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The impact of different patterns of feed restriction between d 1 and 15 of the estrous cycle on subsequent reproductive performance of 23 trios of littermate gilts was tested. Some gilts were fed a high plane of nutrition (HH gilts) throughout the cycle, in contrast to HR gilts, which were restricted from d 8 to 15, and RH gilts, which were restricted from d 1 to 7. During feed restriction, weight gain in RH gilts (2.5 +/- .7 kg) was lower (P = .006) between d 1 and d 7 than in their HH and HR littermates (5.6 +/- .7 and 5.6 +/- .8 kg, respectively) and it was lower (P = .0001) in HR gilts (5.5 +/- .5 kg) between d 8 to d 15 than in their HH and RH counterparts (8.5 +/- .4 and 9.4 +/- .5 kg, respectively). There were no differences in backfat changes among groups. Embryonic survival in HR gilts at d 28 of gestation (68.3 +/- 4.8%) was lower (P < .05) than in HH and RH gilts (83.6 +/- 4.3 and 81.7 +/- 4.5%, respectively). Plasma progesterone concentrations in HR gilts were lower (P < .05) at 48 and 72 h after onset of standing estrus (.82 +/- .2 and 3.6 +/- .5 ng/mL, respectively) than in HH and RH gilts (1.44 +/- .2 and 1.24 +/- .2 ng/mL, 5.0 +/- .4 and 5.0 +/- .5 ng/mL, respectively at 48 and 72 h). No differences in ovulation rate were observed among treatments. Placental area was positively correlated to embryo size at d 28 (embryo size = .0003 x (area) + 18.35; r = .28, P = .03) but placental volume was negatively correlated to the number of embryos in utero (placental volume = -4.317 x (number) + 207.55, r = -.39, P = .002). These data demonstrate that the timing of feed restriction during follicular development has important consequences for subsequent embryo survival, possibly mediated by differences in progesterone concentrations in early pregnancy.

. 1992. Effect of feed intake during lactation and after weaning on sow reproductive performance. Can. J. Anim. To study the effects oi feed intake during lactation and after weaning on reproductive performance. 89 second-parity Lacombe sows were allowed 6 kg feed d-'(H) or were restricted to 3 kg feed d-' (R) of gestation was influenced (P < 0.05) by feed intake during both periods. The highest embryo survival (85 %) was in HR sows, and the lowest (64%) was in RR sows. Blood samples were taken from 12 sows from each of the four treatments by means of indwelling vena cava cannulae at 6-h intervals from weaning until24 h after mating or 10 d after weaning, whichever came first. Plasma gonadotrophin concentrations were reduced (P < 0.05) by low feed intake during lactation but were unaffected by postweaning feed intake. Peak preovulatory LH surge concentrations were highest (9.5 ng ml--r) in HR sows and lowest (1 .6 ng mL-') in RR sows (P < 0.05). These data conhrm the adverse effects of restricted feeding during lactation on the reproductive performance of sows and indicate that such effects may be mediated through changes in plasma LH concentrations. No significant effect of postweaning feed intake on any measured factor was observed.Key words: Sow, feed intake, reproductive performance Baidoo, S. K., Aherne, F. X., Kirkwood, ') o, rationnd (R): (3 kg j 1) durant la lactation et durant I'intervalle sevrage-estrus suivant (ISO), selon un dispositif exp6rimental factoriel 2 x 2 (groupes EE, ER, RE et RR). Pour r6duire le plus possible les effets de confusion (confounding) de la dur6e de I'ISO sur la performance des truies, I'exp6rience, a 6td arr€t au 10 jour aprbs le sevrage. L'aliment fournissait 12,4 MJ EM kg-'et 16% de prot6ines brutes. Le rationnement durant la lactation a allong6 (P < 0,05) le ISO (7,3 j contre 5,9 j), mais l'intervalle n'6tait pas modifi6 par Ie niveau d'ingestion aprbs le sevrage. Moins (P < 0,05) de truies rationn6es durant la lactation 6taient revenues en chaleurs au jour 10 aprbs le sevrage (3 1,8

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Piglets were weaned from multiparous sows at 10 days (Group E; N = 7) or 35 days (Group C; N = 8) of lactation. Blood samples were collected at 8 h intervals from the day before weaning (Day--1) until and including the day of first mating, then once daily until 10 days post coitum. Additionally, 5 sows in each group were sampled at 30 min intervals for 12 h on Days--1, 0 and 1, then at 30 min intervals for 6 h daily until mating, finally at 30 min intervals for 2 h daily until 5 days post coitum. Group E sows had relatively longer weaning to remating intervals (8.3 +/- 0.8 compared with 5.0 +/- 0.7 days; P less than 0.01) and tended, but not significantly, to produce smaller subsequent litters (10.2 +/- 1.9 compared with 12.0 +/- 0.6). Sows in group E had lower lactational and post-weaning plasma LH levels (P less than 0.001). They also had greatly attenuated preovulatory LH rises and the area under the peak was reduced (P less than 0.01 and P less than 0.001, respectively). Preweaning plasma prolactin levels were higher at 9 days of lactation than at 34 days and levels in both groups dropped precipitously subsequent to piglet removal. Although peak levels of prolactin at oestrus did not differ between treatments, they tended to occur before the LH peak in sows of Group C and after the LH peak in Group E.(ABSTRACT TRUNCATED AT 250 WORDS)

ContentsThe objective of the breeding herd is the predictable and consistent production of high quality pigs. To achieve this objective, an appropriate number of females need to be mated in each breeding week and they should maintain their pregnancy and deliver large litters. Many factors can impact achievement of optimal sow productivity, particularly breeding management. Most matings will involve artificial insemination (AI), and successful AI requires deposition into the cervix (or beyond) of sufficient viable high quality sperm at an appropriate time relative to ovulation. This is facilitated by improved knowledge of the sow's ovarian function prior to and during her oestrous period. Realization of the importance of establishing an adequate sperm reservoir in the oviduct at an appropriate time relative to ovulation has led to advances in the management of AI. The future of AI will likely involve insemination of single doses of high genetic merit semen, potentially having a reduced sperm concentration which is made possible by knowledge of the effect of site of sperm deposition on sow fertility. In particular, knowledge of when a sow is likely to ovulate during a natural or induced oestrous period will prove invaluable in the maintenance of herd productivity. This review will examine options for breeding management, including the control of oestrus and ovulation, on sow herd reproductive performance.

Two experiments were performed with 78 second parity Lacombe sows to determine the influence of nutrition on reproductive performance. During a lactation of 35 d sows were fed daily either 3 (L) or 6 kg (H) of a diet having 16% crude protein and 12.5 MJ DE kg−1. For exp. 1, six L- and six H-fed sows were given an intravenous injection of gonadotropin releasing hormone (GnRH) at 21 d of lactation and blood was sampled at −30, −10, 0, 10, 20, 30, 45, 90 and 120 min from the time of injection. Prestimulation luteinizing hormone (LH) levels were lower for L-fed than for the H-fed sows (1.34 ± 0.1 vs. 1.93 ± 0.2 ng mL−1' P < 0.02). Peak LH levels achieved after UnKH injection, however, did not differ significantly (5.0 ± 0.6 and 5.8 ± 0.5 ng mL−1 for L and H sows, respectively). In exp. 2, 38 sows were fed the H and 40 fed the L level of feed throughout a 5-wk lactation. As expected, low-level feeding in lactation resulted in a greater body weight and backfat loss (17.4 ± 1.6 vs 41.2 ± 2.3 kg and 3.2 ± 0.4 vs. 6.3 ± 0.1 mm; P < 0.001 for both). Low-level feeding also resulted in an increased incidence of anestrus (15.0 vs. 0.0%) and an extended remating interval (140.7 ± 11.7 vs. 103.4 ± 2.1 h; P < 0.05). At the postweaning estrus, sows were inseminated with either fresh (F) or thawed (T) semen. Treatment groups were thus HF, LF and LT. Pregnancy rate was influenced by both feed level and semen type (90, 72, 69 and 39% for groups HF, HT, LF and LT, respectively). Ovulation rate was unaffected by feed intake (18.7 ± 0.9 vs. 18.2 ± 0.5 for L and H sows, respectively) but embryo survival was influenced by both feed intake and semen type (82.7 ± 2.5, 46.4 ± 9.7, 68.3 ± 9.6 and 53.7 ± 9.8% for groups HF, HT, LF and LT respectively). Eight H and twelve L-fed sows were blood-sampled via indwelling vena caval cannulae at 6-h intervals from weaning until the end of estrus. No treatment effect was noted for plasma levels of LH, growth hormone, estradiol-17β or testosterone during this period. It was concluded that low-plane feeding in lactation and the consequent increased weight and backfat loss reduce reproductive performance of sows. However, the mechanism(s) controlling this effect remain to be fully elucidated. Key words: Sow, lactation, nutrition, estrus

of lactation feed'intake on endocrine status and metabolite levels in sows. Can. J. Anim. . Two experiments were performed to study the endocrine response of sows to changes in feed intake during lactation. The hormonal status of 24