Developing effective sheep mineral supplementation strategies in Ireland

Minerals perform many important functions in the body with a mineral imbalance having detrimental effects on the performance, fertility, health and profitability of livestock. Co is of particular importance in sheep with even marginal deficiencies leading to poor animal performance. Therefore, there is a need for appropriate effective and sustainable mineral supplementation strategies for grass based sheep systems. The aims of this thesis were to generate new information on the prevalence of mineral deficiencies, current supplementation practices and the response to mineral supplementation in flocks grazing pastures, thus enabling evidence based decisions on mineral nutrition of ewes and lambs. A survey (consisting of 22 questions, and administered to all farmers with a sheep enterprise participating in the Teagasc National Farm Survey (NFS)) was undertaken with the aim of establishing the mineral and vitamin supplementation practices on Irish sheep farms and farmer’s knowledge and opinions in relation to supplementation strategies and mineral deficiencies. Sixty-nine percent of respondents supplemented their flocks with mineral and vitamins in addition to concentrate feed. Supplementation is not evidence based, with only 22% having supplemented based on laboratory analysis results and 13% based on veterinary advice. Generic mineral and vitamin products were the most commonly used followed by Co only products. Forty-six percent of farmers claimed to have limited or no education/knowledge on mineral requirements of sheep. The mineral concentration of herbage, and its variation throughout the grazing season on pastures grazed by sheep were evaluated on 56 farms with a lowland-sheep enterprise. The mean herbage trace mineral concentrations for each farm were compared with dietary requirements of dry ewes and lambs as specified by the National Research Council (NRC, 2007) in order to determine the prevalence of trace mineral deficiencies. The trace mineral status of lambs was classified based on the mean value of all individual lamb blood samples and were compared to diagnostic criteria. Month of sampling had an effect on the concentrations of Co, Cu, I, Zn, Se and Mn with highest concentrations generally occurring in the spring and autumn months, with the exception of Mn. Eighty, 73, 23 and 11% of farms were considered to be deficient for I, Co, Se and Zn, respectively. While 89 and 55%, respectively, were classified as marginal for Se and Zn. Herbage Cu and Mn supply met the dietary requirements of ewes and lambs on all farms. Sixty four and 67% of the lambs blood sampled were considered to be of deficient or marginal status for plasma Co and Vitamin B12, respectively while 69 and 46% of lambs were of deficient or marginal status for plasma Zn and Se, respectively. The effects of supplementing ewes with Co, and of the method of supplementation, on ewe performance, and on the performance of their progeny were evaluated in a 2-year study. Supplementation with Co, via drench or bolus, increased the concentrations of both Co and vitamin B12 in ewe plasma. Supplementation with Co or the method of administration had no effect on ewe BW or BCS, litter size, total lamb mortality, number of lambs reared per ewe joined, or on lamb BW at birth or weaning. The effects of supplementation with Co or vitamin B12, frequency of supplementation (drench administered at 1, 2, 3 or 6 week intervals) and method of administration (drench or ruminal bolus containing Co only) on blood Co and vitamin B12 concentrations in weaned lambs were evaluated. Supplementation with Co was more effective than drenching with vitamin B12 in terms of the effect on plasma B12 concentration. Drenching at weekly or biweekly intervals resulted in higher plasma vitamin B12 concentrations than drenching at intervals of 3 or 6 weeks. The bolus was effective in increasing plasma vitamin B12 concentration and preventing deficiency. The outcomes of this thesis includes an insight into the mineral supplementation practices undertaken on Irish sheep farms as well as the knowledge and opinions of sheep farmers in relation to mineral deficiency and supplementation practices. This thesis also provides new information on when supplementation may be required during the grazing season and what minerals may be inadequate from herbage on Irish sheep farms. The thesis also demonstrated the efficacy of method (drench and bolus) and type (Co and vitamin B12) of supplementation for ewes and weaned lambs grazing pasture. Overall, this thesis provides new knowledge towards the development of effective and sustainable mineral supplementation strategies for grass based sheep systems