This post provides an in-depth overview of sire genetic evaluations in dairy cattle, a critical factor in driving genetic change in the dairy industry.

Here’s a breakdown of the key points:

1. Genetic Change and Artificial Insemination (AI)

• AI’s Role in Genetic Progress: The use of artificial insemination, which began growing in popularity in the 1940s, has been a significant factor in dairy genetic improvements. AI allows farmers to utilize semen from elite bulls worldwide, thus rapidly enhancing the genetic merit of their herds.
• Semen Sales Statistics: Approximately 23 million doses of semen were sold in the United States in 2014, with another 20 million doses exported. About 80% of U.S. cows result from AI, underscoring its importance in dairy breeding.

2. Advantages of AI over Raising Bulls

• Safety and Convenience: Bulls are dangerous animals, and AI allows farmers to avoid the risks associated with keeping them.
• Access to Top Genetics: AI enables farmers to purchase semen from the best bulls globally, significantly improving herd genetics.

3. Case Study: JENNY-LOU MRSHL TOYSTORY

• Prolific Sire: Toystory, a bull with over 2 million doses of semen produced, illustrates the impact of AI. He has over 140,000 daughters worldwide in milk testing programs, providing extensive data for genetic evaluation.
• Genetic Merit and Predicted Transmitting Ability (PTA): Toystory’s daughters produce 488 pounds more milk annually than the average U.S. Holstein cow. His daughters’ milk fat percentage is slightly lower than average, with a PTA of -0.02%.

4. Traits Evaluated in Genetic Testing

• Milk Production and Quality: Traits like milk yield, fat percentage, and protein content are evaluated. For instance, Toystory daughters produce nearly 25,000 pounds of milk annually, with a slightly lower fat content than average.
• Fitness Traits:
  • Longevity (Productive Life): Toystory daughters live 1.7 months less than average, mainly due to lower fertility.
  • Health Indicators: Somatic cell count is used to assess the likelihood of udder infections like mastitis. Toystory daughters are somewhat more prone to mastitis.
• Calving Ability:
  • Calving Ease: Measures the difficulty of calving; Toystory’s daughters are average, with 6.9% expected to have some difficulty.
  • Stillbirth Rate: Toystory’s daughters have a 7.1% stillbirth rate, also an average value.
• Physical Conformation: Traits like cow height, body angularity, udder conformation, and teat placement are also assessed to ensure functionality and health.
  • Udder and Teat Placement: Toystory daughters generally have strong udder attachments and well-placed teats, which reduces injury risk and susceptibility to mastitis.

5. Genetic Evaluations Beyond Sires

• Cows and calves are also evaluated for genetic merit. These evaluations, though less precise due to smaller datasets, use pedigree information, individual records, and genetic markers to estimate genetic potential.