Research| Volume 104, ISSUE 1, P471-485, January 2021
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Effect of reproductive management programs for first service on replacement dairy heifer economics

Open ArchivePublished:November 11, 2020

ABSTRACT

Body Weight Estimation.

During the RP, BW was modeled daily for every heifer using the Gompertz growth function as previously described in
• Winsor C.P.
The Gompertz curve as a growth curve.
:
BW (kg) = A × exp{−exp[B – (C × age)]},

where age = heifer age in days, A = asymptotic weight or maximum growth response, B = scale parameter related to initial weight, and C = growth rate. Body weight data at different time points during the RP for a subgroup of heifers (n = 572), BW of mature (i.e., third and fourth lactation) cows (n = 30), and BW at first calving were only available for Farm B (n = 489). To generate the curve, all body weight data were combined (n = 1,308) and plotted against age in days. The Gompertz growth function was then fitted using the Calculate option of the CurveExpert software (version 2.6.5;
• Hyams D.G.
CurveExpert Professional Documentation. Release 2.6.5.
). Parameters A, B, and C for the resulting equation were 695, 0.90, and 0.004, respectively.
During lactation, BW was modeled daily for every cow using the Korver function as previously described in (
• van Arendonk J.A.M.
A model to estimate the performance, revenues and costs of dairy cows under different production and price situations.
):
BW (kg) = A × {1 – [1 – (B/A)1/3] × exp(–C × age)}3 – (P1/P2) × DIM × exp(1 – DIM/P2),

where age = cow age in days, A = mature live weight (kg), B = birth weight (kg), C = growth rate, P1 = maximum decrease in live weight during lactation, and P2 = time during lactation with minimum live weight. Data used for average mature live weight (720 kg) and birth weight (39 kg) were retrieved from both farms. Parameters C, P1, and P2 were 0.004, 30, and 60, respectively, based on (
• Kalantari A.S.
• Mehrabani-Yeganeh H.
• Sanders A.H.
• De Vries A.
Determining the optimum replacement policy for Holstein dairy herds in Iran.
).

Daily Milk and FCM Production Estimation.

The MilkBot model (
• Ehrlich J.L.
Quantifying inter-group variability in lactation curve shape and magnitude with the MilkBot® lactation model.
) was used to estimate daily milk production for each heifer that calved during the study period (i.e., within 15 mo after the beginning of the AIP). Details about MilkBot parameters and daily milk yield calculations have been previously described (
• Ehrlich J.L.
Quantifying inter-group variability in lactation curve shape and magnitude with the MilkBot® lactation model.
). Briefly, monthly milk data were retrieved from the dairy herd management software to estimate individual lactation curves based on 4 parameters: scale, ramp, offset, and decay. For heifers that calved but left the herd before the second monthly milk test (i.e., either no milk data available or only available for the first test, n = 45), daily milk production was calculated based on the average of each parameter corresponding to the same farm and experimental treatment as the heifer that left the herd. Inclusion of a few monthly test data points (e.g., 2 or less) results in less reliable estimation of milk yield. Nevertheless, the proportion of cows with only 2 test-days available was small and similar across treatments (PGF+AIE = 6%, PGF+TAI = 4%, and ALL-TAI = 5%). Therefore, we did not expect bias for milk production estimations as a result of an unbalanced proportion of cows with few monthly test data points.
To estimate daily DMI during lactation, FCM was calculated based on daily milk weight (kg/d) estimated by the MilkBot and monthly test fat percentage as follows:
FCM (kg/d) = 0.4 × DMW + 0.15 × Fat % × DMW,

where DMW = daily milk weight (kg/d) estimated by the MilkBot model, and Fat % = fat percentage reported in the monthly milk tests. Because daily milk fat percentage data were not available, fat percentage for a specific monthly test was repeated for a 30-d period (i.e., value obtained from first test was used from 1 to 30 DIM, value from second test was used from 31 to 60 DIM, and so on).

Replacement Cost.

For each heifer that left the herd due to death or sale, the replacement cost was equal to the market value of a replacement heifer minus the salvage value of the heifer sold for beef ($0 if the heifer left the herd due to death), and the value of the calf born from the replacement. The salvage value for heifers or cows sold was calculated based on their estimated BW at the time of sale (i.e., average of 308, 276, and 270 d after the beginning of the AIP for heifers in the PGF+AIE, PGF+TAI, and ALL-TAI treatments, respectively) times the beef price. During the RP, the value of the calf born from a replacement virgin heifer was$0 if the replacement did not calve before the 15 mo period for the slot was completed. In contrast, if the replacement heifer was able to conceive and calve during the replacement period, then the value of the calf born was set at the average calf value obtained in the current experiment ($95/calf), which accounts for male, female, stillborn and twin calves. During the FLP, in contrast, calf value was set to$95 in all cases based on the assumption that all replacements entering the herd in their first lactation contributed with a newborn calf. For replacement cost calculations during the RP, the market value of a virgin heifer was set at $700, based on the average value of lean and heavy replacement heifers during the study period ( • Progressive Dairyman Market Watch: Cattle. ). In addition, the beef price for heifers sold during the RP was set at$2.70/kg (
• USDA National Agricultural Statistics Service
Agricultural Prices. Accessed several times from 2018 to 2019.
). In contrast, for replacement cost during the FLP, the market value of a springer heifer (i.e., heifer close to calving) was set at $1,565 ( • USDA Economic Research Service US quarterly milk production and related data. Accessed several times from 2018 to 2019. ), and the value of beef for cows sold was set at$1.50 (
• USDA National Agricultural Statistics Service
Agricultural Prices. Accessed several times from 2018 to 2019.
). Assumed market values were used for purchase cost of heifers to replace those leaving during the RP and cows leaving during lactation because no data were available to estimate raising cost up from birth until the beginning of the AIP for this study.

Daily milk income over feed cost (IOFC) was estimated for all heifers that started first lactation during the 15-mo period by subtracting feed cost from milk revenue (i.e., milk volume kg × milk price per kg). A slot's IOFC was set to $0 when heifers and their corresponding replacement (if present) did not calve within the 15-mo period. Milk price was the average monthly price reported by the Dairy Market Watch report ( • Cornell Cooperative Extension of Chautauqua County Dairy Market Watch. ) from September 2016 (first heifer initiated FLP) to June 2018 (last heifer completed 15-mo experimental period). The weighted average accounting for milk class (class I to IV) usage was$0.36/kg (i.e., $16.5 per 100 lbs). Other Operating Expenses. Other operating expenses not accounted for by reproductive cost, feeding cost, and replacement cost were set at$0.85/d per heifer for the RP (
• Karszes J.
Dairy Replacement Programs: Costs & Analysis 3rd Quarter 2012. Extension Bulletin 2014–02.

Statistical Analysis

Binary outcomes [proportion of heifers AIE; pregnancies per AI (P/AI); proportion of heifers that left the herd, calved, had stillbirths, had a calving ease > 2, and had a female calf] were analyzed using logistic regression with the GLIMMIX procedure of SAS (version 9.4, SAS Institute Inc., Cary, NC) fitting a binomial distribution. Continuous quantitative outcomes [RP and FLP duration, AFC, BW at 1st calving, DMI, milk yield, incomes (milk income, calf value, IOFC), expenses (reproductive cost, replacement cost, feed cost, and other operating expenses), and cash flow] were analyzed by ANOVA using PROC MIXED of SAS. Time to pregnancy for up to 100 d after the beginning of the AIP was analyzed using Cox's proportional hazard regression with the PHREG procedure of SAS. For the analysis of time to pregnancy, a heifer was considered pregnant if pregnancy was maintained until at least 66 ± 3 d of gestation. Heifers that left the herd due to death or sale were right-censored.
For all outcomes, the effect of experimental treatment was included in all models as a fixed effect whereas farm was included as a random effect. In addition, for AI service outcomes (proportion AIE and P/AI) the effect of season of insemination (cold vs. warm) was offered to the models and retained if significant (data not reported). The cold season was defined as the period from September 21 to June 20 and the warm season from June 21 to September 20. Assumptions of normality of residuals and homoscedasticity for linear regression models were tested by evaluating normal probability plots (Q-Q plot) and plotting residuals versus predicted values. For logistic regression models, goodness of fit was evaluated using the ratio between the Pearson statistic and its degrees of freedom. In all cases, model fit was deemed acceptable based on a ratio of approximately one.
All proportions and quantitative (±SEM) outcomes reported are least squares means generated using the LSMEANS statement of PROC GLIMMIX and with the LSMEANS option of PROC MIXED of SAS, respectively. When appropriate, the least significant difference post hoc mean separation test was used to determine differences between least squares means. Variables were considered significant if P ≤ 0.05, whereas P-values >0.05 and ≤0.10 were considered a tendency.

RESULTS

Reproductive Performance and Herd Exit Dynamics During the Rearing Period

For first service, the total proportion of heifers that received AIE was greater (P < 0.01; Table 1) for the PGF+AIE treatment than for the PGF+TAI treatment. For the PGF+AIE treatment (arithmetic mean reported), 78.5% (248/317) of the heifers received AIE after the first PGF, 17.0% (54/317) after the second, and 3.2% (10/317) after the third PGF treatment.
Table 1Effect of first-service management strategy on reproductive performance during the rearing period (RP)
Item
AIE = artificial insemination at detected estrus; P/AI = pregnancies per artificial insemination; NP = not pregnant.
Treatment
Treatment: at 368 ± 10 d of age, heifers received first AI after: (1) PGF+AIE: insemination at detected estrus (AIE) after PGF2α treatments 14 d apart (up to 3) starting at the beginning of the AI period; heifers not AIE within 9 d of the third PGF2α treatment were enrolled in a 5d-Cosynch protocol [5d-Cosynch = controlled internal drug release insert (CIDR) + GnRH-5 d-CIDR-out + PGF2α-3 d-GnRH + TAI]; (2) PGF+TAI: AIE after the second of 2 PGF2α treatments 14 d apart; heifers not AIE within 9 d after the second PGF2α were enrolled in 5d-Cosynch; and (3) ALL-TAI: timed AI after a 5d-Cosynch protocol.
P-value
PGF+AIEPGF+TAIALL-TAI
Heifers AIE 1st service, % (no.)98.7 (317)78.5 (334)<0.01
P/AI 1st service, % (no.)42.0 (317)47.3 (334)43.8 (315)0.38
P/AI 2nd and greater AI, % (no.)58.8 (311)55.7 (318)57.6 (311)0.72
Time to pregnancy
Hazard ratioReferent
Time to pregnancy did not differ for ALL-TAI and PGF+TAI (hazard ratio = 1.13, 95% CI = 0.96 to 1.33).
1.071.200.08
(95% CI)(0.91–1.25)(1.02–1.42)
Mean, d36 ± 1.832 ± 1.828 ± 1.7
Median, d27 (23–36)23 (17–26)21 (10–23)
NP at 100 d, % (no.)7.0 (317)6.5 (334)6.8 (315)0.97
Left the herd, % (no.)4.7 (313)5.4 (330)7.4 (306)0.33
Sold, % (no.)4.4 (313)5.1 (330)7.4 (306)0.23
Died, % (no.)
The proportion of heifers that died was evaluated with the Fisher's exact test using FREQ procedure of SAS because in the ALL-TAI treatment 0% of heifers had a positive outcome.
0.3 (313)0.3 (330)0.0 (306)0.23
RP length, d
Not culled during RP
Heifers that were sold or died during the RP were removed from the analysis.
309 ± 6
Different superscripts within a row indicate significant differences (P ≤ 0.05).
304 ± 6
Different superscripts within a row indicate significant differences (P ≤ 0.05).
300 ± 6
Different superscripts within a row indicate significant differences (P ≤ 0.05).
0.01
Per slot315 ± 7311 ± 7310 ± 70.35
a,b Different superscripts within a row indicate significant differences (P ≤ 0.05).
1 AIE = artificial insemination at detected estrus; P/AI = pregnancies per artificial insemination; NP = not pregnant.
2 Treatment: at 368 ± 10 d of age, heifers received first AI after: (1) PGF+AIE: insemination at detected estrus (AIE) after PGF treatments 14 d apart (up to 3) starting at the beginning of the AI period; heifers not AIE within 9 d of the third PGF treatment were enrolled in a 5d-Cosynch protocol [5d-Cosynch = controlled internal drug release insert (CIDR) + GnRH-5 d-CIDR-out + PGF-3 d-GnRH + TAI]; (2) PGF+TAI: AIE after the second of 2 PGF treatments 14 d apart; heifers not AIE within 9 d after the second PGF were enrolled in 5d-Cosynch; and (3) ALL-TAI: timed AI after a 5d-Cosynch protocol.
3 Time to pregnancy did not differ for ALL-TAI and PGF+TAI (hazard ratio = 1.13, 95% CI = 0.96 to 1.33).
4 The proportion of heifers that died was evaluated with the Fisher's exact test using FREQ procedure of SAS because in the ALL-TAI treatment 0% of heifers had a positive outcome.
5 Heifers that were sold or died during the RP were removed from the analysis.
For all first AI services combined, P/AI 31 ± 3 d after AI did not differ between treatments (P = 0.38; Table 1), and was similar (P = 0.21) for heifers that received AIE after PGF-synchronized estrus (46.1%; n = 582), AIE during the 5-d Cosynch (45.7%; n = 127), or completion of the TAI protocol (40.1%; n = 257). Similarly, overall P/AI for all second and greater AI services combined was not different among treatments (P = 0.72; Table 1).
The hazard of pregnancy for up to 100 d after the beginning of the AIP was greater for the ALL-TAI than the PGF+AIE treatment (Table 1) but was similar for the PGF+AIE and PGF+TAI treatments, and for the ALL-TAI and PGF+TAI treatments. Conversely, the proportion of heifers not pregnant by 100 d after the beginning of the AIP was not different (P = 0.97; Table 1) among treatments.
Overall, the total proportion of heifers that left the herd during the RP did not differ (P = 0.33; Table 1), because treatment did not affect the proportion of heifers sold (P = 0.23) or that died (P = 0.23) during the RP.
The length of the RP (i.e., time from the beginning of the AIP until calving or herd exit), was greatest for the PGF+AIE, intermediate for the PGF+TAI, and least for the ALL-TAI treatment, when only heifers that completed the 15-mo experimental period (P = 0.01) were included in the analysis (Table 1). In contrast, when analyzed per slot (i.e., including replacement dynamics) RP length was not different (P = 0.35; Table 1) among treatments.

Economic Outcomes for the Rearing Period

The effect of treatments on economic outcomes during the RP is presented in Table 2. Reproductive cost was greater (P < 0.001) for the ALL-TAI than for the PGF+AIE and PGF+TAI treatments. In contrast, no difference was observed for DMI (P = 0.23), feed cost (P = 0.23), replacement cost (P = 0.14), and other operating expenses (P = 0.35). When only heifers that completed the 15-mo experimental period were included in the analysis (i.e., not culled only), reproductive cost was also greater (P < 0.001) for the ALL-TAI than the PGF+AIE and PGF+TAI treatments. In addition, for these heifers treatment also affected DMI (P = 0.01), feed cost (P = 0.01) and other operating expenses (P = 0.01), as all were greatest for PGF+AIE, intermediate for PGF+TAI, and lowest for the ALL-TAI treatment.
Table 2Effect of first-service management strategy on expenses during the rearing period
Item (per slot)Treatment
Treatment: at 368 ± 10 d of age, heifers received first AI after: (1) PGF+AIE: insemination at detected estrus (AIE) after PGF2α treatments 14 d apart (up to 3) starting at the beginning of the AI period; heifers not AIE within 9 d of the third PGF2α treatment were enrolled in a 5d-Cosynch protocol [5d-Cosynch = controlled internal drug release insert (CIDR) + GnRH-5 d-CIDR-out + PGF2α-3 d-GnRH + TAI]; (2) PGF+TAI: AIE after the second of 2 PGF2α treatments 14 d apart; heifers not AIE within 9 d after the second PGF2α were enrolled in 5d-Cosynch; and (3) ALL-TAI: timed AI after a 5d-Cosynch protocol.
PGF+AIE (n = 313)PGF+TAI (n = 330)Diff
Difference between PGF+TAI and PGF+AIE.
ALL-TAI (n = 306)Diff
Difference between ALL-TAI and PGF+AIE.
P-value
All heifers
Hormonal treatment, $12.1 ± 4.7 Different superscripts within a row indicate significant differences (P ≤ 0.05). 15.8 ± 4.7 Different superscripts within a row indicate significant differences (P ≤ 0.05). 3.726.9 ± 4.7 Different superscripts within a row indicate significant differences (P ≤ 0.05). 15<0.001 Semen and AI,$40.8 ± 1.140.2 ± 1.1−0.641.6 ± 1.10.80.69
Pregnancy diagnosis, $7.1 ± 0.76.9 ± 0.7−0.27.1 ± 0.7−0.00.60 Detection of estrus,$8.7 ± 0.28.6 ± 0.2−0.18.6 ± 0.2−0.10.35
Total reproductive cost, $68.8 ± 6.0 Different superscripts within a row indicate significant differences (P ≤ 0.05). 71.5 ± 6.0 Different superscripts within a row indicate significant differences (P ≤ 0.05). 2.784.1 ± 6.0 Different superscripts within a row indicate significant differences (P ≤ 0.05). 15<0.001 DMI, kg3,592 ± 873,536 ± 87−563,518 ± 87−740.26 Feed cost,$618 ± 15608 ± 15−10605 ± 15−130.23
Replacement cost, $−27.7 ± 12−35.9 ± 12−8.2−55.7 ± 12−280.14 Other operating expenses,$268 ± 6264 ± 6−4.0264 ± 6−4.00.35
Not culled
Hormonal treatment, $11.0 ± 4.2 Different superscripts within a row indicate significant differences (P ≤ 0.05). 14.4 ± 4.1 Different superscripts within a row indicate significant differences (P ≤ 0.05). 3.424.2 ± 4.2 Different superscripts within a row indicate significant differences (P ≤ 0.05). 13<0.001 Semen and AI,$37.8 ± 0.837.5 ± 0.8−0.337.9 ± 0.80.10.95
Pregnancy diagnosis, $6.7 ± 0.66.5 ± 0.6−0.26.5 ± 0.6−0.20.28 Detection of estrus,$8.6 ± 0.28.4 ± 0.2−0.28.3 ± 0.2−0.30.01
Total reproductive cost, $64.2 ± 5.0 Different superscripts within a row indicate significant differences (P ≤ 0.05). 66.8 ± 5.0 Different superscripts within a row indicate significant differences (P ≤ 0.05). 2.676.9 ± 5.0 Different superscripts within a row indicate significant differences (P ≤ 0.05). 13<0.001 DMI, kg3,526 ± 78 Different superscripts within a row indicate significant differences (P ≤ 0.05). 3,462 ± 77 Different superscripts within a row indicate significant differences (P ≤ 0.05). −643,409 ± 78 Different superscripts within a row indicate significant differences (P ≤ 0.05). −1170.01 Feed cost,$607 ± 13
Different superscripts within a row indicate significant differences (P ≤ 0.05).
595 ± 13
Different superscripts within a row indicate significant differences (P ≤ 0.05).
−12586 ± 13
Different superscripts within a row indicate significant differences (P ≤ 0.05).
−210.01
Replacement cost, $Other operating expenses,$263 ± 5259 ± 5−4.0255 ± 5−8.00.01
a–c Different superscripts within a row indicate significant differences (P ≤ 0.05).
1 Treatment: at 368 ± 10 d of age, heifers received first AI after: (1) PGF+AIE: insemination at detected estrus (AIE) after PGF treatments 14 d apart (up to 3) starting at the beginning of the AI period; heifers not AIE within 9 d of the third PGF treatment were enrolled in a 5d-Cosynch protocol [5d-Cosynch = controlled internal drug release insert (CIDR) + GnRH-5 d-CIDR-out + PGF-3 d-GnRH + TAI]; (2) PGF+TAI: AIE after the second of 2 PGF treatments 14 d apart; heifers not AIE within 9 d after the second PGF were enrolled in 5d-Cosynch; and (3) ALL-TAI: timed AI after a 5d-Cosynch protocol.
2 Difference between PGF+TAI and PGF+AIE.
3 Difference between ALL-TAI and PGF+AIE.

Calving Features and Herd Exit Dynamics

Overall, the proportion of heifers that calved within 15-mo after the beginning of the AIP was similar (P = 0.34; Table 3). In contrast, AFC differed (P = 0.01) among treatments because it was greater for the PGF+AIE than for the ALL-TAI treatment, but similar for the PGF+AIE and PGF+TAI treatments (Table 3).
Table 3Effect of first-service management strategy on calving features and herd exit dynamics during the first lactation
ItemTreatment
Treatment: at 368 ± 10 d of age, heifers received first AI after: 1) PGF+AIE: insemination at detected estrus (AIE) after PGF2α treatments 14 d apart (up to 3) starting at the beginning of the AI period; heifers not AIE within 9 d of the third PGF2α treatment were enrolled in a 5d-Cosynch protocol [5d-Cosynch = controlled internal drug release insert (CIDR) + GnRH-5 d-CIDR-out + PGF2α-3 d-GnRH + TAI]; 2) PGF+TAI: AIE after the second of 2 PGF2α treatments 14 d apart; heifers not AIE within 9 d after the second PGF2α were enrolled in 5d-Cosynch; and 3) ALL-TAI: timed AI after a 5d-Cosynch protocol.
P-value
PGF+AIEPGF+TAIALL-TAI
Calved, % (no.)95.0 (313)94.4 (330)92.4 (306)0.34
Age at 1st calving, mo22.3 ± 0.1
Different superscripts within a row indicate significant differences (P ≤ 0.05).
22.1 ± 0.1
Different superscripts within a row indicate significant differences (P ≤ 0.05).
22.0 ± 0.1
Different superscripts within a row indicate significant differences (P ≤ 0.05).
0.01
Weight at 1st calving, kg565 ± 4559 ± 5557 ± 50.42
Calving ease >24.4 (264)5.8 (281)8.1 (250)0.23
Stillbirths, % (no.)10.6 (297)7.2 (310)11.1 (282)0.21
Female calves, % (no.)68.0 (297)68.4 (310)65.4 (280)0.70
Left the herd, % (no.)8.8 (297)6.6 (311)8.6 (282)0.53
Sold, % (no.)7.2 (297)5.6 (311)7.6 (282)0.60
Died, % (no.)1.7 (287)1.0 (311)1.1 (282)0.70
1st lactation period length, d
Not culled
Heifers that were sold or died during the rearing period and first lactation period were removed from the analysis.
148 ± 6152 ± 6155 ± 60.07
Per slot141 ± 7145 ± 6146 ± 70.35
a,b Different superscripts within a row indicate significant differences (P ≤ 0.05).
1 Treatment: at 368 ± 10 d of age, heifers received first AI after: 1) PGF+AIE: insemination at detected estrus (AIE) after PGF treatments 14 d apart (up to 3) starting at the beginning of the AI period; heifers not AIE within 9 d of the third PGF treatment were enrolled in a 5d-Cosynch protocol [5d-Cosynch = controlled internal drug release insert (CIDR) + GnRH-5 d-CIDR-out + PGF-3 d-GnRH + TAI]; 2) PGF+TAI: AIE after the second of 2 PGF treatments 14 d apart; heifers not AIE within 9 d after the second PGF were enrolled in 5d-Cosynch; and 3) ALL-TAI: timed AI after a 5d-Cosynch protocol.
2 Heifers that were sold or died during the rearing period and first lactation period were removed from the analysis.
For heifers with data for BW at first calving available (n = 489), BW averaged 560 kg and did not differ (P = 0.42) between treatments (Table 3). Similarly, among heifers with calving ease data available (n = 797), the proportion with a calving ease score >2 did not differ (P = 0.23) between treatments (Table 3). In addition, no difference between treatments was observed for the proportion of stillbirths (P = 0.21), proportion of female calves born (P = 0.70), and for the proportion of heifers that left the herd due to sale or death (P = 0.53).
When only heifers that completed the 15-mo period were included in the analysis, overall FLP length tended (P = 0.07) to differ between treatments. Conversely, when analyzed per slot FLP length did not differ (P = 0.35) between treatments (Table 3).

First Lactation Period Economic Outcomes

The effect of treatments on economic and productive outcomes during the FLP is presented in Table 4. When all heifers were included in the analysis, no differences (P > 0.10) were observed for DMI, feed cost, milk yield, milk income, IOFC, replacement cost, and other operating expenses. Conversely, we observed a tendency (P = 0.08) for a treatment effect on calf value, whereby cows in PGF+TAI treatment had the greatest calf value, followed by the PGF+AIE treatment and least for the ALL-TAI treatment (Table 4). When only heifers that completed the 15-mo experimental period were included in the analysis, no differences (P > 0.10) were observed for DMI, feed cost, milk yield, milk income, IOFC, and replacement cost. In contrast, other operating expenses tended (P = 0.07) to differ between treatments, whereby expenses were greatest in ALL-TAI, intermediate in PGF+TAI and lowest in PGF+AIE (Table 4). Similarly, there was a tendency (P = 0.08) for a treatment effect on calf value, whereby ALL-TAI heifers had the lowest calf value, followed by the PGF+AIE and greatest for PGF+TAI heifers.
Table 4Effect of first-service management strategy on productive parameters, revenues and expenses during the first lactation
Item (per slot)
IOFC = income over feed cost; not culled = heifers that were sold or died during the rearing and first lactation period were removed from the analysis.
Treatment
Treatment: at 368 ± 10 d of age, heifers received first AI after: (1) PGF+AIE: insemination at detected estrus (AIE) after PGF2α treatments 14 d apart (up to 3) starting at the beginning of the AI period; heifers not AIE within 9 d of the third PGF2α treatment were enrolled in a 5d-Cosynch protocol [5d-Cosynch = controlled internal drug release insert (CIDR) + GnRH-5 d-CIDR-out + PGF2α-3 d-GnRH + TAI]; (2) PGF+TAI: AIE after the second of 2 PGF2α treatments 14 d apart; heifers not AIE within 9 d after the second PGF2α were enrolled in 5d-Cosynch; and (3) ALL-TAI: timed AI after a 5d-Cosynch protocol.
PGF+AIE (n = 313)PGF+TAI (n = 330)Diff
Difference between PGF+TAI and PGF+AIE.
ALL-TAI (n = 306)Diff
Difference between ALL-TAI and PGF+AIE.
P-value
All heifers
DMI, kg3,240 ± 1643,341 ± 1631013,354 ± 1641140.39
Feed cost, $940 ± 47969 ± 4829973 ± 48330.39 Milk, kg4,858 ± 2004,996 ± 1981385,008 ± 2001500.51 Milk income,$1,749 ± 721,799 ± 71501,803 ± 72540.51
IOFC, $809 ± 26829 ± 2520830 ± 26210.67 Replacement cost,$69.5 ± 15.348.1 ± 14.9−2158.7 ± 15.4−110.50
Other operating expenses, $436 ± 21449 ± 2113452 ± 21160.35 Calf value,$89.1 ± 2.292.4 ± 2.13.385.6 ± 2.2−3.50.08
Not culled
DMI, kg3,426 ± 1523,511 ± 152853,586 ± 1531600.12
Feed cost, $994 ± 441,018 ± 44241,039 ± 44450.12 Milk, kg5,143 ± 1815,252 ± 1791095,360 ± 1822170.22 Milk income,$1,851 ± 651,891 ± 64401,930 ± 65790.22
IOFC, $858 ± 22872 ± 2214889 ± 23310.42 Replacement cost,$
Other operating expenses, $457 ± 20470 ± 2013480 ± 20230.07 Calf value,$94.2 ± 2.298.2 ± 2.24.092.4 ± 2.2−1.80.08
1 IOFC = income over feed cost; not culled = heifers that were sold or died during the rearing and first lactation period were removed from the analysis.
2 Treatment: at 368 ± 10 d of age, heifers received first AI after: (1) PGF+AIE: insemination at detected estrus (AIE) after PGF treatments 14 d apart (up to 3) starting at the beginning of the AI period; heifers not AIE within 9 d of the third PGF treatment were enrolled in a 5d-Cosynch protocol [5d-Cosynch = controlled internal drug release insert (CIDR) + GnRH-5 d-CIDR-out + PGF-3 d-GnRH + TAI]; (2) PGF+TAI: AIE after the second of 2 PGF treatments 14 d apart; heifers not AIE within 9 d after the second PGF were enrolled in 5d-Cosynch; and (3) ALL-TAI: timed AI after a 5d-Cosynch protocol.
3 Difference between PGF+TAI and PGF+AIE.
4 Difference between ALL-TAI and PGF+AIE.

Economic Outcomes for 15 mo After the Beginning of the AIP

The effect of treatments on total RP cost, FLP profit, and the accumulated cash flow for the 15-mo period is presented in Table 5. When all heifers were included in the analysis, we observed a tendency (P = 0.08) for a treatment effect on total RP cost, which was lowest for ALL-TAI, intermediate for PGF+TAI, and highest for the PGF+AIE treatment. In contrast, no treatment effect was observed on total FLP profit (P = 0.92) and on cash flow for the 15-mo period (P = 0.22). When only heifers that completed the 15-mo experimental period were included in the analysis, no differences (P > 0.10) were observed for total RP cost, total FLP profit, and cash flow for the 15-mo period (Table 5).
Table 5Effect of first-service management strategy on revenues and expenses accumulated during 15 mo after the beginning of the AI period (AIP)
Item ($/slot) RP = rearing period; FLP = first lactation period; not culled = heifers that were sold or died during the rearing and first lactation period were removed from the analysis. Treatment Treatment: at 368 ± 10 d of age, heifers received first AI after: (1) PGF+AIE: insemination at detected estrus (AIE) after PGF2α treatments 14 d apart (up to 3) starting at the beginning of the AIP; heifers not AIE within 9 d of the third PGF2α treatment were enrolled in a 5d-Cosynch protocol [5d-Cosynch = controlled internal drug release insert (CIDR) + GnRH-5 d-CIDR-out + PGF2α-3 d-GnRH + TAI]; (2) PGF+TAI: AIE after the second of 2 PGF2α treatments 14 d apart; heifers not AIE within 9 d after the second PGF2α were enrolled in 5d-Cosynch; and (3) ALL-TAI: timed AI after a 5d-Cosynch protocol. PGF+AIE (n = 313)PGF+TAI (n = 330)Diff Difference between PGF+TAI and PGF+AIE. ALL-TAI (n = 306)Diff Difference between ALL-TAI and PGF+AIE. P-value All heifers Total RP cost928 ± 18909 ± 18−19898 ± 18−300.08 Total FLP profit393 ± 20424 ± 1931405 ± 20120.48 Cash flow 15-mo−534 ± 33−483 ± 3251−492 ± 33420.22 Not culled Total RP cost934 ± 23921 ± 23−13918 ± 23−160.36 Total FLP profit496 ± 13501 ± 125.0503 ± 137.00.92 Cash flow 15-mo−436 ± 26−421 ± 2615−421 ± 27150.80 1 RP = rearing period; FLP = first lactation period; not culled = heifers that were sold or died during the rearing and first lactation period were removed from the analysis. 2 Treatment: at 368 ± 10 d of age, heifers received first AI after: (1) PGF+AIE: insemination at detected estrus (AIE) after PGF treatments 14 d apart (up to 3) starting at the beginning of the AIP; heifers not AIE within 9 d of the third PGF treatment were enrolled in a 5d-Cosynch protocol [5d-Cosynch = controlled internal drug release insert (CIDR) + GnRH-5 d-CIDR-out + PGF-3 d-GnRH + TAI]; (2) PGF+TAI: AIE after the second of 2 PGF treatments 14 d apart; heifers not AIE within 9 d after the second PGF were enrolled in 5d-Cosynch; and (3) ALL-TAI: timed AI after a 5d-Cosynch protocol. 3 Difference between PGF+TAI and PGF+AIE. 4 Difference between ALL-TAI and PGF+AIE. Stochastic Analysis Differences in cash flow for the 15-mo period after the beginning of the AIP for all heifers included in the study under diverse pricing scenarios are presented in Figure 1. Differences in cash flow between the PGF+TAI and PGF+AIE treatments were 100% of the time positive values (i.e., in favor of the PGF+TAI treatment). The mean difference after 10,000 iterations was$53.90/slot per 15 mo (95% CI: $29.10–84.10), and it ranged from$10.10 to $128. Milk price was the main contributor to the total variance, explaining ~51% of the total variation in cash flow differences. Greater milk price favored the PGF+TAI treatment. Similarly, differences in cash flow between the ALL-TAI and PGF+AIE ranged from a minimum of$23.40/slot to a maximum of $128/slot per 15 mo, with a positive average (i.e., in favor of the ALL-TAI treatment) of$48.80/slot (95% CI: $17.20 to$84.10) with milk price as the main contributor of the total variance (~40%). Greater milk price favored the ALL-TAI treatment. Finally, results for the differences in cash flow between the ALL-TAI and PGF+TAI treatments had a mean of $-5.01/slot per 15 mo (95% CI:$-23.40 to $12.70) and a minimum and a maximum of$-51.00 and $31.40, respectively. In this case, the contribution to variance was led by the cost of a new replacement heifer (29%) closely followed by the cost of a new replacement cow (24%), and both combined represented ~55% of the total variation in cash flow differences. DISCUSSION Our study examined economic outcomes for replacement Holstein heifers managed with 3 reproductive management programs that varied in method of submission to first service from almost exclusive use of AIE to exclusive use of TAI. We aimed to provide an all-encompassing comparison that reflected to the best extent possible the conditions of commercial dairy farms. Thus, the main outcome of interest was cash flow per slot for a fixed period of time (i.e., 15 mo after the beginning of the AIP) accounting for the multiple interactions among reproductive performance, productivity, and replacement dynamics as previously reported for lactating dairy cows by our group ( • Stangaferro M.L • Wijma R. • Masello M. • Thomas M.J. • Giordano J.O. Economic performance of lactating dairy cows submitted for first service timed artificial insemination after a voluntary waiting period of 60 or 88 days. , • Stangaferro M.L. • Wijma R.W. • Giordano J.O. Profitability of dairy cows submitted to the first service with the Presynch-Ovsynch or Double-Ovsynch protocol and different duration of the voluntary waiting period. ) and others ( • De Vries A. Economics of delayed replacement when cow performance is seasonal. , • De Vries A. Economic value of pregnancy in dairy cattle. ; • Gobikrushanth M. • De Vries A. • Santos J.E.P. • Risco C.A. • Galvão K.N. Effect of delayed breeding during the summer on profitability of dairy cows. ). The evaluation of cash flow without the effect of the replacement dynamics was explored to isolate the effect of timing of pregnancy because replacement cost can have profound effects on overall cash flow. The greatest effect of the treatments evaluated on reproductive performance was shifting timing of pregnancy through different insemination risks as the overall first service fertility was similar regardless of the method of submission to AI. Time to pregnancy was reduced for the programs that relied more on TAI with greatest hazard of pregnancy for ALL-TAI, intermediate for PGF+TAI, and lowest for the PGF+AIE program. In spite of these differences, the proportion of heifers pregnant at the end of the observation period and calving was not affected. A direct consequence of earlier pregnancy for the programs that relied more on TAI was a modest difference in RP length, and consequently AFC, which reduced RP cost and numerically increased cash flow during the FLP. Collectively, these effects resulted in numerical differences in overall cash flow per slot for the 15-mo period that would be of potential value to commercial dairy farms. Nevertheless, from a strict statistical perspective, our hypothesis of improved cash flow for the programs that incorporated more aggressive use of TAI was not supported. Minor monetary differences and compensation among multiple parameters coupled with large variation among heifers likely explained our observations. The dramatic reduction in cash flow differences among treatments for the analysis including only heifers not culled revealed a smaller contribution of differences in time to pregnancy. Moreover, the different magnitude of change in the differences between treatments illustrated the complexity of the effect of replacement cost on cash flow of dairy animals, especially when accounting for the replacement dynamics during rearing and first lactation. Such prominent role of replacement cost on cash flow highlights the need to account for culling practices and potential cost at the time of selecting or comparing reproductive management programs for replacements. In summary, in spite of the lack of statistical significance and based on the accumulated trends for the rearing and lactation periods accounting or not for heifers that exited the herd, total cash flow trended (in order of magnitude) in favor of the PGF+TAI and ALL-TAI relative to the PGF+AIE program. Thus, under similar conditions than those of our study and assuming that results are repeatable, both programs incorporating systematic use of TAI early after the beginning of the AIP would be expected to improve cash flow of the heifer enterprise as compared with programs similar to PGF+AIE which relied primarily on AIE for submission to the first service. In support of our other hypothesis, reproductive cost was greater for the ALL-TAI than for the PGF+AIE and PGF+TAI programs. This difference was largely explained by greater hormonal treatment cost, which accounted for ~94% of the difference in total reproductive cost relative to the PGF+AIE program. These results were expected because previous studies evaluating reproductive management for heifers consistently reported increased hormonal treatment cost for ALL-TAI relative to AIE-based programs ( • Stevenson J.L. • Rodrigues J.A. • Braga F.A. • Bitente S. • Dalton J.C. • Santos J.E.P. • Chebel R.C. Effect of Breeding Protocols and Reproductive Tract Score on Reproductive Performance of Dairy Heifers and Economic Outcome of Breeding Programs1. ; • Lopes Jr., G. • Johnson C. • Mendonça L. • Silva P. • Moraes J. • Ahmadzadeh A. • Dalton J. • Chebel R. Evaluation of reproductive and economic outcomes of dairy heifers inseminated at induced estrus or at fixed time after a 5-day or 7-day progesterone insert-based ovulation synchronization protocol. ; • Silva T.V. • Lima F.S. • Thatcher W.W. • Santos J.E.P. Synchronized ovulation for first insemination improves reproductive performance and reduces cost per pregnancy in dairy heifers. ). On the other hand, the cost of semen and pregnancy diagnosis had a negligible effect on overall reproductive cost (<$1/slot). Such small effect was likely explained by the overall similar fertility observed across treatments not only for first AI service (sexed semen) but also for second and subsequent AI services (conventional semen). Interestingly, although more heifers received TAI in the PGF+TAI than in the PGF+AIE program, the additional cost of synchronization of ovulation did not translate into greater overall reproductive cost. This was because the minor increment in hormone cost was compensated by the accumulation of minor savings in the other items (i.e., semen and AI, pregnancy diagnosis) that also contributed to reproductive cost.
Despite greater reproductive cost, total cost accrued during the RP tended to be lower for ALL-TAI relative to the PGF+AIE program. Rearing cost for PGF+TAI was intermediate but resembled more closely that of the ALL-TAI treatment. These results were expected, because reduced time to pregnancy for ALL-TAI heifers resulted in lower AFC and consequently a numerical reduction in expenses directly affected by RP duration (i.e., feed cost and other operating expenses). This reduction, however, accounted only for ~28% of the total difference in total rearing cost. The main contribution to rearing cost differences was for replacement cost (~46% of the difference) which favored the ALL-TAI program (statistical tendency). Paradoxically, this was the result of a positive cash flow for heifers that were sold because a heifer sold after the beginning of the AIP was heavier than the heifer that replaced it. Conversely, when removing the effect of replacement dynamics (i.e., culled heifers not included in the analysis) the reduction in RP expense was mostly because of reduced feed cost of ALL-TAI heifers, which accounted for ~50% of the difference with PGF+AIE heifers. A substantial proportion of this gain, however, was offset by greater hormonal treatment cost, to the extent that no significant differences in total RP cost were observed. In summary, most economic items trended in favor of the PGF+TAI and ALL-TAI relative to the PGF+AIE program. Nonetheless, the differences in timing of pregnancy between treatments were of insufficient magnitude to have a large effect on RP expenses when other expenses not directly associated with RP duration (i.e., replacement and reproductive cost) were accounted for. Of note, reproductive cost was offset regardless of the method to estimate cash flow indicating that as long as timing of pregnancy is reduced, the additional investment in synchronization of ovulation for TAI seemed justified. On the other hand, given the relevance of replacement cost on cash flow differences, it seems reasonable to suggest considering the potential effect of culling practices and market value of animals (i.e., sold and bought) at the time of evaluating reproductive management strategies for heifers.
Regardless of the type of analysis (i.e., all heifers enrolled vs. not culled only), most economic differences during first lactation presented similar trends as those observed for the RP. Reduced AFC for the ALL-TAI treatment translated into numerically greater IOFC. This gain, however, was offset to the extent of resulting in no statistically significant differences for the FLP by factors not directly affected by lactation length (i.e., calf value and replacement cost) and by the greater cost of maintaining lactating cows than heifers (i.e., other operating expenses). The observed unfavorable differences (statistical tendency) for calf value for the ALL-TAI treatment were in line with the slight numerical reduction in the number of born female calves and with the slight increment in the number of stillbirths as compared with the PGF+AIE treatment. Nevertheless, the contribution of calf value to overall FLP profit was inconsequential (i.e., $3/slot). Similar to the RP, outcomes for the FLP for the PGF+TAI program were mostly intermediate. The tendency for greater calf value and the numerically lower replacement cost resulted in numerically greater FLP profit relative to ALL-TAI. Collectively, we observed that cash flow during the FLP followed expected trends (i.e., greater for ALL-TAI and PGF+TAI than for PGF+AIE), but minor monetary differences and compensation among items not directly affected by the timing of first calving likely resulted in lack of significant differences on total FLP cash flow. Taken together, data from the RP and FLP suggested that the magnitude of the differences observed in timing of pregnancy and consequently on AFC were of sufficient magnitude to generate numerical differences for cash flow over the 15-mo period that would be of economic value to commercial dairy farms but were of insufficient magnitude to be statistically significant. The latter can be explained by the magnitude of the difference in reproductive performance and the effect of large heifer-to-heifer variation on overall cash flow differences. The small magnitude of the differences in time to pregnancy between treatments was the result of the high insemination risk for the PGF+AIE treatment because a high proportion of heifers received AIE within a short time after the beginning of the AIP (i.e., 78% AIE after the first PGF treatment in PGF+AIE) and had similar P/AI than heifers in the other treatments. Our results are in agreement with those of • Ribeiro E.S. • Galvão K.N. • Thatcher W.W. • Santos J.E.P. Economic aspects of applying reproductive technologies to dairy herds. who in a simulation study reported that the economic benefits of incorporating programs that relied mostly on TAI for managing reproduction of replacement heifers were inconsequential when estrus detection efficiency was at least 70%. In contrast, • Silva T.V. • Lima F.S. • Thatcher W.W. • Santos J.E.P. Synchronized ovulation for first insemination improves reproductive performance and reduces cost per pregnancy in dairy heifers. reported reduced rearing cost for heifers managed with an ALL-TAI (5-d Cosynch with initial GnRH and 2 PGF treatments) program compared with a predominant AIE-based program, even when a high proportion of heifers were AIE (>80%) relatively early after the beginning of the AIP. Differences in insemination risk between experiments, and consequently timing of pregnancy imposed by different experimental designs likely explain the contrasts in results observed for our experiment and that of • Silva T.V. • Lima F.S. • Thatcher W.W. • Santos J.E.P. Synchronized ovulation for first insemination improves reproductive performance and reduces cost per pregnancy in dairy heifers. . On the other hand, in spite of the reasonable number of heifers included in each treatment in our study, substantial heifer-to-heifer variation contributed to the lack of statistically significant differences in cash flow per 15 mo. This was a reflection of the major variation in cash flow per slot (range$-2,776 to \$470; data not shown) driven primarily by large differences in replacement cost and milk income between slots. This is in agreement with recent studies that included a similar comprehensive approach to calculate cash flow of dairy cows managed with different reproductive management programs (
• Stangaferro M.L
• Wijma R.
• Masello M.
• Thomas M.J.
• Giordano J.O.
Economic performance of lactating dairy cows submitted for first service timed artificial insemination after a voluntary waiting period of 60 or 88 days.
,
• Stangaferro M.L.
• Wijma R.W.
• Giordano J.O.
Profitability of dairy cows submitted to the first service with the Presynch-Ovsynch or Double-Ovsynch protocol and different duration of the voluntary waiting period.
).
Stochastic analysis with Monte Carlo simulation is a useful tool to estimate trends and the expected magnitude of differences in cash flow for different management strategies when multiple inputs and their variation across time might affect cash flow (
• McArt J.A.A.
• Nydam D.V.
• Oetzel G.R.
• Guard C.L.
An economic analysis of hyperketonemia testing and propylene glycol treatment strategies in early lactation dairy cattle.
;
• McArt J.A.A.
• Oetzel G.R.
A stochastic estimate of the economic impact of oral calcium supplementation in postparturient dairy cows.
). In this case, we estimated a range of differences in cash flow for the programs compared under a wide range of market conditions. We observed that the PGF+TAI and ALL-TAI treatments were economically favorable relative to the PGF+AIE program under all for PGF+TAI or almost all scenarios for ALL-TAI (i.e., > 98%) suggesting that under a wide range of conditions caused by market fluctuations the programs incorporating more aggressive use of TAI would be beneficial to the economics of the heifer enterprise. Based on the range of values and shape of the distribution for cash flow differences, it was apparent that the PGF+TAI treatment would lead to greater and more consistent positive differences compared with the PGF+AIE treatment than the ALL-TAI treatment. Conversely, implementing either the PGF+TAI or ALL-TAI treatments would likely be neutral because values for their cash flow differences were almost equally distributed around zero. Collectively, the results of the stochastic and deterministic analysis suggested that the selection of reproductive management programs for replacement heifers should be made in light of the known or expected insemination risk for AIE or TAI-based programs, the effect of culling practices, and current and future prices for milk and replacements. In addition, the cost of hormonal treatments seemed less relevant because its effect on overall cash flow differences was small compared with the value of earlier pregnancy.
A caveat of our study was that the cash flow estimation did not include the opportunity cost of the investment on the different reproductive programs compared. Nevertheless, estimations of the net present value using a discount rate of 5% (data not shown) resulted in no difference in the direction and magnitude of the differences between treatments.

CONCLUSIONS

We concluded that reproductive management programs that used TAI in combination with AIE or TAI as the primary method to submit heifers for first service generated differences in cash flow of potential value to commercial dairy farms. Reduced rearing cost and more revenue generated during the first lactation increased cash flow for up to 15 mo after heifers became eligible for pregnancy under fixed or simulated variable market conditions. Greater reproductive cost due to use of TAI were offset by the positive effect of earlier pregnancy on cash flow of replacements heifers.

ACKNOWLEDGMENTS

This research was financially supported through a grant (AOR 15-020) from the New York Farm Viability Institute (Syracuse, NY) to J. O. Giordano. We thank the two commercial dairy farms that participated in this research for their support and the use of their cows and facilities. We also extend our gratitude to Zoetis (Parsippany-Troy Hills, NJ) for providing the hormonal products used to synchronize estrus and ovulation. Finally, we thank Jim Ehrlich from DairySights LLC (Argyle, NY) for his calculations of daily milk production using the MilkBot model. The authors have not stated any conflicts of interest.

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