Differences in colostrum components of Katahdin ewes varies with post-weaning FEC EBV

Abstract

Variation in post-weaning fecal egg count (PFEC) estimated breeding values (EBV) has revealed effects beyond the reduction of parasitism. Previous work demonstrated lambs with a PFEC of < −50 (Low-PFEC) have higher survivability to weaning than lambs with a PFEC of > +50 (High-PFEC). In response to clostridial vaccination, Low-PFEC lambs also generate a more robust and rapid antibody response. These findings prompted curiosity of the maternal influence underpinning differences observed in lamb survivability based upon PFEC genotype. Thus, this study aimed to assess the impact of dam PFEC EBV on IgG concentration, Brix values, and color within colostrum. For Year 1 (YR1), Katahdin ewes from the Virginia Tech SWAREC were selected based on the following criteria: age (3–6 years), have a Katahdin Hair Index EBV (>104, pre-genomic EBV), and be twin bearing. Ewes fitting those criteria were sorted by their PFEC EBV into two groups: Low-PFEC (PFEC < −50; n=20) and High-PFEC (PFEC > +50; n=18) and sampled at three distinct time points, early (within 24-hr post-partition), mid (30-d post-parturition) and late (60-d post-parturition) lactation. For Year 2 (YR2), all lactating ewes at the SWAREC were analyzed and were sorted into three groups: Low-PFEC (PFEC < −50; n=39), Mid-PFEC ( −49 < PFEC < +49; n=38), and High-PFEC (PFEC > +50; n=23) and colostrum samples were taken within 6-hrs post-partition. All colostrum and milk samples were collected by milking 10 mL from each half of the ewes' udder. Total IgG within colostrum and milk was measured using an ovine-specific enzyme-linked immunosorbent assay (ELISA). In YR1, main effects of ewe genotype revealed that Low-PFEC ewes had a greater concentration of IgG across all lactation time points (631 ng/mL vs 222 ng/mL; P < 0.0001). This was primarily driven by IgG differences within colostrum, where a 2.5 fold difference in IgG were observed between Low-PFEC and High-PFEC groups (937 ng/mL vs. 319 ng/mL, P < 0.0001). In YR2, a stepwise decrease in average colostrum IgG concentration from Low-PFEC to High-PFEC groups was observed (825 ng/mL, 513 ng/mL, and 258 ng/mL, respectively; P < 0.0429). Likewise, a stepwise decrease in yellow to blue hue or b* value occurs from Low-PFEC to High-PFEC groups (18.97, 16.91, and 15.22, respectively; P < 0.0459). No correlations were found between IgG and Brix values within the Low-PFEC and High-PFEC grouping; remarkably, Mid-PFEC ewes have a slightly positive correlation between IgG and Brix (r= 0.34, P = 0.0334). These data indicate that Low-PFEC Katahdin ewes generate colostrum with greater antibody concentration and more yellow color. Lambs born to these ewes would have a significant advantage in passive immunity from their dams, which may explain some component of the enhanced lamb survivability observed pre-weaning.