While environmental conditions are always fluctuating, cow-calf producers often plan to experience drought. As the saying goes: It’s better to have something and not need it than to need something and not have it. Drought preparation follows the same advice. With the size of the national cow herd at historic lows, maintaining the most productive and valuable females in the herd will ensure a strong foundation to build upon during future herd expansion. While reproductive efficiency should always be a herd priority, it is even more critical to strategize who stays and who goes when facing drought conditions.
Nutrition
The first 90 days after calving are the most nutrient-demanding, as cows reach peak lactation, prepare for the following breeding season and, ideally, become pregnant to maintain a yearly calving interval. It is not uncommon for cattle to lose body condition during this period if their protein and energy requirements are not being met. If overlapping with summer drought conditions, decreased rangeland quality and forage availability quickly exponentiate the loss of body condition during the early postpartum period. Herd productivity and profitability relies on females rebreeding in a timely manner.
Research from Indiana investigated when cattle return to cyclicity based on body condition at calving. Thin cattle required 18 more days, on average, after calving to start having regular estrous cycles compared to moderate-conditioned cattle, perpetuating a cycle of late-bred and late-calving females. The same study indicated how postpartum change in body condition impacts reproduction. Cattle that entered the calving season in moderate condition yet lost condition after calving were reported to have 31% lower pregnancy rates compared to cattle that maintained moderate condition. Cattle losing condition due to inadequate forage quality or availability during drought are less likely to become pregnant during the following breeding season. Knowing the forage species that dominate your pastures during different seasons and their quality can help meet the nutrient requirements of the herd, while accommodating pasture rotations, especially during drought.
Reproductive success
Decreasing the carrying capacity may be necessary during drought and should be considered systematically by identifying and retaining the most productive and profitable females. Reproductive success is the largest driver of profitability in the cow herd, and thus should be a heavy focus for culling criteria. We can learn a lot from our cow herds based on if, but more importantly, when females become pregnant during a breeding season.
While females that become pregnant and subsequently calve earlier in the season require the nutrient demands of lactation earlier compared to late-calving females, data from South Dakota reported that early-calving females were more efficient. More specifically, early-calving heifers utilized less metabolizable energy per unit of calf weaning weight compared to late-calving heifers (44.6 megacalories [Mcal] per kilogram versus 50.9 Mcal per kilogram).
In other words, older calves result in heavier weaning weights, offsetting the production expense associated with greater energy demands during lactation. Lactation requires significant energy and feed resources; thus, milk production potential should be matched to every unique environment. Nevertheless, it is an overall positive economical season for the dam, consistently producing pounds of calf weaned.
Longevity
Longevity should be a strong focus for every cow herd. While specific replacement costs vary due to annual production expenses and replacement rates, as well as the opportunity cost associated with marketing heifer calves, it is routinely one of the largest expenses for the cow-calf producer. The longer each female remains as a productive member of the herd, the lower her depreciation costs are each year and the more profitable years she contributes to the herd after paying for her development.
Research from Nebraska, Montana and Saskatchewan reported that heifers calving in the first 21-day period of their first calving season stayed in the herd longer, produced more calves and had greater lifetime production than heifers calving later in their first calving season. Furthermore, data from Virginia and Montana indicated that heifers calving early (first 21-day period) in their first calving season continued to calve early in future calving seasons as mature cows.
As mature cows calve early and produce future replacement heifers, research from Nebraska reported that more early-born heifer calves were cycling prior to their first breeding season and calved in the first 21 days of their first calving season compared to late-born heifer calves. Focusing the herd on females that become pregnant and calve at the beginning of the season perpetuates an obvious cycle of productivity and longevity. If faced with culling decisions during times of drought, early-calving females should be prioritized in the herd.
Heat stress
Summer drought is often associated with increased temperatures which can negatively impact both male and female reproductive efficiency, affecting when cattle become pregnant during the breeding season or reducing overall pregnancy rates.
During drought, cattle may be moved between pastures more frequently to provide adequate forage or moved to a more reliable water source. Being mindful of transportation and heat stress during these times is incredibly important. Heat stress can decrease estrus behavior, egg cell (oocyte) quality and embryo development during the breeding season, while also putting established pregnancies at risk in cows and heifers. While bulls have thermoregulatory mechanisms in place to support proper sperm production, extreme environmental conditions can still impede production of viable sperm cells.
A decade of pasture breeding system data from late May to early August was summarized by a Nebraska research team to analyze the impact of environmental factors on pregnancy rate. In short, the minimum environmental temperature had the largest influence, over average temperature and temperature-humidity index, on pregnancy rate during the first cycle of the breeding season (first 21-day period). Overall, decreases in average and minimum temperature, as well as temperature-humidity index, significantly increased pregnancy rate in the first 42 days of the breeding season. With that in mind, if drought is imminent, it may be helpful to use reproductive technologies such as estrous synchronization to provide an opportunity for a large proportion of the herd to become pregnant early in the breeding season. The temperature-humidity index accounts for air temperature as well as percent relative humidity and is used to determine the level of risk when handling or moving cattle. Regardless of risk level, handle or transport cattle in the morning and in smaller groups to avoid heat stress, especially during the breeding season.
Culling
Being able to cull less productive cows in a timely manner during drought conditions is key, which may mean performing an early pregnancy diagnosis. Furthermore, having consistent, accurate and complete herd records allows for quick identification of cows that routinely calve late in the calving season, fail to meet structural standards, wean a reduced percentage of bodyweight or otherwise contribute to inefficiency of the cow-calf operation.
References omitted but are available upon request by sending an email to the editor.
