The Effects of Various Sequences of Full and Limited Feeding on the Reproductive Phenomena in Chester White and Poland China Gilts2

Abstract

Gilts of the Chester White (CW) and Poland China (PC) breeds were subjected to different sequences of feed levels; either self-fed (F) or hand-fed at ⅔ the full-fed rate (L) in each of two years to study the effects on ovulation rates, embryo survival and related reproductive phenomena. In each of the two years the experimental period began when the gilts were approximately 70 days of age and continued until the 25th day after the second heat period. The total period was divided into three phases: Phase I—prepuberty; phase II—the first estrual cycle; and phase III—from second heat (at which time all gilts were bred) until the 25th day of gestation. The feeding levels for the three successive phases are designated by a letter sequence, e.g., LFF. The 64 gilts in trial I averaged 215.7 days at puberty (SD of 29.2) and the 74 gilts in trial II averaged 213.2 days (SD of 27.8). Full-fed gilts in trial I and trial II respectively were 223 and 222 days of age at puberty as compared to 208 and 205 days for the limited-fed groups (P<0.01). Breed did not have a consistent effect over the two trials. Weight at 154 days and age at puberty were significantly associated (r of −0.27; P<0.01) within groups for the two years. Puberal age and time of birth (within spring season) were not associated. The first estrual cycle length averaged 21.1 days over both trials. Breed means did not differ but the CW gilts had more variation in each trial than the PC gilts (P<0.02). Fifty-seven gilts in trial I averaged 12.4 (SD of 2.6) at second heat and 53 gilts in trial II averaged 12.9 ova (SD of 3.0). The 13.5 and 14.8 ova means of the CW gilts in the two trials respectively were both greater (P<0.01) than the 11.3 and 11.2 ova means of the PC gilts. Trial I gilts kept on full feed throughout (FFF) had significantly more ova (13.9; P<0.01) than LLL (11.1) or FLL (11.1) gilts. The FFF group did not differ from LFF gilts (13.6 ova). In trial II the FF (L and F) group ovulation rate of 13.6 ova at second heat was greater (P<0.01) than the LLL mean of 11.1 ova but did not differ from the LFL mean of 13.5 ova—indicating the necessity of only a short period of full feeding to stimulate maximum ovulation. Second-heat ovulation rate and rate of gain during the first estrual cycle (within groups) were significantly associated over the two years (r=0.24; P<0.05). Weight of gilt at second heat and ovulation rate at that heat were not associated. The over-all fertilization rate of 96 percent was not affected by the individuality of the boar, breed of boar, mating system, feed level of the gilt, or breed of gilt. Embryo survival averaged 44.3 percent in trial I and 59.4 percent in trial II. The trial I CW and PC gilts had 40.8 percent and 47.9 percent embryo survival and 5.07 and 5.33 embryos respectively (P≅0.05). Trial II CW gilts had more embryos (8.8; P<0.05) than the PC gilts (6.4) but they did not differ in percentage of embryos surviving. Trial I FFF gilts had 32 percent embryo survival and 3.89 embryos as compared to 57 percent survival and 6.4 embryos for the LLL gilts. The trial II FFF gilts did not differ from the LLL gilts in number of surviving embryos (7.6 vs. 8.8) but the difference in percent survival was significant (P<0.01). Pooled probabilities of litter size differences for the two years indicated larger (P<0.02) litter for the LLL gilts. Trial I FLL gilts had 49 percent survival as compared to 32 percent for FFF gilts and the LFF gilts had 38 percent survival as compared to 57 percent for the LLL group. In trial II, FFF gilts had more embryos (7.6 vs. 4.6; P<0.05) and greater survival (53 percent vs. 35 percent; P<0.05) than the FFL gilts. The LFL gilts had 71 percent survival and 9.3 embryos and did not differ from the FFF gilts. Rate of gain both immediately before and immediately after breeding, was associated (P<0.01) in a positive direction in both instances with embryo survival but the second heat ovulation rate was negatively associated with survival rate (r=−0.25; P≅0.05). Standard partial regressions indicate a possible negative effect of back fat thickness on ovulation rate and on embryo survival but a positive effect (P<0.05) of slaughter weight on those two phenomena. Copyright © . .