Lamb Illthrift

Lamb Illthrift: Causes, Investigation and Control

Phil Rogers MRCVS <philrogers@eircom.net>
Grange Research Centre, Dunsany, Co. Meath, Ireland
Thursday, 26 February 2004

FARMERS DETECT MOST LAMB ILLTHRIFT POST-WEANING (say mid June onwards) but main causes need not arise post-weaning; indeed they often arise pre-weaning, or even before birth. In many flocks, failure to detect problems pre-weaning means that corrective efforts are aimed in the wrong direction.

Poor lamb performance, especially in MAY TO JULY increases the days to slaughter and the % of tail-end lambs which must be kept on, or sold as stores.

Lamb drafting rate is the simplest index of lamb performance. Midseason flocks with lamb drafting rates circa 10% on June 1, 20% on July 1, and 50% on August 1 are performing to average targets. Those well above those drafting rates are doing very well; those with much lower rates are doing poorly (Seamus Hanrahan).

The most important factors to ensure fastest lamb growth rates within a flock are:
(a) Optimum ewe health and nutrition pre- and post-lambing, to ensure high lamb birth- and weaning- weights;
(b) Optimum lamb nutrition pre- and post- weaning;
(c) Optimum grazing management and provision of the best winterfeed possible;
(d) Effective parasite control.
(e) Effective mineral supplementation of ewes and lambs, though important, is of lower priority than ensuring that factors (a) to (d) are optimal.
(f) Genetics: Having good quality rams and ewes with plenty of milk increases lamb performance. Unfortunately, most sheep farmers cannot change flock genetics overnight and buying very expensive rams may not be justified. The ram-effect on lamb performance within a flock is less than some would expect, circa 1-2kg/lamb at weaning.
(g) Lamb creep feed: Pre-weaning lamb growth rates and feed conversion efficiency are double those post-weaning. If lamb creep feeding is to be used it is twice as efficient to supply it pre-weaning.

NORMAL growth rates for lambs are hard to define. Twins & triplets can be 0.7-1.3kg lighter at birth than singles and 2-6kg lighter at weaning. But growth rate of twins and triplets post-weaning can be 20-30g/d more than growth of singles. Typical growth targets for mid-season lambs are shown below. A flock is deemed to have illthrift if mean lamb weight for age is >10% below the following targets:

Age (wk)	Single	Twin	Age (wk)	Single	Twin	Age (wk)	Single	Twin	Age (wk)	Single	Twin
Birth	5.2	4.4
1	6.9	6.1	9	25.3	21.6	17	37.8	32.4	25	46.3	40.8
2	9.4	8.1	10	27.5	23.5	18	38.8	33.4	26	47.4	41.9
3	12.0	10.4	11	29.3	24.9	19	39.9	34.5	27	48.5	42.9
4	14.4	12.3	Wean 12	31.1	26.4	20	41.0	35.5	28	49.4	43.9
5	16.5	14.0	13	32.8	27.8	21	42.1	36.6	29	50.5	45.0
6	18.7	15.9	14	34.6	29.2	22	43.2	37.7
7	20.9	17.8	15	35.7	30.3	23	44.2	38.7
8	23.1	19.7	16	36.7	31.3	24	45.3	39.8

CAUSES OF LAMB ILLTHRIFT
There are many causes beyond those listed below, but the following are the most common causes. They should be checked in every investigation of lamb illthrift:

ILLTHRIFT PRE-WEANING	MAIN CAUSES
1. Low birth weight	Ewes underfed in pregnancy have lighter lambs at birth; Ewe age: Ewes of 3rd and 4th parity bear the heaviest and fastest growing lambs. Birth weight is an important determinant of weaning weight; 1kg extra in birth weight gives 2.4-3.3kg extra in weaning weight (Seamus Hanrahan).
2. Reduced milk intake by lambs	Mismothering; too many triplets; Reduced milk yield (inadequate ewe condition/nutrition (grass intake/quality, weather), ewe age (see 1, above), mastitis, ewe diseases (footrot, etc)); Conditions in the lambs (large litter size, infections, parasites, pain, oral lesions, trace element deficiency, etc)
3. Reduced grass intake by lambs	Poor pasture quality and quantity; adverse weather, lamb conditions etc; even unweaned lambs, especially twins & triplets, need access to high quality grass and/or creep-feed to thrive best; Conditions in the lambs (see above)
4. Lamb creep feeding pre-weaning?	If lamb creep feeding is to be used it is more efficient to supply it pre-weaning. Pre-weaning, 5kg concentrate can produce 1kg liveweight; post-weaning, it takes 9-13kg concentrate to produce 1kg liveweight.
ILLTHRIFT POST-WEANING
1. Low weaning weight	Lamb growth rates pre-weaning (270-330g/d) are circa double those post-weaning (130-190g/d). If lambs are below target weight at weaning, they take much longer to finish.
2. Carry-over effects	Later effects of earlier conditions etc.
3. Undernutrition	Low intake/absorption of digestible energy and protein
4. Parasitism	Gastrointestinal, liver, lungs, skin, gid
5. Infections	Viral, bacterial, protozoal
6. Poor water supply	Poor quality or quantity; frozen water pipes (very common in urolithiasis)
7. Other	Pain, lameness, oral/throat lesions, trace element deficiency etc

INVESTIGATION OF FLOCK ILLTHRIFT:

EXAMINE FOR	CHECK DETAILS OF
1. Poor nutrition, grassland management and winter feeding	Ewe nutrition in pregnancy, especially the second half of pregnancy; are ewes fed to match the needs of single versus multiple foetuses? Ewe and lamb nutrition pre- and post-weaning (weights, milk yield, water supply, quality and quantity of grass available and eaten, grazing management etc). Note that lamb thrive can be poor in cold, wet, overcast conditions. Age structure of the ewes; Dr. Hanrahan and his colleagues report that 3rd and 4th parity ewes have the fastest growing lambs. Younger and older ewes produce less milk.
2. Parasitism	Efficiency of anthelmintic use and if anthelmintic resistance is present;
3. Flock diseases	Bacterial, viral, protozoal diseases or other disorders, especially severe footrot. If necessary, samples of faeces or blood etc may be taken for investigation, for example at the RVL, Athlone.
4. Trace element disorders	Samples of heparinised blood from 10 sheep in the affected group may be tested for Cu, GPx, I + P. Liver may be tested for Cu. Soil may be tested for Co and Mn levels. Postmortem examination.

Deficiency of Co, Se, I + Cu: Many perceive trace element imbalance as a major cause of lamb illthrift, especially post-weaning. Though it may be important in some flocks, it is much less important nationally than the other causes listed above.

Nationally, low or very low status of blood I, Se and Cu were found in 77, 41 and 9% of sheep flocks tested at Grange in the period Nov '92 to Oct '93. Not one case of Co deficiency was identified on blood test, probably because most flock owners routinely use Co supplements of some kind.

Note that PII (plasma inorganic iodine) is the only accurate blood test for iodine status in ruminants. The PII test is not available in the Republic now. Results of blood tests for levels of thyroid hormones (T3, T4) and PBI (protein-bound iodine) usually are misleading; they do not correlate well with iodine intakes by cattle or sheep.

REMEDIAL ACTIONS::

1. Correct detected faults	Correct all detected faults in nutrition, grass and silage quality, grazing management, water intake/quality; ensure good control of parasitism, infection, poisoning/intoxication, pain/inflammation, internal disorders, abscess/sepsis, anaemia, allergy, immunosuppression, cancer, fever; improve the genetics?
2. Mineral supplements?	If the levels of P, Cu, Se, I, Co are low or very low on blood test, you may wish to increase their supply.

One of the quickest ways to check if mineral deficiency is involved is to use a good mineral supplement (or drench) high in trace elements. Note that many unsupplemented flocks have multiple deficiency (Se, I and Co, +/- Cu). Many farmers report that regular use of a drench combining Co, Se and I gave better lamb growth and wool quality than use of Co alone. See details of an effective sheep drench in Periodic drenching with trace element supplements. Ideally, a random half of the lambs should be dosed 3 or 2 times at intervals of 2 or 3 weeks, and the other half left as untreated controls. Weighing the lambs at dosing, and 3 and 6 weeks later allows an objective assessment of the effect of the dosing. If the treated lambs do not perform better than the controls within 3-6 weeks, the cause is unlikely to be mineral deficiency. See also: Examples of mineral mix formulations for sheep (lambs).

If a Cu supplement is needed, slow-release Cu capsules are safer than other methods. See Control of Copper (Cu) Deficiency/Molybdenum (Mo) Excess in Cattle and Sheep. To limit the risk of poisoning, Cu should be given under veterinary advice only. See Control of Copper (Cu) Poisoning in Sheep.

Note that if minerals are only marginally deficient in blood, further supplementation with those minerals is unlikely to improve growth rate.

Further data on mineral supplementation of sheep are online at Control of Mineral Imbalances in Cattle and Sheep: A Reference Manual for Advisers and Vets.

Acknowledgements: This article depended heavily on experimental and on-farm data collected by Drs. Seamus Hanrahan, Tom Nolan, Sean Flanagan and their colleagues in the Teagasc Research Centre, Athenry, and on field observations by Teagasc Sheep Specialists, especially Gerry Scully (Athenry) and Andrew Kinsella (Wicklow), and many other Sheep Advisers with whom I had the privilege of working over the past 35 years. I also thank my colleague, Dr. David Poole, who was my main mentor for almost 25 years on methods of investigation and control of mineral imbalances and metabolic disorders in ruminants.