One sure sign that spring is near is seeing newborn calves on the ground. People not familiar with ranching or beef cattle production may ask, "Why do ranchers have their cows calve in the winter time?" Calving season affects beef cattle production and associated costs and returns. It is important for an operation to choose an appropriate calving season for that particular ranch. The following are calving season decisions each rancher needs to consider:
• Cattle nutrient demand
• Nutrient supply from forage and feed
• Seasonal effects on fertility
• Seasonal effects on calf performance
• Seasonal markets and profit potential
No one calving season works best for all Nevada beef cattle operations in terms of length or time of year. Each producer must make an informed decision on which calving season is ideal for the operation.
A controlled calving season allows matching nutritional needs of the herd to forage resources, facilitates more intense monitoring of breeding and calving, facilitates working more calves of a similar age at once (vaccinating, castrating, growth implanting), and produces calves of uniform age that can be marketed in groups to capture sale premiums.
One argument for not moving to a controlled calving season is that with calves of different ages scattered throughout the year, income can be spread throughout the year. This is the notion of using a year-round calf crop as a checking/savings account.
When comparing spring- and fall-calving seasons, there are advantages and disadvantages
to each. Nutrient demands of beef females are generally highest in the first few months after calving. Cows calving in the fall normally need more winter supplementation than spring-calving females.
The supply of nutrients available at any particular time during the year depends largely upon the forage base. Feed resources can become limiting during winter months, necessitating a winter-feeding period of stored feeds and forages. These winter-feeding costs often make up a large percentage of the cash costs in a cow-calf operation.
Seasonal effects on fertility exist. Increased numbers of follicles and larger follicle size in beef females are generally seen in spring over fall. During late fall and winter, lower fertility rates have been documented in Bos indicus (Brahman influence) cows compared to other times of the year.
The effects of heat stress on fertility are of more cause for concern than cool season effects. Heat stress is the result of a combination of both ambient temperature and humidity (heat index). The hot summer months in the state can depress bovine fertility in both females and males. The negative effects of heat stress on cows include hormone imbalances, reduced ova quality, lower conception rates, early embryo death and reduced blood flow to the uterus.
Conception rate averages are greatly depressed in July, while late spring conception rates are three to five times higher. Bulls experiencing heat stress lasting only 12 hours can have impaired spermatogenesis (sperm production). The recovery time to normal sperm production takes six to eight weeks after the heat stress period. Libido and serving capacity can decline during hot weather as well. In short, for optimum reproductive performance, beef producers should avoid breeding during the late, hot summer months.
Seasonal markets and profit potential are another factor in choosing appropriate calving seasons. For producers who traditionally market calves immediately after weaning, spring-born calves are marketed in the fall, and fall-born calves are marketed in the spring. Seasonal highs for feeder calf prices usually hit in the spring as feeder calf supplies tighten and demand for calves increases to use spring and summer forages.
Decisions on when to calve should be based on site-specific conditions affecting production, costs, and returns. What works in another region of the country or even another area of the state may not work for the current operation. By keeping good production and financial records and assessing forage resources, herd fertility, calf performance, and marketing options, a suitable calving season can be found for the ranch.
Source: Calving Season Selection Considerations, Dr. Jane A. Parish, and Dr. Justin D. Rhinehart.
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