Flushing and altrenogest affect litter traits in gilts.

Gilts (n = 267) were allotted to flushing (1.55 kg/d additional grain sorghum), altrenogest (15 mg.gilt-1.d-1) and control treatments in a 2 x 2 factorial arrangement. Altrenogest was fed for 14 d. Flushing began on d 9 of the altrenogest treatment and continued until first observed estrus; 209 gilts (78%) were detected in estrus. The interval from the last day of altrenogest feeding to estrus was shorter (P less than .05) with the altrenogest + flushing treatment (6.6 +/- .2 d) than with flushing alone (7.6 + .3 d). Ovulation rates (no. of corpora lutea) were higher (P less than .05) in all flushed gilts (14.5 +/- .4 vs 13.4 +/- .4), whether or not they received altrenogest. Flushing also increased the total number of pigs farrowed (.9 pigs/litter; P = .06) and total litter weight (1.43 kg/litter; P = .01), independent of altrenogest treatment. Number of pigs born alive and weight of live pigs were higher for gilts treated with altrenogest + flushing and inseminated at their pubertal estrus than for gilts in all other treatment combinations. In contrast, gilts receiving only altrenogest had greater live litter weight and more live pigs born when inseminated at a postpubertal estrus than when inseminated at pubertal estrus. We conclude that flushing increased litter size and litter weight, particularly for gilts that were inseminated at their pubertal estrus. Increased litter size resulted from increased ovulation rates, which, in nonflushed gilts, limited litter size at first farrowing.