Time of ovulation and reproductive performance over three parities after treatment of primiparous sows with PG600

Too late or too soon? The replacement gilt paradox

Due to high annual culling rates, pig farms require a constant income of replacement gilts. Gilts typically reach puberty at nearly six months of age. Puberty may be induced through early boar exposure, therapy with steroid hormones and chorionic gonadotropins, and optimized by identifying biological predictors and risk factors. Old age at the time of the first mating is associated with an increased risk of premature culling, often attributed to reproductive failures and locomotor problems. While female prolifacy has increased substantially during the last few decades, selecting for litter size to optimize lifetime productivity would be more efficient after two parities. Additionally, uterine capacity and the number of functional teats should be considered in selecting future dams. For each female, the cost-effective number of parities at removal is determined by the cumulative number of pigs born and weaned during the total herd days.

Effects of nursing a large litter and ovarian response to gonadotropins at weaning on subsequent fertility in first parity sows

Post-weaning fertility failures occur more often in parity 1 (P1) sows due to high metabolic demands for lactation and their inability to meet energy requirements for maintenance, growth, and reproduction. We hypothesized that body condition loss occurs more frequently in P1 sows nursing a large litter, resulting in impairment of ovarian follicle development during lactation and post-weaning, which can negatively impact estrus and subsequent fertility. At 24 h post-farrowing, P1 sows (n = 123) were assigned to treatment (TRT) based on sow weight and the number of functional teats to receive a high number (HN, 15 to 16) or low number (LN, 12) of nursing piglets. At weaning, sows in each TRT were assigned to receive PG600 or None (Control). During lactation, sow body measures were obtained and ovarian follicles were assessed in mid-lactation and post-weaning. Lactation data were analyzed for the effects of TRT, and fertility data after weaning were assessed for TRT x PG600, but there were no interactions (P > 0.10). During lactation, 22.2 % of HN sows lost ≥ 4 piglets due to death or removal, and so these sows were excluded from further analysis. The HN sows were lighter (-6.2 kg), had less backfat (-1.0 mm), had lower body condition score (-0.4), and lost more nursing piglets (-1.2) than LN sows (P < 0.05). However, HN sows weaned more pigs (14.0) than LN sows (11.0). There was no effect of TRT on wean to estrus interval (4.2 d), but the interval was 0.5 days shorter for PG600 (P = 0.004) than control. There were no effects of TRT or PG600 on estrus within seven days after weaning (87.3 %), but PG600 induced smaller (P = 0.002) follicles at estrus (6.7 mm) than control (7.3 mm). In the subsequent parity, there were no effects of TRT or PG600 on farrowing rate (93.9%) and total born (13.2). Overall, HN sows lost more piglets and body condition but still weaned more pigs without any detrimental effects on subsequent reproductive performance.

Unraveling the actual background of second litter syndrome in pigs: based on Large White data

Second litter syndrome (SLS) in sows is when fertility performance is lower in the second parity than in the first parity. The causes of SLS have been associated with lactation weight loss, premature first insemination, short lactation length, short weaning to insemination interval, season, and farm of farrowing. There is little known about the genetic background of SLS or if it is a real biological problem or just a statistical issue. Thus, we aimed to evaluate risk factors, investigate genetic background of SLS, and estimate the probability of SLS existing due to the statistical properties of the trait. The records of 246 799 litters (total number born, TNB) from 46 218 Large White sows were used. A total of 15 398 sows had SLS. Two traits were defined: first a binominal trait if a sow had SLS or not (biSLS) and second a continuous trait (Range) created by subtracting the total number of piglets born in the first parity (TNB1) from the piglets born in the second parity (TNB2). Lactation length, farm, and season of the farrowing had significant effects on SLS traits when tested as fixed effects in the genetic model. These effects are farm management-related factors. The age at first insemination and weaning to insemination interval were significant only for other reproduction traits (e.g., TNB1, TNB2, litter weight in parity 1 and 2). The heritability of biSLS was 0.05 (on observed scale), whereas heritability of Range was 0.03. To verify the existence of SLS data with records of 50 000 sows and 9 parities was simulated. The simulations showed that the average expected frequency of SLS across all the parities was 0.49 (±0.05) while the observed frequency in the actual data was 0.46 (±0.04). We compared this to SLS frequencies in 67 farms and only 2 farms had more piglets born in the first parity compared to the second. Therefore, on the individual sow level SLS is likely due to statistical properties of the trait, whereas on the farm level SLS is likely due to farm management. Thus, SLS should not be considered an abnormality nor a syndrome if on average the herd litter size in parity 2 is larger than in parity 1.

Risk factors associated with the occurrence of the second-litter syndrome in sows in southeastern Mexico

The objective was to estimate the incidence of and to determine the effect of some risk factors on the decrease of litter size at parity 2 of sows in three commercial farms in Yucatan, Mexico. Data on 8,592 farrowing records of 4,296 sows were analyzed using a binomial logistic regression procedure. The model included the fixed effect of farm (1, 2, and 3), year of farrowing (2003–2011), season of farrowing (dry, rainy, and windy), number of pigs born alive at first parity (<9, 9-10, 11-12, and >12 piglets), lactation length (<18, 18–24, and >24 days), and weaning to conception intervals (<4, 4–11, and >11 days). Fifty-five point eight percent of all sows presented a reduced or similar litter size at parity 2. The odds of decrease in the second litter size were 1.56 and 2.01 for farms 2 and 3, respectively. Higher odds were found for sows farrowing during the rainy and dry seasons (1.20 and 1.24, resp.) and for sows with large litters at parity 1 (>12 piglets, odds = 33.2). Sows with weaning to conception intervals <4 days and between 4 and 11 days had higher odds of a decrease in the second litter (1.78 and 2.74 pigs, resp.).

Differences in maternal plane of nutrition and body condition during late gestation coupled with estrus synchronization at weaning do not result in differences in embryonic development at 4 days of gestation

This study was conducted to assess the effects of dietary energy in late pregnancy and hormone therapy at weaning on plasma metabolite profile, litter performance, reproductive parameters, and embryo viability in the second pregnancy. A total of 23 first-parity sows at 75 d of pregnancy were randomly allocated to 4 treatments. Treatments were factorial (2 × 2) combinations of 2 nutritional strategies [standard-energy feed (SEF) and high-energy feed (HEF)] and 2 hormone therapies [600 IU eCG and 2.5 mg swine LH 72 h later (HO) and no hormone (WH)]. Sows were weighed weekly from 75 d of pregnancy until 3 d before farrowing; 1 d after farrowing; 7, 14, and 21 d into lactation; and at weaning. Back fat (BF) was measured at 75 d of pregnancy, 3 d before farrowing, and at weaning. Average daily gain and ADFI were also calculated. Plasma metabolites were analyzed after 82, 89, 96, and 103 d of pregnancy, at farrowing, and after 7, 14, and 21 d of lactation. Embryo viability was assessed after 4.55 d of second pregnancy. During pregnancy, HEF-treated sows displayed greater BW (P < 0.05) compared with SEF-treated females, but no differences were observed during lactation. There were no differences in BW of the piglets caused by the treatments. High-energy-treated females showed superior BF (P > 0.05) in all periods; however, significant differences were detected only at the prefarrowing measurement (P < 0.05). No differences in ADFI were observed during lactation. The SEF group showed positive ADG, whereas the HEF group showed negative ADG (0.216 vs. -0.266 kg/d for SEF and HEF, respectively; P < 0.05). High-energy-treated sows presented greater concentrations of total cholesterol after 89 and 103 d of pregnancy and greater concentrations of high-density lipid cholesterol (HDL) after 89 and 96 d. At farrowing and 14 and 21 d of lactation, NEFA concentrations were greater (P < 0.05) in the HEF group. After hormone treatment, no differences were observed on weaning-to-estrus intervals and estrus duration. Greater mobilization of body reserves observed in the HEF group during lactation did not affect reproductive performance negatively, suggesting that metabolic status was adequate for the first lactational catabolism.