Genetic progress is accom- plished when a heifer calf has better genetics than her mother.
The rate of genetic progress can be improved by making breeding decisions that widen the genetic gap between off- spring and parent. Speeding up genetic progress means the opportunity to milk better cows sooner, which leads to enhanced profitability.
Making breeding decisions that will push genetic progress is not easy, but with available technology the process is at least more predictable. The key is to identify the females in your herd that have the best genetics, then make sure those females have heifer calves.
Mating the Right Cows
A study conducted at the Livestock Improvement Corporation in New Zealand (T. Johnson, et. al., 2018), and recently published in the Journal of Dairy Science, identified the impact of segregating the herd by genetic merit(or breeding worth, in their terminology) to determine which females would produce offspring that would be part of the future milking herd. Through computer modeling the team used three breeding strategies:
- Breeding the entire herd to any bull available.
- Excluding low-ranked cows from producing replacement heifers.
- Breeding highly-ranked cows to the most highly ranked bulls.
Simulations were undertaken using four different groups of bulls currently marketed in New Zealand.
“Excluding the lowest ranked cows from producing replacements resulted in the greatest increase in average replacement heifer breeding worth across all herds and bull groups,” researchers note. Breeding worth values improved 0.4 points for each 1% of cows excluded. Nominating top- ranking cows to be bred to the highest ranking bulls had little effect (0.06 to 0.13 increase in breeding worth for each 1% of top cows nominated).
Researchers note although excluding cows with the lowest breeding value from producing replacement heifers is the most effective at improving overall genetic merit of the herd, it’s important to ensure the number of heifers born is sufficient to replace cows leaving the herd.
Knowing which females to exclude has to be done with accuracy. While knowing parent average values is a start, using genomics to rank females is a much more accurate way to make breeding and herd inventory decisions.
Using Sexed Semen
While genomics will tell you which females you don’t want heifers from, just as important are the genomic results that tell you which females you do want more heifers from. When those females are identified, using sexed semen on those animals can make financial sense.
A study conducted at the University College in Dublin, Ireland (D. J. Cottle et. al, 2018) looked at the best management strategy to get the greatest economic return from using sexed semen. Results were published in the May 2018 Journal of Dairy Science. Researchers explored three management strategies:
- Inseminating heifers with sex-sorted semen and using conventional semen in lactating cows.
- Breeding both cows and heifers to sexed semen.
- Breeding all females to conventional semen, which acted as the control group.
Results indicate using sexed semen was profitable, even when used in both heifers and cows.
“The returns on assets were higher when only heifers were inseminated with sexed semen,” researchers say.
Several factors had an impact on profitability, including pregnancy rate, genetic merit of the bulls used, costs of sexed and conventional semen, and bull and heifer calf prices. According to the research team, the study “highlights the relatively high effect of pregnancy rate and the genetic value of dairy bulls in determining the level of financial advantage from using sex-sorted semen in a dairy herd.”
Creating your future milking herd shouldn’t be left to chance. Know which females you want to populate your future herd, then get as many heifer calves from those females as possible.
Note: This story appears in the May/June 2018 magazine issue of Dairy Herd Management.