Effect of consuming endophyte-infected fescue seed on transcript abundance in the mammary gland of lactating and dry cows, as assessed by RNA sequencing

Authors: Capuco, Anthony; Bickhart, Derek; Li, Congjun - Cj; Clover, Christina; CHOUDHARY, RATAN - University Of Maryland; GROSSI, PAOLO - Catholic University Of The Sacred Heart Italy; BERTONI, GIUSEPPE - Catholic University Of The Sacred Heart Italy; TREVISI, ERMINIO - Catholic University Of The Sacred Heart Italy; Aiken, Glen; MCLEOD, KYLE - University Of Kentucky; Baldwin, Ransom - Randy

Submitted to: Journal of Dairy Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/27/2018
Publication Date: 11/1/2018
Citation: Capuco, A.V., Bickhart, D.M., Li, C., Clover, C.M., Choudhary, R., Grossi, P., Bertoni, G., Trevisi, E., Aiken, G.E., Mcleod, K.R., Baldwin, R.L. 2018. Effect of consuming endophyte-infected fescue seed on transcript abundance in the mammary gland of lactating and dry cows, as assessed by RNA sequencing. Journal of Dairy Science. 101(11):10478–10494. https://doi.org/10.3168/jds.2018-14735.
DOI: https://doi.org/10.3168/jds.2018-14735

Interpretive Summary: Tall fescue is a common pasture grass throughout much of the United States due to its persistence and drought tolerance. However, animal productivity is often reduced when animals graze on tall fescue, due to ingestion of ergot alkaloids found in the fungal endophyte-infected plant. Little is known regarding the effect of ergot alkaloids on mammary growth and development. Previously, we demonstrated that consumption of endophyte-infected fescue seed during the dry period did not significantly impact parameters of mammary growth nor decrease milk production in the subsequent lactation. Elucidation of the cellular and molecular mechanisms by which ingestion of endophyte-infected grasses impairs milk production and mammary gland function should reveal methods to offset or alleviate these effects, and thus enhance animal productivity and health. Gene expression changes in mammary glands of cows consuming endophyte-infected fescue seed during lactation and the nonlactating (dry) period between lactations. Genes relating to mammary growth, development and turnover were dominant during the dry period; genes relating to secretory activity were dominant during lactation. Patterns of gene expression were very similar to those evident in mammary glands of cows treated with a known inhibitor of prolactin secretion. This infers that prolactin signaling pathways are important in mediating the depression of milk production during the consumption of endophyte-infected fescue and the rebound of milk production following its discontinuation.

Technical Abstract: Ergot alkaloids in endophyte-infected grasses inhibit prolactin secretion and reduce milk production when fed to lactating cows. However, we have shown that pre-partum consumption of infected seed throughout the dry period does not inhibit subsequent milk production and in fact, prior exposure to bromocriptine (ergot peptide) increases production in the succeeding lactation. To identify changes in the transcriptome and molecular pathways mediating the mammary gland's response to ergot alkaloids in the diet, RNA sequencing (RNA-Seq) was performed on mammary tissues obtained from 24 multiparous Holstein cows exposed to one of three treatments. Starting at 90 ± 4 d pre-partum, cows were fed endophyte-free fescue seed (control, CON), endophyte-free fescue seed plus 3x/wk subcutaneous injections of bromocriptine (0.1 mg/kg BW, BROMO), or endophyte-infected fescue seed (INF), as 10% of the diet on an as fed basis. Mammary biopsies from 4 or 5 cows/treatment at each of 3 distinct phases were obtained: 7 d prior to dry off during the initial lactation (L1), mid-dry period (D), and 10 d post partum (L2). Biopsy samples from each treatment group at the three phases of the lactation cycle (L1, D, L2) were used to generate individual RNA-Seq libraries. Normalized reads of the RNA-Seq data were organized into technical and biological replicates before processing with the RSEM software package. Each lactation phase was processed separately with the "rsem-run-ebseq" pipeline, and genes that differed between any of three treatments were identified from program output. A large proportion of genes considered to be differentially expressed in at least one treatment with a posterior probability of differential expression greater than 90% (n = 866) were found to be similarly expressed in BROMO and INF treatments, but differentially expressed from CON (n = 575, total for all three phases). When phases were compared, 104 genes that were differentially expressed compared to CON were found to be common to the L1 and L2 phases. Consistent with the production findings, networks most affected by treatments in L1 and L2 included lipid metabolism, small molecule biochemistry and molecular transport, while networks related more to developmental and cellular functions and maintenance were evident during the D phase. The strong similarity in pattern of expression in BROMO and INF treatments during both late and early lactation, suggests the involvement of similar cell signaling pathways or mechanisms of action for both BROMO and INF, and the importance of prolactin messaging pathways.