1. T229 EFFECTS OF INCREASED GnRH DOSE POST–TAI IN BRAHMAN INFLUENCED CATTLE B. Pousson1*, D.J. Kesler2, M. Poole1, C.E. Ferguson1 1Department of Agricultural Sciences, McNeese State University, Lake Charles, LA
2Department of Animal Sciences, University of Illinois, Champaign-Urbana, IL
Table 2. Comparison of pregnancy rates for Bos indicus females receiving either a 100 µg or 200 µg dose
of GnRH at time of artificial insemination for each
location.
With an increasing population the need for increased efficiency in the beef industry becomes even more important. One method of improving production is to improve first service pregnancy rates. Stress at or near the time of breeding can decrease pregnancy rates. Acute stress decreases pregnancy rate by compromising hypothalamic-pituitary function resulting in a suppressed or delayed LH surge.
In beef cattle, the Brahman (Bos indicus) breed is more susceptible to short-term stress such as routine handling or restraint within a chute. This increased stress response among Brahman cattle may be one factor responsible for the observed lower pregnancy rates among Brahman cattle (30 to 45%) compared with non-Brahman (Bos tarus) cattle (55 to 65%) using the same estrus synchronization protocol.
INTRODUCTION
A total of 165 Bos indicus breed type cows and heifers from six different locations in Texas and Louisiana and 123 Bos tarus breed type heifers were used in this experiment.
In location 1, Beefmaster heifers (n = 19) that ranged from 14 to 18 months of age were bred using conventional Beefmaster semen.
In location 2, Brahman heifers (n = 5) between the age of 16 and 20 months were bred using conventional Brahman semen.
In location 3, dry Brahman cows (n = 32) between the ages of 3 to 6 years were bred with sex-sorted semen (for X-chromosome).
In location 4, Brangus heifers between the ages of 14 and 18 months were bred with conventional Angus semen.
In location 5, lactating Beefmaster cows (n = 83) ranging in age from 3 to 10 years and a minimum of 50 days post-partum were bred with conventional Beefmaster semen.
In location 6, crossbred Brahman heifers (n = 21) between the ages of 13 to 18 months and crossbred Angus heifers (n = 123) with no Brahman influence were all bred with conventional semen.
All cows and heifers were bred using the CO-Synch + CIDR estrus synchronization protocol, between 56 and 66 hours post-PGF2α (Fig. 1) and ultrasound for pregnancy between 30 and 35 days post-AI.
Proc GLM and LS Means post-hoc tests were used to determine statistically differences in pregnancy rates among the following variables and their possible interactions; treatments, location, semen, age, breed type and pregnancy.
MATERIALS & METHODS
The objective of this experiment was to determine if an increased GnRH dose following AI would improve pregnancy rate in Brahman and Brahman–type cattle.
OBJECTIVES
Table 3. Comparison of pooled pregnancy rates for Bos
indicus heifers receiving either a 100 µg or 200 µg
dose of GnRH at time of artificial insemination.
Figure 1. The CO-Synch + CIDR estrous synchronization protocol used for artificial insemination and experimental treatment regimes.
Table 4. Comparison of pregnancy rates for Bos taurus females receiving either a 100 µg or 200 µg dose of GnRH at time of artificial insemination.
RESULTS
The authors would like to thank the following companies; Pfizer, Merial and Teva Animal Health who donated pharmaceuticals for use in estrous cycle synchronization during this experiment.
Also we would like the thank the following producers for their participation in this study;
Sam Parigi (Jefferson County Poor Farm)
Gilbert Adams (Adam’s Beefmaster Farm)
Lorenzo Lasater (Isa Cattle Co.)
All producers participating in McNeese Heifer Development Program
Acknowledgements
Table 1. Comparison of pooled pregnancy rates for Bos indicus females receiving either a 100 µg or 200 µg
dose of GnRH at time of artificial insemination.
These results support that increasing the GnRH dose at time of AI in Bos indicus cattle can significantly improve pregnancy rates. This increase is observed in mature open cows, lactating cows and heifers, however increasing the dose in Bos tarus heifers does not affect pregnancy rates. This supports the observations that Bos indicus females tend to stress more than Bos tarus which may be a cause of lowered pregnancy rates.
DISCUSSION