by: Lee Jones

Part 1 of 2

Reproductive efficiency is essential for beef herd success and profitability. Basically, it is the measure of the productivity of the cow herd considering pregnancy rate, birth rate, weaning weight and weaning rate. Cow herd efficiency can be measured by pounds of calf weaned per cow or per acre of pasture. One measurement tells the owner if the herd is producing enough to cover the costs of maintenance and the other analyzes opportunity costs of the land and whether it might be more profitable to use land for other uses.

Diversified farmers often use a cow herd or stockers to increase land use and productivity. Cow herd reproductive potential is 10 times more important than calf growth traits and 20 times more important than calf carcass traits to herd profitability because without reproduction and a live birth calves aren't produced and don't grow.

Reproductive efficiency has three main components: fertility of the herd, herd health and nutrition. In a cow herd these components are interdependent but I will discuss them separately for this article. Herd fertility also is subdivided into the replacement heifers, mature cow herd and bulls. Some farmers also use artificial insemination and estrous synchronization.

Reproductive efficiency begins with replacement selection. There have been numerous articles in several publications lately about heifer selection and there are also as many philosophies and opinions. A heifer has to work in a given operation. I know many producers who have spent a lot of money buying fancy replacements only to cull them after a year or two because they did not breed back under their management program. Now buying replacements might be the best economic decision for your operation because it frees up resources for the cow herd and you don't have to own a heifer bull but that decision has to be made based on the resources of the farm. Another option might be to have someone else develop heifers that you select from your herd (heifer selection will be dealt with in another article). Either way, selecting and developing heifers that breed and calve early gives them more time to recover and breed back after calving. First calf heifers have higher nutritional needs than older cows and this group often has the highest percentage of opens if those needs aren't satisfied. A heifer can't really be called a replacement heifer until she has her second calf and most aren't even profitable until they wean their third calf. So, it is critical to meet her nutritional needs during the early years in her life so she can become a productive member of the herd.

Fertility of the cow herd depends mostly on nutrition. Beef cow nutritional needs are discussed in four stages: early lactation, late lactation, dry and late gestation. The highest nutritional needs are in early lactation when the cow is feeding the calf and preparing for breeding. This period is the hardest time to manage the body condition of the cow because she often cannot consume enough feed to make up for energy needs of lactation and replacing body condition. Late gestation is the next highest nutrition demand. Due to the low nutrient requirements, the dry, mid gestation stage is an effective time to improve body condition of the cow herd. Some farmers may separate some of the poorer condition cattle and provide supplement feed to them during the dry period and late gestation to improve body condition prior to calving. Cows that calves with a body condition score of 5 or 6 (BCS 1-9; 3 is poor, thin cow and 8 is fat) will cycle and rebreed sooner than cows that have a BSC of 4 or less at calving. Feeding the cow not only meets the cow's needs but also the needs of the growing, developing fetus. Adequate prenatal nutrition has been shown to improve the calf's health and growth as well as future growth performance and fertility.

Having a controlled breeding season helps facilitate efficient, effective cow herd management not just for feed efficiency and body condition but also for herd health. Matching herd production with forage availability is essential for efficient herd production. It is important that the cow herd's highest nutritional needs coincide with the availability of sufficient, high quality forage. Feed cost is the single highest expense in a cow herd. The most efficient herds manage their cow herds so cows satisfy most of their nutritional requirements through grazing available high, quality forage.

Healthy, fertile bulls are essential for a productive herd. A fertile, healthy mature bull can breed 30 or more cows in a 75 to 90 day breeding season. Bulls have to be managed in the off season to maintain health and fertility. Prior to each season bulls need to be evaluated for their ability to breed cows. It is important to evaluate their feet and legs, their overall health and their fertility. Having a thorough breeding soundness examination performed at least 30 days prior to the breeding season is important to find out if he has the ability to breed cows. (A BSE does not measure a bull's libido or sex drive.) Bulls use a lot of energy finding and breeding cows in heat during the breeding season. It is important that bulls be in peak body condition prior to breeding season for optimum performance especially in extensive pastures. It is common for bulls to lose body weight during the breeding season due to the increased activity and decreased intake. It is essential they have adequate body reserves to get through the season. It is important also to have adequate bull power. A good rule of thumb for a bull-to-cow ratio is 1:15-20 for a bull two years old or less and 1:25-30 for older bulls. Thin bulls are often infertile or sub-fertile and do not have the endurance required to cover all cows during a controlled breeding season.

Mineral nutrition is often overlooked in beef herds. It is relatively simple to recognize energy deficiency in a cow herd by looking at body condition. However, mineral deficiency may not be as apparent. Subtle mineral deficiencies do not usually result in clinical signs such as down or dead cows. Typically, we see production losses such as delayed or failed conception, slight increase in incidence of calf diseases like scours or pneumonia, decline in weaning weight and fertility of replacements, as well as reduced growth and future feedlot performance. Like energy and protein the cow's mineral requirements also change with the production cycle with the highest needs in lactation and increasing during gestation due to fetal development.

To say mineral management is complicated is an understatement. Mineral deficiency can be caused by lack of availability or competition between minerals. Nor are all mineral requirements the same. Some minerals are needed in large quantities (macrominerals) and others in smaller amounts (microminerals) but all are very important to growth, health and reproduction. Macrominerals included calcium, phosphorus, sodium, chloride, potassium, magnesium and sulfur. Cows require 10 microminerals; cobalt, copper, selenium, zinc, iodine, iron, manganese, chromium, nickel and molybdenum. Deficiencies in macrominerals can cause disease in cows like milk fever (Ca, Ph or Mg Deficiency), grass tetany, (Mg or Na deficiency) or more generalized problems like infertility or low milk production and calf growth. Micromineral deficiencies vary but most often affect fertility, growth and the immune system. Copper deficiency is very common and can be caused by deficiencies in the diet or by competition from high sulfur or Mo levels or even high iron levels in water. Ethanol production co-product feeds are usually very high (sometimes dangerously so) in sulfur and feeding them at high levels in the diet can reduce Cu absorption. Some researchers have advocated using chelated or additional Cu in mineral mixes to compensate. Some of our areas can be deficient of Se or Zn. Zn is essential for the immune system and fertility. Diets high in sulfur also reduce Se absorption. Se deficient soils occur throughout the coastal plain and in many areas of Georgia resulting in Se deficient forage and grain. Since the primary source of Se is through grazing, cattle consuming Se deficient forage are Se deficient as well. Deficiencies in Se can cause calves and lambs to be born weak and in severe cases result in white muscle disease. Se deficiency reduces reproductive performance of cows resulting in delayed conception, embryonic loss and an increased incidence of retained placenta following calving. Calves born to deficient cows are at an increased risk of experiencing scours or pneumonia.

Not all mineral supplements for cows are equal. Some mineral formulas are absorbed better by cattle than others. Many inorganic mineral mixes include the sulfate from which is usually well absorbed by cows. The oxide forms are not absorbed as well. However, the chelated or protein complexed forms are highly available. These organic minerals are also usually more expensive so it is not recommended to feed them year round. It is important to find mineral supplements the cows will consume in a consistent manner. Consumption should be monitored to make sure cows are eating enough but not too much. Careful placement of mineral feeders and making sure there are enough for even timid cows to consume minerals is important. It is critical that high quality minerals be available to our herds one to two months prior to calving until breeding season is over. It is important to test forages not only for total digestible nutrients (TDN) and protein but for minerals as well. The best method to diagnose whether the animals in a herd are deficient in mineral levels is through analysis of liver biopsies from a portion of the herd. Using appropriate testing and supplementing based on the results is the best way to address possible deficiencies and results in the best herd health and performance.

Reproduction is more than just getting cows pregnant. It is also about getting live healthy calves and helping them grow to their genetic potential, getting cows to rebreed after calving and for cows to produce enough milk for their calves to grow and flourish. Having a quality mineral program plays a critical role in making sure we have a healthy calf crop each and every year.

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