for annual pasture might be from April to October, the stocking rate might be 16 DSE/ha providing that soil phosphorus is at least 20 mg/kg (Saul et al 2002). Shorter growing seasons or poorer soil fertility will reduce the carrying capacity;
- Pasture availability of at least 1500 kg DM/ha is required to achieve 200 g/hd/day.
Lucerne is a high nutritive value legume that is grown for its feed value, its contribution of legume nitrogen to the soil and for its deep root system and ability to use water. Lucerne is rated on its winter activity level with varieties having high or low winter growth activity. Lucerne is suited
to soils with a pH (CaCl2) between 5.5 and 8.0 and to soils that are not prone to water-logging. It can be grown in areas receiving 300 - 600 mm annual rainfall. It has CP of 12-24%, ME of 8-11 MJ/kg DM and a DMD of 65-72%. In a dryland lucerne system the green feed production from lucerne can be 5-10
kg/ha/day in the summer/autumn season so it is well suited to lamb finishing outside of the main spring period.
In the Burraja Lucerne Experiment where lambs were grown and finished through the spring and summer seasons, lamb growth rates between 350-450 g/day were achieved in late spring when the lucerne was growing at an average rate of 20-25 kg DM/ha.day. This lucerne growth rate had declined to 5-10 kg DM/ ha.day by mid-late summer and the lamb growth rates had declined to less than 100 g/day by mid February (Hirth et al 2000). Higher growth rates for lambs grazing lucerne over summer may be achieved depending on seasonal conditions, stocking rate and grazing management.
- Lucerne should be rotationally grazed to allow adequate time for recovery;
- Recovery time for a lucerne pasture will be dependent on seasonal conditions but as a general rule, lucerne should not be re-grazed until the secondary regrowth is 5cm high. This usually occurs between 4-5 weeks after grazing but may be longer if dry conditions occur;
- Stocking rates will determine the length of time in each grazing period. For example, a high stocking rate will mean the pasture is grazed quickly and sheep can then be removed. A lower stocking rate will mean that the pasture is grazed slowly and there may not be efficient pasture utilisation;
- The minor animal health problems of bloat and red gut can be largely avoided if hungry lambs are not put on to lush lucerne pasture, such as might be seen during the spring season;
- Pasture availability of 800-1200 kg DM/ha is required to achieve 200 g/hd/day lamb growth.
Finishing lambs on specialist forages
A variety of forage options have become available to producers in recent years, all of which have different periods when green forage is available. The benefits of using different forages to finish lambs include greater choice of feed for lambs, differing nutrient profiles in the forages, mitigation against climate variability by having a range of plant species growing on farm, and potential health benefits for lambs from consumption of different forages.
Forages including Sulla (Hedysarium coronarium), Birdsfoot Trefoil (Lotus corniculatus), Chicory (Chicorium intybus) and Plantain (Plantago lanceolata) offer additional benefits for lamb finishing due to the presence of condensed tannins and other secondary compounds within the plant. These compounds can have positive effects on internal parasites, can reduce methane production and can increase the reproductive rate in sheep. These forages can also affect meat colour, the proportion of muscle and may reduce pastoral flavour in lamb meat. Lamb growth rates on these forages will also vary and be dependent on seasonal conditions and grazing management.
The challenges of using new forage options to finish lambs include different grazing management strategies and agronomic skills associated with their establishment and management.
1. Sulla (Hedysarium coronarium)
Sulla is a short-lived (2-3 years) perennial legume native to the Mediterranean region. Sulla is suited to well-drained neutral to alkaline soils (pH CaCl2 5.5 – 8.5) in regions with annual rainfall between 400 – 1200 mm. It has similar requirements to lucerne and is not tolerant of acidic soils or water-logging. Sulla forage is highly palatable with CP at 26%, digestibility over 80% and ME of 10.5 – 13.0 MJ/kg DM. Sulla is usually sown in autumn with its most productive growth occurring during the spring period from October to December. Sulla is dormant during the summer months and has little growth during winter.
Sulla can improve lamb growth rate, fatty acid profiles and reduce internal parasite infection. In a winter grazing comparison in South Australia between a sulla-based pasture (46% sulla with annual ryegrass, capeweed and Paterson's curse) and a control pasture comprising re-generated subterranean clover (26%) and barley grass, ewe hoggets grazing the sulla pasture grew 144 g/hd/day compared with 104 g/hd/day on the control pasture (de Koning et al 2010). In the same comparison conducted during spring, sheep that grazed the sulla pasture gained an average of 176 g/hd/day whilst those that grazed the control pasture lost weight (average 94 g/h/d/day).
In research overseas lambs that have been fed fresh sulla can also have lower proportions of saturated fatty acids and higher amounts of long chain polyunsaturated fatty acids (omega 3) (Priolo et al 2005) . Sulla has also been shown to positively affect the lamb's resistance to internal parasite infection through higher levels of antibodies to internal parasites (Niezen et al 2002).
- Sulla has its main growth period during spring in temperate regions;
- Sulla should be rotationally grazed to 15 cm in height after reaching about 40 cm;
- Strip grazing should be considered with high stocking rates for fast grazing and removal;
- Sulla regrowth is slower than lucerne and the grazing interval should be at least 6 weeks;
- Forage availability of 1500 – 3000 kg DM/ha is required to achieve 200 g/hd/day.
2. Birdsfoot Trefoil (Lotus corniculatus)
Birdsfoot Trefoil is a perennial pasture legume with high nutritive value suited to acidic soil conditions (pH CaCl2 4.7- 5.5) with low phosphorus fertility. A minimum annual rainfall of 650 – 750 mm is required for optimal growth. It has moderate autumn/winter growth with high spring growth. It requires long day length for flowering and seed production. Birdsfoot Trefoil puts less energy into root growth than lucerne, relying more on leaf development, so rest periods after grazing will generally be longer than for lucerne. Birdsfoot Trefoil has CP at 19-22%, dry matter digestibility at 60-68% and ME of at least 10.0 MJ/kg DM.
There is insufficient data available on the performance of Birdsfoot Trefoil for Victorian lamb finishing systems. However, in an experiment conducted in NSW under irrigation that investigated forages for the dairy industry, Birdsfoot Trefoil pastures produced 11, 15.2 and 13.4 t DM/ha/year in 2004-2006 (pastures were cut to 8 cm in height over two growth periods of April to August and September to March). This compared to perennial ryegrass production of 28.4, 19.5, 15.3 t DM/ha/year for the same years (Neal et al 2009).
In research conducted in the US Birdsfoot Trefoil may improve lamb average daily weight gains over existing pasture systems. A control pasture comprising lucerne/brome grass (Bromus inermis) and cocksfoot (Dactylis glomerata) was divided into three rotationally grazed paddocks and this was compared to another set of three paddocks where the first two paddocks comprised the control mixture but the third paddock comprised Birdsfoot Trefoil, increases of between 22-24 % in average daily weight gains were achieved with lambs grazing the Birdsfoot Trefoil treatment (Marten and Jordan, 1979). Whilst there was lower carrying capacity on the Birdsfoot Trefoil paddock, the nutritive value of this feed was higher than the lucerne brome grass control, thereby allowing for a 17-18% increase in lamb production per hectare.
Higher lamb growth rates have also been achieved with lambs grazing Birdsfoot Trefoil in Wales (Speijers et al 2004). In a comparison between red clover (Trifolium pratense), lucerne, Birdsfoot Trefoil and perennial ryegrass, weaned lambs grazing the Birdsfoot Trefoil had the highest growth rates and shortest finishing times (278 g/hd/day for 35 days) compared with lucerne (200 g/hd/day for 37 days), red clover (228 g/hd/day for 40 days) and ryegrass (182 g/hd/day for 49 days).
- Birdsfoot Trefoil should be rotationally grazed to no less than 10 cm;
- Some leaf should be retained on the plant after grazing to assist with re-growth;
- Re-growth is generally slower than lucerne and stand persistence will require seedling recruitment;
- Forage availability of 1500-3000 kg DM/ha is required for 200 g/hd/day.
3. Chicory (Chicorium intybus)
Chicory is a perennial herb highly suited to lamb finishing. It requires a minimum annual rainfall of 600 mm and will tolerate low soil pH. Its forage has high nutritive value, consisting of 14 – 24 % CP, 70 – 80 % digestibility in the leaves, and ME of 13.7 MJ/kg DM. Chicory is usually sown in autumn and has its main growth period in spring and summer.
Lambs grazing chicory can have faster growth rates than lambs grazing other pastures. For example lambs grazing chicory can have growth rates of 190-370 g/day compared with ryegrass at 160-230 g/day or lucerne at 170-300 g/day (Chicory factsheet, NSW DPI 2011). This may be important in areas where summer rainfall is unreliable and faster turn-off of lambs is required. Grazing management for chicory is similar to that of lucerne but some additional management (topping) over summer to limit stem growth may be necessary.
In a lamb finishing experiment in New South Wales, lambs were finished on either lucerne based pasture or on chicory swards. Lambs grazing chicory grew faster than lambs grazing lucerne in 3 out of 5 groups with average growth rates of between 172-312 g/day (Holst et al 1998). In the Central Tablelands
region of NSW, chicory produced lamb growth rates of 125 g/day during finishing, allowing greater opportunities for producers in an environment where summer rainfall is unreliable (Holst et al 2006).
Lambs fed chicory during the finishing phase showed no adverse effects in terms of meat quality and were not fatter than lambs finished on lucerne pastures (Hopkins et al 1995).
- Chicory must be rotationally grazed and it is recommended to have at least a 4-paddock rotation;
- Chicory can be grown on its own or in combinations with other legumes, for example, clovers; when grown on its own, additions of nitrogen fertiliser will be required;
- Plants should not be grazed below 5 cm and rest periods of 3-4 weeks are generally required;
- In spring and summer when growth is rapid, graze for short periods to maintain more leaf, and less stem growth;
- Topping may be necessary in summer to limit stem growth;
- In autumn and winter, graze only lightly for short periods and allow long rest periods to avoid damage to crowns and disease; don't graze below 1500 kg DM/ha;
- Forage availability of 1500-3000 kg DM/ha is required for 200 g/hd/day.
4. Plantain (Plantago lanceolata)
Plantain is a perennial herb requiring 550 - 650 mm annual rainfall. It is adapted to a wide pH range (pH CaCl2 4.2 – 7.8) and will tolerate low fertility soils and drought. Plantain may have a nutritive value of 13.8% CP in the vegetative stage, ME of 10 MJ/kg DM with dry matter digestibility of 72% (leaf) and 59% (stems). It has lower palatability compared with other forage species. Plantain has its main growing season in winter and spring with some opportunistic growth in summer. Plantain has a relatively high concentration of magnesium (Mg) and calcium (Ca) which may assist in reducing the risk of grass tetany in mixed pastures. Plantain is generally unsuited to monoculture because of its poor competitive ability but it can be included in pasture mixes containing grasses and legumes.
Lambs grazing plantain put on more weight (222 g/head/day) than lambs grazing perennial ryegrass (135 g/head/day) when both were offered an allowance of 2.5kg DM/head/day (Moorhead et al., 2002). However, lamb liveweight gain and hot carcass weight was lower when lambs grazed on plantain compared to chicory (Fraser and Rowarth, 1996).
- Depending on the variety, plantain can tolerate some set stocking but rotational grazing is desirable for persistence and plant recovery after grazing;
- Rotational grazing should aim to maintain leaf over stem;
- Plantain responds to nitrogen application;
- Plantain is a poor competitor so grazing management needs to ensure other species in the sward do not smother plantain;
- Forage availability of at least 2000 – 3000 kg DM/ha is required for 200 g/hd/day.
5. Saltbush (Atriplex spp.)
Saltbush can be used as a forage plant for strategic grazing but it is not a species to be used when high lamb growth rates during the finishing phase are required. Saltbush can provide high levels of Vitamin E to the lamb but growth rates can be lower than other forages. In Australia there are two main species of saltbush, River Saltbush (Atriplex amnicola) and Old Man Saltbush (Atriplex nummularia). Low growth rates have been observed in saltbush fed lambs (50 g/head/day) and it is thought that this is due to low feed intake from the high salt content, low edible biomass available and poor energy utilisation from processing the high salt load. Saltbush can be used as occasional strategic grazing to fill feed gaps and when alternative green forage is not available.
- Saltbush is not a preferred lamb finishing forage due to low feed intake and low growth rates;
- Saltbush can be used as an alternative forage when green feed from other species is not available;
- Saltbush should not be grazed in the first year after establishment;
- Graze for short periods of 2-3 weeks, with extended rest periods of 6-12 months for plant recovery.
Finishing lambs using hay and silage
Lamb performance on hay or silage will depend on the nutritive characteristics of the hay or silage, the percentage of hay or silage in the total diet, the time of year when it is fed and the growth stage of the pasture base. Hay or silage can provide sufficient energy and protein to finish lambs providing the nutritive characteristics of the hay or silage meet the requirements of the growing animal so a 30 kg lamb growing at 200 g/day will require 1.3 kg dry matter (DM) intake per day with CP at 14-16% and estimated ME of 10.5-11MJ/kg DM.
It is important that silage and hay are cut at the right time when there is sufficient dry matter but also when the forage has an optimum nutritional profile. For example, established lucerne should be cut for hay when it is at about 10% flowering to achieve maximum nutritive value. Cutting hay and silage at the right time will ensure that leaf material is retained and the digestibility of the forage remains high (at least 70%). Hay or silage that has been subject to weather damage after cutting will reduce its nutritive value. Feeding silage may not always compensate for green pasture and lamb growth rates can be reduced, resulting in a longer period of time before lambs are finished. Also, essential fatty acids and Vitamin E will decline after pasture has been cut. However, silage that has been cut at the right time and preserved effectively can supply forage with sufficient nutritive characteristics for growing lambs. When lambs are fed hay or silage in their diet there is generally no difference in the acceptability of the meat or the level of fat on the carcase.
- Ensure hay or silage is cut at the right time to optimise the nutrient value of the feed;
- Use good quality hay or silage to meet feed gaps in fresh pasture production.
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This Information Note was developed by Viv Burnett (Rutherglen) and Dr Eric Ponnampalam (Werribee) of the Future Farming Systems Research Division of the Department of Environment and Primary Industries Victoria with assistance from the Rural Industries Research and Development Corporation.