A successful breeding season begins months before the first A.I. straw or bull turnout. In the 90 days before breeding, cows and heifers move through metabolic, immune and reproductive shifts that shape follicle quality, uterine readiness and embryo survival. One of our program’s works here at South Dakota State University (SDSU) emphasizes targeted supplementation of fatty acids, showing that what we feed now influences the egg she’ll ovulate in late spring and the environment that the embryo encounters.
90 days out
Ninety days out, body condition is the first and most consequential checkpoint. Mature cows should be near a body condition score (BCS) 5 to 6, and first‑calf heifers closer to 6. It’s easier to build condition before calving than to “chase” it after lactation begins, when negative energy balance may delay cyclicity resumption. Sorting thinner females for priority feed access and propping up energy density pays back in stronger estrus expression and more predictable responses to synchronization. Immune planning belongs in this window, too: set prebreeding vaccine timing now so cows are nutritionally supported and not mounting peak immune responses right on top of breeding.
60 days out
By 60 days before breeding, fine‑tune rations with reproduction in mind. Forage test results should drive supplementation; hidden shortfalls in energy or protein lengthen postpartum anestrus. Minerals need to be balanced to your region and delivered consistently; sporadic intake undermines immune function, follicle development and uterine recovery. This is also the right time to look into a supplementation strategy. In our heifer work, researchers in 2025 evaluated an eight‑week flaxseed oil-based omega‑3 supplement under ad libitum conditions with a fixed‑time A.I. protocol, finding lower water intake, a trend toward greater total mixed ration (TMR) intake, faster attainment of puberty and clear shifts in plasma fatty acid profiles, alongside a modest decrease in progesterone on the day of the A.I. Those results signal that diet was altering both metabolic and reproductive physiology around breeding time.
These data support a practical message: Start supplementation well ahead of breeding and maintain daily consistent intake to influence follicle development and peri‑ovulatory physiology. While these are minor results in that particular case, it suggests a potential for effect on better synchronization, as demonstrated by the decrease in progesterone at A.I.
If you plan to synchronize or use A.I., it is recommended to decide sooner rather than later and match the protocol to cow condition, facilities and labor. Utilize tools to plan your synch program, like the ones offered at the Beef Reproduction Taskforce website. Those tools were developed for experts to help organize and choose the best strategy for your system. In practice, protocols rarely fail because the hormones don’t work; they stumble when cattle are metabolically unprepared or steps are not properly conducted. In addition, the SDSU heifer study underscores that nutrition can subtly shift the physiological backdrop on which synchronization puberty status, steroid milieu and fatty acid profile rely, so lock in the management strategy before you open the hormone bag.
45 days out
About 45 days before breeding, shift attention to the bull battery. If using A.I., it is time to make sure you have your equipment ready and the supplies ordered. Semen companies usually test the semen before shipping, but as the weather sometimes becomes unpredictable, your storage conditions may be affected. When receiving semen, always check the shipping tank for its integrity and nitrogen vapor. If something looks odd, contact your seller immediately. We personally recommend, when possible, cracking one straw ahead of time to confirm semen viability. For the bulls, schedule breeding soundness exams with enough runway to retest or replace if weather or illness has temporarily suppressed semen quality. Don’t stop at motility and morphology; watch feet, eyes and social behavior. Fertility in bulls, like cows, reflects weeks of nutrition and micronutrient status. Trace minerals and appropriate body condition contribute to membrane integrity and sperm function; the same disciplined mineral and supplementation program you apply to cows should extend to sires. However, watch out for the “overdoing it.” While a thin bull can be very detrimental to its ability to breed, overnutrition has been recently demonstrated to be harmful to the bull’s metabolism as well as to semen quality.
30 days out
At least 30 days before breeding is the sweet spot for prebreeding vaccines such as infectious bovine rhinotracheitis (IBR), bovine viral diarrhea (BVD) (Types 1 and 2), leptospirosis and campylobacter, where indicated, allowing the immune system to respond before insemination. If not possible, studies performed by my colleagues at SDSU recommend vaccinations of live-modified vaccines at least 45 days after breeding, avoiding pregnancy losses stimulated by the vaccine immune response.
Heifers deserve special focus here. Confirm they’re 55% to 65% of mature weight, with adequate reproductive tract scores, and ensure their mineral and food intake has been stable. The 2025 study results and others suggest supplementation programs may advance puberty attainment and shift circulating lipid profiles in ways consistent with improved reproductive readiness; those gains are realized only with steady, daily intake over several weeks.
14 days out
In the two weeks before breeding, it is time to maintain the schedule. Avoid ration changes, minimize handling and keep water clean and abundant. Small disruptions now, like abrupt diet switches, muddy working conditions and rushed processing, translate into stress spikes that can alter ovulation timing or impair early embryo survival.
The home stretch
Seven days before breeding, clean up and check facilities so synchronization days run quietly and on time. Smooth cattle flow lowers stress for cattle and crew, and helps you respect the protocol time points, which are precisely critical during the embryo’s most vulnerable first days.
When breeding kicks off, the winning picture looks like this: cows in the right body condition, metabolically steady, on a consistent mineral and supplementation plan (if needed), vaccinated at the correct interval and matched with fertile, motivated bulls or a good A.I. technician. The outcome is more cows bred early, more calving early in the season and more pounds of calf weaned per cow exposed. From a research standpoint, the thread is consistent: The reproductive system responds to the cow’s metabolic story, and supplementation strategies implemented early and consistently are one pedal to push that story toward better synchronization, a calmer immune environment and improved odds of embryo survival.
References omitted but are available upon request by sending an email to the editor.
