Sow body condition losses during first lactation impaired conceptus size on day-8 postovulation

In young modern hybrid sows, excessive body tissue mobilizationdue to a large litter size during lactation is often associated withimpaired reproductive performance in the subsequent cycle, suchas decreased farrowing rate, number of piglets born and pigletviability. These effects may be related to early embryo developmentbeing affected by previous body condition losses. In thisstudy, the relationships between primiparous sow body conditionlosses during lactation and conceptus size on Day 8 postovulationin the subsequent pregnancy were investigated. A total of 31primiparous sows (209.5 ± 14.7 kg on Day 1 postfarrowing) weremeasured for body weight, loin muscle, and backfat thickness(ultrasound) at farrowing and at weaning. Blood samples werecollected before and after morning feeding on Day 14 postfarrowingto measure nonesterified fatty acid, creatinine, Insulinlikegrowth factor‐1, and urea levels. After weaning, thediameters of the five largest follicles on Day 3 postweaning andweaning‐to‐ovulation interval were recorded using ultrasound.On Day 8 postovulation, all sows were dissected to collectconceptuses and ovaries. The relationships between sow bodycondition loss, blood metabolites, follicle development on Day 3postweaning, conceptus numbers and development on Day 8postovulation were studied using GLM models. In the 21‐daylactation, primiparous sows lost 23.9 ± 7.1 kg (11.4 ± 3.0%) bodyweight, 4.4 ± 1.8 mm backfat, and 9.1 ± 5.8 mm loin musclethickness. The body fat and protein losses (10.8 ± 3.2 kg and2.6 ± 1.1 kg, respectively) were estimated based on changes inbody weight and backfat (Dourmad et al., 1998). Sows ovulated at5.9 ± 1.2 days postweaning, with a total of 20.8 ± 4.2 conceptuses(mean diameter = 823 ± 150 μm) on Day 8 postovulation. Themean diameter of the conceptus on Day 8 postovulationdecreased with higher body weight loss (β = −10 μm × kg−1,p < 0.01, R2 = 0.25), with higher estimated body protein loss(β = −6 μm · kg−1, p = 0.02, R2 = 0.18), with higher estimated bodyfat loss (β = −2 μm × kg−1, p = 0.04, R2 = 0.15) during lactation, andwith a greater increase of urea level after feeding (β = −56 μm ×mmol/L−1, p = 0.04, R2 = 0.14), but was not affected by sow loinmuscle, backfat losses or other plasma metabolites. The meansize of the five largest follicles on Day 3 postweaning, theweaning‐to‐ovulation interval, the total number of conceptus ortheir survival rate to Day 8 postovulation were not affected bythe body condition loss during the previous lactation. The presentstudy demonstrated that a high total weight loss, including bodyfat and protein mobilizations during the first lactation, negativelyaffected conceptus development to Day 8 postovulation, whichmay consequently impact litter size. Also, the decrease inconceptus size with increase in urea level after feeding suggeststhat dietary and body protein breakdown may have a detrimentaleffect on conceptus development.