Estrous Synchronization and Fertility in Gilts after 14- or 18-Day Feeding of Altrenogest Beginning at Estrus or Diestrus2

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Abstract
A synthetic progestogen (altrenogest) was used to synchronize estrus in 160 Yorkshire and Duroc × Yorkshire gilts (6 to 11 mo old) in four trials. Gilts were fed 15 mg altrenogest for 14 or 18 d beginning either at or near estrus (d −1, 0, +1 or +2) or at diestrus (d +3 to +21). Mean intervals to estrus after treatment did not differ between 14- and 18-d treatments (5.4 ± .1 vs 5.3 ± .1 d, respectively), but were slightly longer (P<.01) in gilts beginning treatment at or near estrus than in diestrus (5.6 ± .1 vs 5.2 ± .1, respectively). Average intervals to estrus were similar between treatment groups and among stages of the cycle even though more gilts (P<.01) beginning treatment at estrus had serum progesterone concentrations >2 ng/ml at the end of progestogen treatment. Although more 18- than 14-d treated gilts (P<.05) were in estrus on d 5 post-treatment, proportions in estrus from 3 to 10 d post-treatment were similar (>98%). Neither stage of estrous cycle at onset of treatment nor duration of progestogen treatment affected percentages of gilts farrowing (>73%), average gestation length (116.5 d), or total (10.3), live (9.7) and dead (.6) pigs at birth after artificial insemination at the post-treatment estrus. We concluded that 14-d feeding of altrenogest effectively synchronized fertile estrus in gilts regardless of stage of estrous cycle at the onset of progestogen treatment. Although 18-d treatment of gilts with altrenogest improved estrous synchronization precision compared to 14-d treatment, there was no advantage of the 18-d treatment for subsequent farrowing responses. Copyright © 1982. American Society of Animal Science . Copyright 1982 by American Society of Animal Science

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