Putting stock onto winter crops

Most winter forage crops provide good quality, highly palatable feed, with energy (ME) ranging from 8 -14 (MJME/kg DM), protein (CP) 14-32% and dry matter (DM) ranging from 15 – 32%. From May-June, you may be starting or planning to put stock onto winter forage crops. Before you do, there are a few things to consider to get the most out of your forages.

Introducing stock to winter pasture

Like all new pastures and crops, introduction needs to be slow. Ruminants tend to graze at a ratio of 70:30, 70% in the morning vs 30% in the afternoon. Therefore it is best to fill livestock up with hay during the morning graze and then introduce them to the new crop in the afternoon. This will decrease the risk of digestive upset in an unadjusted rumen.

Remember you are feeding the microbes not the animal, so introduce livestock slowly so that the rumen microflora have a chance to adjust to the high quality diet. It will normally take up to 7 to 10 days to become accustomed to the new feed. Restricting grazing to 1-2 hrs per day, slowly increasing to unrestricted access over 7-10 days will allow stock to become more accustomed to their feed (NSW DPI, 2002).

If this is not possible for you to slowly introduce the livestock, ensure you have a roughage source available in the paddock, such as medium to good quality hay. The hay’s quality is important. If poor in quality animals will not eat it, so it becomes ineffective in providing roughage to the animals.

Effective fibre

As stated above, roughage is important when introducing livestock onto a new high quality pasture or crop. Roughage reduces the rate of gut flow, contains enzymes that breakdown fat and starch and helps stabilise rumen fermentation.

Fibre is also important at other times. This includes:

At late pregnant and early lactation to help rumen function and improve milk fat production
When scouring is caused by excess protein
When moisture content is above 83%
When grazing brassica species, such as canola, as brassicas are highly digestible and have low fibre content, so access to hay may provide a more balanced diet and improve weight gains (NSW DPI, 2002).

Your local Ag officer can help with pre-planning and advice on the best winter feed options to suit local conditions.

Animal health

Mineral supplementation

Cereals and brassicas can provide high quality forage, as they are high in digestibility, crude protein and metabolisable energy (Kirkegaard et al. 2008; Dove and McMullen 2009; Dove and Kelman 2015; McGrath et al. 2015), however grazing crops can have mineral imbalances.

The main deficiencies are magnesium (Mg) and calcium (Ca), also known as grass tetany and milk fever, respectively. These deficiencies usually occur when livestock are grazing winter or spring pastures or young vegetative dual-purpose cereal crops. This is due to these crops being low in sodium (Na), Mg and Ca, as well as being high in potassium (K), which inhibits the absorption of Ca and Mg (Masters et al. 2019).

Therefore mineral supplementation is needed to get the best out of your livestock on these forages. Mineral supplementation can be either in a form of a loose lick or other commercial products, as long as they contain Mg, Na and Ca.

For example, there are three types of loose lick minerals mixes you can used for supplementation:

1:1 mix of Causmag® and salt, for growing livestock
2:2:1 mix limestone, salt and Causmag®, recommended for pregnant and lactating livestock
1:1 mix of lime and salt, recommended for all stock if they find the Causmag® unpalatable

Vaccination

A change in feed, particularly of high quality such as cereal crops are a common factor in animals developing pulpy kidney (enterotoxaemia). It occurs in when a bacterium that normally inhabits the animal’s intestines without causing problems begins to multiply and produce a toxin that poisons the animal. Pulpy kidney most commonly occurs in rapidly growing unweaned or weaned lambs, on lush pasture or grain (NSW DPI, 2007; DPIRD WA, 2018). This disease affects both sheep and cattle, in which they can be found dead with no previous sign of ill health. Therefore, all livestock should be bought up to date with their clostridial vaccinations, i.e. 3-in-1, 5-in-1, 6-in-1 and 7-in-1, prior to being introduced to the crop (NSW DPI, 2020). It is recommended that if it is a booster vaccination they can be released immediately onto the crop, but if not, leave around 7 to 10 days before introduction.

Other management considerations

There are a few more things that you need to be cautious about when grazing winter forage crops they are as follows:

Nitrates

Nitrate/nitrite poisoning is common during drought or after subsequent rain. This is due to soil nitrate increasing greatly as a result of reduced leaching and lower plant uptake, in combination with increasing availability due to organic matter decomposition (NSW DPI, 2018; 2020).

Factors which cause nitrate to accumulate in the plant include:

drought
cloudy or cold weather
herbicide application
wilting

The amount of nitrate in plant tissues also depends on:

plant species
stage of maturity
part of the plant
fertiliser application
soil nitrogen availability

Nitrate concentrations are usually higher in young plants and decrease as plants mature. Most of the plant nitrate is also located in the bottom third of the stalk, hence the leaves contain less nitrate and the flowers or grain contain little to no nitrate. Common plant and weed species that accumulate nitrates are seen in Table 1. Symptoms appear within a day of stock grazing affected plants, though sudden death is also possible, so gradual transition onto these feeds is required.

If you have recently applied nitrogen fertiliser, the risk of nitrate poisoning is higher. The nitrogen in the fertiliser needs rainfall to become available therefor do not introduce stock into a paddock that has had nitrogen applied until two weeks after the first effective rainfall event following application.

Producers also need to be mindful of recent herbicide applications. It is always critical to comply with any herbicides grazing withholding period which is stated on the label. Another consideration is that many common broadleaf herbicides will increase the palatability of some weeds. If there is weeds like the ones listed in Table 1, they become more palatable and therefore the risk of nitrate poisoning is much higher.

Photosensitisation

Photosensitisation is an ailment in which the skin becomes sensitive to bright sunlight, especially in areas of non-pigmented skin with little hair or wool cover, i.e. in sheep; the face, muzzle and ears. It usually occurs when livestock have eaten certain toxic plants.

Photosensitisation can be primary or secondary. Primary is caused by ingestion of plants that contain light-sensitive substances. If enough compound accumulates in the blood vessels, close to the skin, light transforms it into a toxin and skin damage results. Secondary photosensitisation is the most common cause of the disease in Australia. It occurs following liver damage from consuming the plant toxins. In all cases the photosensitising compound is phylloerythrin, produced in the breakdown of chlorophyll in the gastrointestinal tract. Normally it is absorbed in the blood, then removed in the liver and excreted in the bile. However with liver damage, this process is disrupted leading to accumulation of phylloerythrin in the blood and subsequent photosensitisation (DPIRD WA, 2018).

Although most issues with photosensitisation occurs due to the consumption of plants that are toxic to livestock, such as Paterson’s curse and St John’s wort, it can also occur in livestock when grazing canola, kale, oats, medic and lucerne. However, the precise cause is not clear (NSW DPI, 2007). Prompt removal of stock from the source of the toxin, keeping them out of direct sunlight and providing water and cereal hay or lower quality pasture hay with no green colour should help in recovery.

For more information on moving stock onto winter cereal crops contact your nearest Local Land Services Ag advisory team member or District Vet.

References/Resources:

NSW DPI (2002) AgFacts: Forage brassicas – quality crops for livestock production. Source: https://www.dpi.nsw.gov.au/__data/assets/pdf_file/0003/146730/forage-brassicas-quality-crops-for-livestock-production.pdf

Kirkegaard JA, Sprague SJ, Dove H, Kelman WM, Marcroft SJ, Lieschke AK (2008) Dual-purpose canola – a new opportunity in mixed farming systems. Australian Journal of Agricultural Research 59, 291–302.

Dove H, McMullen KG (2009) Diet selection, herbage intake and liveweight gain in young sheep grazing dual-purpose wheats and their responses to mineral supplements. Animal Production Science 49, 749–758.

Dove H, Kelman W (2015) Responses of young sheep grazing dual-purpose wheat to supplementary sodium and magnesium supplied as direct supplement, or to magnesium supplied as a fertiliser. Animal Production Science 55, 1217–1229.

McGrath SR, Bhanugopan MS, Dove H, Clayton EH, Virgona JM, Friend MA (2015) Mineral supplementation of lambing ewes grazing dual-purpose wheat. Animal Production Science 55, 526–534.

Masters DG, Hancock S, Refshauge G, Robertson SM, McGrath S, Bhanugopan M, Friend MA, Thompson AN (2019) Mineral supplementation improve the calcium status of pregnant ewes grazing vegetative cereals. Animal Production Science 59, 1299-1309.

NSW DPI (2020) Drought recovery guide. Source: https://www.dpi.nsw.gov.au/__data/assets/pdf_file/0009/1199925/Drought-recovery-guide.pdf

NSW DPI (2007) Prime Facts: Enterotoxaemia in cattle. Source: http://www.dpi.nsw.gov.au/__data/assets/pdf_file/0013/110092/enterotoxaemia-in-cattle.pdf

DPIRD WA (2018) Pulpy kidney (enterotoxaemia) of sheep. Source: https://www.agric.wa.gov.au/livestock-biosecurity/pulpy-kidney-enterotoxaemia-sheep

NSW DPI (2018) Prime fact: Nitrate and nitrite poisoning in livestock. Source: https://www.dpi.nsw.gov.au/__data/assets/pdf_file/0006/111003/nitrate-and-nitrite-poisoning-in-livestock.pdf

DPIRD WA (2018) Photosensitisation in livestock. Source: https://www.agric.wa.gov.au/livestock-biosecurity/photosensitisation-livestock

NSW DPI (2007) Prime fact: Photosensitisation in stock. Source: http://www.dpi.nsw.gov.au/__data/assets/pdf_file/0016/111157/photosensitisation-in-stock.pdf

Adapted from content by Dr Sue Street - Livestock Officer