Effects of maternal plane of nutrition, selenium supply, and physiological stage on digestibility and ruminal fermentation in ewes

Abstract Text: Objectives were to investigate effects of nutritional plane and Se supply during gestation on digestibility and ruminal fermentation at parturition and early lactation. Primiparous Rambouillet ewes (n = 84, age = 240 ± 17 d, BW = 52.1 ± 6.2 kg) were allocated to 2 × 3 × 2 factorial arrangement of treatments. Factors included dietary Se (adequate Se [11.5 µg/kg BW] or high Se [77.0 µg/kg BW]), nutritional plane (60% [restricted], 100% [control], or 140% [high]), and physiological stage at necropsy (parturition or d 20 of lactation). At parturition, lambs were removed from all ewes and 42 ewes (n = 7 per treatment) were necropsied. Remaining ewes were transitioned to a common diet, which met lactation requirements, and mechanically milked for 20 d.   Three way interactions were not present (P > 0.10).  As expected, DMI was altered by both nutritional plane and physiological stage. In pregnancy and lactation, DMI increased with plane of nutrition (P < 0.001; 500 vs. 755 vs. 1,183 and 1,173 vs. 1,237 vs. 1,295 ± 19 g for restricted, control, and high ewes during pregnancy and lactation, respectively). Neither DMI nor total OM digestion were altered by Se supply. Total OM digestion was greater (P = 0.03) in restricted compared with high ewes during both gestation (75.8 and 67.0 ± 1.2 %, respectively) and lactation (68.4 and 64.8 ± 1.2 %, respectively). Both apparent (P < 0.01) and true (P = 0.04) ruminal OM digestion was greater in restricted (60.7 ± 1.42 %) vs. control and high ewes (56.4 and 54.4 ± 1.42 %, respectively).  Ewes fed high Se during gestation had greater (P = 0.03) apparent and true ruminal OM digestion during gestation but were not different at d 20 of lactation. Ruminal acetate proportions were lower (P = 0.03) and the ratio of acetate + butyrate over propionate tended (P = 0.09) to be greater in high Se vs. adequate Se fed ewes. Ewes fed restricted diets had greater acetate (P < 0.001), lower propionate proportions (P < 0.001), and lower total VFA concentrations (P < 0.01). Ewes at parturition had greater total VFA (P < 0.001) than ewes during lactation. These data indicate that maternal plane of nutrition, Se supply, and physiological stage all impact digestion and ruminal fermentation which will influence circulating nutrients available for fetal growth and milk production.

Keywords: digestibility, ewes, selenium