North Central Research Extension Center


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Building Blocks to High Reproductive Efficiency

Herd reproduction is considered to be the output or production trait with the greatest economic impact on commercial cow calf profitability. Likewise feed is the input cost of greatest significance in differentiating high or low profit operations. The heritability of reproductive traits is considered low. Most of the differences we see in herd reproductive rates are attributable to non-genetic environmental factors, primarily nutrition. Herd reproduction and nutrition, the two biggest influences on profitability are closely connected and need to be evaluated together. Often times, small investments can have a high rate of return. However further investments in feed to get maximum reproduction aren’t likely to maximize profit.

Herd economics are affected through reproduction in both the number of calves produced and the culling and replacement rate. As pregnancy rates increase and calf losses are minimized, cowherd expenses are spread over more marketed calves and the cost of production is lowered. With annual cow costs of around $400 per cow, each additional 1% weaned calf per cow maintained lowers the cost per calf by around $5. Open and late bred cows are typically sold and make up the largest portion of culled cows. Income from culled cows will typically offset only 50 to 60% of the expense of developing or buying replacements. At a differential of $500 between culls and replacements, every additional 1% culled increases ownership cost per cow by about $5 per cow. Increasing reproductive success produces more calves, prolongs cow’s life in herd, and reduces the number of replacements needed.

The development of heifers and management of young cows set the stage for overall herd reproduction. In general terms, heifers should be grown out from weaning to breeding at not more than around two pounds per day to minimize fat deposition targeting a body weight at breeding of at least 60% of expected mature size. By achieving such growth we expect heifers to reach puberty and be ready to breed at 13 to 14 months of age. Adding an ionophore to heifer development rations will increase growth and hasten puberty.

There are several advantages related to synchronizing estrus of heifers to increase percentage exhibiting heat at the start of breeding season. It helps insure a “tight” calving season which reduces labor at calving but also contributes to shorten subsequent calving. Synchronized heifers also create an opportunity to use A.I. breeding for greater accuracy in selecting superior calving ease sires. From breeding on to calving heifers must be grown out to about 80-85% of their mature weight by time of calving and be in good flesh. By doing so, calving problems will be minimized and the probability higher for the first calf heifer to return to estrus in time to stay on schedule and remain in the herd.

Since first calf heifers are still growing and partitioning nutrients between growth, milk, and reproduction they often have difficulty rebreeding. The key to breed back and staying on schedule is nutrition. The heifer’s body condition should be monitored during the months prior to calving. It is often necessary to sort from mature cows to provide supplemental or higher quality feed. This is often the case for 2nd and 3rd calf cows that may have been pulled down in condition during lactation.

Using the body condition scoring system to assess the nutritional status is helpful. BCS at calving is a good predictor of subsequent pregnancy rate. The target for heifers is 6+ while for mature cows a 5 is adequate. Cows that calve at a BCS of 4 will typically have a 25% lower bred back in a 60 day breeding season than cows at desired condition. By supplemental feeding or flushing thin cows after calving this difference may be improved to 5-10% difference, but is still likely to be less. Pregnancy rates of late calving cows can be enhanced with some estrus synchronizing protocols. “Priming” the reproductive system with progesterone as through using a CIDR can help induce non-cycling cows to exhibit estrus and breed.

Limiting the breeding season along with management procedures such as vaccination and pregnancy testing can help identify fertility problems and assist in culling and replacement decisions. Placing some limits on the breeding or calving season prevents perpetuating poor reproductive performance and greatly aids in producing a more uniform, manageable, and marketable calf crop. It also allows for defined analysis and benchmarking of herd growth and reproductive performance.

From the commercial producers point of view there is greatest biological efficiency when the breeding and calving season is matched with forage production. The peak nutrition time for cows will be 45 to 60 days into lactation, which is just prior to breeding. Pasture type, grass species, and grazing management can affect forage curves which peak in June for many cool season grasses in the northern plains. From an economic perspective many seed stock breeders calve a month or two earlier than optimum to meet the needs of customers for older bigger bulls. As well a number of commercial producers calve earlier targeting heavier calves capable of capturing valve for finishing at seasonal market highs. Some premium is needed to offset additional feed inputs to achieve high herd breeding when calving out of season.

Matching nutritional demand to forage quality and availability is not only influenced by scheduling the cow herd, but also through genetic selection. Herd reproduction is greatest when genetics for size, milk, and productivity are matched to the available forage resources which generally favor moderation in biological type. Furthermore, planned use of crossbreeding to utilize crossbred cows of adapted breeds of appropriate productivity, can greatly impact reproductive traits and longevity in the herd. The overall benefit equates an additional calf per cow.

One of the more difficult challenges is how to match the cow herd to the forage resource and still produce calves with the greatest feedlot and carcass value. New heifer pregnancy, cow maintenance, and carcass EPD’s are tools to help manage this compromise. Further advancements in DNA technology and sexed semen will make efficiencies of terminal crossing superior product lines on best fit material lines more feasible.

While concerning ourselves with cow fertility, herd nutrition, and feed costs; we can’t overlook the bull. Lots of things can reduce a bull’s ability to breed and settle cows, and the impact of an unsound or infertile bull is huge. Good selection, nutrition, conditioning, and health are critical. A breeding soundness exam on each bull each season will help determine bull fertility and fitness for use. Testing bulls not only helps insure against a breeding disaster, but in general pregnancy rates, and first service conceptions are higher in herds using bulls that pass a breeding exam compared to bulls of unknown classifications.

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