CASE NOTES

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Bone problems in lambs on grazing cereals

Bruce Watt, DV Central Tablelands

Posted Flock & Herd August 2008

Introduction

Lambs are reported to develop skeletal bone problems due to calcium deficiency, internal parasitism, copper deficiency, vitamin D deficiency and from general malnutrition. Rickets is the term sometimes used to describe the skeletal defects caused by failure of mineralisation in young animals (Jubb, et al. 1991) but the terms osteoporosis and osteodystrophy have also been used in sheep. I have previously seen rickets in lambs fed cereals grain without calcium supplementation. However I have not previously seen rickets associated with grazing oats. This condition is however not uncommon in autumn lambs or spring carry over lambs especially those grazing winter oats (Caple 1994, Hodge 2006 and Evers pers. comm.). This is a report on three cases from the central slopes and tablelands in 2007.

CASE STUDIES

Case 1

On 26th and 31 of July 2007 I examined 15 of 620 April drop second cross lambs that were either lame or collapsed. The lambs were marked six weeks previously and returned to a phalaris based pasture. Three weeks later the ewes and lambs were moved onto a fresh paddock of March sown Nile oats. On 24th July the manager when moving the mob noticed about 20 lame lambs. He yarded the mob to draft off the ewes for crutching and counted 50 affected lambs. He also vaccinated the lambs with 5:1 and drenched them with albendazole. Fifteen very lame or recumbent lambs were retained in the yards for examination and treatment.

Case 1 A sample of the 15 lame or recumbent lambs

Of the 15 lambs examined 6 were ewes and 9 were wethers. I estimated their weights as from 10 to 22 kg. All were bright and alert with normal mucous membranes and no evidence of scouring. Nine could stand although most were favouring one or two limbs. Six were recumbent. The bones over the frontal sinuses were usually easily compressed. Fourteen of the 15 lambs had evidence of fractures through either one or both proximal tibial epiphyses. On one lamb that stood normally I could find no evidence of fractures and one lamb may also have had an unstable distal humerus.

I post-mortemed one approximately 22 kg wether lamb that was recumbent and unable to stand. This lamb had soft frontal sinus bones and instability below both stifles suggesting fractures through both proximal tibial growth plates. This was confirmed on post-mortem. The ribs were also noticeably soft on post-mortem.

BIOCHEMISTRY

	Normal	Units	1	2	3	4
Copper	7.5-20.0	umol/L	18.7	13.6	14.9	16.5
Calcium	2.12-2.87	mmol/L	2.66	2.16	2.49	2.87
Magnesium	0.74-1.44	mmol/L	0.89	0.97	0.93	0.93
Vitamin D	>25	mmol/L	15	23	40	33

The manager of this property moved the ewes and lambs (apart from the 14 remaining affected lambs) onto a paddock of mixed perennial grasses and clovers and reported no further problems. He treated the 14 affected lambs with injectible vitamin D (dose not recorded) and fed them entirely on dry lucerne hay. All but one lamb recovered within two weeks. One lamb remained recumbent and was euthanased by the manager.

Case 2

On 7th August 2007 I examined four approximately 35-42 kg second cross lambs after an owner complained of some lambs collapsing and some with fractures after consignment to the saleyards. The mob consisted of 600 February 2007 drop lambs that were weaned in early May and drenched with Firstmectin. The lambs were weaned into a health crop of Bimble oats and also had access to self feeders of grain oats. One month later wheat was added to the self feeders producing 5-6 cases of acidosis. There was no supplementary lime or salt in the grain or elsewhere.

On 2nd July the owner sold his first consignment of 20 lambs without problems. However in two consignments from 9th to 16th July, totalling 238 lambs, buyers complained of 40 lambs with fractured ribs. Two lambs had to be returned home as they were collapsed and trembling. These lambs subsequently recovered.

Finally on the 6th August the owner while loading 120 lambs he had mustered, crutched and ear tagged the day before noticed one ‘tucked up’ lamb that he removed from the consignment. However 7 lambs from this consignment were sent home from the sale as they were reluctant to walk and were shaking.

Of the four lambs I examined two were lame but able to stand and two were recumbent. While the bones over the frontal sinuses were soft no fractures were palpable. The lambs that could walk were reluctant to do so and stood with arched backs and front and hind feet together. The first here lambs examined were bright and alert whereas the fourth was in sternal recumbency and was weak.

BIOCHEMISTRY

	Normal	Units	1	2	3	4
Calcium	2.12-2.87	mmol/L	1.60	1.40	1.26	1.36
Magnesium	0.74-1.44	mmol/L	1.01	1.09	0.87	1.01

I recommended that the owner treat affected lambs with injectible calcium borogluconate, immediately commence calcium supplementation and withhold further lambs from sale until the problem was resolved. I also recommended that they be moved to a legume based pasture if possible. On 17th August the owner reported that three of the remaining 330 lambs had collapsed and died as he moved them to another paddock. Another 13 were too lame to move and had to be transported. He also reported that of the 120 lambs sold on 6th August, 16 were condemned as they were lame and lethargic.

The owner also reported that the lambs ate calcium supplemented oats readily (I recommended 2% lime and 0.5% salt be added to the grain in the self feeders). He also moved them to a barley grass, lucerne, clover paddock and supplemented the lambs with a mix of lime, salt and molasses in troughs. The lambs also readily consumed the mix in the troughs.

On 23 rd of August the owner reported that all lambs were now moving freely and he had no further losses. The 13 lambs previously too lame to walk were now moving normally and couldn't be caught.

Case 3

On 28th of August I was called to examine a mob of 450 September 2006 drop Dohne cross lambs because when they were yarded five days previously four collapsed and 15% of the remainder were lame, tending to drag their hind legs. The lambs were weaned onto a green pick in December. In February 2007 the owner drenched the lambs and commenced trail feeding them with barley. In May the lambs were run into a paddock of grazing oats and fed barley in self feeders. No supplementary calcium was provided. The lambs were shorn and given a vitamin AD and E injection in late July and were returned to paddocks of grazing oats.

I examined three well grown 30-35 kg wethers and an equally well grown ewe lamb. All were bright and alert. All four were able to stand with assistance but were reluctant to bear weight on the hind limbs or move. The lambs also had palpably soft bones over their frontal sinuses. Three has evidence of fractures of one or both proximal tibial epiphyses. Case 4 which was euthanased and post-mortemed had marked instability in the right stifle and a slightly unstable left stifle. On post-mortem this lamb had multiple mature rib fractures. Radiographs of the right stifle showed a displaced proximal tibial epiphyseal fracture.

I also inspected the remainder of the mob in the paddock. I could see lame lambs dragging a hind limb.

I recommended that the owners immediately supplement these sheep with lime and salt as a loose mix in troughs. They noted immediate acceptance by the lambs. I did not recommend vitamin D supplementation for several reasons. I considered that calcium deficiency was the primary problem but was also concerned that yarding and handling to treat the lambs may have caused further injury. As it was now late August I also thought that sunlight should be adequate to enable the lambs to synthesise their own vitamin D.

On 24th September the owners reported it took 2-3 weeks for all lambs to stop limping and dragging limbs and one month later all lambs seemed recovered and growing well.

Multiple rib fractures in a lamb from case 3

BIOCHEMISTRY case 3

	Normal	Units	1	2	3	4
Copper	7.5-20.0	umol/L	17.8	23.7	37.4	25.8
Calcium	2.12-2.87	mmol/L	1.93	2.64	2.64	2.40
Magnesium	0.74-1.44	mmol/L	0.87	0.97	1.24	1.02
Vitamin D	>25	mmol/L	15	63	13	49

Discussion

All three of these cases occurred in July- August 2007 on grazing oats. In two cases the lambs were also supplemented with cereal grain without added calcium. Cereal grain is well known to be calcium deficient whereas grazing oats is variably low. There has been conjecture that a factor in grazing oats may act as an anti-metabolite suppressing vitamin D synthesis.

Blood calcium levels in cases 1 and 3 were mostly normal whereas in case 2 they were clearly hypocalcaemia. Vitamin D assays were not particularly convincing. In both cases 1 and 3, two of four sheep had low vitamin D levels. These assays performed by Sydney South West Pathology Service are reported as 25-OH Vitamin D and are the sum of Vitamin D2 and vitamin D3 levels. The pathology report qualified these results and noted a lack of reference values for sheep for this laboratory. The normal values were given from Bonniwell et al., 1988.

The most encouraging aspect of all these cases was the rapid response to treatment. I have had previous experience with a farmer treating a recumbent, osteoporotic lamb with calcium and lucerne hay and achieving recovery in about two weeks. Virtually all the lambs with fractures of the proximal tibial epiphysis recovered uneventfully. Mid shaft fractures and severely displaced fractures necessitating euthanasia were rare.

References

1. Bonniwell et al. (1988) The Veterinary Record 122:386-388
2. Caple IW (1994) Hypocalcaemia and osteoporosis in lambs and weaners Proceedings of the Australian Sheep Veterinary Society AVA Annual Conference 56-60
3. Hodge B (2006) Osteoporosis in lambs on grazing oats. District Veterinarian's Annual Conference (no proceedings)
4. Jubb KVF, Kennedy PC and Palmer N (editors). Pathology of Domestic Animals. Fourth Ed, Vol. 1, 1993