221 Assessment of Modern Gilts and Sows Body Weight (BW) Throughout Gestation and how Different Gilt BW at Breeding Impact the Energy Requirement for Maintenance at Each Parity

Abstract

Abstract In addition to reproductive traits, growth, robustness, and carcass traits also contribute to the selection index of maternal lines, resulting in leaner and faster-growing modern genotype females. As a consequence, today’s gilts achieve heavier BW at a similar breeding age and remain heavier throughout their lifetime. Larger and heavier females are expected to have increased energy requirements for maintenance (MEm). Our objective was to describe the BW change of females across gestation according to the parity category and assess the impacts of the increasing average BW of gilts at breeding on the MEm requirement throughout their productive life. Two datasets were used to estimate gilt and sow BW:1) 1,903 PIC Camborough gilts were weighed at breeding and at d 112 of each gestation from parity 0-3; 2) 1,150 PIC Camborough gilts and sows (ranging from parity 0-12) were weighed at d 4 and d 112 within one gestation (Thomas et al., 2018). Average maternal BW gain observed between each cycle were +31, +28, +19, -7, +6, +5, and +11kg for parities 1, 2, 3, 4, 5, 6, and 7+, respectively. Growth of females throughout each stage of gestation was estimated assuming that 30% of the BW gain occurred until d 60, and 70% from d 61-112. A quadratic equation was fit to describe the BW change as a function of the day of gestation for each parity category (Table 1). An equation to estimate the maternal net gain in each cycle (Gain, kg = 0.5357 ′ parity2 – 8.8929 ′ parity + 35.857) was used to determine the BW of the female at weaning based on gilt BW at breeding. Different gilt BW at breeding (144, 155, and 166 kg) were simulated to estimate the estimated sow BW and their MEm at each parity category across gestation. The MEm was calculated according to NRC (2012) model, and a feeding level of 5.9 Mcal of ME/d was assumed. When gilt BW at breeding is 144 kg, it is estimated that only parity 4+ females would be fed below maintenance from d 90-112 of gestation (Figure 1). Increasing average gilt BW at breeding to 155 kg would result in P5+ sows fed below maintenance throughout gestation, P4 sows fed below maintenance from d 30 of gestation, and P2 and P3 sows fed below maintenance from d 9 0 to 112. At 166kg of gilt BW at breeding, P4+ females would be fed below maintenance throughout gestation, P2 and P3 sows would be fed below maintenance in mid and late gestation, and P1 sows would be fed below maintenance in late gestation. In summary, increased growth rates in maternal lines may result in heavier gilts at breeding who become heavier sows in subsequent parities, leading to increased energy intake during gestation to meet the maintenance demand.