Optimal Mineral Nutrition of Cattle and Sheep on Irish Farms

Phil Rogers MRCVS, Agricultural Research Unit, Teagasc National Office

A seminar for Teagasc Livestock Specialists, Teagasc Office Portlaoise, July 22^nd, 2003

 Executive Summary | Introduction | Mineral Targets for cattle & sheep | High-spec mineral mixes for cattle & sheep | Mg supply re grass tetany | Ca supply re milk fever | Optimal supply of N, P, K and S | Ca, P, Mg and Na nutrition to prevent urinary calculi | Optimal supply of Cu, Co, Se and I | Cu toxicity in sheep and calves | Se toxicity  | Pb toxicity | Where to look for technical data | Aide Memoire | References | Questions

Executive Summary

Irish ruminants ingest minerals from four main sources:  

Mineral levels in Irish forages depend on many factors, only some of which are under the farmer’s control. Factors that influence forage mineral levels include:  

Table 1 shows the mean mineral levels in Irish forages (pasture and grass silage) in the early 1990s (3). Values highlighted in yellow indicate abnormal national means for that element.

Table 1: Mean mineral levels in Irish forages (pasture and grass silage) in the early 1990s.  

*Sd (standard deviation): 95% of values fall in the range (mean +/- 1*Sd), i.e. 95% of Irish herbage Ca values lay between 0.47 and 0.83 %DM; 99% of values fall in the range (mean +/- 2*Sd), i.e. 99% of Irish herbage Ca values lay between 0.29 and 1.01 %DM.  

The main imbalances found in Irish pasture (3) were:

• N, K and S and Mo were high in 65, 32, 80 and 42% of samples, respectively
• P, Mg, Na, Cu and Zn were subnormal in 32, 49, 19, 65 and 25% of samples, respectively
• Se and I were subnormal in 94 and 97% of samples, respectively
• High Se was found in 1.2% of pasture samples; endemic Se toxicity occurs on circa 50 farms in the Republic
• Mn deficiency was not a problem; only 2% of samples were subnormal
• Co levels are not shown, because much Co found on pasture (or silage) analysis is surface contamination from soil. However, Co deficiency is common in Irish herbage.

From these national data, it follows that optimal mineral nutrition of Irish cattle and sheep on forage-based diets involves routine supplementation to ensure balanced inputs of the essential major- and trace- elements to ensure that neither deficiencies (primary or secondary) nor toxicities occur.

We will discuss the following topics:

• Mineral Targets for cattle and sheep
• Typical high-spec mineral mixes for cattle and sheep
• Mg supply in relation to grass tetany
• Ca supply in relation to milk fever
• Optimal supply of N, P, K and S
• Use balanced Ca, P, Mg and Na nutrition o prevent urinary calculi (typically Mg phosphate) in concentrate-fed sheep
• We will also discuss optimal supply of Cu, Co, Se and I
• Finally, we will discuss Cu, Se and lead (Pb) toxicity

Introduction

Useful background data are in the Teagasc Manual, “Control of Mineral Imbalances in Cattle & Sheep: A Reference Manual for Vets and Advisers” (1). Siobhan Kavanagh has some spare copies of the manual, or you can download it from the Teagasc Web Pages (1). Other details of most topics covered in this seminar are available on the Teagasc Webpages – see the references at the end of this paper, especially references 2, 3, 4, 5, 6, 7, 8.

Mineral Targets for cattle and sheep

Table 2 summarises the range of values of major- and trace- elements in TDMI that are classed as “normal” for cattle and sheep.

Table 3 summarises the range of values of trace elements in TDMI that are classed as “normal” for cattle and sheep.

When assessing the adequacy of total feedstuffs, values outside of these ranges can be regarded as abnormal (undesirable). The tables also give the Recommended Optimum Dietary Level (RODL). This usually is at or above the “mid-normal range”, but physiological and species differences influence RODL. For example, dairy cows milking on spring grass need more Mg and P than dry cows in winter; sheep need more Co and less Cu than cattle.

Table 2: Major element levels (%TDMI) classed as “normal” and the RODLs for cows and ewes.

*           Excessive K and S is undesirable;

**          Extra Mg (usually 30-50g/cow/d and 10-20g/cow/d) is needed during tetany-risk periods and the last 4-6 weeks prepartum, respectively;

**          Extra Mg (usually 3-7g Mg/ewe/d) is needed during tetany-risk periods. If Mg supplements are given routinely prepartum, they should not exceed 2g/ewe/d; excess Mg in late pregnancy can increase the risk of hypocalcaemic paresis (“Lambing Sickness”).

Table 3:            Trace element levels (mg/kg TDMI) classed as “normal” in feed, inclusion rates permitted under EU Feed Regulations, and the RODLs for cows and ewes in Ireland.

*           Mo levels >2mg/kg DM antagonise Cu absorption by cattle/sheep;

**          These high Cu, Se and I levels in feed are advised for beef and dairy cows for at least 5 months (1 month pre- to 4 months post- calving)

***        Avoid Cu supplements for sheep except on specific veterinary advice  

Typical high-spec mineral mixes for cattle and sheep

For more details on the composition of high-spec cattle and sheep Mins, see references 1, 10, 11, 13. Note that cattle need at least 7 different formulations:

(1) Dry Cow Mins;

(2) Dairy/Beef Cow Winter Mins;

(3) Tetany Control Mins (for lactating cows at grass in risk periods);

(4) Calf and grower/finisher Mins;

(5) Fodder Beet Balancer Mins;

(6) Maize silage Balancer Mins;

(7) Balancer minerals for cattle on ad libitum concentrates.

Table 4 gives examples of top-class formulations for mineral mixes for COWS AND OTHER CATTLE on grass silage or herbage as the main forage. Different formulations are needed for cattle on high intakes of special feeds, like fodder-beet silage, maize silage, or ad libitum concentrates.

Table 4:           Examples of top-class formulations for mineral mixes for COWS AND OTHER CATTLE on grass silage or herbage as the main forage.

⁽¹⁾ Never feed cattle minerals to sheep, and vice-versa. Cattle minerals may cause copper toxicity in sheep. Never feed cow minerals to calves, as scouring and urinary stones and copper toxicity may follow.
⁽²⁾ If recommended daily allowances are above or below those shown, adjust the trace-element and vitamin levels down or up, accordingly. One would normally feed 150-180 g minerals in home-mixed lactation diets. Special minerals are needed if silages based on whole-crop maize or fodderbeet are fed.
⁽³⁾ To prevent urinary stones in drystock, feed low levels (0-3%) of Mg in mineral mixes.
⁽⁴⁾ Some authorities double these amounts of Mn for breeding females, especially in groups with severe infertility and suspected Mn deficiency
⁽⁵⁾ The maximum Se supplement was reduced to 5 mg Se/cow/d, as from January 1 1996. Do not feed high Se minerals to cattle within 5 miles of a known Se-toxic farm unless blood test indicates no risk of Se toxicity.
⁽⁶⁾ The higher Vit E levels are 4-6 times higher than usual (underlined values are more usual). Research in USA and elsewhere shows that high levels of Vit E improve immunity and reduce mastitis incidence.

In theory, sheep also need a wide range of mineral formulations to cater for different physiological states (pregnancy, lactation, tetany-risk, lamb fattening minerals, etc). However, because the total mineral market for sheep is so small relative to that for cattle, the trade does not provide the optimum range of formulas and reaches a compromise with a smaller range.

Mg supply in relation to grass tetany: See references 1, 9,