The economic effect of estrus synchronization in beef heifers on average weaning weight of calves.
Prostaglandin was used to induce estrus in 129 Hereford x Holstein heifers for artificial insemination. At the start of the breeding season heifers were observed twice daily and inseminated 12 hours after first being observed in estrus. On the morning of the sixth day of the breeding season all heifers not yet observed in estrus or inseminated were treated with prostaglandin (25 mg Lutalyse(R)). Observation was continued and heifers were bred 12 hours after first observed in estrus. Of the 129 heifers 33 were inseminated before prostaglandin treatment, the remainder of the heifers were bred within 4 days of treatment. Two heifers developed cysts and did not express estrus. First service pregnancy rates were 70% before treatment and 79% after treatment. All heifers were inseminated the first time within the first 10 days of the breeding season and 100 pregnancies occurred in the first 10 days of the season. As a result median days to pregnancy was 8. Calves were all weaned and weighed at approximately 150 days of age. These results were then used to model the economic impact of estrus synchronization of beef heifers on the increased weaning weights of their calves. Prostaglandin treatment altered the distribution of pregnancies and resulted in a cluster of conceptions from Day 7 to 10 of the breeding season with no conceptions from Day 11 to 19. In order to study the influence of estrus synchronization on weaning weights a simulation model was constructed. All heifers that conceived on the first service after prostaglandin were assigned an alternate date of conception from Day 7 to 21 of the breeding season with a random number generator. In this way a uniform random distribution of pregnancies over the first 21 days of the breeding season was constructed. An alternate calving date was then estimated using the known gestation length and this date was used to calculate the weaning weight of the calf using the known weight per day of age. The average weaning weight of the uniform random distribution was then compared to the synchronized distribution with Student's t -test. The simulation model was repeated 10 times and each time weaning weights of the uniform random distribution were significantly less than with the synchronization program (p<.01). At a value of $4.00 for prostaglandin and $1.76 for each kilogram of calf the average increase of 3.8 kgs in weaning weight per calf resulted in a return on investment of $1.92 for every dollar invested in prostaglandin.
Gaines
J D
JD
Kansas State University, Manhattan, KS USA.
Galland
J
J
Schaefer
D
D
Nusbaum
R
R
Peschel
D
D