| Abstrakt: |
Ten trials involving 340 sows were conducted to determine the effects of lactation length and antibiotics at breeding on reproductive performance. Litters were removed from sows following a 6-, 12-, 18- or 24-day lactation. In six trials (224 sows), two dietary treatments [with or without 1.0 g of an antibiotic-sulfa combination (two parts chlortetracycline, two parts sulfamethazine and one part penicillin) per sow per day from weaning to 3 days postmating] were superimposed on the four lactation lengths to provide a 4 × 2 factorial arrangement of treatments. Following mating at the first estrus, 80 sows were slaughtered 3 days postmating to determine fertilization rate, ovulation rate and uterine characteristics. The remaining 260 sows were taken to term to determine farrowing rate and litter size.Ovulation rate, ova recovered and fertility rate (percent of sows with fertilized ova or percent of ova fertilized) were not significantly (P<.05) affected by lactation length. Number of cystic follicles decreased linearly (P<.05) as lactation length increased to 24 days. Uterine wall and myometrial thickness, uterine weight and uterine horn length decreased linearly (P<.01) as lactation length increased. Antibiotic treatment did not significantly influence ovulation rate, fertility rate or uterine characteristics.Days to first postweaning estrus decreased quadratically (P<.05) as lactation length increased. Neither conception rate nor farrowing rate was significantly affected by length of lactation, though farrowing rate was slightly higher (68.2 vs64.6%) following 18- and 24-day lactations as compared with that following the 6- and 12-day lactations. Total or live pigs farrowed per litter increased (P<.01) as lactation length increased. Potential sow productivity (pigs born/sow/year) was maximized at the 18-day weaning schedule. The estimated productivities were 24.1, 23.9, 25.4 and 24.6 live pigs born/sow/year, respectively, for the 6-, 12-, 18- and 24-day lactations. In comparison with controls, the conception rate (68.5 vs75.6%), farrowing rate (60.9 vs70%) and number of live pigs per litter (9.8 vs10.0) were higher for antibiotic-fed sows; however, the differences were not significant. Neither was there evidence of a significant antibiotics × lactation length interaction. |
