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Effect of selenium supplementation and plane of nutrition on mares and their foals: Foaling data

J. F. Thorson^*,, B. J. Karren, M. L. Bauer^*, C. A. Cavinder, J. A. Coverdale and C. J. Hammer^*,

^* Department of Animal Sciences, North Dakota State University, Fargo 58105 , Center for Nutrition and Pregnancy, Fargo 58105 Department of Animal Science, Texas A&M University, College Station 77843

carrie.hammer{at}ndsu.edu

Abstract

To investigate maternal plane of nutrition and role of Se yeast on foaling variables and passive transfer of immunoglobulin G (IgG), 28 Quarter Horse mares were used in a study utilizing a randomized complete block design. Mares were blocked by expected foaling date and assigned randomly within block to dietary treatments. Dietary treatments were arranged as a 2 x 2 factorial with 2 planes of nutrition, pasture or pasture plus grain mix (fed at 0.75% BW on an as-fed basis) and 2 concentrations of Se yeast (0 or 0.3 mg/kg DMI). This resulted in 4 treatments: pasture (P), pasture + Se (PS), pasture + grain mix (PG), and pasture + grain mix + Se (PGS). Assuming DMI at 2% BW, the P and PS mares received approximately 100% of calculated 2007 NRC DE requirements, while PG and PGS received 120%. Selenium supplementation began 110 d prior to the estimated foaling date and all dietary treatments were terminated at parturition. At parturition, foaling variables were recorded. Additionally, placental weight was recorded and 2 samples from each placenta were collected for analysis of DNA, RNA, and protein. Colostrum was obtained for fat, protein, milk urea nitrogen (MUN), somatic cell count (SCC), and IgG analyses. Foal blood samples were collected at 0, 6, 12, 18, and 24 h after parturition for IgG analysis. There was no effect of Se or plane of nutrition on foaling variables; however, foal BW as a percentage of mare BW tended (P = 0.10) to be reduced in foals from mares on grain mix (PG and PGS; 7.6%) compared to mares not fed grain mix (P and PS; 8.0%). There was also no effect of Se or plane of nutrition on placental cell number (mg DNA/g), potential cellular activity (RNA/DNA), expulsion time, or weight. However, mares fed supplemental Se (PS and PGS) had decreased (P = 0.02) placental cell size (24.1 mg protein/mg DNA) compared to mares not fed supplemental Se (P and PG; 32.5 mg protein/mg DNA). There was also no effect of Se or plane of nutrition on colostral fat, protein, MUN, or SCC. However, mares fed grain mix (PG and PGS) had lower (P = 0.03) colostral IgG (76.5 g/L) compared to mares not fed grain mix (P and PS; 126.6 g/L). Foals from mares fed grain (PG and PGS) tended (P = 0.06) to have lower overall serum IgG (13.6 g/L) compared to foals from mares not fed grain (P and PS; 15.3 g/L). These data indicate that maternal diet during the last third of gestation affects placental efficiency and colostral IgG.

Key Words: equine • immunoglobulin G • passive immunity • placenta • selenium