Effects of iodine supplementation on the productivity of Romney ewes in the Wairarapa region of New Zealand

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This article was downloaded by: [Adams State University]On: 03 November 2014, At: 12:16Publisher: Taylor & FrancisInforma Ltd Registered in England and Wales Registered Number: 1072954 Registeredoffice: Mortimer House, 37-41 Mortimer Street, London W1T 3JH, UKNew Zealand Journal of AgriculturalResearchPublication details, including instructions for authors andsubscription information:http://www.tandfonline.com/loi/tnza20Effects of iodine supplementation onthe productivity of Romney ewes inthe Wairarapa region of New ZealandW.J. Parker a & S. N. McCutcheon ba Department of Agricultural and Horticultural SystemsManagement , Massey University , Palmerston North , NewZealandb Department of Animal Science , Massey University , PalmerstonNorth , New ZealandPublished online: 30 Jan 2012.To cite this article: W.J. Parker & S. N. McCutcheon (1989) Effects of iodine supplementation onthe productivity of Romney ewes in the Wairarapa region of New Zealand, New Zealand Journal ofAgricultural Research, 32:2, 207-212, DOI: 10.1080/00288233.1989.10423455To link to this article: http://dx.doi.org/10.1080/00288233.1989.10423455PLEASE SCROLL DOWN FOR ARTICLETaylor & Francis makes every effort to ensure the accuracy of all the information (theContent) contained in the publications on our platform. However, Taylor & Francis,our agents, and our licensors make no representations or warranties whatsoever as tothe accuracy, completeness, or suitability for any purpose of the Content. Any opinionsand views expressed in this publication are the opinions and views of the authors,and are not the views of or endorsed by Taylor & Francis. The accuracy of the Contentshould not be relied upon and should be independently verified with primary sourcesof information. 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Terms &http://www.tandfonline.com/loi/tnza20http://www.tandfonline.com/action/showCitFormats?doi=10.1080/00288233.1989.10423455http://dx.doi.org/10.1080/00288233.1989.10423455Conditions of access and use can be found at http://www.tandfonline.com/page/terms-and-conditionsDownloaded by [Adams State University] at 12:16 03 November 2014http://www.tandfonline.com/page/terms-and-conditionshttp://www.tandfonline.com/page/terms-and-conditionsNew Zealand Journal of Agricultural Research. 1989. Vol. 32: 207-212 0028-8233/89/3202-0207 $2.50/0 Crown copyright 1989 207 Effects of iodine supplementation on the productivity of Romney ewes in the Wairarapa region of New Zealand W.J.PARKER Department of Agricultural and Horticultural Systems Management Massey University Palmerston North, New Zealand S. N. McCUTCHEON Department of Animal Science Massey University Palmerston North, New Zealand Abstract The objective of this study was to examine the effects of iodine supplementation of ewes on their plasma thyroid hormone concentrations and production of ewes and their lambs. The study was conducted in the Wairarapa, a region where apparent subclinical iodine deficiency has been reported. Two groups of 200 Romney ewes, one of which was injected with iodised oil (Lipiodol) 3 weeks before mating, were monitored for 1 year from mating. Thyroxine concentrations were significantly (P < 0.0 1) elevated in the iodine-supple-mented ewes 113 days after treatment. Supple-mented ewes were heavier at mating (P < 0.05) but did not differ significantly from controls in lambing performance, lamb growth rate, or ewe fleece production. Lipiodol was shown to be an effective means of supplementing ewes with iodine, but untreated ewes apparently obtained adequate levels of iodine from plant and soil material ingested. High soil intakes associated with intensive winter rotational grazing are likely to have been responsible for adequate iodine intakes in control ewes. Received 18 August 1988; accepted 17 February 1989 Keywords iodine; thyroid hormones; sheep performance; grazing systems INTRODUCTION In recent years, evidence has been accumulating that sheep in the Wairarapa region may be in a state of subclinical iodine deficiency. The region lies on the west coast of the North Island, isolated from marine influence. Enlarged thyroid glands have been observed in sheep grazing at low stocking rates (and hence with low soil intakes) at the Taratahi Research Station, Masterton (Healey et al. 1972). In an extensive study of lamb mortality at Massey University's Wairarapa property, "Riverside", 11 % of dead lambs were found to have ratios of fresh thyroid weight to bodyweight in excess of 0.46 g/kg (Duff 1981). This is the level above which lambs are considered to be clinically goitrous (Mason 1975). Moreover, 40% of perinatal deaths at "Riverside" were a result of starvation-exposure (Duff 1981). This is an unusually high rate of starvation-exposure mortality given that the overall death rate (lambs dead/lambs born) was 16% which is close to the national average (McCutcheon et al. 1981). Hypothyroid lambs are known to have a poor capacity for body heat production (Alexander 1962) which would make them particularly susceptible to body cooling in cold spring conditions. Thus there may be a connection between low iodine status and high starvation-exposure mortality rates in lambs at "Riverside" and other Wairarapra properties. Supplementation of ewes with iodine can improve performance in situations where subclinical deficiency exists. Responses to iodine supplement-ation have been reported in ewe and lamb liveweight gains, increased ewe fertility and wool production, and improved lamb survival (Coop & Clark 1958; Sinclair & Andrews 1961; Grace et al. 1974; Knights et al. 1979; McGowan 1983). The objective of this study was to examine the effects of iodine supplementation of ewes on their plasma thyroid hormone concentrations and production of ewes and their lambs. Downloaded by [Adams State University] at 12:16 03 November 2014208 New Zealand Journal of Agricultural Research, 1989, Vol. 32 MATERIALS AND METHODS Animals and management Four hundred freshly shorn Romney ewes (aged 18 months) were selected at random from a larger group of commercial ewes at "Riverside", 15 km north-eastofMasterton. Experimental ewes were randomly allocated into two groups (n = 200) and identified by individually numbered eartags. Three weeks before mating, one group received an intramuscular injection of 1 ml/ewe iodised oil (Lipiodol, May and Baker N.Z. Ltd, Wellington). Thereafter, both groups were managed as a single flock for the duration of the trial as part of the normal farming operation. All ewes were vaccinated against campylobacter before mating. Mating started on 8 April. Ewes were joined with harnessed mature Romney rams (1 ram:125 ewes) and harness crayon colours were changed on Days 8, 17, and 34 of mating to monitor oestrous cycle submission rates. Rams were withdrawn after 42 days of mating. Ewe pregnancy status (bearing 0, 1,2, or 3 lambs ) was assessed by realtime ultrasound scanning (Carter 1986) 92 days after the start of mating. Barren ewes were culled. Pregnant ewes were divided into single- and multiple-bearing groups-and set-stocked as lambing commenced. Multiple-bearing ewes were allocated to the most sheltered paddocks. Ewes were shepherded twice daily and lambs weighed and tagged within 12 h of birth. Lambs dying within a week of birth were autopsied, using procedures based on those of McFarlane (1965) and Haughey (1973), to determine the probable cause of death. Ewes and lambs were drenched at docking (on 5 November) with a levamisole-based drench. Ewes and their lambs were recombined into a single flock at docking and remained set-stocked until weaning on 7 December. Fleeceweights and bodyweights All ewes were shorn on 22 December and fleeceweights were measured in a random sample of 50 ewes from each treatment group (balanced for birthrank). Bodyweights of ewes were recorded at the time of iodine injection (i.e., start of the trial), start of mating, pregnancy diagnosis, pre-lambing (i.e., at set-stocking), weaning, and immediately before mating in the following season. A sample bodyweight (c. 100 ewes per treatment) was obtained for ewes and their lambs at docking, for lambs at weaning, and for ewe lambs retained (as potential flock replacements) the following autumn. Selection of ewe lambs retained was at random across the control and iodine-supplemented groups. Blood sampling and thyroid hormone assay Immediately after pregnancy diagnosis, 50 ewes in each treatment group (balanced for pregnancy status - single versus multiple) were blood-sampled. Samples (8 ml) were obtained by jugular venipuncture into pre-chilled vacutainers containing EDT A as the anticoagulant. They were centrifuged at 2000 g and 5C for 20 min. Plasma was harvested and stored at -20C until assay. Concentrations of th yroxine and triiodothyronine in plasma were measured using solid phase radioimmunoassay kits (TKT41 and TKT31 respectively, Diagnostic Products Corporation, California). These kits, which are designed for human diagnostic purposes, were validated forovine samples before use. Serial dilutions of ovine plasma exhibited parallelism with the standard curve in both Table 1 Effects of iodine supplementation and pregnancy status of ewes on circulating thyroxine and triiodothyronine concentrations (Mean SE) at pregnancy diagnosis. Treatment (T): Control + Iodine Significance Pregnancy status (S): Single" Multiple Single Multiple T S TXS Number 25 24 24 23 Thyroxine (Jlg/dl) 4.8 0.2 4.5 0.3 5.3 0.3 4.8 0.3 * NS NS Triiodothyronine (ng/dl) 72.7 4.5 79.1 4.3 82.2 6.080.0 5.0 NS NS NS " Pregnancy status as assessed by ultrasound diagnosis and subsequently confIrmed at lambing. * = p < 0.05; NS = not significant. Downloaded by [Adams State University] at 12:16 03 November 2014Parker & McCutcheon-Effects of iodine supplementation on Romney ewes 209 kits. Internal recoveries of added standards averaged 100% (thyroxine) and 95% (triiodothyronine). The thyroxine assay had a linear range of 1-24 Jlg/dl, intra-assay coefficient of variation (CV) of 7.6%, and inter-assay CV of 9.7%. Corresponding para-meters for the triiodothyronine assay were 20--600 ng/dllinearrange, 9.7% intra-assay CV, and 11.3% inter-assay CV. For each hormone, all samples were run in a single assay. Statistical analyses Analyses of variance were used to compare treatment effects on ewe liveweight (with pre-treatment liveweight as a covariate) and lamb birth weight and growth rates (corrected for birth rank and sex). Effects of treatment and pregnancy status on plasma hormone concentrations were also assessed by ANOV A using liveweight at pregnancy diagnosis as the covariate. Birth rank data were cross-tabulated and tested by chi-square analysis. All analyses were performed using the SPSSX statistical package (SPSSX 1985). RESULTS Plasma hormone levels Table 1 shows the effects of treatment and pregnancy status on plasma hormone concentrations. Concentrations of thyroxine at the time of sampling (113 days after Lipiodol administration) were significantly (P < 0.05) elevated by supplementation but there was no significant effect on triiodothyronine concentrations. Circulating thyroid hormone concen-trations were not influenced by whether the ewes were carrying singles versus multiples, or by their liveweight at the time of sampling. Table 2 Effects of iodine supplementation of ewes on predicted pregnancy status of ewes at ultrasound pregnancy diagnosis 92 days after the start of mating. Number of foetuses Control + Iodine Total 0 6 ( 3.1)" 12 ( 6.1) 18 (4.6) 89 (46.1) 95 (48.2) 184 (47.2) ~2 98 (50.8) 90 (45.7) 188 (48.2) Totals 193 197 390 r} = 2.495, 2 d.f., NS " Nos in parentheses are percentages within columns. NS = not significant. 68 64 en 60 :OS E OJ 56 a; >: I ill > 52 ~ 48 44~~~-+~--~+-~~-+~~~+-~~ FMAMJJASONDJFMA Month Fig. 1 Mean liveweights of control (*-*) and iodine-supplemented (+--+) ewes. (All SEM are < 0.41 kg.) Table 3 Effects of iodine supplementation of ewes on lambing performance. Ewes joined to ram Ewes present at lambing Barren ewes/ewes joined (%)b Ewes lambing/ewes joined (%) Lambs bom/ewes lambing (%) Distribution of litter sizes Single Twin Triplet Lambs dead/lambs born: First 7 days (%) 8 days to docking (%) Ewes pregnant but failing to rear lamb/ewes lambing (%) Lambs docked/ewes joined Control 200 183 3.0 88.5 154.2 82 94 1 7.7 2.6 7.3 122.5 + Iodine" 199 176 3.5 84.5 152.7 81 87 1 7.8 3.9 10.7 114.6 " All treatment effects not significant (P > 0.10). b Ewes not pregnant at lambing but previously diagnosed as being pregnant 92 days after the start of mating. Ewe bodyweights Iodine-supplementedewes were significantly heavier than control ewes at mating (P < 0.05), mid preg-nancy, and lambing (P < 0.10) (Fig 1). Differences between the treatment groups were not significant at docking but the iodine-supplemented group gained more weight through to weaning. At the following mating, iodine-supplemented ewes were 1.7 kg heavier than controls (P> 0.10). Reproductive performance Submission rates were similar in both groups, 93 and 92% of control and iodine-supplemented ewes being Downloaded by [Adams State University] at 12:16 03 November 2014210 New Zealand Journal of Agricultural Research, 1989, Vol. 32 marked as mated during the first two cycles. However, 6% more iodine-supplemented ewes were mated during the first 7 days, resulting in the mean lambing date for this group being 1 day earlier than that of the controls (P > 0.10). Ultrasound scanning showed no difference (P> 0.10) in pregnancy status, although twice as many iodine-supplemented ewes as controls were predicted to be not pregnant (Table 2). A further 3.2% of ewes were not pregnant at lambing, giving an overall non-pregnancy rate of 7.8% of ewes joined with the ram (controls 6.5%, iodine-supplemented 9.0%). Table 3 gives lambing performance data. Performance of the ewes was generally superior to that experienced in recent years, partly because of the c. 7 kg bodyweight gain during flushing (Fig. 1) but also because of the settled mild conditions at lambing. None of the measures of reproductive performance was significantly influenced by iodine supplementation. Control ewes docked 7.9% more lambs per ewe joined but neither the number of lambs born nor the distribution of birth ranks were affected by treatment (X2:0.09, 2 dJ., P > 0.10, n = 346 births). Lamb birthweights, mortality, and growth rates Lamb birthweights were collected on 160 singles, 171 sets of twins, and one set of triplets during lambing. This included 38 lambs which died at or soon after birth, leaving 27 lambs (out of 531 born) on whom weights were not obtained. Birthweights were not influenced by iodine supplementation (P> 0.10) but were different between singles and twins (P < 0.001) and between ram and ewe lambs (P < 0.001, Table 4). Of the 41 lambs found dead in the lambing paddocks within 7 days of birth, 38 (18 controls, 20 iodine-supplemented) were in suitable condition for autopsy. Half of the lamb deaths in each treatment were attributed to starvation-exposure. Average birthweightofthese lambs was 2.44 kg, considerably lower than that of their surviving contemporaries (Table 4). Dystocia was deemed responsible for 33 and 20% of lamb deaths in the control and iodine-supplemented groups, respectively. Average weight of these lambs was 3.80 kg. Table 4 Effects of iodine supplementation of ewes and birthrank and sex of lambs on lamb birth weights and growth rates from birth to docking or weaning. Daily gain (g/day) from birth to: Birth weight Treatment Sex Rank (kg) Dockinga Weaning Control Male Single 4.61 0.11 261 17 227 15 (39)b (11) (11) Multiple 3.71 0.07 171 9 174 6 (87) (31) (29) Female Single 4.190.10 255 14 222 6 (40) (13) (15) Multiple 3.33 0.06 165 8 149 5 (95) (28) (40) +Iodine Male Single 4.47 0.14 280 18 243 7 (38) (12) (14) Multiple 3.61 0.07 176 8 180 6 (82) (21) (23) Female Single 4.35 0.15 247 14 204 10 (43) (15) (14) Multiple 3.30 0.08 17211 155 6 (81) (22) (30) Effects: Treatment NS NS NS Sex *** * ** Rank *** *** *** a Growth rates to docking based on 153 lamb sample weighed at birth and at docking. b Number of lambs per group. * = p < 0.05; ** = p < 0.01; *** = P < 0.001; NS = not significant. Downloaded by [Adams State University] at 12:16 03 November 2014Parker & McCutcheon-Effects of iodine supplementation on Romney ewes 211 Lambs were weaned at an average age of 82 days. Average daily liveweight gain from birth to weaning was not influenced by treatment (Table 4). Single and ram lambs grew faster than twin or ewe lambs respectively, but there were no interactions between the effects of rank or sex and those of iodine supplementation. Similarly, no effect of treatment was apparent on growth rates from birth to docking in the sample of 170 lambs weighed at docking. Bodyweights of retained ewe lambs in the following autumn (mid April) were identical in the control (36.9 0.5 kg, n = 45) and iodine-supplemented (36.9 0.6 kg, n = 51) groups. Ewe wool production No improvement in wool production was found in the iodine-supplemented ewes (3.39 0.6 kg) compared with the controls (3045 0.7 kg,P > 0.10). Single-bearing ewes in both treatments produced 004 kg more wool than their twin-bearing counterparts (P < 0.001). DISCUSSION Administration of a single dose of LipiodolThe elevated iodine status of the supplemented ewes and their small (1.3 kg) liveweight advantage at mating, did not improve lambing performance. However,lambing percentage increases of 8-10% in ewes supplemented with LipiodolFavourable climatic conditions during lambing reduced perinatal lamb mortality to an unusually low level but no marked change in the cause of death was apparent in the progeny of the iodine-treated ewes. A 45% increase in lamb survival in ewes treated with iodine and grazing kale during the last trimester of pregnancy was obtained by Sinclair & Andrews (1961). Kale has a goitrogenic effect and, although clover may produce a similar effect (Flux et al. 1956), New Zealand pastures rarely have suffIcient clover during winter and spring to induce hypothyroidism in lambs. No increases in lamb birthweights, or in lamb growth rates to docking and weaning, were obtained in the progeny of the supplemented ewes, although it is likely that higher plasma iodine levels in the ewes would have been associated with increased milk concentration of iodine (Caple et al. 1982). These results therefore suggest that the untreated ewes were ingesting adequate levels of iodine to meet the requirements of foetal growth, lactation, and wool production. The high stocking rate (500-1000 ewes/lm per day) rotational grazing system adopted at "Riverside" from the end of mating to the start of lambing has probably contributed to increased ingestion of soil iodine (Healey et al. 1972), in comparison to the less intensive set-stocking grazing systems that have historically been adopted by most Wairarapa sheepfarmers. This form of grazing management was not adopted at "Riverside" until the year following the lamb mortality study by Duff (1981) and may explain why a high incidence of enlarged thyroids was observed during the 1980 lambing. Rotational grazing with low residual levels is an inexpensive and practical method of eliminating the effects of marginal iodine defIciencies where background levels of iodine are at medium-high concentrations. Healey et al. (1972) postulated that variable responses to iodine would occur between seasons according to the level of pasture production and hence intensity of grazing. The results of Caple etal. (1982), and the equivocal responses obtained in other iodine supplementation studies (Millar & Albyt 1985), support this hypothesis. However, if environmental iodine levels are low, such as those encountered by Knights et al. (1979), in Queensland, artifIcial supplementation of iodine will be required. This trial has demonstrated that LipiodolACKNOWLEDGMENTS We thankN. andP. Kilminster for collection oflamb birth weight and mortality data analysis. Downloaded by [Adams State University] at 12:16 03 November 2014212 New Zealand Journal of Agricultural Research, 1989, Vol. 32 REFERENCES Alexander, G. 1962: Temperature regulation in the newborn lamb. V. Summit metabolism. Australianjournal of agricultural research 13: 100-12l. Coop, I. E.; Clark, V. R.1958: The effect of thyroxine on wool growth and lamb production. New Zealand journal of experimental agriculture 1: 365-38l. Caple, I. W.; Nugent, G. F.; Azuolas, J. K.; Foot, J. Z; Thompson, R. L. 1982: Effects of iodine supplementation of ewes on survival and growth of lambs. Proceedings of Australian Society of Animal Production 14: 535-538. Carter, M. L. 1986: Pregnancy diagnosis of ewes using realtime ultrasound imaging. Proceedings of Sheep and Beef Cattle Society of the New Zealand Veterinary Association 16th seminar: 105-118. Duff, X. J. 1981: An investigation of perinatal lamb mortality in a flock of Romney ewes in the Wairarapa district of New Zealand. Riverside Farm publication no. 4, Massey University. Grace, N. D.; Maunsel, L. A.; Scott, D. 1974: Growth responses of ewe hoggets supplemented with Se, Cu, Co and I in the Lake Ohau area. New Zealand journal of experimental agriculture 2: 99-102. Flux, D. S.; Butler, G. W.; Johnson, J. M.; Glenday, A. C.; Peterson, G.B.1956: Goitrogenic effects of clover. New Zealand journal of science and technology 38A: 88-102. Haughey, K. G. 1973: Vascular abnormalities in the central nervous system associated with perinatal lamb mortality. I. Pathology. Australian veterinary journal49: 1-8. Healey, W. B.; Crouchley, G.; Gillet, R. L.; Rankin, P. C.; Watts, H. M. 1972: Ingested soil and iodine deficiency in lambs. New Zealand journal of agricultural research 15: 778-782. Knights, G. E.; O'Rourke, P. K.; Hopkins, P. S. 1979: The effects of iodine supplementation of pregnant and lactating ewes on the growth and maturation of their offspring. Australian journal of experimental agriculture and animal husbandry 19: 19-22. Mason, R. W. 1975: Congenital goitre in lambs. Proceedings of a workshop onperinatal mortality in farm animals; Prospect, N.S.W., Australia: 63-66. McCutcheon, S. N.; Holmes, C. W., McDonald, M. F. 1981: The starvation-exposure syndrome and neonatal lamb mortality: A review. Proceedings of N ew Zealand Society of Animal Production 41 : 209-217. McFarlane, D. 1965: Perinatal lamb losses. I. An autopsy method for the investigation of perinatal losses. New Zealand veterinary journal 14: 137-144. Millar, K. R.; Albyt, A. T. 1985: EvaluationofR.1. A. kits for the measurement of thyroid hormones in sheep and cattle sera. New Zealand veterinary journal 33: 116-117. McGowan, A. C. 1983: The use of 'Lipiodol' for sub-clinical iodine deficiency in livestock. Proceedings of New Zealand Society of AnimalProduction43: 153-136. Sinclair, D. P.; Andrews, E. D. 1961: Deaths due to goitre in new-born lambs prevented by iodized poppy-seed oil. New Zealand veterinary journal 9: 96-100. SPSSX (1985) SPSSX User's Guide (Second ed.). New York, McGraw-Hill. Downloaded by [Adams State University] at 12:16 03 November 2014


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