Variability and repeatability in gestation length related to litter performance in female pigs on commercial farms
Introduction
Approximately 40% of preweaning mortality occurs within 1 d after farrowing; consequently, supervision and assistance to sows and piglets during perinatal periods reduced piglet mortality [1], [2]. By predicting gestation length (GL) on commercial farms, producers can supervise the farrowing and treat sows at the appropriate time to induce farrowing. However, the variability and repeatability of GL has been reported only for purebred sows [3], [4]; the repeatability and the correlation of GL between parities using crossbred sows on commercial farms has not been reported.
Sows with a GL of 112 d produced approximately 1.0 stillborn pigs [5], but GL was not correlated with the number of pigs born alive to purebred sows on university farms [4]. However, no study has reported the associations of GL with all three litter size variables, i.e. total pigs born, pigs born alive, and dead piglets. Additionally, associations of GL with lactation length and farrowing rate at subsequent farrowings have not been investigated. In a batch farrowing system in which sows are weaned on a certain day of the week, prolonged GL may be related to short lactation length and suboptimal reproductive performance in the following parity. For example, prolonged GL may result in sows with a short lactation length that was associated with a decreased subsequent farrowing rate [6].
Longevity of sows affects the productivity of the farm [7]; sows with a short or prolonged GL may be more likely culled than those with GL that is within the normal range. However, an association between GL and longevity has not been reported.
The objectives of the present study were to measure GL across parities, to determine the repeatability and the correlation of GL, and to examine the associations of GL with reproductive performance and longevity.
Section snippets
Data collection
All producers (approximately 140 farms) using a recording software system (PigCHAMP Inc. Ames, IA, USA) in Japan were requested to mail their data files to the School of Agriculture, Meiji University, when they purchased PigCHAMP or renewed the yearly maintenance contract. By 31 August 2005, the files were mailed from 122 farms. Of the 122 farms, 21 had no records with birth dates; those farms were excluded from this study. Records of birth dates on each farm were checked for a histogram of the
Results
Means of parity and parity at removal were 3.6 ± 0.01 and 4.8 ± 0.02, respectively. Table 1 shows comparisons of GL between parity groups in 66,254 farrowing records of 13,715 sows. The mean of GL across parities was 115.2–115.4 d, and the individual GL ranged from 105 to 125 d in all sow records. Approximately 70% of total farrowing events occurred between 114 and 116 d (Fig. 1). No difference was found in the GL among the parity groups except for GL at Parity 2, in which sows had 0.09 d longer
Discussion
In this study, mean GL on commercial farms was approximately 115 d; individual GL ranged from 105 to 125 d. Approximately 70% of farrowing events between 114 and 116 d indicated low variability of GL in sows on commercial farms. In addition, a difference within 0.1 d of GL between parities in this study may not be large enough to be meaningful in practice. Although GL varied among individual sows, it did not change with parity.
Based on the repeatability and the correlation coefficients in this
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