Impact of Uterine Crowding on Farrowing Performance, Postnatal Performance and Adrenal Stress Response

Abstract

The main purpose of this study was to determine the associations between uterine crowding and embryonic and fetal survival in gestation, and postnatal performance (birth weight, postnatal growth and survival, backfat depth, and adrenocorticotrophic hormone (ACTH)-induced cortisol responses in pigs. The present research was based on the hypothesis that piglets from the less crowded (unilateral oviduct cauterized; CAUT) litters will exhibit superior postnatal performance compared to piglets from control (non-cauterized; CTRL). For this purpose, 13 unilaterally oviduct cauterized (CAUT) and 12 non-cauterized control (CTRL) sows were studied. At gestation day (D) 35 a laparotomy surgery was performed on all sows and the total number of corpora lutea and embryos present was used to calculate embryo survival. Piglet weight, gender and morphometrics were measured at birth. Piglet weights were again measured at D21, week (W) 3, W7, W12, W16, and W19 of age. Available stillborn piglets were dissected from litters of each group to assess the weights of vital organs. Average daily gain (ADG) was calculated for the lactation (ADGLACT; 0-21 days of age), nursery (ADGNUR; W3-7 of age), finisher (ADGFIN; W7-19) period, and from birth to market (ADGLIFETIME; W0-19). Backfat (P2) and loin eye depth were measured when pigs were approximately 70 kg and 110 kg live weight. Saliva samples were collected from offspring following ACTH challenges at W12 and 20 of age. Our results showed that uterine crowding in CTRL compared to CAUT resulted in a decrease in embryonic survival rate (CAUT = 66%, CTRL = 53%; P=0.04), fetal survival rate (CAUT = 59%, CTRL = 42.4%; P = 0.007), WTD0 (CAUT = 1.7 ± 0.3 kg, CTRL = 1.4 ± 0.2 kg; P < 0.001), and body mass index (CAUT = 0.18 ±0.01, CTRL = 0.17 ± 0.01; P = 0.04) at birth. Adrenal weight (CAUT = 0.5 ± 0.1 gm, CTRL = 0.3 ± 0.1 gm; P = 0.005) and adrenal:brain weight ratio (CAUT = 0.02 ± 0.004, CTRL = 0.01 ± 0.002; P = 0.009) in dissected stillborns (CAUT = 7, CTRL = 10) were lower in pigs from CTRL compared to CAUT sows, demonstrating that the brain sparing associated with intrauterine growth retardation markedly affected development of the adrenal gland. Pre-weaning survival (CAUT = 92.9%, CTRL = 82.1%; P = 0.01) was lower in pigs from CTRL sows. While doing overall analysis across the progeny, birth weight was most significant factor affecting ADG. Heavier birth weight pigs had higher ADGLACT (P =0.01). Pigs with higher ADGLACT, a potential proxy measure of post-natal catch up growth, had higher ADGLIFETIME (P < 0.001) after controlling for WTD0. In summary, uterine crowding negatively affected pre-natal growth and development, as manifested by decreased birth weight and body mass index. Birth weight was the most consistent factor affecting ADG throughout life, and the effects of uterine crowding per se were mediated through its impact on birth weight. In spite of having only one “functional” ovary in CAUT sows, the total litter weight at lactation D21 was not different between CTRL and CAUT litters. As both birth weight and piglet growth during lactation contribute to the pig’s lifetime performance, the intra- uterine environment, as well as the size of the litter and lactational environment, needs critical consideration for efficient pork production.