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January is an extremely important “checkpoint” in spring heifer-development programs.
The key to proper heifer development lies in understanding the factors that influence conception in yearling heifers.
One key factor regulating heifer fertility is age at puberty. Most producers do not consider age at puberty of their heifers to be a major problem, yet few know how many heifers are actually cyclic at the beginning of the breeding season.
A Nebraska study demonstrated that the proportion of heifers that were pubertal on the first day of the breeding season varied greatly over five consecutive years in a single herd. The percentage of heifers that were pubertal on the first day of the breeding season ranged from only 21 percent to as high as 64 percent over the five-year period.
For maximum fertility and reproductive performance, heifers must have had at least one estrus before the beginning of the breeding season. Our goal, then, is to incorporate reproductive-management techniques to reduce the age of puberty, increase fertility and shorten the interval to conception.
One of the largest factors responsible for regulating puberty in heifers is weight. For puberty to occur, heifers must weigh at least 65 percent of their mature weight. This weight is referred to as their target weight.
Most heifer-development programs require that heifers reach their target weight by the onset of their first breeding season.
Because fertility increases until the third estrus after puberty, heifers should reach their target weight at least 30 days before the start of the breeding season (target date).
January is the time to determine if your heifers are “on track.” Most yearling heifers will need to reach 700 to 800 pounds (their projected target weight) by mid-April to ensure high fertility, assuming that the heifer breeding season starts about mid-May.
Weigh your heifers to determine how much they have left to gain to reach their target weight. If the heifers weighed on average 600 pounds and their target weight is 750 pounds, then they will need to gain 150 pounds or 1.5 to 1.6 pounds each day to reach their target weight by mid-April. Heifers should reach a body condition score of 5.0 to 5.5 by their target date.
The next important phase in heifer development occurs one month prior to the start of the breeding season. At this time, heifers should be vaccinated (Vibrio fetus, Leptospirosis and the respiratory disease complex, which includes PI3, BRSV, BVD and IBR; modified-live vaccine is preferred), dewormed and pelvic area measured. Heifers with small pelvic areas, especially if they are also large, tend to have greater difficulty calving. Now is the time to contact your local veterinarian to schedule this pre-breeding work.
For a continuation of this article, check out my Extension blog, “Extension to the Third Degree.”
Dates of interest
Jan. 28: 2013 Pasture and Hay Improvement Strategies, 7 p.m., Carroll County Extension Office.
Jan. 29: Growing a Three-Season Garden, 6:30 p.m., Carroll County Extension Office.
Jan. 31: 2013 Grain Production Meeting, 7 p.m., Carroll County Extension Office.
Christin Herbst is the Carroll County Extension agent for agriculture and natural resources. Call her at (502) 732-7030 or send e-mail to Christin.Herbst@uky.edu.