The impact of in utero heat stress and nutrient restriction on progeny body composition
We demonstrated that in utero heat stress (IUHS) alters future tissue accretion in pig progeny. Whether this results from reduced maternal feed intake (FI) or the direct effect of heat stress (HS) is not clear. Study objectives were to compare the rate and quantity of tissue accretion in growing rats exposed to differing in utero environments. On gestation d3, pregnant Sprague Dawley rats were exposed to either thermoneutral (TN; constant 22ºC; n = 4), HS (cyclical 34ºC nighttime and 30ºC daytime; n = 4), or pair-fed to HS-counterparts in TN conditions (PFTN; constant 22ºC; n = 4) until d19 of gestation. HS increased (P < 0.01) dam rectal temperature (1.3ºC) compared to TN and PFTN conditions, and reduced FI (P < 0.01; 14.1 vs. 21.0 g/d) compared to TN controls. Litter size was similar (P > 0.96; 10.9 pups/litter) for all treatments and pup birth weight was reduced (P < 0.04; 29.7%) in HS dams versus TN controls. At d26 of life, two male pups per dam [n = 8 in utero TN (IUTN); n = 8 IUHS; n = 8 in utero PFTN (IUPFTN)] were selected, and initial body composition was determined using dual-energy x-ray absorptiometry (DXA). Following the initial scan, all offspring were individually housed in TN conditions (21.8 ± 0.1ºC) and DXA analyses were repeated on d46 and d66 of life. In utero treatment did not alter (P > 0.81) offspring BW, FI (18.6 g/d) or ADG (5.8 g/d) from d26 to d66. Body fat content and total adipose tissue were increased (P < 0.01) in IUPFTN (19.8% and 39.6 g, respectively) compared to IUTN and IUHS offspring (17.9% and 35.9 g, and 17.6% and 34.1 g, respectively). IUPFTN offspring had reduced (P < 0.01) body lean tissue compared to IUTN and IUHS counterparts (77.9 vs. 79.8 and 80.1%, respectively). Body composition did not differ between IUHS and IUTN offspring. In utero treatment did not alter body ash content. From d26 to d66 the adipose to lean tissue accretion ratio was greater (P < 0.01; 19.2%) for IUPFTN compared to IUHS offspring. Epididymal fat pad weight was increased (P< 0.04; 21.6%) in IUPFTN versus IUHS offspring. In summary and in contrast to pigs, IUHS did not appear to impact body composition; however, IUPFTN rats likely experienced prenatal imprinting that altered the future hierarchy of tissue accretion.
Keywords: in utero heat stress, rat, tissue accretion