A response of sheep to cobalt supplementation in south eastern Queensland.

Abstract

A RESPONSE OF SHEEP TO COBALT SUPPLEMENTATION IN SOUTH-EASTERN QUEENSLAND B.W. NORTON* AND J.W. HALES* Summary Two separate experiments were conducted with sheep` grazing Pangola grass pastures. In the first experiment, eight groups of pregnant ewes (six ewes/group) were used. Each group received one of the following supplements, no supplement (control), phosphorus, sodium, iodine, cobalt, mineral mixture, sorghum grain and sorghum grain plus urea. Ewes supplemented with cobalt lost less weight during lactation and their lambs showed a higher and more sustained growth than did ewes or lambs from the other groups. In the second experiment, one group of weaned lambs (27) was drenched fortnightly with cobalt and their growth compared with a similar group of unsupplemented controls. All lambs given cobalt increased in live weight during which time 52% of the control lambs died. Evidence is presented which suggests that cobalt deficiency was the primary cause of the high mortality rate. I. INTRODUCTION Previous attempts to study the potential of tropical pastures for lamb production in south-eastern Queensland,have demonstrated poor lamb growth and high levels of ewe and lamb mortality (Robertson 1972, Fleming 1974). Growth failure in these studies was not related to the type of pasture used (grass-legume mixtures), stocking rate or to the incidence endoparasitic or ectoparasitic diseases. The following experiments were designed to study the effects of various mineral and grain supplements on the growth of ewes and their lambs and to specifically investigate the response of weaned lambs to cobalt supplementation. Whilst cobalt deficiency in sheep has been demonstrated in many' areas of Southern Australia, there have been no previous reports of responses of sheep or cattle to cobalt supplementationin Queensland. MATERIALS AND METHODS (a) Location The following experiments were conducted at the University of Queensland's ,research farm at Mt. Cotton in south-eastern Queensland. The climate of the region is humid, sub-tropical, with a marked summer dominance of rainfall. Average annual rainfall is 1400 mm. Soils on the farm are acidicj red-yellow podzols (Beckman 1967) and are representative of the soils found in some k million ha. of coastal Queensland. These soils show major deficiencies of most elements need,ed for plant growth (Blunt and Humphreys 1970). . (b) Pasture Management Pangola grass [Digitaria decumbens, Stent.) pastures were established in 1970 with the following application of fertilizers (Kg/ha), superphosphate; 493, potassium chloride; 117, copper sulphate; 0.4, II. *Department of Agriculture, University of Queensland, St. Lucia, Qld. 393 sodium molybdate; 0.2, zinc sulphate; 0.4. Since establishment maintenance dressings of superphosphate (250 Kg/ha) and potassium chloride (125 kgkha) have been annually applied. Ammonium nitrate was applied as split dressings (60 Kg N/ha in May and August and 40 Kg N/ha in November and February). Pangola grass has proved to be well adapted to the area and negligible weed invasion has occurred. All supplements were discontinued one week prior tolambing. Ewes and lambs were weighed (after an overnight fast) and drenched with tetramisole (Nilverm) at fortnightly intervals during the trial. blY ewes which had received supplements for the full experimental period and raised a lamb to weaning were considered in the analysis of results. Treatment replicates were combined for statistical analyses. Experiment 2. Sixty Border Leicester x Merino ewes (3-4 years), which had been on the property for at least two years, were mated to Merino rams in March, 1974 and were maintained on Perennial Rye Grass pastures (N fertilized and irrigated) during pregnancy. Lambs from this flock were weaned in November onto Pangola grass pastures and maintained as a flock until January, 1975. Fifty-four lambswere then paired for weight and one of each pair allocated to one of the following treatments: control (no supplement) or cobalt (0.4 mg CoC12.6H20/hd/d). Groups of paired lambs (16,16 and 22 lambs) were held in three separate paddocks (66,66'and 72 lambs/ha respectively) for the ten week experimental period. Lambs were weighed after an overnight fast and drenched with their respective supplements and Nilverm every two weeks. Blood samples were taken from all surviving lambs at the end of the experiment. Four lambs from each group were slaughtered for post mortem inspection. Pasture . samples were also collected during the experimental period. (d) Analytical Methods Cobalt levels in pasture were determined by the method of Simmonds (1973). Packed cell volume (PCV) and the concentration of haemoglobin (Hb) in blood were determined by standard clinical methods. Duplicate smears of fresh blood from each lamb were fixed in methanol and stained with Giesma stain and inspected for the presence of Eperythrozoon ovis. III. RESULTS AND DISCUSSION Mean values for the live weight changes of ewes and lambs in Experiment 1 are shown in Table 1. Ewes supplemented with either cobalt or cobalt containing mineral mixture lost significantly less weight (PcO.05) during lactation than did the unsupplemented controls. These 394 TABLE I results suggest that unsupplemented ewes drew heavily on body tissues to meet the demands of lactation, whilst supplemented ewes were able to increase feed intake sufficiently to offset some of these demands. Lambs from supplemented ewes showed significantly higher and more sustained- growth during the post-natal period than did the unsupplemented controls. These differences may be due to either a higher quality and/or quantity of milk production by supplemented ewes thus permitting better growth of their lambs or may indicate that the lambs were receiving sufficient cobalt from the milk to initiate effective fermentation in the rumen and were therefore better able to wean themselves onto pasture when the milk supply from the ewe declined. The live weight changes of lambs from experiment 2 are shown in Fig. 1. Prior to supplement,ation the growth rates of lambs in each group were similar. The live weight of lambs supplemented with cobalt increased throughout the experimental period. During the same time, 52% of the lambs in the control group died and the remaining lambs lost weight. Lambs from the control group appeared listless, usually had pale mucous membranes symptomatic of anaemia and showed respiratory distress when moved with the flock. Post mortem examination,revealed no significant gross or histological abnormalities and death was attributed to malnutrition. Cobalt supplementation did alleviate a normochromic, normocytic. anaemia found in the control group. Mean values (kstandard error) for PCV and Hb in the cob.alt supplemented (n=25) and.the control (n=14) groups were, respectively: PCV (%) 30.4 vs 26.0 (21.2) and Hb (g/l), 106 vs 88 (?4). Both differences were significant (P<O.OS). Anaemia associated with weaner ill-thrift has been related to Haemonchosis, deficiencies of Se, Cu and Co and to the presence of the blood parasite E. ovis (Pulsford, Rat and Irving 1966). In the present experiment, negligib le worm burdens were found (x600 eggs/g faeces) and E. ovis was not detected in blood, indicating that the anaemia found-was primarily due to Co deficiency. Mean levels of cobalt inthe pastures grazed was 0.11+0.02 mg Co/Kg dry matter. 395 IV. CONCLUSIONS The experiments described above clearly demonstrate that the availability of dietary cobalt was limiting the growth and survival of lambs on Pangola grass pastures. The levels of cobalt in pasture . appeared adequate for mature and dry stock, but were inadequate to support more intensive forms of production such as lactation and lamb growth. Even when cobalt supplements were provided growth was relatively poor, suggesting that higher levels and/or more frequent supplementation may be required or that other properties of the pasture were limiting growth. Studies are continuing in this area to define more clearly the factors limiting lamb production from Pangola grass pastures. v. ACKNOWLEDGEMENTS The authors wish to thank Dr. H.M.D. Hoyte, Dept. Parasitology, University of Queensland, for his assistance in the detection of E. ovis and Mr. W.R. Kelly, Dept. Veterinary Preventative Medicine, Unive%iF of Queensland, for the post mortem examination of the lambs. VI. 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