Hay and silage quality is impacted greatly by stage of maturity. As forage crops mature fibre increases while digestibility and crude protein decreases.
A basic nutrient analysis will measure forage moisture, fibre, energy and protein. These figures contribute in balancing the diet and estimating intake levels relative to performance. An example silage analysis is listed below on a ‘dry matter’ (DM) basis. Additional tests can be made for minerals. Since silage is a fermentation product estimates can be made for silage fermentation quality (pH and ammonia–N) and corrections can be made for volatile compounds lost during oven drying.
| Pasture response | Land condition | Grazing options | |
|---|---|---|---|
| Sheep and/or goats | Cattle | ||
| Mitchell grass tussocks are reshooting as expected and desirable herbage species are germinating. | A-B | Ideal for sheep and/or goats to graze, as they prefer the herbage and will allow the tussocks to seed with follow up rain. If tussocks are slow to reshoot consider reducing livestock numbers. | Consider delaying grazing by cattle until tussocks have set seed. |
| Mitchell grass tussocks are not reshooting as expected. Desirable herbage species are germinating. | B-C | Consider reducing livestock numbers. | Consider reducing livestock numbers and delaying grazing by cattle until tussocks have set seed. |
| Mitchell grass tussocks are not reshooting as expected and seedlings present. None or limited desirable herbage germinating. | Any | If possible, rest paddocks until tussocks have set seed. If grazing must occur, consider reducing livestock numbers and the length of time they are grazing in the paddock. | |
| Mitchell grass seedlings with herbage present. | Any | Tend to prefer herbage and will leave seedlings. Allows 3P grasses and seedlings to be spelled while herbage is available. Need to monitor seedlings to make sure they are not being over-grazed. | Cattle cannot access seedlings until they are around 10 to 15 cm in height. Once at this height there is a risk that cattle may pull out seedlings. Need to monitor seedlings to make sure they are not being over-grazed. |
Using the figures
The analysis enables us to estimate intakes of dry matter, energy and protein. Using a 300 kg steer as an example the analysis estimates an ‘ad lib’ intake of 2.1% of body weight in dry matter. For example, 2.1% x 300 kg steer = 6.3 kg of dry matter. The silage is 32% DM (or 68% water) therefore the wet weight of silage eaten is calculated as 6.3 kg DM divided by 32% = 19.7 kg ‘as fed’ silage. The silage metabolisable energy is 9.3 MJ/kg DM and crude protein is 7.2%. Therefore 6.3 kg DM supplies 58 MJ ME and 454 g of protein. Nutrient requirement tables list a requirement for a 300 kg steer gaining 500 g per day liveweight at approximately 54 MJ and 425 g of crude protein. This suggests performance close to half a kilogram per head per day.
Moisture and dry matter content
An oven is used to remove all the moisture to determine a samples moisture percentage.
It is best to compare feed nutrient values on a dry matter basis, i.e. with the water removed. For example, a hay and silage sample may both have the same energy content on a dry matter basis but because the silage is wetter it has much lower energy per kilogram on an ‘as fed’ basis (also known as ‘wet’ or ‘fresh’). For example:
| ‘2001 fires were hot but not widespread. We only had one good rain following the fires and the country is only just coming back two and a half years later. We’ve had no really big fires since the 1930s.’ |
|---|
| ‘Not really affected because we actively use fire as often as we can, and the country was broken up.’ |
| ‘We had volunteers helping us fight wildfires in 2001-02. They were excellent; without them, fires would have been a lot worse.’ |
| ‘In 2001, one third of total property burnt. We spent 10 days fighting fires, starting on Melbourne Cup day, then had a total of 101ml or rain for November. There was small grass growth after this. We have been doing some preventative burning on the southern part of the place this year to reduce the risk of any more big fires coming through.’ |
| ‘There were about 100 small grass fires lit from the highway. This caused us a lot of trouble.’ |
| ‘85% of the property burnt between April and October 2001.’ |
| ‘Big hot fires came through from the north. We spent a lot of time chasing fires and putting in back-burns, but our efforts were worthless and the fires jumped the breaks, and the wind changed. We had good rains after the fires, and it has done amazing things for the country. Having known what we know now, we wouldn’t have put so much time and effort into trying to stop the fires.’ |
| ‘Fires threatened from the desert country, but we were able to keep it under control.’ |
| ‘We got burnt out to the north-east from the neighbours. There was no control attempted by the neighbouring property, and we suffered as a consequence.’ |
| ‘We weren’t here in the 2001 fires but we are seeing a good response in some of the areas that were burnt. There is lots of parakeelya now growing in the sandhill country where the fires were in the east of the property.’ |
| ‘I caught 23 different fires being lit in 2001-02 by Indigenous mob. We are not sure what the answer is to fixing this problem.’ |
| ‘We were hammered by wildfires. Most were deliberately lit. The country is only just starting to come back in places. It has cleaned up a lot of scrub, but also meant we lost a hell of a lot of feed for stock. We spent weeks fighting fires, as it turns out we were wasting our time and efforts.’ |
| ‘We’ve seen fire bring on the germination of acacia shrubs and thicken up country. The gidgee country is a good break because there is no understorey fuel.’ |
| ‘We try to burn when we can to strategically break up the country, especially along boundaries. We have had a good response from the country following the 2002 fires. It cleaned up a lot of mulga.’ |
| ‘We didn’t suffer any loss of infrastructure or stock. However, we were forced to sell cattle. The fires have buggered up drought reserve country that would otherwise be in production now. The effects of fires on our pasture management have been lost feed, and forced selling of cattle. There has been no rain on the burnt areas, which has depleted the pasture base. We have had to reorganise our grazing management.’ |
One kilogram of the hay gives 890 g of dry matter and 7.6 MJ of metabolisable energy (ME).
One kilogram of the silage gives 320 g of dry matter and 2.7 MJ ME.
Conversely if you wanted to supply a beast with 8.5 MJ of ME then you would need 1.12 kg of the hay or 3.13 kg of the silage.
Crude protein (CP)
Laboratories measure the nitrogen (N) content of the forage and calculate crude protein using the formula: CP = % N x 6.25. Crude protein includes both true protein and non-protein nitrogen. Crude protein values give no indication if heat damage has occurred, which may alter protein availability. The digestible protein % is an estimate of the protein available to the rumen bugs. The crude protein figure is used in balancing the total protein in the diet while the digestible protein can be used as a guide to protein levels for the rumen bugs.
Acid detergent fibre (ADF)
ADF refers to the cell wall portions of the forage that are made up of cellulose and lignin. These values relate to the ability of an animal to digest the forage. As ADF increases, digestibility of forage usually decreases. Many of the calculated values appearing on the forage reports are generated using ADF values.
Neutral detergent fibre (NDF)
The NDF value is the total cell wall, which is comprised of the ADF fraction plus hemicellulose. Cellulose and hemicellulose is partially digested in the rumen while lignin is indigestible fibre. As lignin increases, digestibility, intake, and animal performance usually decrease and the percent ADF and NDF increase. Neutral detergent fibre values reflect the amount of forage the animal can consume. As NDF percentages increase animals will generally eat less due to the rising fibre content which takes longer to digest in the rumen.
Digestible dry matter (DDM) and Total digestible nutrients (TDN)
These are estimates of forage digestibility generated from the ADF value. As ADF increases, digestibility and total digestible nutrients available to the animal decreases.
Dry matter intake (DMI) as a percentage of body weight
Some studies have shown that feed intake declines with increasing NDF. NDF is used to estimate ad lib dry matter intake for example 2.1% of body weight in dry matter in the above analysis.
Net energy-lactation, Net energy-maintenance, and Net energy-gain
These net energy values are often calculated from TDN values, which in turn are generated from percent ADF. As ADF increases, net energy values will decrease. The net energy system is more commonly used in the USA whilst metabolisable energy or the estimates used to calculate ME are more commonly used in Australia.
Relative feed value (RFV)
Relative feed value is an index reflecting fibre content and its effects on intake and digestibility. It has no units but is used to compare the potential of forages for energy intake. RFV ranks forages relative to the digestible dry matter intake of full bloom lucerne (RFV of 100, ADF of 41, and NDF of 53). The higher the RFV the higher feed value obtained from the forage. RFV reduces with maturity and increasing fibre. RFV does not take into account protein content.
| Purpose | Fire intensity and season | Aims and concerns |
|---|---|---|
| Reduce wildfire risk in spinifex or buffel grass | Cool, winter fire | Break up fuel continuity, reduce wildfire risk and protect adjacent, more valuable grazing country. Spinifex burnt in previous years makes the best firebreak. Experience is the key to success; fuel consistency and fire created winds lead to unpredictability. |
| Improve grazing value of hard spinifex country | Cool, winter fire | Summer rain after fire can provide temporary growth of useful grasses. N.B. Soft spinifex species are different to the ‘hard’ spinifex. There is little to be gained from burning soft spinifex as the post-fire grasses are no more palatable or nutritious than the spinifex itself. |
| Reduce small shrubs/seedlings | Cool, winter fire | Killing seedlings and young shrubs (less than about 2.5m) before they become well established. Relies on good ground cover to carry fire. |
| Open-up thick stands of mature shrubs | Hot, summer fire | Trade off: hot, summer fires may be needed to carry through canopy of mature trees however, germination can also be promoted in these conditions. A second, cooler fire to burn the seedlings may help. |
| Legume production | Legume growth (dry matter per hectare) | Average amount of nitrogen supplied per hectare per year | Potential amount of extra grass grown per hectare per year | Value of the nitrogen supplied (based on $1.30/kg nitrogen) |
|---|---|---|---|---|
| Low | 1300 kg | 20 kg | 600 kg | $26 |
| Medium | 2300 kg | 35 kg | 1000 kg | $46 |
| High | 4400 kg | 67 kg | 2000 kg | $87 |
| Nitrogen fertiliser | N/A | 100 kg | 3000 kg | Cost $130/ha plus application |
Metabolisable energy (ME)
Metabolisable energy (ME) is the dietary energy available to the animal for heat production, maintenance and production. High fibre feeds are less digestible and lower in ME. Low fibre diets are more digestible and higher in ME. For silages, ME (and digestibility) will be underestimated if the laboratory does not take account of the volatile compounds lost during oven drying. The error is likely to be bigger when silage DM content is low (<30%), and silage protein content is high and the silage is poorly preserved (has a higher pH).
| Days from start of mating (1/12/2009) | Conception date | Calving date | Weaning age (months) | Estimated weaner weight (kg) | Estimated weaner value @ $1.90/kg ($) |
|---|---|---|---|---|---|
| 1 | 1/12/2009 | 10/09/2010 | 8.8 | 245 | 466 |
| 60 | 30/01/2010 | 9/11/2010 | 6.8 | 197 | 374 |
| 120 | 31/03/2010 | 8/01/2011 | 4.8 | 149 | 283 |
| 180 | 30/05/2010 | 9/03/2011 | 2.8 | 101 | 192 |
Source: ‘Successful silage’, page 327, 2004.
Silage fermentation quality – ammonia N and pH
The type of silage fermentation influences the losses during fermentation and the intake of silage by livestock. Poor silage fermentation produces unpalatable silage and even if ME and crude protein content are high, intake and animal production will be low. Silage ammonia-N and pH are useful indicators of silage fermentation quality. In poorly preserved silages the protein fraction is extensively degraded, so high ammonia-N (as a % of total nitrogen) indicates poor fermentation. Levels <10% of total nitrogen indicate good fermentation. Silage pH measures silage acidity and hence the extent of fermentation. Lower pH is preferable. pH is considered a useful indicator of silage fermentation quality for silages with DM content less than 35%.
| Year | 1999 | 2002 |
|---|---|---|
| Pregnancy test date | 12/05/1999 | 21/05/1999 |
| Average heifer weight (kg) | 402 | 388 |
| Pregnancy rate (%) | 91 | 79 |
Source: ‘Successful silage’, page 332, 2004.
Silage pH as a guide to silage fermentation quality
| Calving Data | |
|---|---|
| Pregnancy test date | 1/06/2004 |
| Gestation length (days) | 290 |
| Estimated breeder mortality (%) | 1 |
| Estimated foetal and calf losses (%) | 6 |
| Mean birth weight (kg) | 31 |
| Mean calf growth rate (kg/hd/day) | 0.8 |
Source: ‘Successful silage’, page 332, 2004.
Oil or fat content is measured in some analyses and is often recorded as ‘ether extract’. The aim is to have total oil in the diet less than 5% otherwise it starts to reduce fibre digestion.
Written by Roger Sneath and reviewed by Bernie English, Department of Primary Industries.
This document was reviewed as part of the GrazingFutures Project. GrazingFutures is funded by the Queensland Government’s Drought and Climate Adaptation Program (DCAP) that aims to build drought and business resilience for Queensland livestock producers.