Levels of Dry Matter, Major Elements (calcium, magnesium, nitrogen, phosphorus, potassium, sodium and sulphur) and Trace Elements (cobalt, copper, iodine, manganese, molybdenum, selenium and zinc) in Irish Grass, Silage and Hay

Authors: Phil Rogers and Willie Murphy [02/02/2000]

| Introduction | Forage Tables | Summary & Conclusions |
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Introduction
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The following is a summary of the typical levels of Major- and Trace- Elements in Irish forages, based on samples analysed over a 4-year period in Johnstown Castle, Wexford.

The following were omitted from the original Johnstown data: DM <10% (6 grasses/silages); Ca <.10% DM (2 grasses) or >2.00% DM (2 grasses, 4 silages); K <.50% DM (4 grasses); Mg >.50% DM (2 grasses); Na <.03% DM (2 grasses, 1 silage) or >1.40% DM (1 grass, 5 silages); S <.05% DM (2 grasses) or >1.00% DM (1 grass).

Trace Element data excluded (because of experimental, slurry or soil contamination) were: Cu: 12 grasses >25 ppm DM; 6 silages >40 ppm DM; Mo: 1=400; 1 = 88; Se: 5 =>4; 2 = 4-84; I : 22 = >1; 14 = >1; Zn: 7 = >100; 19 = >100; Mn: 8 = 708-980; Co: 8 = >.39; 2 = >.39 

Forage Tables
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Summary & Conclusions

| Grass | Grass silage | Hay | Forage Tables | Top |

1. Multiple imbalances: Irish forages (grass, grass silage and hay) have multiple imbalances of Major- and Trace- Elements. Routine mineral supplementation of Irish cattle and sheep (young-, growing-, adult-, breeding- and lactating stock) is sound national policy, both indoors and at pasture. The most important minerals for routine supplementation are Cu, Se, I and Co, but it is advisable to include a proper balance of the other Major- and Trace- Elements in vitamin-mineral supplements also.
2. Grass has a poor balance of Major Elements (high N, K, S, and many low Mg and Na values) (Table 1a, Table 2a). It also has multiple deficiencies of Trace Elements (Cu, Se, I and, sometimes, Co values) and many high Mo levels (Table 1b, Table 2b).
3. At pasture, routine supplementation of susceptible stock (lactating cows and ewes) with Mg is advisable during periods of tetany-risk. Routine supplementation with Trace Elements is also advisable. In particular, a generous I-supply is advisable during the breeding season, as blood I-values (plasma inorganic iodine) fall within days of withdrawal of I-supplement.
4. Farmers should avoid unnecessary use of N, P, K and S fertilisers, as high levels of these Elements in grass can compromise the absorption of Mg and Trace Elements. If they must apply lime to improve their swards, they should also take great care to provide generous supplements of Cu, Co, I and Zn to their cattle and sheep. (See note on Cu for sheep, below).
5. Hay is very deficient in N (protein), P and Mg (Table 5a, Table 6a). Many samples are also low in Ca and Na. It is also very deficient in Cu, I, Se, Zn and of unknown Co status (Table 5b, Table 6b). High-producing animals fed a lot of hay (or straw) in winter should receive additional protein, Trace Elements, P, Mg and vitamin A, D3 and E supplements.
6. Grass silage has a Major Element composition somewhere between that of grass and hay (Table 3a, Table 4a). It is often low in Mg, N (protein) and P and often needs supplements of those Elements, plus protein. It has Trace Element levels somewhere between those of grass and hay (Table 3b, Table 4b). Its levels of Se and I are often too low for dairy cows. Ruminants should receive routine supplementation with those minerals (plus Cu and vitamins A, D3 and E) when fed silage in winter.
7. Cu-poisoning in sheep: Sheep are very susceptible to Cu-poisoning. They should not receive Cu supplements except on veterinary advice. If needed, slow-release forms of copper (i.e. Cu-oxide capsules) are the safer than other forms of Cu-supplements for sheep.

Table 1a. DM (%), Ca, P, K, Mg, N, Na, S levels (% DM) in IRISH GRASS
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Table 1b. Cu, Mo, Se, I, Zn, Mn, Co levels (mg/kg DM) in IRISH GRASS
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Table 2a. Major Element Assessment in IRISH GRASS: % Samples in each category (see Assessment Criteria) in relation to dairy cow requirement
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Table 2b. Trace Element Assessment in IRISH GRASS: % Samples in each category (see Assessment Criteria) in relation to dairy cow requirement
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Table 3a. DM (%), Ca, P, K, Mg, N, Na, S levels (% DM) in IRISH SILAGE
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Table 3b. Cu, Mo, Se, I, Zn, Mn, Co levels (mg/kg DM) in IRISH SILAGE
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