University of Missouri--Columbia. Office of Undergraduate Research
Abstract
Abstract only availableEffective estrous synchronization protocols frequently utilize progestins (melengestrol acetate [MGA] and Controlled Internal Drug Release [CIDR] inserts) to synchronize estrus. Previous research demonstrated that long-term treatment with MGA, in the absence of a corpus luteum, caused formation of persistent follicles and resulted in low fertility. The specific aims of this project were to determine if the presence of a new or used CIDR, in heifers without a corpus luteum, would induce the formation of persistent follicles and to compare the pattern of serum concentrations of progesterone in heifers treated with a new or used CIDR to luteal phase concentrations of progesterone (P4) in non-treated heifers. Normally cycling heifers were allocated by age, weight, and breed into four treatment groups: Control (n=8), MGA (n=4; 0.5 lbs-1hd-1day), new CIDR (n=7; 1.38 g P4), and used CIDR (n=8; new CIDR's previously inserted into cows for 7 d). Progestin treatment (MGA or CIDR) began on d 4 post-estrus and PG was injected on d 6 to induce luteolysis (d 0 = estrus). MGA or CIDR treatment continued for 14 d and length of a follicular wave was defined as the interval from follicular recruitment to ovulation or initiation of a new wave. Length of the first follicular wave (d) was 10.9a, 18.0b, 17.1b, and 16.9b (abP.05) throughout the 14 d treatment period but lower than in the control group. In summary, treatment with a new or used CIDR induced formation of persistent follicles in beef heifers and there was no difference in serum concentrations of progesterone between the two CIDR groups.CAFNR On Campus Research Internshi
