Economic consequences of postponed first insemination of cows in a dairy cattle herd

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1 Livestock Production Science 79 (2003) locte/ livprodsci Economic consequences of postponed first insemintion of cows in diry cttle herd * Jn Tind Sørensen, Søren Østergrd Deprtment of Animl Helth nd Welfre, Dnish Institute of Agriculturl Sciences, Reserch Centre Foulum, P.O. Box 50, DK-8830 Tjele, Denmrk Received 27 November 2001; received in revised form 24 June 2002; ccepted 24 June 2002 Abstrct The purpose ws to nlyse the economic consequences of postponed first insemintion of cows in diry herds with different reproduction mngement, nd to nlyse the sensitivity of the results to further decrese in beef prices, using model simulting production nd helth in diry cttle herd. Three different period-to-first-insemintion scenrios were nlysed. Period to first insemintion ws defined s dys post prtum for inititing insemintion t observed het. The three scenrios consisted of short period to first insemintion (70 dys for primiprous nd 35 dys for older cows), 70 dys postponed first insemintion of primiprous cows nd scenrio with 70 dys postponed first insemintion for ll cows. At 70 dys postponed first insemintion for primiprous cows decrese in nnul herd profit of 1% were found. A 70 dys postponed first insemintion for ll cows led to decrese in nnul herd profit by 3% t good reproductive efficiency nd 4% t poor reproductive efficiency. The herd profit ws clculted s the profit to cover lbour costs nd fixed costs. Postponed insemintions might reduce lbour per cow-yer. The reduction in lbour per cow-yer need to be 3.2 h t good reproductive efficiency nd 4.3 h t poor reproductive efficiency to counterblnce the reduction in herd profit by postponing first insemintion for ll cows by 70 dys. In sitution with 50% decrese in beef prices in herd constrined by milk quot (optimising profit per kg milk) herd profit ws incresed by 0.8% t good reproductive efficiency nd 0.3% t poor reproductive efficiency by postponing first insemintion for ll cows by 70 dys Elsevier Science B.V. All rights reserved. Keywords: Cttle; Reproduction; Clving intervls; Milk yield; Replcement 1. Introduction intervl. This prctice hs been supported by economic clcultions for typicl diry cttle herds It hs been generl prctice to inseminte cows s (Oltencu et l., 1981; Dijkhuizen et l., 1985; erly s possible in order to chieve short clving Strndberg nd Oltencu, 1989). The dvntge of short clving intervl is more offspring nd higher milk yield per dy from cows in milk. The disdvntge of short clving intervls, is tht the cow *Corresponding uthor. Tel.: ; fx: hs more dys dry (less dys in milk per yer). Short E-mil ddress: jntind.sorensen@grsci.dk (J. Tind Sørensen). clving intervls gives more clvings per cow-yer /02/$ see front mtter 2002 Elsevier Science B.V. All rights reserved. PII: S (02)

2 146 J. Tind Sørensen, S. Østergrd / Livestock Production Science 79 (2003) nd therefore higher risk for periprturient diseses effect ws estimted to be 4 nd 1% for primiprous per cow-yer. nd multiprous cows, respectively, during the first The stedy increse in milk production per cow 150 dys of lcttion. combined with only minor chnges in live weight The price of beef met dropped in the utumn gin hs in generl incresed the milk to met 2000 ll over Europe due to n incresed wreness production rtio in diry herd. Especilly in of BSE in the cttle popultion. Also, the costs from situtions with incresed lcttion persistency ( incresed control mesures in the beef industry hs lower rte of decline in milk yield), it hs been decresed the profit from beef production. Low beef questioned whether short clving intervl is still prices hve ccentuted the question of whether short economiclly optiml. The question of optiml lct- clving intervl is still economiclly optiml for the tion length hs been rised in the debte on BST diry producer. dministrtion to cows in mid-lte lcttion to in- The effect of different clving intervls t herd crese lcttion persistency (Knight nd Minlnd, level is complex nd therefore difficult to nlyse. 1994; Knight, 1997; Allore nd Erb, 2000). Chnges in clving intervl chnge the production of Experiments with different lengths of lcttions replcement heifers nd interct with the reproduchve been conducted to estimte the effect on milk tion nd replcement strtegy in the herd. A relevnt production t cow level. The results show tht method, for nlysing such complex herd effects, is delyed pregnncy cn led to incresed lcttion computer simultion with model cpble of persistency (Bertilsson et l., 1997; Arbel et l., simulting herd dynmics nd production circum- 2001) nd cn lso to some extent led to incresed stnces. milk yield in the subsequent lcttion (Arbel et l., The purpose of this pper is to nlyse the 2001). economic consequences of postponed first insemin- The effect of postponed first insemintion of cows tion of cows in diry herds with different reproducws quntified in n experiment in Isrel (Arbel et tion mngement, nd to nlyse the sensitivity of l., 2001). The tril involved 1008 high yielding the results to further decrese in beef prices, using cows from 19 herds. The cows were rndomly model simulting production nd helth in diry ssigned to control group nd tretment group. cttle herd. The period from clving to first insemintion ws 60 dys longer for cows in the tretment group compred to the control group. The period from clving 2. Mteril nd methods to first insemintion ws plnned to be 30 dys longer for primiprous cows thn for multiprous 2.1. The simultion model cows, both in the tretment nd control group. Arbel et l. (2001) found 1 nd 2% increse in The computer model SimHerd III (Østergrd et milk production in first nd lter lcttions, respec- l., 2002), ws used for simultion of the consetively, during the first 10 months of the lcttion by quences of different reproduction strtegies in diry extending the lcttion by 60 dys. Milk production herds with different reproduction efficiency. ws mesured in vlue corrected milk (VCM). The SimHerd III is dynmic (weekly time stepping) increse in milk production ws primrily due to discrete model, simulting production nd stte higher lcttion persistency. However, there ws chnges of the diry herd with dditionl young 0.7% higher milk production in 1 3 months of stock. All discrete events such s het detection, lcttion for multiprous cows in the tretment conception, diseses, involuntry culling nd deth, group, compred to the control group. Thus, the re simulted stochsticlly using rndom numbers effect of the postponed first insemintion on lcttion from relevnt distributions. Different mngement yield in multiprous cows cn be clculted to be scenrios cn be simulted by chnging set of user 1.75%, 1 10 months of lcttion. Arbel et l. (2001) defined decision vribles. The consequences t herd lso found tht cows with extended lcttion hd level re simulted indirectly by prllel simultion higher milk production in subsequent lcttion. The of stte chnges of ech individul niml in the

3 J. Tind Sørensen, S. Østergrd / Livestock Production Science 79 (2003) herd. The generl frmework concerning reproduc- lcttion 1 44 weeks post prtum (w.p.p.) ws tion, replcement, feeding nd production in incresed by 1.06, 1.79 nd 1.69%, respectively, SimHerd III, is similr to SimHerd II, which is under specified feeding regimen. described by Østergrd et l. (2000). The diseses: Cows simulted in SimHerd III hve higher milk milk fever, ketosis, mstitis, metritis, retined yield in lcttion fter long clving intervl complcent, displced bomsum, nd dystoci re pred to the milk production fter short clving included in SimHerd III (Østergrd et l., 2002). intervl, due to liveweight closer to mture weight. A 63 dy increse in clving intervl for first, second 2.2. Simulted effect of extended lcttion t cow nd third lctting cows ws followed by 0.9, 0.7 level nd 0.6% increse, respectively, during the first 22 weeks of the subsequent lcttion in SimHerd III. The milk production in SimHerd III t cow level is Lcttion curves for extended nd not extended feed driven. The priorities for net-energy between cows used in simultions with SimHerd III re milk production nd liveweight gin depend on milk shown in Figs. 1 nd 2. Fig. 1 shows lcttion curves production cpcity, prity, stge of lcttion, current for first nd second lcttion from cow not liveweight nd mture weight (Østergrd et l., extended nd cow extended with 9 weeks in first 1994). A feed intke cpcity nd the bulk content of lcttion. Fig. 2 shows lcttion curves for second the feed determine feed intke of the cow in nd third lcttion from cow not extended nd SimHerd III. The feed intke cpcity is function cow extended with 9 weeks in second lcttion. of milk production cpcity, prity nd stge of lcttion. The requirement for fetus production hs 2.3. Modelling scenrios first priority in SimHerd III. Long lcttion s in SimHerd III, re therefore more persistent thn short The generl production system nd lcttions becuse feed required for fetus production mngement strtegy is delyed. The effect found by Arbel et l. (2001) The defult prmeters were intended to represent ws, however, lrger thn wht cn be explined by typicl production system nd mngement delyed fetus requirements. The lcttion curve strtegy for 120 cow cubicle diry herd with slopes used in SimHerd, were therefore ltered so dditionl young stock. The milk production level tht the milk production in first, second nd third ws 7400 kg energy corrected milk (ECM) 1 44 Fig. 1. Lcttion curves for first nd subsequent lcttion for cow with 364 dys clving intervl (control) nd 427 dys clving intervl (extended).

4 148 J. Tind Sørensen, S. Østergrd / Livestock Production Science 79 (2003) Fig. 2. Lcttion curves for second nd subsequent lcttion for cow with 364 dys clving intervl (control) nd 427 dys clving intervl (extended). w.p.p. for primiprous cows nd 8800 kg ECM for period to first insemintion, 70 dys postponed first older cows. insemintion of primiprous cows nd scenrio All cows in milk were fed d libitum with one of with 70 dys postponed first insemintion for ll three totl mixed rtions (TMR). The first rtion ws cows. fed to ll cows within 24 w.p.p. nd to high yielding The three scenrios were nlysed with good nd cows. The second rtion ws fed to medium yielding poor reproductive efficiency. Different efficiency cows (fter 24 w.p.p.), nd the third rtion ws fed to ws defined by using two levels of het detection low yielding cows. Cows selected for culling were rte; 60% for good reproductive efficiency nd 45% fed the first rtion regrdless of milk yield nd stge for poor reproductive efficiency. The insemintion of lcttion. The clssifiction for cows being high period is mjor determinnt for voluntry replceyielding, medium yielding nd low yielding, ws ment in SimHerd III. The insemintion period ws bsed on the current dily milk production nd set to 133 dys for low yielding cows nd 175 dys specified for primiprous nd multiprous cows, for high yielding cows in herd with good reproducrespectively. tive efficiency. In herd with poor reproductive Non-pregnnt cows producing less thn 12 kg efficiency, the insemintion period ws set to 147 milk per dy were discrded immeditely. Involun- dys for low yielding cows nd 189 dys for high try culling ws defined s constnt risk for ll yielding cows. The conception rte were ssumed to cows, summing up to 18 20% per yer, depending be unffected by period to first insemintion. This is on the mngement strtegy. in ccordnce with results found by Bertilsson et l. (1997) nd by Schindler et l. (1991) Vribles defining the modelling scenrios In ll scenrios, replcement ws bsed on own Three different period-to-first-insemintion production of replcement heifers. All heifers re scenrios were nlysed. Period to first insemintion kept nd inseminted if possible. A down clving ws defined s dys post prtum for inititing heifer will enter the herd if herd size is below insemintion t observed het. It ws decided to hve mximum size or if lest one cow is selected for in generl 35 dys longer period to first insemin- culling. Surplus production of heifers is sold s down tion for primiprous cows compred to older cows. clving heifers. If herd size decrese below certin The three scenrios consisted of trditionl short size down clving heifer is bought.

5 J. Tind Sørensen, S. Østergrd / Livestock Production Science 79 (2003) The simultion procedure poning ll cows t poor reproductive efficiency). Due An initil herd ws generted by 10 yers of to involuntry culling (ccidents, cute disese, etc.), simultion with the control strtegy. Using the sme the requirements of replcements per lcttion re initil herd, ech of the six scenrios were then mrginlly lrger in herd with extended lcttion simulted for 10 yers nd replicted 50 times. thn in herds with short lcttions. This leds to Averge nnul vlues from the lst 5 of the 10 mrginl shortge of replcement heifers in herds simulted yers were used. with postponed first insemintion. From time to time cubicle will be empty for few weeks before it is filled with heifer. This sitution will occur slightly 3. Results more frequently in the scenrios with postponed first insemintion compred to the short lcttions. It 3.1. Technicl results ppers from Tble 1 tht the replcement rte ws 5% lower in herds postponing first insemintion for The technicl results for the six scenrios re ll cows (long clving intervls) compred to herds shown in Tble 1. It ppers tht postponed first not postponing first insemintion (short clving insemintion is followed by decrese in number of intervls). heifers nd clvings per cow-yer. At good reproduc- The milk yield per cow-yer decreses with tive efficiency the number of heifers decresed by 8 postponed first insemintion for primiprous cows nd 17% when postponing first insemintion for nd further with postponed first insemintion for ll primiprous nd ll cows, respectively. At poor cows. With poor reproductive efficiency the milk reproductive efficiency the decrese for similr yield decresed by 3.3% when first insemintion ws chnges ws 6 nd 18%, respectively. Postponed first postponed for ll cows. The similr decrese t good insemintion for ll cows hs led to slight decrese reproductive efficiency ws 2.6%. With poor rein herd size, in terms of cows per yer (0.1 cow-yer productive efficiency nd postponed first inseminfor postponing first insemintion for ll cows t good tion, reltively high proportion of cows will hve reproductive efficiency nd 0.6 cow-yer for post- very long lcttions nd consequently low milk Tble 1 Annul technicl effects of postponed first insemintion of cows in herds with good nd poor reproductive efficiency Result Good reproductive efficiency Poor reproductive efficiency Short fi, Postponed Postponed Short fi, Postponed Postponed ll cows fi, primi- fi, ll cows fi, primi- fi, prous ll cows prous ll cows Cow yer Heifers yer Milk per cow yer, kg ECM Replcement rte, % Clvings per cow yer Weight of slughter cows, kg Pct ded cows Feed per cow yer, SFU Insemintions per cow yer Diseses per 100 cow yer Mstitis Milk fever Metritis Ketosis Dystoci fi 5 first insemintion.

6 150 J. Tind Sørensen, S. Østergrd / Livestock Production Science 79 (2003) production for long period. These long lcttions Tble 2 lso result in reltively high liveweights of slughter Prices nd costs in Dnish kroner (DKK) (1 EURO DKK) cows, especilly in herds with poor reproductive Fctor Unit Vlue efficiency. It ppers from Tble 1, tht verge Milk DKK/ kg ECM 2.48 liveweight for slughter cows were incresed by 30 nd 37 kg when insemintion ws postponed for ll Livestock cows t good nd poor reproductive efficiency, Slughter cows DKK/ kg 6.00 Slughter culled heifers DKK 3400 respectively. Bull clves DKK 800 The incidence of diseses is reltively high fter Fresh replcement heifers DKK 7000 clving. This is the reson for reltively low Ded cow DKK number of diseses in herds with postponed first insemintions, when mesured per cow-yer. Feed cows b Mix 1 DKK/ SFU Economic results Mix 2 DKK/ SFU 1.20 Mix 3 DKK/ SFU 1.10 The economic consequences of postponed first Feed heifer insemintion t herd level, were studied by using Milk replcer for clves DKK/ kg powder Concentrtes for clves DKK/ SFU 1.20 set of typiclly Dnish prices nd costs (Tble 2). Roughge for clves DKK/ SFU 1.00 Herd profit ws clculted s sles income less Grzing heifers vrible costs (feed, insemintions, veterinry ssis- First yer DKK/ dy 1.00 tnce, medicine nd other costs) for cows nd Second yer DKK/ dy 2.00 heifers. Lbour nd mngement costs were not c Veterinry costs included s vrible costs. Milk fever DKK/ cse 715 The nnul economic figures for the six scenrios Dystoci DKK/ cse 800 re shown in Tble 3. It ppers tht the income Downer (destruction) DKK/ cse 200 from milk nd met in generl ws less for the Retined plcent DKK/ cse 280 scenrios with postponed first insemintion nd Metritis DKK/ cse 330 Ketosis DKK/ cse 330 lowest for the scenrios with postponed insemintion Mstitis DKK/ cse 520 for ll cows. When postponing first insemintion for ll cows the income ws decresed by 4.4 nd 5.3% Other costs d for good nd poor reproductive efficiency, respec- Cows DKK/ cow/ yer 300 d tively. The income from slughter cows ws high for Heifers DKK/ heifer/ yer 100 Insemintion DKK 120 scenrios where first insemintion on primiprous cows were postponed, compred to scenrios with Interest rte of the herd vlue % 7 postponed first insemintions for ll cows. First ECM 5 energy-corrected milk. lctting cows hve high potentil for growth nd b SFU 5 Scndinvin feed unit. c when these cows re culled lte they will hve Covering lso retretment costs within current lcttion. reltively high liveweight. d Covering verge costs for bedding, milk recording, preg- The nnul expenses were 94.0 nd 93.5% for nncy test, dditionl veterinry ssistnce nd drugs, etc. postponing first insemintion for ll cows t good nd poor reproductive efficiency, respectively com- nnul profit, the profit per cow (yer) nd the profit pred with no postponed first insemintion. How- per kg ECM. The ltter is especilly interesting if ever, the reduction in costs when postponing first milk quot restricts the herd. insemintion ws not big enough to counterblnce The nnul profits for the strtegies with postthe decrese in income. The nnul profit ws poned first insemintion compred to the strtegies consequently lower for the strtegies with postponed with erly first insemintions re shown in Fig. 3. first insemintion compred to the erly first insemi- The strtegy with good reproductive efficiency nd ntions. The nnul profit is clculted s the totl erly first insemintion for ll cows (Strtegy GSA)

7 J. Tind Sørensen, S. Østergrd / Livestock Production Science 79 (2003) Tble 3 Annul economic effects of postponed first insemintion of cows in herds with good nd poor reproductive efficiency Results Good reproductive efficiency Poor reproductive efficiency Short fi Postponed Postponed Short fi Postponed Postponed ll cows fi, primi- fi ll cows fi, primi- fi prous ll cows prous ll cows Annul income 1000 DKK Milk production Slughter nd ded cows Heifers Bull clves Blnce displcement Totl Annul expense 1000 DKK Feeds for cows Feeds for young stock Other costs cows Other costs heifers Interest of the herd vlue Totl Annul profit Totl 1000 DKK Per cow-yer DKK Per 100 kg ECM DKK fi 5 first insemintion. is set to 100 nd ll other strtegies re expressed s price did not lter the conclusion. However, 50% proportionl to this strtegy in Fig. 3. reduction in the beef price will mke it profitble to It ppers from Fig. 3, tht the totl profit for postpone first insemintion for ll cows if the frmer herd with good reproductive efficiency will de- wishes to optimise the nnul profit per kg milk crese by 1% if the diry frmer chooses to postpone produced. The nnul profit per kg milk ws 0.8% first insemintion for first lctting cows (Strtegy higher t good reproductive efficiency nd 0.3% GLP) nd 3% if he chooses to postpone first higher t poor reproductive efficiency for postponing insemintion for ll cows (Strtegy GLA). A frmer first insemintion for ll cows. with poor reproductive efficiency nd n erly first insemintion (Strtegy PSA) hs n nnul profit, which is 2% lower thn frmer with good 4. Discussion reproduction mngement nd erly first insemintion. With reference to strtegy PSA, postponed first The conclusions from this nlysis re different insemintion for first lctting cows (Strtegy PLP) from the conclusions drwn by Arbel et l. (2001), led to 1% decrese in nnul profit nd postponed lthough both nlysis were bsed on comprble first insemintion for ll cows (Strtegy PLA) led to effects t cow level. There re severl resons for 4% decrese in nnul profit. this. In our nlysis, we were ble to simulte herd If the prices of beef met decrese compred to sitution, which is quite different from the economic the current price sitution, it might chnge the clcultion mde on two subsequent lcttions (s rnking of the six scenrios. The consequences of mde by Arbel et l., 2001). At herd level, replce- 50% beef met price reduction re shown in Fig. 4. It ment of cows ffects the results nd chnge the ppers from Fig. 4 tht reduction in beef met conclusions drwn t cow level. All cows will

8 152 J. Tind Sørensen, S. Østergrd / Livestock Production Science 79 (2003) Fig. 3. Annul economic effect in the scenrios expressed reltive to the nnul income of the strtegy with good reproductive efficiency nd short lcttions for ll cows (GSA). Prices nd costs from Tble 2. GSA, good reproductive efficiency, erly first insemintion ll cows; GLP, good reproductive efficiency, postponed first insemintion primiprous cows; GLA, good reproductive efficiency, postponed first insemintion ll cows; PSA, poor reproductive efficiency, erly first insemintion ll cows; PLP, poor reproductive efficiency, postponed first insemintion primiprous cows; nd PLA, poor reproductive efficiency, postponed first insemintion ll cows. Fig. 4. Annul economic effect in the scenrios expressed reltive to the nnul income of the strtegy with good reproductive efficiency nd short lcttions for ll cows (GSA). Prices for beef met reduced by 50% per kg nd ll other prices nd costs from Tble 2. GSA, good reproductive efficiency, erly first insemintion ll cows; GLP, good reproductive efficiency, postponed first insemintion primiprous cows; GLA, good reproductive efficiency, postponed first insemintion ll cows; PSA, poor reproductive efficiency, erly first insemintion ll cows; PLP, poor reproductive efficiency, postponed first insemintion primiprous cows; nd PLA, poor reproductive efficiency, postponed first insemintion ll cows.

9 J. Tind Sørensen, S. Østergrd / Livestock Production Science 79 (2003) experience first lcttion, fewer cows will experience high level. If this is the cse, herd with poor second lcttion nd even fewer cows third reproductive efficiency might shift to herd with lcttion. It is therefore not relistic herd scenrio good reproductive efficiency, if first insemintion is to nlyse the results from three consecutive lctprofit postponed. It ppers from Fig. 3 tht the nnul tions. Another direct effect of replcement t herd for strtegy GLP ws mrginlly higher thn level, is tht on verge there will be more cows in the nnul profit for strtegy PSA. Therefore, in erly lcttion thn in lte lcttion. At herd level, some situtions it might be n dvntge to postpone lcttion persistency will therefore be less importnt first insemintion for first lctting cows, if it would thn if we evlute it for single cow. The number led to significnt improvement of reproductive of dry dys per cow-yer t herd level is lso less efficiency. In loose housed cow herds, however, it thn for t subsequent lcttions t cow level. might be disdvntge to hve high proportion of Arbel et l. (2001) ssumed tht the feed consumption non-pregnnt cows creting disturbnces in the flock. per lcttion month would be the sme regrdless of the milk production t certin stge of lcttion. In our nlysis we hve used the sme References feeding pln cross ll scenrios, but becuse the cows re fed differently depending on their milk Allore, H.G., Erb, H.N., Simulted effects on diry cttle helth of extending the postponed first insemintion with production nd stge of lcttion, the feed consumprecombinnt bovine somtotropin. Prev. Vet. Med. 46, tion differs between strtegies. Arbel, R., Bigun, Y., Ezr, E., Sturmn, H., Hojmn, D., The Arbel et l. (2001) included only high yielding effect of extended clving intervls in high lctting cows on cows in their study. Primiprous cows should yield milk production nd profitbility. J. Diry Sci. 84, Bertilsson, J., Berglund, B., Rtnyke, G., Svennersten-Sjunj, more thn 30 kg in one of the first three milk K., Wiktorsson, H., Optimising lcttion cycles for the recordings. Multiprous cows should hve n bove high-yielding diry cow. A Europen perspective. Livest. Prod. verge 305-dys milk yield in previous lcttion. In Sci. 50, our study we pplied the effects on milk yield found Dijkhuizen, A.A., Stelwgen, J., Renkem, J.A., Economic by Arbel et l. (2001) to be vlid for ll cows. The spects of reproductive filure in diry cttle. I. Finncil loss t frm level. Prev. Vet. Med. 3, effects of strtegy of postponed first insemintion Knight, C.H., Biologicl control of lctting length. Livest. only for high yielding cows within the herd therefore Prod. Sci. 50, 1 3. tend be less thn the effects found in our study. Knight, C.H., Minlnd, D., Mnipultion of milk yield nd The herd profit ws clculted s the profit to lcttion persistency: Physiologicl nd economic considertions. Pper presented t 45th Meeting of EAAP, 5 8 Sepcover lbour nd fixed costs. Postponed first insemitember 1994, Edinburgh, UK, 4 pp. ntion leds to fewer clvings per cow per yer nd Oltencu, P.A., Rounsville, T.R., Millign, R.A., Foote, R.H., lso less youngstock. Postponed first insemintion Systems nlysis for designing reproductive mngement might therefore led to reduction in lbour per progrms to increse production nd profit in diry herds. J. cow-yer. At slry of 120 Dnish kroner (DKK)/ Diry Sci. 64, Østergrd, S., Sørensen, J.T., Kristensen, V.F., Kristensen, T., h it cn be clculted tht lbour per cow-yer Modelling of the production of diry cow in net should be reduced by 3.2 h t good reproductive energy system. presenttion nd documenttion of the PCefficiency nd 4.3 h t poor reproductive efficiency model SIMCOW. Report No. 24 from the Ntionl Institute of to counterblnce the reduction in nnul profit by Animl Science, Denmrk, 32 pp. postponing first insemintion for ll cows. Dependtic model simulting the feeding-helth-production complex in Østergrd, S., Sørensen, J.T., Kristensen, A.R., A stochs- ing on herd specific circumstnces postponing first diry herd. J. Diry Sci. 83, insemintion might therefore be profitble. Østergrd, S., Sørensen, J.T., Houe, H., A stochstic model An interesting question when evluting the ef- simulting milk fever in diry herd (submitted). fects of postponed first insemintion, is whether Schindler, H., Eger, M., Dvidson, M., Ochowski, D., Schermer- postponed first insemintion will ese the het horn, E.C., Foote, R.H., Fctors ffecting response of groups of diry cows mnnged different clving-conception detection nd thereby the het detection efficiency. intervl. Theriogenology 36, Bertilsson et l. (1997) found tht the intensity of Strndberg, E., Oltencu, P.A., Economic consequences of oestrus incresed until oestrus No. 4 nd continues t different clving intervls. Act Agric. Scnd. 39,