Breeding Replacement Heifers to the Top AI Sires
Dairy Pipeline: July 1997
Virginia-Maryland Regional College of Vet Medicine
Breeding replacement heifers to the top AI sires remains an area for improvement in most herds. Research has consistently demonstrated that a good artificial insemination program will produce an annual genetic gain of at least 200 lb of milk per heifer. Conception rates decline with advancing age of the cow, but the biggest drop is from replacement heifers to first lactation cows. Heifers have a 60 to 70 percent pregnancy rate per service across almost all herd management levels, while first lactation and greater cows will have pregnancy rates of 40 to 50 percent Another reason for breeding heifers to superior sires is that first lactation heifers represent the highest number of calvings per lactation group on most farms. First lactation heifers have 31.9 percent of the calves born, while second lactation have 25.1 percent, and third lactation cows produce 18.6 percent of the calf crop. The remaining 24.4 percent is divided among the fourth, fifth and sixth or greater lactation cows. Therefore, breeding to natural or inferior genetic sires puts approximately 32 percent of the herd's potential genetics at risk. One major argument against the use of artificial insemination on many dairies, is a question of calving-ease. The most recent sire summary of Holstein sires demonstrates that of the top 100 Holstein sires, 38 percent are calving-ease sires. Sires with scores below the average of 9 percent difficult births are considered to be calving-ease sires. Calving-ease bulls may not always be the answer, as heifer development may be inadequate for calving. Studies have also been conducted to determine the differential cost between maintaining a natural service sire versus an A.I. program. Although producers incur the added cost of semen, handling facilities, and labor for heat detection, researchers have indicated that artificial insemination provides cost savings. However, improved genetic progress remains the best reason to use artificial insemination. A recent review of the USDA sire summary shows that active AI Holstein bulls average Predicted Transmitting Ability (PTA$) for milk, fat, and protein of $167. The same summary indicated that natural service sires are less than $0 to $39. This would mean that if 25 heifers were mated to the active A.I. Holstein sires and 25 were mated to natural service sires, the A.I. produced offspring would potentially produce $3200 more from milk sales. Very few dairies have access to natural-service sires that can compare with the genetic progress available through artificial insemination. To provide adequate genetics for future generations in the herd it is generally recommended that service sires be above the 80th percentile.