Effect of reproductive management programs for first service on replacement dairy heifer economics

摘要

Our objective was to evaluate cash flow for dairyheifers managed for first service with programs that reliedprimarily on insemination at detected estrus (AIE),timed AI (TAI), or a combination of both. Holstein heifersfrom 2 commercial farms were randomized to receivefirst service with sexed semen after the beginning of theAI period (AIP) at 12 mo of age with 1 of 3 treatments:(1) PGF+AIE (n = 317): AIE after PGF_(2α) injectionsevery 14 d (up to 3) starting at the beginning of theAIP; heifers not AIE 9 d after the third PGF_(2α) wereenrolled in the 5d-Cosynch (5dCP) protocol; (2) ALLTAI(n = 315): TAI after ovulation synchronizationwith the 5dCP protocol; and (3) PGF+TAI (n = 334):AIE after 2 PGF_(2α) injections 14 d apart (second PGF_(2α)at beginning of AIP). If not AIE 9 d after the secondPGF_(2α), the 5dCP protocol was used for TAI. After firstservice heifers were AIE or received TAI after the 5dCPwith conventional semen. Individual heifer cash flow(CF) for up to a 15-mo period (d 0 = beginning of AIP)was calculated using reproductive cost (rearing only),feed cost (rearing only), income over feed cost (lactationonly), calf value, operating cost, and with or withoutreplacement cost. A stochastic analysis with MonteCarlo simulation was used to estimate differences inCF for a range of market values for inputs and outputs.Time to pregnancy for up to 100 d after the beginningof the AIP was analyzed by Cox’s proportional regression,binary data with logistic regression, and continuousoutcomes by ANOVA. Time to pregnancy (hazardratio and 95% CI) was reduced for the ALL-TAI versusthe PGF+AIE treatment (1.20; 1.02–1.42), but it wassimilar for ALL-TAI and PGF+TAI (1.13; 0.95–1.33)and the PGF+AIE and PGF+TAI treatments (1.07;0.91–1.25). The proportion of heifers not pregnant by100 d did not differ (PGF+AIE = 7.0%; PGF+TAI =6.5%; ALL-TAI = 6.8%). When including replacementcost, CF ($/slot per 15 mo) differences were $51 and$42 in favor of the PGF+TAI and ALL-TAI comparedwith the PGF+AIE treatment, and $9 in favor of thePGF+TAI compared with the ALL-TAI treatmentbut did not differ statistically. Excluding heifers thatwere replaced to evaluate the effect of timing of pregnancydifferences only, the difference in CF between thePGF+AIE with the PGF+TAI and ALL-TAI treatmentwas the same (i.e., $15) and favored the programsthat used more TAI, but also did not differ statistically.Stochastic simulation results were in line with thoseof the deterministic analysis confirming the benefit ofthe programs that used more TAI. We concluded thatsubmission of heifers for first service with TAI onlyor TAI in combination with AIE generated numericaldifferences in CF of potential value to commercial dairyfarms. Reduced rearing cost and increased revenue duringlactation increased CF under fixed (not statisticallysignificant) or simulated variable market conditions.