ARS | Publication request: EFFICACY OF AN INTRAVAGINAL PROGESTERONE INSERT AND AN INJECTION OF PGF*2ALPHA TO ADVANCE DATE OF BREEDING IN POSTPARTUM BEEF COWS WHILE UTILIZING NATURAL SERVICE

Submitted to: Western Section of Animal Science Proceedings
Publication Type: Proceedings
Publication Acceptance Date: May 15, 2004
Publication Date: June 15, 2004
Citation: Olson, J.L., Roberts, A.J., Ansotegui, R.P., Paterson, J.A., Funston, R.N. 2004. Efficacy of an intravaginal progesterone insert and an injection of pgf*2alpha to advance date of breeding in postpartum beef cows while utilizing natural service. Western Section of Animal Science Proceedings 55:11-14.

Interpretive Summary: Numerous studies indicate that administration of exogenous progestins may hasten return of estrus in postpartum cows and thereby advance date of breeding and over all conception rate. A new intravaginal progesterone-releasing device, referred to as CIDR, recently became available for use in the US. While several recent studies have evaluated the efficacy of using a CIDR in estrous synchronization protocols to facilitate AI, the present study was conducted to determine if the CIDR would advance date of conception and improve overall pregnancy rate in postpartum cows mated to bulls in a pasture situation. Crossbred cows from two locations (224 and 73 cows) were stratified by age within location and randomly allotted to either a 7 day treatment with a CIDR followed by an injection of PGF (Lutalyse) when CIDRs were remove, or a control group which only received the injection of PGF; CIDRs were inserted on d 0 of a 60 day breeding season. Day of conception was estimated by ultrasonography after the breeding season. Average days to conception were lightly less (but not statistically different) for CIDR treated cows (26 days) than control cows (29 days), and overall pregnancy rates were similar between the CIDR (96%) and control (94%) groups. In conclusion, treatment with a CIDR before an injection of PGF2' was not effective in increasing overall pregnancy rates or advancing breeding date compared to cows receiving PGF2' on day 7 of the breeding season. Further research with a larger number of animals and more locations may demonstrate a statistical advantage of such progestin treatments, especially if the proportion of anestrous cows at the beginning of the breeding season exceeds those observed in the present study (24% ranch 1, 46% ranch 2). However, the cost of the CIDR treatment will be an important consideration in determining the benefits for producers.

Technical Abstract: The objective of this experiment was to compare conception date and overall pregnancy rates in beef cows given a single i.m. injection of 25 mg PGF2' (Lutalyse; control) on d 7 of a natural breeding season with or without 7-d pretreatment with an intravaginal progesterone insert (CIDR). Crossbred cows from two locations were stratified by age within location and randomly allotted to either treatment or control; CIDR were inserted on d 0 and removed on d 7; location 1:n=224, 3.36 ' .04 yr age, 62.5 ± 1.21 d postpartum (PP), 513.9 ± 4.6 kg BW, and 3.9 ± .04 BCS; location 2:n=73, 4.64 ' .15 yr age, 58.4 ± 1.17 d PP, 488.8 ± 6.4 kg BW, and 4.74 ± 0.57 BCS. Bulls were placed with cows in each herd from d 0 to d 60. Day of conception and cycle conceived (21 day periods) were estimated by ultrasonography on d 66 and 73; and again by rectal palpation on d 176 and 123 for locations 1 and 2, respectively. These response variables were analyzed with a model that included d PP, BCS and BW at d 0 as covariates and cow age (2, 3, 4+ yr), location, and treatment as fixed effects (location by treatment not significant). Days to conception (24 vs. 27 d for CIDR vs. control) and cycle (1.53 vs. 1.66 for CIDR vs. control) of conception tended (P < 0.13) to be decreased with CIDR. The number of pregnancies lost between first and second pregnancy diagnosis, did not differ (P = 0.31) between CIDR (7) and control (8). No beneficial affect of CIDR was observed (P = 0.22) for the cycle that cows became pregnant and remained pregnant. Overall pregnancy rates were not affected by treatment (P =0.32) for CIDR (94.6%) or control groups (93.2%). In conclusion, treatment with a CIDR and an injection of PGF2' was not effective in increasing overall pregnancy rates or advancing breeding date compared to cows receiving PGF2' on day 7 of the breeding season.