Introduction

1. An Economic Evaluation of the Main Factors Affecting Fertility of Scottish Beef Suckler Herds. • A. Varo Barbudo1, A.W. Stott1 and G.J. Gunn2 1Scottish Agricultural College (SAC), Aberdeen; 2 SAC Epidemiology Research Unit, Inverness Telephone - 0044 (0)1224 711245 Facsimile - 0044 (0)1224 711270; e-mail - Antonio.Varo@sac.ac.uk Numerical Specifications • Conception rates represent the probability of cows conceiving at the first, second, third or successive oestrus after parturition. They are modified to represent the effect of each factor on the reproductive performance of the herd. Introduction • In Scotland, 70% of the national herd is comprised of beef suckler cows. In this type of production system fertility is the major determinant of production efficiency. Fertility is affected by both infectious agents (e.g. bovine viral diarrhoea virus (BVDV) and Campylobacter spp.) and managerial factors (e.g. length of breeding season, feeding and bull performance). These factors produce financial losses due to failure to conceive, abortions, increase in culling rate for infertility, decrease in live-weight of calves and heterogeneity at sales (Figure 1). This poster examines the impact that BVDV, acting in isolation from the other factors, has on fertility in beef suckler herds in marginal farming areas of Scotland. Results • Feeding management was found to be the most important factor diminishing the financial performance of suckler herds (Figure 3). The simulations showed that the gross margin is diminished by 25%, from £191/cow to £143/cow, between the two optima as a result of the application of an adequate and a poor feeding regime, which is denoted by cows being in body condition score (BCS) 3 and 2 respectively at parturition. Figure 3. Optimal length of the breeding season. Figure 1. Schematic representation of the effects on fertility of certain factors The effect of poor bull performance is markedly increased by the employment of a short length of breeding season (Figure 4). Method Figure 4. Gross Margins (£/cow) of a typical Scottish suckler enterprise as a result of alternative reductions in bull fertility. A Markov chain model of a suckler herd, based on the cow's reproductive cycle, was used to create data on the reproductive performance of beef suckler herds. These were then used to assess the impact on enterprise gross margin of alternative management practices and/or disease that affect fertility. Figure 2: Markov-chain model structure • The proportion of animals infected by BVDV and hence the reproductive performance of the herd will vary over time as the epidemic progresses. This aspect was estimated using the model of Gunn et al. (2004) (Vet.J.167:143-149) which then provided inputs for the estimation of reproductive performance and gross margins using the model reported here (Figure 5). The financial impact of this one disease on fertility (187-144=£43, Fig 5) is similar to that of body condition score (BCS) (191-143=£49, Fig 3). Figure 5. Expected gross margins resulting from herd reproductive performance indicated at different stages in a 10-year simulated BVDV epidemic in a typical Scottish beef suckler herd. • Each state vector of the model represents the distribution of cows (and heifers) of a suckler herd at different reproductive states, i.e. “oestrus, pregnancy, calving and postpartum; infertility, pre-culling” (Figure 2). A dynamic transition matrix of probabilities determines the reproductive development of the herd. Numerical Specifications The numerical specifications were obtained from a survey amongst Scottish beef suckler farmers (n=106) and different published sources. The main specifications were: • All calves are sold October 1st. • Herd size (cows) 56 • Length breeding season (days) between 42 and 147 • Onset breeding season (date) 9th May • Store cattle price (£/kg LW) 1.1 males (0.98 females) • Replacement costs (£) 750/heifer • Post-partum interval (days) 60/90 • Pre-CAP reform subsidies (£/cow) 196. Conclusions • These results highlight the importance of good management of fertility in achieving sustainable beef suckler farming in marginal rural areas of Scotland and the considerable impact that diseases such as BVD can make via impaired fertility. Acknowledgements • This work is funded by the Scottish Executive Environment and Rural Affairs Department.