Part II: Nutrition (B 1343-2)Download PDF
Nutrition is the most costly component of heifer development and can have a great impact on lifetime productivity. Nutritional requirements for heifers are different from lactating or dry cows. Heifers require a higher quality diet than mature cows and must be fed separately from the mature cow herd.
Heifers must be bred to calve at two years of age. It is imperative that heifers reach 65 percent of their estimated mature weight prior to breeding. Heifers generally need to gain 1.25 to 1.75 pounds per day from weaning to breeding to reach the target weight.
Replacement heifer development in Georgia usually occurs during the fall and winter months. When these heifers need additional supplementation, they may be fed a combination of small grain pastures, hay and grain. Typically, cattle producers develop heifers using hay plus a supplement. It is important to determine hay quality to accurately calculate the necessary supplementation needed to balance the ration. Producers who fail to analyze their hay take risks that may result in heifers not receiving a balanced ration.
A well-designed feeding program starts with a feed nutrient analysis. Feed samples can be submitted to the University of Georgia Feed and Environmental Water Lab. Sample submission forms and information about forage testing can be obtained by contacting your county Extension agent. Upon request, an Extension animal scientist will custom balance a ration based on analyses of the forage and feedstuffs available.
The majority of cattle producers develop heifers using hay-based diets. Grass hay will not provide enough energy for heifers to gain at optimal rates. Therefore, producers will need to supplement heifers with grains, by-product feeds and/or high quality winter annual pasture. Nutrient requirements of a 650-pound developing heifer are listed in Table 1. Feeding hay that is greater than 12 percent protein will require an energy supplement that is at least 9 percent or higher in crude protein. High quality hay (TDN > 55 percent) fed with approximately 0.75 to 1 percent body weight of a dry grain supplement should provide gains of at least 1.5 pounds per day. Suggested supplements and feeding amounts for a 650-pound heifer to gain 1.5 pounds per day are listed in Table 2.
Hay quality will have a dramatic effect on daily gains. Test hay for nutrient content prior to feeding to ensure supplementation is adequate. By testing the hay, a feed can be selected that meets the energy and protein requirements of the heifer and, in turn, reduces feed costs. Hay intake should be 1.75 to 2 percent of body weight when the heifer is fed grain at 1 percent of her body weight. If hay intake is lower than the recommended level, then hay quality is likely poor. A body condition score (BCS) of 6 is recommended and is a good indicator that heifers are gaining at adequate levels.
Winter annual pastures
Winter annual pastures such as wheat, rye, oats and ryegrass can provide sufficient nutrients for developing heifers with only a mineral supplement required. The primary problem with using winter annuals is there will likely be a period of time of little or no grazing. Gains will be reduced significantly when grass is below 4 inches in height. Producers should offer high quality hay plus a supplement until sufficient grazing is available. The key to effectively using winter annuals is beginning supplementation as soon as grazing becomes limited.
New research has shown that high levels of protein in winter annual forages can reduce reproductive efficiency (Beck et al., 2005). Most winter annual pastures (wheat, rye, ryegrass) are very high in protein. Fescue is used in some parts of the state and may affect reproductive efficiency in a similar way. When protein is degraded in the rumen, ammonia forms and is transported to the liver where it is converted into urea. This will increase the blood urea nitrogen (BUN) levels. Reduced reproductive efficiency has been observed when BUN levels are elevated (Beck et al., 2005).
It has also been shown that the high levels of urea in the blood will reduce the pH in the uterus, causing poor fetal survivability in early pregnancy. This has only been documented when cows have continuous access to winter annual pasture. A study conducted at the University of Arkansas compared the reproductive efficiency of heifers grazed on either wheat and ryegrass pastures or fed a drylot ration of 75 percent grain and 25 percent hay for five months prior to breeding (Beck et al., 2005). Daily gain was approximately 1.22 pounds per day for each group. Heifers were synchronized and artificially inseminated (AI) once and then clean-up bulls were placed with the heifers for 56 days. There was no statistically significant difference in either AI or overall pregnancy rates between the two groups. However, some trends were noticed in pregnancy rates. Overall, pregnancy rates were 88 percent and 69 percent for grain-fed heifers and grazed heifers, respectively. Heifers that grazed the winter annuals calved 14 days later than heifers fed the grainbased diet during development. Conceiving early in the breeding season is especially important for heifers, as this will allow them more time to breed back after having their first calf.
Reduced pregnancy rates from grazing winter annual pastures have only been observed when animals had continuous access to the pasture. Often, cows are limit-grazed a few hours a day and supplemented with hay. There should be few or no problems with reproduction when using this feeding strategy. If animals are allowed to graze continuously during the early part of the breeding season, then do not feed any supplemental protein. There may be some alleviation of the problem if low protein grains such as corn are fed during this time to increase the use of nitrogen in the rumen, which should lower BUN levels.
Warm season annual/perennial pastures
Fall-born heifers are weaned in the spring and will spend a portion of the development period on summer forages. Bermudagrass is the primary summer perennial forage used for heifer development in Georgia. Heifers will usually gain about 1 pound per day grazing bermudagrass. However, this can vary considerably with variety (for example, Tifton 85 produces greater gains than other varieties), forage availability and time of year. In most cases, heifers will need some supplementation when grazing summer perennial forages to maintain adequate gains. Heifers should gain adequately when fed 0.25 to 0.5 percent body weight of a high-protein (> 20 percent) supplement. Warm season annual pastures such as pearl millet and sorghum/ sudangrass can provide gains of approximately 1.5 pounds per day with no supplementation (Hill et al., 1995). If higher gains are desired, supplementation guidelines would be similar to bermudagrass.
Corn silage is another feeding option that works well for developing heifers and should only need a protein supplement to provide adequate gains. The supplement (at least 20 percent protein) should provide 1 pound of protein per day. Common feeds used to supply additional protein include soybean meal, cottonseed meal, commercial pelleted supplements or a high protein by-product feed such as corn gluten, distillers grains or cottonseed. In general, a ration will consist of 85 to 90 percent silage (30 to 35 percent dry matter) and 10 to 15 percent dry supplement to achieve gains of 1.5 to 1.75 pounds per day. It is critical to have feed analyzed for nutrient content. This will determine the appropriate amount of supplemental protein, energy and proportion of silage required in the diet.
Grain-based diets can be limit-fed to properly develop replacement heifers (Beck et al., 2005). This feeding system requires increased management because heifers will gain too rapidly for proper development if allowed free-choice access to a grain-based diet. Limit-fed diets generally consist of 80 percent concentrate consisting of grain, by-product feeds and protein supplements. The remainder consists of a roughage source and a mineral supplement. Feed intake is usually 2.0 to 2.3 percent of body weight to achieve gains of 1.5 to 2.0 pounds per day. This feeding system requires bulk storage of feeds and some mechanism to mix and deliver feed into bunks. There are many combinations of feedstuffs that can be used to maintain proper weight gains. Prior to feeding, make sure the diet is properly balanced and correct amounts are fed each day to maintain desired weight gains.
Ionophores (e.g., Bovatec® and Rumensin®) have been shown to reduce age at puberty in replacement heifers by 14 to 28 days. Heifers that reach puberty earlier are more likely to breed early in the breeding season and continue producing a calf every 12 months. Rumensin® has been shown to consistently reduce age at puberty in many research trials (Sprott, et al., 1988). Less research has been conducted using Bovatec®, but it has been shown to reduce age at puberty in heifers with low weight gains (0.75 pounds per day) during the development period (Goehring, et al., 1984). Ionophores have the added advantage of improving feed efficiency and increasing weight gains.
The easiest method to feed ionophores is via a freechoice mineral mix. Most manufacturers have mineral mixes available that contain an ionophore for use in growing cattle. However, consumption by individual animals can vary. Monitor intake of minerals closely for both under- and over-consumption. Bovatec® is used in many mineral supplements because mineral intake is often greater when compared with Rumensin®. If low consumption is a problem, mixing the ionophore supplement with grain and hand-feeding is an option to consider. However, the ionophore supplement must be thoroughly mixed with the supplement to ensure equal distribution among heifers. Always follow label directions to ensure proper amounts of the mineral supplements are fed.
Research has demonstrated the importance of weight gain timing. If heifers are growing more slowly than expected and must gain rapidly to reach their target weight before breeding, lost weight gain can be made up rapidly without any loss in pregnancy rates. As long as heifers reach the target body weight before breeding, the timing of weight gain is not very important.
Kansas State researchers fed heifers to gain 0.55 pounds per day until the last two months before breeding, and then fed the heifers to gain 2.5 pounds per day for the last 60 days before breeding (Lynch, et al., 1997). Another group of heifers was fed to gain 1.31 pounds per day for the entire development period. Both groups of heifers were equal in reproductive performance. However, heifers fed to gain 2.5 pounds per day the last 60 days were actually more efficient and consumed 12 percent less feed than the heifers fed to gain at a constant rate, due to compensatory gain. This heifer development protocol will usually be implemented when lower-than-expected hay quality reduces gains.
Always evaluate heifers at least 60 days prior to the start of the breeding season to ensure enough time to adjust rations to reach target weights. Request help from your county Extension agent to properly adjust the ration to ensure desired gains are attained.
In almost every herd, first-calf heifers are the most difficult group to re-breed. Providing supplemental feed to improve body condition score (BCS) for acceptable pregnancy rates is an economical practice. However, this is the most difficult time period to increase body condition score. Research has shown that first-calf heifers having a BCS of 4 at breeding time will have pregnancy rates of approximately 50 percent, and firstcalf heifers having a BCS of 5 at breeding time will have about a 90 percent pregnancy rate (Bell et al., 1990). Even in well-developed heifers, body weight and condition can be rapidly lost after calving if they are fed only hay or grazed on poor-quality pasture. To maintain a high re-breeding rate, producers can supplement existing forages or hay, graze winter annual pasture or early wean the calf.
When feeding hay, plan to supplement energy and possibly provide additional protein to meet demands of lactation, growth and reproduction of the first-calf heifer. Table 3 lists example supplementation amounts for heifers in early lactation fed hay of various qualities. It is important to assess both body condition score and nutrient content of the forage prior to starting a supplementation program. Body condition scoring will identify the growth rate needed to achieve the desired body condition, and the nutrient content of the forage will show what nutrients are deficient. Ask for help when formulating a supplement to ensure that the proper amount and composition of nutrients are fed.
A multitude of feedstuffs can be fed to first-calf heifers. By-product feeds are an increasing source of winter supplementation in the Southeast. They are often competitive with corn and oilseed meals. Some by-product feeds have a moderate protein content, which reduces feed costs compared with a traditional corn/soybean meal mixture or a commercial protein supplement. In addition, by-product feeds such as soybean hulls, wheat middlings, corn gluten feed, distillers grains and citrus pulp are low in starch but high in digestible fiber. These by-products can be fed at higher levels than corn before intake and digestibility of forage is depressed. When high levels of supplements are required, a low-starch by-product feed is recommended.
Many producers supplement cows using winter annual pastures, which are high in quality and provide extra energy and protein for lactating heifers while decreasing the feeding of hay. Heifers can be fed approximately half of their daily energy needs from winter pasture along with good hay (55 percent TDN) to maintain body condition. Intake of pasture forage is difficult to determine, but plan for five to eight hours of grazing per day to keep heifers in adequate condition.
Nutrition costs are the most expensive component of a heifer development budget. It is critical to have all feedstuffs analyzed for nutrient content prior to feeding. A balanced ration can then be developed to achieve the desired rate of gain. Many forages and concentrate supplements can be used to successfully develop heifers. Feed heifers separately from the mature cow herd at all times. Ionophores should be fed and can be purchased in a commercial mineral mix. Contact your local county Extension agent for information about testing feeds for nutrient content.
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