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Six component intervals of nonproductive days by breeding-female pigs on commercial farms¹

School of Agriculture, Meiji University, Kawasaki, Japan 214-8571

	Abstract

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Of 105 swine herds using a production record system for breeding female pigs, 95 farms were used to analyze nonproductive female days (NPD), the six component intervals of NPD, and related measurements. The NPD was defined as the days when mated gilts and sows were neither gestating nor lactating, and it was calculated by summing the six component intervals in the average mated female inventory. The mean NPD was 57.9 d (SD = 20.5), and the proportions of six component intervals of gilt first-mating-to-pregnancy interval, gilt first-mating-to-culling interval, unmated weaning-to-culling interval, weaning-to-first-mating interval, sow first-mating-to-pregnancy interval, and sow first-mating-to-culling interval were 9.24, 7.82, 6.85, 27.9, 18.9, and 29.3%, respectively. Farms in the upper 25th percentile of the ranking for number of pigs weaned·mated female^–1·yr^–1 were designated as 25 high-performing farms. The remaining farms were designated as an ordinary farm group for comparisons. High-performing farms had 21.1 d fewer NPD, and five of the six component intervals were lower compared with the ordinary farms (P < 0.05). Regression analyses indicated that the number of litters·mated female^–1·yr^–1 increased by 0.07 in both farm groups as NPD decreased every 10 d. Fewer NPD were correlated with a higher percentage of multiple matings during estrus (P < 0.05) but were not correlated with removal risk and replacement risk in both farm groups. The average parity of culled females was negatively correlated with NPD in the ordinary farm group, and the average farrowed parity was positively correlated with NPD in the high-performing farm group (P < 0.01). Decreasing each component interval of the NPD six components is critical to increasing herd productivity. A high percentage of multiple matings during estrus and appropriate culling management may be key factors to decrease NPD.

Key Words: Management • Nonproductive Female Days • Pigs • Reproductive Efficiency • Sow Productivity

	Introduction

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Among herd performance measurements of breeding female pigs (females), the best indicator is the number of pigs weaned·mated female^–1·yr^–1 (PWMFY), which is the product of the number of litters·mated female^–1 ·yr^–1 (LMFY) and the number of pigs weaned per sow (Dial et al., 1992). The LMFY depends on the number of nonproductive mated female days (NPD), lactation duration, and gestation duration within a productivity tree of breeding herds. Decreasing the NPD is the best way to improve herd productivity as measured by the LMFY and PWMFY (Wilson et al., 1986).

The mean NPD, including unbred gilts, in 615 U.S. herds was 93 d (SE = 1.3; Koketsu, 2000). Six component intervals of NPD for mated gilts and sows (mated females) were identified: gilt first-mating-to-pregnancy interval, gilt first-mating-to-culling interval, unmated weaning-to-culling interval, weaning-to-first-mating interval, sow first-mating-to-pregnancy interval, and sow first-mating-to-culling interval (Polson et al., 1992). These six intervals were calculated by using the number of culled or mated gilts or sows as a denominator, and the NPD was calculated by using the average number of mated females in an inventory (average mated female inventory) as a denominator. By using the same denominator of average mated female inventory, the six component intervals and proportions are comparable to each other and are useful for producers and veterinarians to prioritize their actions to increase herd productivity.

Management measurements associated with NPD in high-performing farm groups and ordinary groups were not previously reported. The relationships between NPD, LMFY, and PWMFY have not been examined thoroughly on high-performing and ordinary farm groups. The objectives of this study were to measure NPD and NPD component intervals and their proportions to quantify the relationship between NPD and LMFY, and to calculate correlations between NPD and management measurements in the two farm groups.

	Materials and Methods

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Data
The average mated female inventory was calculated as the total days mated females were fed in a herd (pig days) during 1 yr divided by 365 (PigCHAMP, 1996). Mated females included mated gilts and sows. A mated gilt (parity 0) was defined as a female that was mated but had not farrowed. Culled females included females shipped to a slaughter house or destroyed in a barn. Removed females included culled females and dead females in a barn. Removal, culling, or replacement risks were defined as the number of removed, culled, or replaced females, respectively, multiplied by 100, and then divided by average mated female inventory.

Definitions
The NPD was the average number of days when mated females were neither gestating nor lactating. The NPD in this study was calculated by summing the six component intervals. Each of the six component intervals was calculated as nonproductive days in each component interval category divided by the average mated female inventory. Gilt NPD, sow NPD, culling interval NPD, and pregnancy interval NPD were formed as NPD subgroups. Gilt NPD included gilt first-mating-to-pregnancy interval and gilt first-mating-to-culling interval, and sow NPD included the unmated weaning-to-culling interval, weaning-to-first-mating interval, sow first-mating-to-pregnancy interval, and sow first-mating-to-culling interval. Culling intervals included gilt and sow first-mating-to-culling intervals, and unmated weaning-to-culling intervals. Pregnancy intervals included gilt and sow first-mating-to-pregnancy intervals. The first-mating-to-pregnancy interval was defined as the interval between the first mating date and the date of mating that produced her farrowing event.

Participating Farms
All 117 commercial farms using a computerized record software program (PigCHAMP, 1996) in Japan were requested from December 2001 to mail their data files to the animal production laboratory at the School of Agriculture, Meiji University, when they purchased software or renewed their yearly maintenance contract. By August 31, 2002, PigCHAMP files were received from 107 farms. Of these 107 farms, two farms were grow-to-finish operations and were not used. Each farm file was checked for producer’s missing records during 2001 as a data-integrity analysis. In the analysis, 10 farms had 0 d of gilt first-mating-to-culling interval and were not used because the 10 farms may not have recorded culled gilts with reproductive problems after mating. The remaining 95 farms were used for further analyses.

Annual performance measurements of production were extracted from the records of each farm. Farms were ranked and grouped according to the PWMFY. Farms in the upper 25th percentile of this ranking were then designated as high-performing farms, and the remaining farms were used as ordinary farms for comparison. Their farm locations in Japan were grouped into five regional blocks.

Breeding stock on these farms in this study was originally imported from the United States or Europe. Lactation and gestation diets were formulated by using imported corn and soybean meal. Sows were mated at first estrus after weaning, and delayed mating after weaning was not practiced. Both AI and natural matings were practiced. Double or triple mating of females during an estrous period (multiple matings during estrus) was recommended by breeding management on these commercial farms. Natural or mechanical ventilation was used in gestation and lactation barns. The use of evaporating drip coolers and partially slatted floors in breeding herds were common on these farms.

Statistical Analyses
Summary statistics and frequency distributions were obtained by using the UNIVARIATE and FREQ procedures of SAS (SAS Inst., Inc., Cary, NC). Statistical models were used to compare measurements between high-performing and ordinary farms by the MIXED procedure using the five regional blocks as a random effect. The regional blocks were used as random effects in this study because a random sample of a large set of population levels was used.

Multiple regression analyses were done to obtain regression coefficients of measurements in the REG procedure of SAS. The five variables (LMFY, pigs weaned per sow, NPD, lactation duration, and gestation duration) related to PWMFY in a productivity tree of breeding herds were chosen. The productivity tree was proposed as a tree-like figure indicating interrelationships between key herd measurements (Dial et al., 1992). Farms were coded 1 for high-performing farms or 0 for ordinary farms. The variance inflation factor of each independent variable in each model was calculated to check collinearity in the models (Kleinbaum et al., 1988). Keeping the component variables within a productivity tree of breeding herds in the models, two-way interactions of all variables were then examined (P < 0.10). The normality of the residuals from all the regression models was confirmed using rankit plots and the Wilk-Shapiro test in the UNIVARIATE procedure of SAS (W: Normal = 0.95; P < W 0.01). Partial Pearson correlation analyses between NPD and management-related measurements were done with SAS using percent changes in the average female inventory as a controlled variable.

	Results

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Table 1 shows summary statistics of key measurements, and the comparisons of productivity measurements for the two farm groups. The mean NPD was 57.9 d (SD = 20.5) on 95 commercial farms. The high-performing farms had 21.1 d fewer NPD, 0.20 greater LMFY, and 3.7 pigs greater PWMFY than the ordinary farms (P < 0.05). High-performing farms also had a higher percentage of multiple matings during estrus than ordinary farms (P < 0.05). The data integrity analysis showed that 55 of the 95 farms had 0% of missing mating records in farrowed sow records.

	Discussion

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Sow NPD was approximately 83% of NPD because sow numbers were greater than gilts on commercial farms; however, producers should not ignore gilt NPD because high-performing farms had approximately six fewer NPD by gilts than ordinary farms. The 6 d are sufficient to decrease NPD.

Culling risks on commercial farms due to reproductive failure are approximately 12 to 40% according to a review of 16 previous studies (D’Allaire and Drolet, 1999). Both gilts and sows in a breeding herd increase the number of NPD before being removed from the herd when they are found not to be pregnant. The present study, showing 10 d or longer differences in first-mating-to-culling intervals by gilts and sows between high-performing and ordinary farms, may indicate that decreasing the culling intervals in gilts and sows is important to reducing NPD. However, increasing productive midparity female proportions in a breeding herd, not implementing strict culling policies for young females, is recommended because the average parity at culling and removal risks are not as critical as a parity distribution of culled females to improve culling intervals (D’Allaire and Drolet, 1999). No difference in unmated weaning-to-culling intervals between the two farm groups indicates that culling policy and practices for unmated sows were similar in both farm groups.

The pregnancy intervals were the two component intervals of gilt and sow first-mating-to-pregnancy intervals. Our results showing 10 d or longer differences in gilt and sow first-mating-to-pregnancy intervals between the high-performing and ordinary farms may indicate that decreasing the postmating intervals is critical to decreasing NPD. Performance measurements related to pregnancy intervals are farrowing rate and remating interval. An average remating interval by individual remated females was approximately 48.0 d in the 149 U.S. breeding herds (Koketsu, 2003). Real-time ultrasonography can be effectively used to discover pregnancy at 25 to 35 d after mating (Kober, 2003), and mating management using AI has recently been improved (Singleton, 2001).

This study quantitatively assessed the relationships between NPD and its related performance within a breeding herd productivity tree proposed by previous researchers (Dial et al., 1992). Decreasing NPD from 60 to 50 d would increase LMFY by 0.07, and PWMFY would then increase by 0.74 pigs (0.07 LMFY x 10.5 pigs per sow) on high-performing farms or by 0.63 pigs (0.07 LMFY x 9.03 pigs per sow) on ordinary farms. These values from regression coefficients are consistent with previous studies of 143 North American pig farms, suggesting that every 10-d decrease of NPD increases LMFY by 0.07 litters and PWMFY by 0.5 pigs (Polson et al., 1992); however, unbred gilts were used in their calculations. Mated females (Wilson et al., 1986) and females with maiden gilts (Stein et al., 1990) were used for NPD calculations by other researchers. For herd-to-herd comparisons, using only mated females is better than using all females, including maiden gilts, because the herd entry age varies among commercial swine farms, and prolonged periods of isolation and acclimation practices currently are recommended to minimize losses due to exposure to specific diseases (Dee et al., 1995). The mean of isolation and acclimation in current practice on 2,499 farms is 38.7 d and varied from 35.1 d on small farms to 51.1 d on large farms (NAHMS, 2000).

Negative correlations between percentage of multiple matings during estrus and NPD in both farm groups indicate that increasing the percentage of multiple matings during estrus is a good management practice (King et al., 1998; Xue et al., 1998) to decrease NPD on commercial farms.

It is interesting that decreased NPD was correlated with lower farrowed parity and larger gilt pool size, but not with culled parity, on high-performing farms, whereas a decreased NPD was correlated with higher culled parity and smaller gilt pool size, but not with farrowed parity, on ordinary farms. Although the correlation coefficients were not very high (–0.5 < r < 0.5), these complex correlations can be explained by herd management differences between high-performing farms and ordinary farms (Koketsu, 2000, 2005). For example, these correlations may be interpreted as indicating that high-performing farms may keep old sows too long because they do not have enough gilts to replace the sows in a timely manner, but ordinary farms may cull sows too early because they have many gilts to replace sows. High-performing farms could have a more stable age structure than ordinary farms by using constant deliveries of gilts and sow removal (Koketsu, 2005). Additionally, a decision on which sows should be culled is more important than annual culling risk. High productivity by high-performing herds is attributable to better and different farm management (Koketsu, 2000), including careful day-to-day management with an appropriate culling policy (Stein et al., 1990; Dial et al., 1992).

Short lactation duration was reported to be associated with suboptimal reproductive performance, such as prolonged weaning-to-first-mating interval (Koketsu and Dial, 1997). No correlation between NPD and lactation duration may be interpreted as indicating that high-performing farms are under better management, including nutrition during lactation and postweaning mating, than ordinary farms, although high-performing farms were using shorter lactation durations than ordinary farms.

In conclusion, it is recommended that producers and veterinarians should pay close attention to the NPD and its six component intervals to improve breeding herd productivity. However, this summarizes a retrospective observational study using production records from commercial farms. The results could be biased against housing, nutrition, environment, and genotype conditions that were not measured. Thus, the findings in this study should be interpreted only as an association or correlation, not as indicators of biological causation.

	Implications

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Swine producers should measure herd performance continuously and compare the measurements with standards and targets to identify improvement. For benchmarking purposes, the use nonproductive days for mated gilts and sows and its six component intervals per average mated female inventory is recommended.

	Footnotes

 
¹ Appreciation is expressed to the PigCHAMP staff in Global Pig Farms, Inc. (Setagun, Gunma, Japan) for their technical assistance.

² Correspondence—phone: 81-44-934-7826; fax: 81-44-934-7902; e-mail: koket001{at}isc.meiji.ac.jp.

Received for publication September 14, 2004. Accepted for publication March 4, 2005.

	Literature Cited

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