USING A BIOECONOMIC MODEL FOR ESTIMATION OF ECONOMIC IMPORTANCE OF SOW REPRODUCTIVE TRAITS

Economic weights of sow reproductive traits were estimated by means of a bioeconomic model of pig nucleus herd (programme EPOS, Houska et al ., 1992). The estimation was done on the basis of the simulation of di fferent levels of litter size, number of days till 1st conception, far rowing interval, number of heats per conception and the number of inse mination doses (ID) per conception. The influence of the level of the above mentioned observed traits on the costs in sows per all sows' lif etime and on the costs per sow/year, resp., was tested. Costs per sow are reflected both in costs per piglet till weaning and in costs per w eaner (till 30 kg of liveweight). Profit change in weaners produced pe r sow/year while changing the level of only one tested trait was used as a criterion of economic efficiency of the herd. Economic weight was then expressed as a regression of profit on the unit of performance. Litter size at weaning (correlated with litter weight) was observed at four levels, differences between them being one piglet converted to h erd average with respect to parity. Tab. I shows the influence of litt er size at weaning on costs and profit in weaners. Costs per piglet ti ll weaning and costs per weaner till 30 kg of liveweight display a dec reasing tendency while average litter size at weaning increases. Avera ge costs per sow/year are constant because of the same length of sow s tay in a herd. Profit per weaners produced on average per sow/year (y) increased by 1,380.32 Czech crowns with an increase in litter size at weaning (x) by a piglet according to the regression equation y = -8,7 02.66 + 1,380.32 x. We can consider this value as economic weight of l itter size at weaning. Four levels of age of gilts at first conception (matching the variability of dam breeds in the Czech Republic) were u sed. The relation between the age at first conception and longevity an d culling rate at 1st to 5th parity, resp., were considered at the sam e time. The influence of age of gilts at first conception on costs and profit in weaners is shown in Tab. II. Profit for weaners sold (conve rted per sow/year) (y) decreases with increasing age at first concepti on of sows (x), which shows the regression equation y = 2,619.95 - 6.8 6 x. Four levels of farrowing interval, differing in the level of the first litter by 10 days (160-190 days), were used. In this case the re lation between average length of farrowing interval and parity was con sidered. Tab. III describes the influence of farrowing interval length on costs and profit in weaners. It is clear from regression equation y = 4,536.66 - 22.30 x that profit for weaners sold (converted per sow /year) (y) decreases by 22.30 Czech crowns with an increase in the ave rage length of farrowing interval (x) by a day. Tab. IV demonstrates t he influence of the number of heats realized till conception of the so w on costs and profit in weaners. The consequence of repeated heats is a different number of ID used for conception of sow. So costs per sow /year, costs per piglet till weaning and costs per weaner increase. Th e regression equation for determination of profit for weaners sold per sow/year (y) as influenced by percentage of sows conceived at first h eat (x) is as follows: y = 311.00 - 7.33 x. Tab. V describes the influ ence of ID number within a heat on costs and profit in weaners. Profit for weaners sold (converted per sow/year) (y) decreases with an incre ase in costs per sow/year caused by the higher number of ID within a h eat (x), according to the regression equation y = 1,483.71 - 252.45 x. Described regression equations evaluating the change in profit with t he change in age at the first conception and the change in farrowing i nterval were calculated at litter size of seven piglets. With the high er average litter size regression coefficients somewhat increase becau se of increasing profit for weaners sold per year (Tab. VI). Regressio n does not change itself in the observed breeding disposals (the perce ntage of sows conceived at the 1st to 4th heat, the number of ID used for conception of the sow) because the number of weaners per sow/year does not change itself either.