DNA paternity identification (ID) and progeny testing may be profitable for open-range beef cattle operations with bull-culling rates of 20% or greater, University of Nevada researchers say.

A panel of 15 microsatellites was genotyped in 2,196 animals from eight ranches with a total of 31,571 genotypes.

Probabilities of exclusion for each marker within ranch and across ranches were computed. Joint probabilities of exclusion for the 15 microsatellites were also determined, resulting in values over 0.99 for any individual ranch and across ranches. Dropping 1 or 2 microsatellites with the lowest probabilities of exclusion resulted in joint probabilities greater than 0.99 and with marginal reduction compared with the probabilities with 15 microsatellites.

Using a lower number of microsatellites is cheaper and may result in larger benefit-cost ratios (around 20% increase for 10 vs. 12 microsatellites), but may not lead to full identification of paternities, and therefore reduce accuracy of evaluation and response to selection.

Benefit-cost ratio in DNA paternity ID programs in herds with a large number of bulls (and cows) would be reduced compared to herds with a smaller number of bulls. This is because more genotyping efforts are needed to reject alleged parents.

Economic assessment of a DNA paternity ID program relies on:

  • Highly polymorphic DNA markers with many alleles at intermediate frequencies,

  • Increased performance of calves after culling low-production bulls, and

  • Cost of genotyping and price of liveweight at weaning.

The benefits of a DNA paternity-testing program may vary depending on the particular beef cattle operation.

Genotyping 15 microsatellites with 20 calves/sire resulted in benefits of $1.71 and $2.44/dollar invested at bull culling rates of 20% and 30%, respectively. Bull culling rate is the single most important factor affecting the profitability of a DNA paternity-testing program.

The breakpoints for the program to be profitable occurred when the ratio of the price of 1 kg of calf liveweight over the cost of genotyping one microsatellite was greater than 1.1 for a bull-culling rate of 30%.

The number of bulls in the herd has a dramatic impact on the benefit-cost ratio when probabilities of exclusion are below 0.95. In any circumstance, increasing the number of bulls results in reduced benefit-cost ratio.

Researchers conclude the greater the number of bulls in an operation, the lower the benefit-cost ratio of the paternity-testing program. Low probabilities of exclusion and a high number of bulls in the beef operation reduced the benefit-cost ratio. A DNA paternity-testing program would be profitable when the benefits of an increase in overall calf weaning weight override the cost of genotyping, and when culling percentages of unproductive bulls are 20% or greater.
Gomez-Raya, et al, 2008, Journal of Animal Science, 86:17-24.

In a comparison of estrus synchronization programs, University of Missouri researchers found comparable pregnancy rates for fixed-time artificial insemination (AI) of postpartum cows using MGA Select or Co-Synch + CIDR protocols.

Suckled beef cows at four locations were assigned to melengestrol acetate (MGA) Select and Co-Synch+CIDR protocols based on age, days postpartum and body condition score (BCS).

Cows in the MGA Select treatment were fed MGA (0.5 mg/head/day) for 14 days. GnRH was injected on day 26 and prostaglandin (PG) was injected on day 33. Cows assigned to the CO-Synch+CIDR protocol were fed a carrier for 14 days, injected with GnRH and equipped with a CIDR insert 12 days after carrier removal, and PG was injected at CIDR removal on day 33.

Fixed-time AI was performed at 72 hours after PG injection for the MGA Select treatment, and 66 hours after PG injection for the CO-Synch+CIDR groups. All cows were injected with GnRH at time of insemination.

Blood samples were collected 8 days and 1 day prior to beginning of MGA or carrier to determine the estrous cycling status of cows before treatment. The MGA Select group had a 57% cycling rate, and CO-Synch+CIDR group was 55%.

MGA Select resulted in a 61% pregnancy rate to fixed-time AI, and CO-Synch+CIDR was 66%, but results were not statistically significant. There were also no differences in final pregnancy rate at the end of the breeding period; 93% for MGA Select, and 95% for CO-Synch+CIDR.
Schafer, et al, 2007, Journal of Animal Science, 85:1940-1945.

Synchronizing estrus and artificial insemination (AI) of replacement beef heifers with the CIDR Select protocol resulted in greater estrus response and fixed-time AI pregnancy rates, researchers at the University of Missouri-Columbia found.

Heifers at three different locations were assigned to either CIDR Select or CO-Synch + CIDR protocols within reproductive tract scores by age and body weight. Heifers receiving the CIDR Select received a CIDR insert from day 0 to 14, followed by GnRH 9 days after CIDR removal and prostaglandin (PG) 7 days after GnRH treatment. Heifers assigned to CO-Synch + CIDR were administered GnRH and received a CIDR insert on day 23, and PG and CIDR removal on day 30.

AI was performed and PG administered at 72 hours for the CIDR Select treatment, and 54 hours for the CO-Synch + CIDR treatment. All heifers received GnRH at time of insemination.

Blood samples were collected 10 days before and immediately before synchronization (day 0) to determine pretreatment estrous cycling. Estrous response was 87% for CIDR Select and 69% for Co-Synch+CIDR.

Fixed-time pregnancy rates were 62% after the CIDR Select protocol and 47% after the CO-Synch + CIDR protocol.

The authors concluded that the CIDR Select protocol resulted in a greater, more synchronized estrous response and greater fixed-time AI pregnancy rates compared with CO-Synch + CIDR.
D.C. Busch, et al, 2007, Journal of Animal Science, 85:1933-1939.