For decades producers have focused on bending the growth curve as a means to improve production efficiency. Standardized performance analysis repeatedly shows, however, that the most profitable producers are not those weaning the heaviest calves, but those that sell the highest number of calves. While efficient growth is important, most beef herds are in a position to gain more profits from improved reproductive efficiency. As milk production and calf growth increases, reproductive efficiency decreases. Therefore, to maximize profits, the right balance between growth performance and reproductive performance must be met. Accomplishing these two goals simultaneously requires a high conception rate early in the breeding season. Reproductive efficiency can be measured by the percent of calves weaned from your cowherd annually. It is estimated that each 1 percent increase in net calf crop will increase profits by $6 per cow. As a result, 5 percent more calves in a 100-cow herd could boost profits as much as $3,000. In addition, increasing the number of calves conceived in the first cycle of the breeding season means more pounds to sell at weaning.

Returning to estrus

There are a lot of demands placed on a cow that has just calved. In addition to the initiation and maintenance of lactation, the cow must repair her reproductive tract and resume normal estrous cycles. A cow should produce a calf every 365 days. To do that she must be bred within 83 days after calving. It takes an average of 40 days from calving before the uterus is in condition for pregnancy, which leaves only two heat periods for her to rebreed. Two significant events must take place during the postpartum period in order for a cow to cycle and conceive again according to veterinarian Bob Larson with the University of Missouri-Columbia. First, the uterus must return to a pre-pregnancy state known as involution. Second, the hormones that control the estrous cycle must resume normal function and signal the ovaries to resume fertile ovulation. "The uterus decreases in weight from 20 or 25 pounds at parturition to less than one pound 25 days later," Dr. Larson says. In the normal process of involution the attachment between the uterus and the placenta is expelled. Uterine involution is not a significant reason for infertility following calving unless infection is present. If you suspect uterine infection because of the odor or nature of the uterine discharge or if a placenta is retained for more than three days, a veterinarian should examine the cow and will possibly prescribe antibiotic treatment to speed uterine recovery. "The estrous cycle is controlled by the hypothalamus (an area of the brain), the pituitary, the structures on the ovaries such as the follicles and the luteal tissue, and the hormones that each of these structures secretes," says Dr. Larson. "Suckling and nutrient status have powerful influences on the control system."

Factors affecting estrus

The 25 percent infertility rate many producers experience is the result of several factors including genetics, nutrition, environment, herd health, and production potential of the cow herd. Getting a high percentage of your cowherd bred should start when you begin selecting replacement heifers. "I try to select all of my replacements out of the calves that were born during the first cycle. That way my replacements come from mothers that have been consistent breeders in the first cycle," says cow-calf producer Dave Petty of Union, Iowa. "It's important that heifers are managed to have calves early in the cycle. Once they are behind as a heifer they have a very difficult time of catching up." However, because of the low heritability of fertility traits, improvements through genetic selection take far longer to achieve. Factors that affect fertility can be controlled to a higher degree by management.

Nutrition is critical

Nutrition is one of the most important factors influencing reproductive performance. Energy and nutrition are utilized in progressive stages in the female. The requirements of the preceding stages must be met before energy is used for the next function. Failure to provide energy and nutrition that exceeds the demands of all her body functions will result in failure to conceive. Because first calf heifers are still growing, their nutritional requirements must be monitored closely. "I keep two-year-old, first-calf heifers separate from other age cattle. I make absolutely sure they are increasing their body condition before and after they calve," says Mr. Petty. Body condition is an indicator of nutrition. If cows are thin at calving, getting them bred in a timely manner is more difficult. Likewise, cows that maintain adequate condition at calving, but are then stressed post-calving, will have a longer postpartum period. "It's important to not let nutrition slide in either case," says Dr. Larson. "The best indicator is body-condition scores." Both underfeeding and overfeeding supplements can be expensive. Analyze the major roughage for nutrient content then supplement to provide a balanced ration.

External factors

Extreme environmental conditions such as temperature and humidity also can cause decreases in reproductive performance. Changes in the cow's body temperature, as little as 1.5 to 2 degrees, can result in embryonic mortality and abortions. Providing access to shade and fresh water will minimize the effects of heat stress during summer months. A sound herd health program is an essential part of any reproductive management system. Cattle are susceptible to a variety of diseases detrimental to reproduction. In addition to disease, parasites damage internal organs of their host, cause loss of appetite and weight loss. Under the guidance of your veterinarian, map out vaccination and parasite control programs that maximize protection and minimize costs. Suckling The effects of suckling on the length of the postpartum period are quite dramatic. When calves are weaned at birth, the dam will have a shorter postpartum period than do cows that are suckled. If calves are weaned after birth but before estrous cycles begin, cows will return to estrus within a few days of weaning. Postpartum intervals can be decreased by complete weaning, short-term weaning for 48 hours or partial weaning by restricting suckling to short periods of time each day. Short-term calf removal can stimulate hormone production and estrous activity in cows not cycling due to late calving, high milk production, or climatic stress. (See sidebar for more information.)

Jump-start the cycle

Once a cow begins to cycle following involution, the function of the first corpus luteum (CL) is not normal. The conception rate during a cow's first estrous cycle is very low. "Normal CL function during an early postpartum estrous cycle can be obtained by pretreating with a progesterone-like product such as MGA in the feed or the norgestomet implant associated with the SyncroMate-B estrous-synchronization product," says Dr. Larson.

Calving difficulty

There is a strong correlation between the severity of calving difficulty and the length of the postpartum period. If a cow has trouble calving, she is going to move herself back by at least one cycle. "The sooner you intervene and the less severe the intervention, the better. If she is having calving difficulty the best thing from a rebreeding stand point is to get in there and start helping, don't let it go another two hours," says Dr. Larson. "An all encom passing strategy would be to have them in the proper body condition prior to calving to minimize dystocia." Bull selection plays a major roll in eliminating calving problems as well. "It is important that your heifers are bred to a calving ease bull to reduce calving problems," says Mr. Petty. "I will sacrifice a few pounds come weaning time just to make sure I don't have trouble calving."