The impact of predation on a sheep enterprise in the Free State Province
Strauss, Andries Jacobus
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The Free State Wool Sheep Project was initiated in 1998 at the Glen Agricultural Institute (AI) and a selection of 280 of the available Merino ewes were randomly divided in the following four production system treatments, namely: · Treatment SL-V(C) Spring Lambing season on Veld with a salt (NaCl) lick only (control) · Treatment SL-V&S Spring Lambing season on Veld with Supplementary feeding · Treatment SL-R&V Spring Lambing season on irrigated Rye-grass (Lolium multiflorum and L. perenne) and veld · Treatment AL-O&V Autumn Lambing season on Oats (Avena sativa) pasture in winter and Veld in summer and spring The broad aim of the Free State Wool Sheep Project was to “develop profitable and sustainable wool farming systems on the resource combination of Glen AI”. However, it was not foreseen at the conceptualization of the Project in 1998 that the impact of predation, mostly by black-backed jackal Canis mesomelas on the sheep flocks at Glen AI would soon reach the high levels experienced in later years. A Merino shearing flock (77 ewes in 2003) and a Dorper flock (219 ewes in 2003) at the Glen AI were also severely impacted by predation. These two flocks were managed in the same way as the Merino ewes in Treatment SL-V(C), therefore, it was decided to include the results of these two flocks also in this study. The impact of predation on reproduction and production performance of sheep flocks (Merino and Dorper) are reviewed and put into perspective for the period 1999 to 2007. Four categories of sheep losses were identified namely: predation, diseases, metabolic disorders or accidents and stock theft. Direct financial losses, veterinary and shearing cost, lick, labour and planted pasture cost were calculated for each of these categories of losses. The calculations were included in the review and served as basis for determining the extent to which financial losses ascribed to predation exceeded the financial losses due to diseases, metabolic disorders or accidents and stock theft. Ewe productivity was negatively influenced by predation. The Merino and Dorper flocks decreased in numbers from 1 130 sheep to 552 sheep over a period of nine years. From 1999 until 2007, a total of 747 lambs were lost to predation before weaning and a total of 1 422 lambs were lost post weaning. The number of reproductive Merino and Dorper ewes that were available for mating declined from 506 ewes in 2003 to 316 ewes in 2007. Some of the ewes in the four Merino production system flocks, the shearing flock, and the Dorper flock could not raise one lamb in a six-year production cycle due to predation. Therefore, it became increasingly difficult to replace older ewes and maintain flock sizes for the respective flocks. The only exception was the Treatment SL-R&V flock, because they were better protected from predation during critical phases in the reproduction cycle. The black-backed jackal specifically, had a big impact on the sheep flocks at the Glen AI (70% of the 730 post-weaning losses from 2003 until 2007). Losses ascribed to predation contributed to 72% of the total annual financial losses, diseases 2%, metabolic disorders or accidental mortalities 20% and stock theft only 6%. Therefore, the financial impact ascribed to predation at an average of R129 562/year overshadowed the losses due to diseases (average R4 337/year), metabolic disorders or accidents (average R35 299/year) and stock theft (average R9 843/year) by a considerable margin. The negative impact of predation on the sheep flocks at the Glen AI made it impossible to evaluate the economical viability and sustainability of the Merinos in the different treatment flocks as envisaged in the protocol of the Free State Wool Sheep Project. Furthermore, a large component of the genetic base of the two sheep breeds at the Glen AI has been lost for the future, due to the effect of predation. An urgent and concerted approach of all role-players in the sheep industry is needed to develop and implement effective predator management programmes to reduce the negative impact of predation.
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