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Optimizing Replacement Decisions for Finnish Dairy Herds

Optimering av rekryterinsbeslut in finska mjölkbesättningar

Abstract

The purposes of the study were to determine how “an optimal herd” would be structured with respect to its calving pattern, average herdlife and calving interval, and to evaluate how sensitive the optimal solution was to changes in input prices, which reflected the situation in Finland in 1998. The study used Finnish input values in an optimization model developed for dairy cow insemination and replacement decisions. The objective of the optimization model was to maximize the expected net present value from present and replacement cows over a given decision horizon. In the optimal solution, the average net revenues per cow were highest in December and lowest in July, due to seasonal milk pricing. Based on the expected net present value of a replacement heifer over the decision horizon, calving in September was optimal. In the optimal solution, an average calving interval was 363 days and average herdlife after first calving was 48.2 months (i.e., approximately 4 complete lactations). However, there was a marked seasonal variation in the length of a calving interval (it being longest in spring and early summer) that can be explained by the goal of having more cows calving in the fall. This, in turn, was due to seasonal milk pricing and higher production in the fall. In the optimal solution, total replacement percentage was 26, with the highest frequency of voluntary culling occurring at the end of the year. Seasonal patterns in calving and replacement frequencies by calendar month and variation in calving interval length or herdlife did not change meaningfully (<1%–2% change in the output variables) with changes in calf, carcass or feed prices. When the price of a replacement heifer decreased, average herdlife was shorter and replacement percentage increased. When the price increased, the effect was the opposite.

Sammendrag

Meningen med denna studie var att bestämma strukturen i en ‘optimal besättning’, gällande kalvningsmönster, besättningens medellivslängd och kalvingsintervall samt art evaluera hur känslig denna optimala lösning var för förändringar i inputpriser, som reflekterade situationen i Finland år 1998. Studien utnyttjade en optimeringsmodell, utvecklad som beslutstöd for inseminering och rekrytering av mjölkkor, med finska inputvärden. Syftet med den dynamiska programmeringsmodellen var att maximera det väntade rådande nettovärdet av existerande och rekryteringskor över en bestämd beslutshorisont.

I den optimala lösningen var medelnettoinkomst per ko högst i december och lägst i juli, p.g.a. årstidsberoende prissättning av mjölk. Gällande det väntade rådande nettovärdet av kontant inkomst från en rekryterad kviga, var den bästa tiden för hennes kalvning i september. I den optimala lösningen var besättningens medellivslängd efter första kalvning 48.2 månader, vilket motsvarar ungefär 4 hela laktationer, och medeltalet för kalvningsintervallet var 363 dagar. Dock syntes en tydlig variation mellan årstider i kalvningsintervall (intervallet var längst på våren och under tidig sommar), som kan förklaras av en strävan till flera kalvningar på hösten. Detta, i sin tur, berodde på en högre produktion samt årstidsberoende prissättning av mjölk. I den optimala lösningen var den totala rekryteringsprocenten 26, den högsta frekvensen av frivillig utmönstring sågs i slutet av året och de flesta kalvningarna på hösten. Månatliga säsongsmönster i kalvnings- och rekryteringsfrekvenser och variation i kalvningsintervallens längd eller besättningenslivslängd påverkades inte betydelsefullt av förändringar i kalv-, slaktkropps- eller foderpriser. När priset på rekryterinskvigor minskade var besättningens medellivslängd kortare och rekryterinsprocenten högre. När priset ökade var effekten den motsatta.

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Rajala-Schultz, P.J., Gröhn, Y.T. & Allore, H.G. Optimizing Replacement Decisions for Finnish Dairy Herds. Acta Vet Scand 41, 185–198 (2000). https://doi.org/10.1186/BF03549650

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