Impact of Progesterone Supplementation on Pregnancy Rates Following Timed Artificial Insemination or Embryo Transfer in Beef Cattle Consuming Endophyte-Infected Tall Fescue.

MACKEY, JOSEPH CHRISTOPHER. Impact of Progesterone Supplementation on Pregnancy Rates Following Timed Artificial Insemination or Embryo Transfer in Beef Cattle Consuming Endophyte-Infected Tall Fescue. (Under the direction of Dr. Daniel H. Poole). Most tall fescue (Lolium arundinaceum [Schreb.]) is infected with a fungal endophyte (Epichloë typhina) that produces ergot alkaloids; hindering reproductive success by decreasing pregnancy rates and suppressing progesterone (P4) concentrations. The objective of this study was to determine if P4 supplementation following timed artificial insemination (TAI) or embryo transfer (ET) increases pregnancy rates (PR) of cattle consuming endophyte-infected tall fescue. Nulliparous and multiparous beef cattle were maintained on stockpiled endophyte-infected tall fescue. All cattle were synchronized using the Select Synch + CIDR® program. Cattle were inseminated followed by estrus detection 12 h after visual observation of estrous. Cattle that did not display estrous were inseminated 72 h after CIDR removal. In the ET group, cattle received either a fresh or frozen embryo on d 10 postCIDR removal. Cattle were randomly assigned to receive either a CIDR blank (C) or active CIDR (Trt) on d 7 post insemination or at the time of embryo transfer and remained in the vagina through d 18. Pregnancy and embryo area were determined by ultrasonography at d 30 of gestation. Data were analyzed using a PROC MIXED procedure of SAS and examined for effects of treatment, year, location, and age. Statistical significance was determined at P < 0.05 and a tendency at 0.05 < P < 0.10. There was no difference in pregnancy rate with supplemental P4 7d following TAI in multiparous cattle (Trt45.91% vs. C53.98%; P > 0.05) or nulliparous cattle (Trt57.76% vs. C57.53%; P > 0.05). However, PR in heifers receiving P4 supplementation tended to differ by location (BBCFL43.75% vs. UPRS71.78%). There was a significant effect of year (P < 0.05) for ET groups, thus yr 1 and 2 were analyzed independently. In yr 1, P4 supplementation increased PR in ET cattle compared to controls (84.6% vs. 60.1%, respectfully; P < 0.05). Additionally, supplemental P4 improved PR in cattle >7 yrs old (Trt98.7% vs. C57.2%; P < 0.05) and increased embryo retention in cattle receiving a frozen embryo (Trt96.7% vs. C59.7%; P < 0.05); this was not observed with fresh embryos. In yr 2, there was no difference in PR with supplemental P4 (Trt36.8% vs C34.5%; P > 0.05). Additional P4 did not affect embryo area in either the TAI or ET groups. While P4 supplementation throughout maternal recognition of pregnancy significantly increased PR in cattle receiving embryos in yr 1, it did not show significant impact in yr 2 or following TAI in cattle consuming endophyte-infected tall fescue for both years. Progesterone supplementation is well documented using dairy cattle, fewer data is available for beef cattle. © Copyright 2015 J. Christopher Mackey All Rights Reserved Impact of Progesterone Supplementation on Pregnancy Rates Following Timed Artificial Insemination or Embryo Transfer in Beef Cattle Consuming Endophyte-Infected Tall Fescue by Joseph Christopher Mackey A thesis submitted to the Graduate Faculty of North Carolina State University in partial fulfillment of the requirements for the degree of Master of Science