Impact of the Birth Weight of Landrace x Large White Dam Line Gilts on Mortality, Culling and Growth Performance until Selection for Breeding Herd

Background: Piglets weighing less than 1 kg have become a common occurrence in pig farms due to selection for increasing litter size. Large litters imply a decrease in the mean piglet birth weight and an increase in the within-litter variability of birth weight with a greater risk of mortality and lower growth performance. The aim of this study was to evaluate the effects of birth weight of female piglets on growth performance and on removal rates until selection for entry into the breeding herd (170 days) of Landrace x Large White crossbred gilts. Materials, Methods & Results: A total of 1495 Landrace x Large White (DB 25® - DanBred) crossbred female piglets were individually weighed after birth (BiW) and housed on the same farm from birth onwards. During the following developmental stages, gilts were again individually weighed: at 10 days, at weaning, nursery, rearing and selection (170 days). A phenotypic evaluation was performed to select the gilts that would be included in the breeding herd. Predicted probabilities for mortality, according to BiW, were estimated using logistic regression models. Female piglets were also retrospectively classified into eight classes of BiW based on percentiles, i.e., approximately 12.5% in each group. Cumulative losses by death or removal until weaning, nursery and selection phase were analysed using logistic regression models. The ability of pigs to compensate for low BiW was estimated using the percentages of gilts that changed at least one body weight (BW) category from birth to 170 days of age. For this purpose, eight classes of BW at 170 days were also created. BW and average daily weight gain (ADWG) were analysed as repeated measures. Overall, the mean BiW of the female piglets was 1387.8 ± 8.8 g, with a coefficient of variation of 24.4%. The removal rate until 170 days was 27.0% (403/1495) and locomotion problems were the major cause of culling (16.4%). The best cut-off point estimation for mortality until 24 h after birth was 1020 g (Area Under the Curve - AUC = 0.98%; P < 0.0001), increasing to 1090 g for mortality until 20 days (AUC = 0.87%; P < 0.0001) and to 1100 g for mortality until 70 days (AUC = 0.79%; P < 0.0001). Cumulative mortality and cumulative losses until 170 days were greater for piglets born weighing less than 1000 g (P < 0.0001). Piglets of the three lightest BiW classes had the greatest percentage of compensatory increase in the weight category (ranging from 52% to 57%). Throughout the developmental stages, the ADWG was different between the two lightest BiW categories (410-1160 g) and those belonging to the three heaviest BiW classes (1510-2400 g). This resulted in the lower BW of the lightest BiW piglets at the end of rearing and finishing phases compared with other BiW categories. Discussion: The great occurrence of low BiW piglets in high prolific females and their high susceptibility to mortality and poor growth performance were confirmed in the present study. The most serious consequences for survival and growth occurred in piglets with a BiW of <1.1 kg. It has been reported that smaller piglets have lower colostrum intake and hepatic glycogen reserves, are more susceptible to hypothermia and have a higher risk of crushing. In spite of the partial ability for growth compensation shown by lighter piglets, the differences in BiW seemed to have an amplified detrimental effect on growth, mainly at rearing and finishing periods, since differences between the lightest and the heaviest BiW category increased from 1.1 kg at birth to 21 kg at 170 days of age. The implications of the present study are that piglets with low BiW have low survival and poor growth to finishing, hence reducing the opportunity for their selection as future breeders.