10/6/2015. Markov decision process: Case example. Optimal management of replacement heifers in beef herd. Age, body weight, season Late breeding

Transcription

1 Polish beef industry Markov decision process: Case example Optimal management of replacement heifers in beef herd Anna Helena Stygar Department of Large Animal Sciences University of Copenhagen Where is a problem?? Early breeding Age, body weight, season Late breeding The goal of work? The objective of this study was to develop a multi-level hierarchic Markov model to determine the economically optimal management strategy for the replacement beef heifers. 3 Material and methods data Material and methods data from the herd The mean and limit values were estimated on the basis of the empirical data representing the Limousin cattle population in Poland ( Limousin heifers born between 1991 and 2008) and on the literature review. The main data set, used for the estimation of model parameters, was obtained from the Polish Association of Beef Cattle Breeders and Producers (PABCBP). The following data were collected: heifer identification number, date of birth, birth weight, standardized on 210th day body weight, body weight at first calving, date of first and subsequent calvings, calves' sex, birth weight and standardized on 210th day body weight of the first and subsequent calves. 1

2 Number of heifers Empirical data Number of heifers Percentage Empirical data Heifers born between 1991 and 2008 Percentage Cows and heifers in Season 1 Season 2 Season 3 Season 4 Season 1 Season 2 Season 3 Season 4 Age (months) Body weight (kg) Fig. 1. The distribution of the age and body weight at conception of the Limousin heifers born in Poland between 1991 and 2008, based on data from PABCBP Season 1: February, March, April; Season 2: May, June, July; Season 3: August, September, October; Season 4: November, December, January. Fig. 2. The distribution of the conception seasons of Limousin females in Poland, based on data from PABCBAP Stage I Stages and statesin the model Stage II Heifer management as a sequential problem State II Stage III Stage IV State I Age, body weight, season State III State IV The optimized decisions concerned: feeding level during the pre-puberty period, time of weaning, feeding level during the reproductive period and age, body weight and season at conception. The uncertainty in the model was represented by the involuntary disposal probability, the probability of attaining body weight gain, the probability of onset of puberty and the probability of conception. 2

3 The objective function was set to maximise the average net returns per heifer inserted. Revenues were derived either from the predicted future profitability of a replacement (pregnant) heifer or from the value of culled heifer sold on a live weight basis. MLHMP Platform The costs in heifer rearing included: the cost of replacement, feeding costs, breeding and veterinary treatment costs, direct labor costs. MLHMP Platform in JAVA The value of objective function and the values of decision variables (e.g. age at weaning and breeding, body weight at breeding) were observed for different: weaning strategies, varied breeding costs, probability of conception, feed costs, 3

4 slaughter prices, varied rearing conditions: decrease in ADG during the pre-puberty period traditional target breeding weight - breeding decision only for heifers that exhibit estrus and reached 65% of mature body weight, the alternative use of breeding methods (AI, NS) throughout a year Short break!!! After the break we will be downloading model and working with it Downloading beef heifer model Downloading beef heifer model Model can be dowloaded from: Installing and removing plug-in How it could look on your computer 4

5 How it could look on your computer How it could look on your computer Tasks after installing : Time to look on results!! Calculate optimal policy Find average net return per heifer Check the result table Calculate sub-optimal strategy Breeding possible only for heifers with BW > 330kg Simulation Calculate average BW at conception Calculate average age at conception Results: Month of Results birth I II III IV V VI VII VIII IX X XI XII Average Optimal month and age (mo) at weaning Optimal age at conception (mo) Optimal body weight at conception (kg) ADG from birth to conception (g) Average net return per heifer (PLN) Average net return per heifer (EUR) X XI XII I II III X (3) V VI VII VIII IX - 14,4 13,0 12,9 12,8 12,8 13,4 11,0 18,2 15,6 15,2 16,7 14,5 13, , Results Percentage Season 1 Season 2 Season 3 Season 4 Season 1: February, March, April; Season 2: May, June, July; Season 3: August, September, October; Season 4: November, December, January. Fig. 5. The distribution of heifer breeding seasons under the optimal rearing strategy 5

6 Average age at conception (mo) Average body weight at conception (kg) Baseline ADG decreased by 200 g/d Breeding weight 65% of average mature body weight AI scenario NS scenario 13,2 15,7 16,5 13,5 13,5 361,7 352,0 446,6 367,5 347,6 ADG during rearing period (g) Average net return / heifer (PLN) Average net return / heifer (EUR) Average breeding costs (PLN) 183,5 183,6 181,5 208,5 178,7 Average breeding costs / heifer (EUR) 44,1 44,1 43,6 50,1 43,0 Average rearing costs (PLN) 2264,4 2373,8 2510, , Average rearing costs / heifer (EUR) 544,3 570,6 603,6 573,0 564,9 The feed costs The slaughter prices Baseline +20% -20% +20% -20% Average age at conception (mo) 13,2 13,0 13,2 13,2 13,0 Average body weight at conception (kg) 361,7 352,6 367,9 368,1 350,9 ADG during rearing period (g) Average net return / heifer (PLN) Average net return / heifer (EUR) 311,6 165,6 460,8 604,3 22,9 Average breeding costs (PLN) 183,5 193,6 177,0 177,2 193,2 Average breeding costs / heifer (EUR) 44,1 46,5 42,5 42,6 46,4 Average rearing costs(pln) 2264,4 2575,3 1857,5 2190,7 2233,0 Average rearing costs / heifer (EUR) 544,3 619,1 446,5 526,6 536,8 Conclusions 1450 Strategies Non-optimal - weaning at the beginning of November Optimal - weaning after 9 months of suckling PLN (339.3 EUR) Average net return in PLN (EUR)/ heifer PLN (315.3 EUR) PLN (318.5 EUR) PLN (323.6 EUR) PLN (328.9 EUR) PLN (332.5 EUR) The economic efficiency of beef cattle operations can be considerably improved by breeding heifers as yearlings, however the optimal age at breeding depends on feeding intensity which determines reaching optimal body weight and sufficient body development March April May Comparison of average net return per heifer under the optimal (weaning after 9 months of suckling) and non optimal strategy (weaning at the beginning of November) Breeding heifers at the body weight lower then 65% body weight of mature cow can be economically beneficial. Conclusions Conclusions Commonly practised weaning at the end of pasture season is economically justified as indicated by only slightly better economic results for optimal rearing period (lasting 9 months) compared to weaning at the end of pasture season. The net return per heifer is primarily subject to changes in slaughter prices and feed costs. The replacement beef heifer model is an effective tool that can be used to support farmers decisions by determining the economically optimal management strategy for the replacement heifers. By changing the key variables and parameters as well as the production conditions the model allows an insight into the critical components of heifer rearing. 6

7 Any questions?? 7