Recipient Organization
TEXAS A&M UNIVERSITY
750 AGRONOMY RD STE 2701
COLLEGE STATION,TX 77843-0001
Performing Department
Beeville-TAMU Agr Res Station
Non Technical Summary
It has been estimated that nearly 30% of the cattle in the U.S. have some percentage of Bos indicus breeding, primarily American Brahman (Chase et al., 2005). Breeds and breed types with Bos indicus influence are adapted to and predominate in the southern regions of the U.S. where approximately 42% of the nation's beef cows and nearly 50% of its cow-calf producers reside (SAAESD, 2005). When Brahman or Brahman-influenced cattle are crossed with English and Continental breeds, the resulting offspring exhibit wide adaptability, heterosis for important growth and carcass traits, and the capability of meeting national carcass quality targets when fed and managed appropriately. The current national focus on consistent beef quality, and the genetic strategies needed to achieve that quality, require the use of technologies such as artificial insemination (AI) and synchronization of estrus/ovulation in to be optimally successful. Although the adoption of AI by the beef industry in the US has been remarkably slow compared to other locations around the world, there has been a steady trend in the U.S. toward identifying and rewarding cattlemen for producing cattle with desired genetics. In one market summary, the average value of carcasses from progeny sired by the top 10% of Angus sires was nearly $206 greater than those sired by the lower 10% (Angus Beef Bulletin, Jan. 2000). Unfortunately, additional complexities exist in the application of AI in the southern and southwestern U.S. because of the behavioral and physiological characteristics of the Bos indicus-influenced cattle that predominate in these regions.Studies at this location during the last 10-15 years have resulted in the development of improved synchronization protocols for Bos indicus-influenced cattle. Specifically, the development of the 5-day Bee Synch + CIDR (Bee Synch I) procedure consistently resulted in average fixed-time AI (FTAI) pregnancy rates of > 50%. This protocol, referred to nationally in Beef Sire Directories as PG-5-day-Co-Synch + CIDR became the only nationally-recommended approach for synchronization of ovulation for FTAI of Bos-indicus-influenced cattle. However, additional experiments using mature cows indicated the gonadotropin-releasing hormone (GnRH) injection given at the time of CIDR insertion with Bee Synch I was unnecessary and that fixed-time AI pregnancy rates were similar in mature beef cows treated with (Bee Synch I) or without (Bee Synch II) the GnRH injection on day 0. In addition, by eliminating GnRH on Day 0, the requirement for a double dose of a second hormone, prostaglandin (PGF) on Day 5 is eliminated. Results indicated that Bee Synch II gave virtually identical results to Bee Synch I (51-52% FTAI pregnancy) in mature cows at a cost savings of $8.00 to $10.00 per animal and Bee Synch II has now replaced Bee Synch I as the recommended protocol for use in Bos indicus-influenced females. Unfortunately, data using Bee Synch II in nulliparous Bos indicus-influenced heifers have remained sparse; thus, recommendations for its use in this class of females have been limited. The specific aims of this project are to 1) determine how the currently recommended version of Bee Synch (Bee Synch II) for use in mature Bos indicus-influenced cows can be most effectively incorporated for use in nulliparous, pubertal heifers, including any necessary modifications in timing of hormone treatments or AI, 2) Examine managerial factors that influence the outcome to FTAI in Bos indicus-influenced first-calf heifers, including nutritional management and length of the postpartum interval at synchronization onset.
Animal Health Component
75%
Research Effort Categories
Basic
25%
Applied
75%
Developmental
(N/A)
Goals / Objectives
Our long-term goals are to develop and optimize strategies for synchronization of ovulation for fixed-time artificial insemination (FTAI) in Bos indicus-influenced beef heifers using a 5-day protocol established at this station, the 5-Day Bee Synch + CIDR protocol (Bee Synch). Previously, we developed a protocol termed Bee Synch I in mature cows which evolved eventually to Bee Synch II. However, little data are available for use of this protocol in nulliparous heifers but data generated to data have been highly promising. It appears that the majority of synchronized heifers exhibit estrus between 42 and 48 hours after removal of the progesterone-eluting intravaginal device (CIDR). On this basis, FTAI has been set at 54-60 hours and pregnancy rates using this approach has averaged 56%. Therefore, more data are required using a variety of Bos indicus breed types at different locations to confirm these findings and make final recommendations to cattlemen regarding its efficacy. In addition, there is a parcity of information regarding how to manage first-calf heifers with regard to the integration of Bee Synch II. The latter are notoriously the most difficult females in the herd to rebreed due to their nutritional reguirements to sustain continued growth, lactation and rebreeding. Managerial approaches for optimizing the timing of Bee Synch II applications are needed.
Project Methods
Nulliparous Bos indicus x Bos taurus beef heifers will be used for these studies. Percentage Bos indicus influence will range from approximately 25 to 50%. and will include approximately 150 Braford (Brahman x Hereford; F1) and Brangus heifers located at the Texas A&M AgriLife Research Station, Beeville, TX. Additional Brangus and Nellore x Angus crossbred heifers will be utilized from the Texas A&M herd located at McGregor, TX. Specific Aim 1. Determine how the currently recommended version of Bee Synch (Bee Synch II) for use in mature Bos indicus-influenced cows can be most effectively incorporated for use in nulliparous heifers, including any necessary modifications in timing of hormone treatments or FTAI,Methods. Bos indicus-influenced (1/4 to 1/2 Bos indicus) heifers (n = 200-300) will be used. Heifers will be Braford, Brangus or Nellore x Angus heifers typically utilized in the south and central Texas environments. The Bee Synch II procedure consists of the vaginal insertion of a controlled internal drug-releasing insert (CIDR; Zoetis) plus a 25-mg injection (im) of PGF (Lutalyse) on day 0. On the afternoon of day 5, the CIDR is removed and all females receive an im injection of 50 mg PGF. Based on results from initial studies in which estrus was monitored using Estrotect heat detection devices on the tail head, heifers will be inseminated at 54-60 h after CIDR removal. All heifers will be administered 100 µg (im) GnRH at the time of insemination. Experiments will consist of one to three replicates at up to 3 locations. Pregnancy rates to FTAI will be determined by transrectal ultrasonography 30 to 40 days following TAI. The GLIMMIX procedure of SAS will be utilized to contrast pregnancy rates by location, age, body condition score, breed type, estrus detection score and all appropriate interactions as sources of variation in the model. Specific Aim 2. Examine managerial factors that influence the outcome to FTAI in Bos indicus-influenced first-calf heifers, including nutritional management and length of the postpartum interval at synchronization onset. The experimental design associated with this aim will be developed following completion of Aim 1. Additional studies will be designed on the basis of the outcome of the foregoing experiments.