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Superintendent
David Davis
21262 Genoa Road
Linneus, MO 64653
Phone: 660 895-5121
FAX: 660 895=5122
Email: DavisDK@missouri.edu

Forage Systems Update
Vol 12, No. 4

Introduction

Artificial insemination (AI) is a management practice that allows producers to make more rapid genetic improvement in their herds by facilitating the use of genetically superior bulls with high accuracy. The beef industry, however, only has a small percentage (fewer than 5%) of producers that utilize this management practice. The time, labor, and facilities required to detect estrus, and to sort and inseminate cows prevents many producers from implementing the practices of estrus synchronization and AI in their herds. The development of convenient and economical protocols that facilitate the use of fixed-time AI and that achieve high fertility among cows and heifers would theoretically result in a marked increase in utilization of these important management practices. Given the fact Missouri ranks second in the U.S. in total beef cow numbers, widespread adoption of this technology in the state could lead to significant economic benefits to producers through careful consideration and selection of sires, and a higher percentage of calves that are born early during the calving season. Our research program has focused on the development of strategies to effectively synchronize estrus in beef cows, and reduce the period of time over which heat detection is required, or ultimately facilitate the use of fixed-time AI without detecting estrus.

New Protocols Developed at Mizzou

One of the obvious benefits of estrus synchronization is a shortened calving season that results in more uniform calves at weaning. Reduced length of the calving season translates into a greater number of days for postpartum recovery of the cow to occur prior to the subsequent breeding season. Over the past several years our group at Mizzou developed two protocols for estrus synchronization in beef cows that show great promise for the industry. These protocols are now referred to as the MGAŽ Select and 7-11 Synch protocols and are illustrated in Figure 1. Cows assigned to the MGAŽ Select protocol are fed melengestrol acetate (MGA) for 14 days, GnRH is administered 12 days after MGA withdrawal and prostaglandin is administered 7 days after GnRH. Cows assigned to the 7-11 Synch protocol are fed MGA for 7 days and are injected with prostaglandin on day 7 of MGA, GnRH on day 11, and prostaglandin on day 18. We evaluated these two protocols over the last several years at the University of Missouri Thompson Farm at Spickard, the University of Missouri South Farm at Columbia, the Greenley Center at Novelty, in addition to numerous cooperator farms across the state.

The calving distribution is illustrated in Figure 2 for cows that calved this past winter at Thompson Farm that were assigned to the MGAŽ Select and 7-11 Synch protocols during the Spring 2002 breeding season. As you can see, a very high proportion of calves were delivered within the first 15 (roughly 65%) and cumulative 30 (roughly 90%) days of the calving season for each protocol, with no differences between treatments. These data support the use of estrus synchronization not only as a means of facilitating more rapid genetic improvement of beef herds, but perhaps, more importantly, as a powerful reproductive management tool. Profitability may be increased by reducing the extent to which labor is required during the calving period, and increasing the pounds of calf weaned that occurs as a result of a more concentrated calving distribution.

Results from the Spring 2003 Breeding Season

This past Spring (2003) 422 crossbred, lactating, first calf heifers and mature cows at three locations (Thompson Farm at Spickard, South Farm at Columbia and Greenley Center at Novelty) were assigned (Table 1) to either the MGAŽ Select or 7-11 Synch protocols. Blood samples were collected 8 days and 1 day prior to treatments to determine serum progesterone (P4) concentrations at the respective times, which identified the percentage of cows that were cycling (returned to heat and ovulated following calving) prior to the initiation of treatments. Cows were inseminated at 72 hours after PG for the MGAŽ Select treated cows and 60 hours after PG for the 7-11 Synch treated cows. Cows in both groups received an additional injection of GnRH at the time of insemination to synchronize ovulation (Figure 3).

Previous research from our lab has shown that fixed-time artificial insemination utilizing either the 7-11 Synch or MGAŽ Select protocols resulted in highly acceptable and comparable fertility (pregnancy) in postpartum, lactating beef cows. The results from this past spring's breeding season are shown in Table 2. These data indicate that pregnancy rates resulting from fixed-timed AI following administration of the 7-11 Synch or MGAŽ Select protocols are comparable. These results

further suggest that more producers may be able to utilize AI in their herds that previously were unable to because of the time and labor constraints that are required to detect estrus.

Comparing Fixed-time AI with Insemination Based on Detected Heat

Table 3 summarizes results from data we have collected with these protocols over the past several years. The table summarizes pregnancy rates of cows that were inseminated based on detected heat (estrus), and results from fixed-time AI for the 7-11 Synch and MGAŽ Select protocols. These data suggest that there are now protocols available that will help beef producers to facilitate the use of artificial insemination in their herds without having to detect heat.

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