by Bob Weaber, Ph.D., cow-calf specialist
Over the winter, I’ve had several discussions with extension agents and producers trying to sort out what went wrong last summer during breeding season. Although the ‘wreck’ happened last spring or summer, the high percentage of open cows wasn’t discovered until preg check or, worse yet, calving. Accurate diagnosis of the problem is difficult at this stage but the circumstances give us pause to consider our production system and the critical control points. All too often when producers and specialists talk about ‘fertility’ we gravitate to a discussion of reproductive failure in cows and subsequent culling or management strategies. It is, however, important to recognize the importance of bull fertility as well, especially in commercial operations that rely heavily on natural service sires.
With tighter margins, it is tempting to stretch the cow to bull ratio. This strategy may decrease the breeding cost per pregnancy but it may also put your herd’s reproductive potential at greater risk. The risks of male reproductive failure tend to increase following nutritional or environmental insults to the bull and in large populations of bulls, 10 to 30% of mature bulls will fail a breeding soundness exam annually. Environmental conditions such as drought or extended winter and cold temperatures can adversely affect body condition score and fertility in cows, they can take their toll on bull fertility as well. It is good risk management to employ strategies to assure a successful breeding season. Bulls should be in moderate (5-5.5), athletic body condition at turn out. It is undesirable to have bulls that are over or under conditioned.
It is always a good idea to have a breeding soundness exam performed on bulls prior to turn out to identify potentially unsatisfactory breeders. Because we don’t have repeatable methods to assess bull libido and serving capacity, it is critical for producers to observe bull activity and mating throughout the breeding season. In multi-sire breeding pastures, injuries are fairly common. Injury to feet and legs or the reproductive tract can disrupt the libido and serving capacity of the bull. Fertility issues can and do present themselves in otherwise healthy and fit appearing bulls. Some of the fertility problems are associated with a range of venereal diseases including Trichomoniasis (a protozoan disease) causing a significant number of early embryonic losses in cows bred by infected bulls. Other causes are less specific and hard to diagnose but result in a fewer pregnancies and /or a very protracted breeding season.
The value of a tight calving distribution is often measured in the weight advantage of older calves at weaning time. A tight breeding season is a good sign that many of the nutrition and management decisions/practices are working well. If you still have a large percentage of cows calving in the last 30 days of a 90 breeding season an investigation into the cause is warranted.
Producers are advised to periodically monitor estrus behavior in their cowherd to see if the service sires are settling cows. If all cows in a group are cycling then roughly 5 percent should be in heat each day. In optimal conditions, nearly all the cows should exhibit estrous and be bred over the first 42 days of the breeding season. A percentage of these cows will not conceive and will return to estrus. If we assume that 80% of the cows bred during the first 42 days of the breeding season conceive, then 20% of these should return to estrus. During the middle and latter parts of the breeding season, approximately 1% or fewer of the cows should cycle each day. If after 45 days of the breeding season you still have about 3-5% of the cows cycling each day, you should pull bulls for either a breeding soundness exam to confirm fertility status and/or replace these bulls with bulls known to have recently passed a breeding soundness exam.
It is common for bulls to lose body condition during the early part of the breeding season when working hard to cover a high percentage of the cows in the herd. If body condition continues to decline measurably after the middle of the breeding season and bulls are still very active in monitoring and breeding cows, you should check for fertility problems in the bulls. Bulls in low body condition score should be replaced in the breeding pasture by bulls in adequate condition. You should record body condition scores on bulls at turnout and then periodically during the breeding season for use in management decisions.
Estrous detection should be conducted at least once per week (preferably twice) during the breeding season. Estrus should be observed at a distance from the cows early in the morning or near dusk when it cools off just as you would for an artificial insemination program. While finding an infertile bull during the breeding season is a bad thing, waiting until preg check in the fall or calving season to figure out you had a bad bull is even worse. Remember, getting cows bred is profit mission number one! Fertile bulls are needed to get pregnant cows. It pays to keep tabs on the breeding performance of your bulls during the breeding season.