THE INFLUENCE OF NUTRITION DURING POST\x=req-\ LACTATIONAL OESTRUS ON OVULATION RATE IN THE SOW AND THE ACCURACY OF CORPORA LUTEA COUNTS IN ESTIMATING OVULATIONS

Summary. Five mature sows, given a double feed approximately 12 hr after onset of oestrus, ovulated 16\m=.\8\m=+-\0\m=.\95,compared with 14\m=.\5\m=+-\ 0\m=.\86for six controls (P\m=simeq\0\m=.\10).Corpora lutea counts at laparotomy 3 to 7 days post coitum (p.c.), and at slaughter 25 days p.c. by visual count and by dissection of the ovaries, were 12\m=.\1\m=+-\0\m=.\33,14\m=.\0\m=+-\0\m=.\33and 15\m=.\5\m=+-\0\m=.\33, respectively. An increase in ovulation rate has been reported previously in nulliparous gilts(Lodge & Hardy, 1968) following the consumption of extra feed after onset of oestrus. The same effect had been noted in sows (Heap, Lodge & Lamming, 1967) but the increase in ova in the animals given extra feed failed to be statistically significant. In that experiment, assessment of ovulation rate was by corpora lutea count at the 28th day of pregnancy but there is evidence to suggest that the number of corpora lutea may change with the time ofcounting(Reitmeyer & Sorensen, 1965; Longenecker, Waite & Day, 1967). The objects of the present experiment were to investigate the effect of increasing the feed allowance at a single feed during oestrus and to determine whether the number of corpora lutea changed during the first 25 days o