The first week of January is an extremely important "check-point" 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 don't 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 5 consecutive years in a single a herd. The percentage of heifers that were pubertal on the first day of the breeding season ranged from only 21% to as high as 64% over the 5-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 that regulate puberty in the heifer is weight. For puberty to occur, heifers must weigh at least 65% of their mature weight. This weight is referred to as their target weight. Most heifer development programs require that heifers reach their target weight, approximately 65% of their expected mature 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. I refer to this date as the target date.
January is the time to determine if your heifers are "on track". Most yearling heifers will need to reach 700-800 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 - 1.6 pounds each day to reach their target weight by mid-April. Heifers should reach a BCS of 5.0-5.5 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 measurements should be obtained. Heifers with small pelvic areas and especially large heifers with small pelvic areas tend to have greater difficulty calving. Now is the time to contact you local veterinarian to schedule this pre-breeding work.