Effects of maternal nutrition and stage of gestation on body weight, visceral organ mass, and indices of jejunal cellularity, proliferation, and vascularity in pregnant ewe lambs.

Peripubertal ewe lambs (44.3 +/- 1.1 kg of initial BW) were used in a 2 x 3 factorial design to test the effects of plane of nutrition (diet) and stage of gestation on maternal visceral tissue mass, intestinal cellularity, crypt cell proliferation, and jejunal mucosal vascularity. Singleton pregnancies to a single sire were established by embryo transfer, and thereafter ewes were offered a control (Control) or high (High) amount of a complete diet (2.84 Mcal/kg and 15.9% CP; DM basis) to promote slow or rapid maternal growth rates. After d 90 of gestation, feed intake of the Control group was adjusted weekly to maintain BCS and meet the increasing nutrient demands of the gravid uterus. Ewes were slaughtered at 50 d (n = 6 Control; n = 5 High), 90 d (n = 8 Control; n = 6 High), or 130 d (n = 8 Control; n = 6 High) of gestation. Ewes were eviscerated and masses of individual organs were recorded. The jejunum was sampled and processed for subsequent analyses. Final ewe BW for Control-fed ewes was similar at d 50 and 90 and increased (P = 0.10) from d 90 to 130 (46.0, 48.9, and 58.2 +/- 1.6 kg, respectively), whereas final BW increased (P <or= 0.01) throughout gestation in High-fed ewes (58.3, 68.8, and 81.1 +/- 1.6 kg, respectively). Relative jejunum mass (g/kg of maternal BW) was greater (P = 0.003) in Control-fed ewes compared with High-fed ewes and tended (P = 0.11) to decrease from d 50 to 130. There were diet x stage of gestation interactions (P <or= 0.08) for ileum and small intestinal total and relative weights. Ileum mass (g/kg of maternal BW) in Control-fed ewes was less (P = 0.07) compared with High-fed ewes at d 50, was equal (P = 0.19) to High-fed ewes at d 90, and was greater (P = 0.02) than High-fed ewes at d 130. Small intestine mass (g/kg of maternal BW) was similar between Control- and High-fed ewes at d 50 and 90, but Control-fed ewes had greater (P = 0.01) mass at d 130. Jejunal RNA and protein concentrations were less (P <or= 0.07) and DNA was unaffected (P = 0.43) in Control-fed compared with High-fed ewes. Stage of gestation did not affect jejunal RNA, DNA (mg/g), or protein concentrations. Jejunal cellular proliferation was not affected by diet or stage of gestation. In jejunal mucosal tissue, capillary number decreased, whereas capillary surface density and area per capillary increased (P = 0.01) with advancing pregnancy (d 50 vs. d 130), but were independent of diet. Data indicated that intestinal mass as a proportion of maternal BW declined in overnourished, gestating ewe lambs. This response was more pronounced during late gestation and is likely explained by the increasing maternal BW and adiposity rather than by the changing cellularity or cell proliferation.