NUTRITIONAL MANAGEMENT and HOW to CALCULATE Ron Lemenager, Extension Beef Specialist Purdue University, Department of Animal Sciences Feed Requirements Nutrient requirements of the beef herd vary according to age, gender, stage of production, animal weight, body condition and desired level of performance. In general, the priority of nutrient use from first to last is; maintenance, fetal development, lactation, growth, and conception. It is not unusual, however, for late gestation and early lactation cows to lose weight and body condition to maintain a pregnancy, or some level of lactation to support a calf, respectively. In beef cow herds, the nutrients of greatest concern are energy, protein, calcium, phosphorus, salt, vitamin A, water and sometimes magnesium, copper, sulfur and zinc. In most cases, the vitamin and mineral requirements can be balanced by the use of a good commercial vitamin/mineral supplement designed for the type of ration being fed. There are differences, however, between vitamin/mineral supplements that should be considered before purchase. Many different mineral sources are available for use in beef cattle diets and it is important to check the mineral tag to be sure the ingredients being used are high in bioavailability. For example, the oxide and carbonate forms of some minerals are not as available to the animal as other mineral forms such as the sulfate form. Minerals are often described as being either inorganic or organic. Inorganic mineral sources generally are associated with oxygen, chloride or other non-carbon based compounds. Organic mineral sources are often referred to as “chelated” minerals which are metals bound to an organic compound such as an amino acid. Because chelated minerals are associated with organic compounds they can in some cases, but not all cases, be more readily absorbed in the small intestine. The primary disadvantage of chelated minerals is their cost. Table 1 shows the mineral composition and relative bioavailabilities of common mineral forms used in mineral supplements. Table 1. Source, empirical formulas, mineral concentrations and relative bioavailabilities of common mineral sourcesa. Mineral Supplement Mineral Relative Mineral Empirical concen- bioavail- avail- formula tration ability ability (MC, %) (RV) (MC x RV) Calcium Calcium carbonate CaCO3 38 100 38.00 Bone meal variable 24 110 26.40 Calcium chloride (dihydrate) CaCl2(H2O) 31 125 38.75 Dicalcium phosphate Ca2(PO4) 20 110 22.00 36 90 32.40 Limestone Cobalt Copper Iodine Iron Monocalcium phosphate Ca(PO4) 17 130 22.10 Cobaltous sulfate CoSO4(H2O)7 21 100 21.00 Cobaltic oxide Co3O4 73 20 14.60 Cobaltous carbonate CoCO3 47 110 51.70 Cobaltous oxide CoO 70 55 38.50 Cupric sulfate CuSO4(H2O)5 25 100 25.00 Copper EDTA variable variable 95 variable Copper lysine variable variable 100 variable Cupric chloride (tribasic) Cu2(OH)3 Cl 58 115 66.70 Cupric oxide CuO 75 15 11.25 Cupric sulfide CuS 66 25 16.50 Cuprous acetate CuC2O2H3 51 100 51.00 Potassium iodide KI 69 100 69.00 Sodium iodide NaI 84 100 84.00 Calcium iodate Ca(IO)3 64 95 60.80 Diiodosalicyclic acid C7H4I2O3 65 15 9.75 Ethylenediamine dihydriodine C2H8N2(HI)2 80 105 84.00 Pentacalcium orthoperiodate Ca5(IO6)2 39 100 39.00 Ferrous sulfate heptahydrate FeSO4(H2O)7 20 100 20.00 Ferric citrate variable variable 110 variable Ferric EDTA variable variable 95 variable Ferric phytate variable variable 45 variable Ferrous carbonate FeCO3 38 10 3.80 Magnesium Magnesium sulfate MgSO4 20 100 20.00 Magnesium acetate MgC2O2H4 29 110 31.90 Magnesium basic carbonate MgCO3 31 100 31.00 Magnesium oxide MgO 55 100 55.00 MnSO4(H2O) 30 100 30.00 Manganese carbonate MnCO3 46 30 13.80 Manganese dioxide MnO2 63 35 22.05 Manganese methionine variable variable 125 variable Manganese monoxide MnO 60 60 36.00 Manganese Manganese sulfate Phosphorus Sodium phosphate Selenium Sodium Zinc NaPO4 variable variable Bone meal variable 21 100 21.00 Defluorinated phosphate variable 12 80 9.60 Dicalcium phosphate CaHPO4 18 85 15.30 Sodium selenite Na2SeO3 45 100 45.00 Cobalt selenite variable variable 105 variable Selenomethionine variable variable 245 variable Selenoyeast variable variable 290 variable Sodium chloride NaCl 40 100 40.00 Sodium bicarbonate Na(CO3)2 27 95 25.65 Zinc sulfate ZnSO4(H2O) 36 100 36.00 Zinc carbonate ZnCO3 56 60 33.60 Zinc oxide ZnO 72 100 72.00 a Adapted from: Ammerman, C.B., D.H. Baker, and A.J. Lewis. 1995. Bioavailability of Nutrients for Animals. New York: Academic Press; National Research Council. 1998. Nutrient Requirements of Swine, 10th revised edition. Washington, D.C.: National Academy Press; and Mineral Supplements for Beef Cattle, University of Missouri Extension, Chad Hale and K.C. Olson. Understanding the types and amounts of minerals provided by the base ration ingredients is also important. For example, rations containing corn co-products (distiller’s grains and corn gluten feed) require a mineral supplement with a high level of calcium (Ca) and low level of phosphorus (P) to assure the correct Ca:P ratio in the diet. In addition, these corn co-products contain relatively high levels of sulfur which can complex with copper, making it less available. Since copper is important in reproduction and immune function, a mineral supplement that contains higher levels of copper may be needed. Higher copper levels are also recommended for cattle consuming endophyte-infected fescue. Help in design rations for the cow herd that are correctly balanced for all the nutrients of concern can be obtained by consulting with a professional animal nutritionist, your local Extension educator, or the state beef specialist at your land-grant agricultural college. The cow herd should be divided into management groups by nutritional requirements. In herds where a limited breeding season is used (45-75 days), the management groups might be; 1) replacement heifers, 2) young cows plus thin older cows, 3) mature cows in moderate and above condition, and 4) bulls. If the breeding season is significantly longer than 75 days, groups 2 and 3 could be divided into early and late calving groups to allow delivery of feed to cows according to their requirements (gestation vs. lactation). Tables 2 through 6 show the nutrient requirements of beef cattle at various stages of production. Table 2 shows the requirements of a mature (four years or older), 1200 pound, body condition score (BCS) 5 cow during the course of a complete production cycle. The weight of a BCS 5 cow shortly after calving is considered her base weight and the dry matter intake and nutrient requirements are based on that weight. As the cow moves through the production cycle she typically gains weight due to advancing pregnancy (developing fetus, gravid uterus, fluids, and membranes). Requirements are the lowest for cows shortly after their calves are weaned and they are in mid-gestation. Requirements increase significantly as cows advance into the last trimester of pregnancy and into early lactation. Nutrient requirements are highest approximately two months after calving when cows reach peak lactation and then begin to decrease until their calves are weaned. For these reasons, the lowest quality forages should be fed to animals with the lowest nutrient requirements (dry cows in mid-gestation) and highest quality forages should be fed to animals with higher requirements (cows in late pregnancy and early lactation). Additionally, the cow’s genetic potential for milk production should be matched to forage quality. When excess nutrients are supplied to low-producing cows, surplus nutrient intake will be seen as an increase in cow weight and BCS. Conversely, inadequate nutrients supplied to high producing cows will cause them to; lose weight and body condition, delay return estrus, have lower fertility, and produce calves with lighter weaning weights, unless they are provided supplements to correct nutrient deficiencies. It is common to strategically supplement cows during some phases of the production cycle, but the need to routinely provide significant amounts of supplement can be expensive. Table 2. Daily Energy and Protein Requirements for a 1200 l b., BCS 5, Mature Cow a,b Expected Peak Milk (lbs/day) Months Cow Low (15 l bs) Moderate (20 l bs) High (25 l bs) d c CP Since Scale Wt. NEm NEm CP NEm CP Calving BCS = 5 Mcal lbs Mcal lbs Mcal lbs 1 1200 14.5 2.4 15.8 2.7 17.2 3.0 2 (peak l actation) 1200 15.3 2.6 16.9 3.0 18.6 3.4 3 1205 14.8 2.5 16.3 2.8 17.8 3.2 4 1205 14.0 2.3 15.1 2.5 16.3 2.8 5 1205 13.1 2.1 14.0 2.3 14.9 2.5 6 1210 12.5 1.9 13.1 2.0 13.7 2.2 7 (weaning) 1215 9.0 1.5 9.0 1.5 9.0 1.5 8 1225 9.3 1.5 9.3 1.5 9.3 1.5 9 1240 9.8 1.6 9.8 1.6 9.8 1.6 10 1260 10.7 1.7 10.7 1.7 10.7 1.7 11 1290 12.0 1.9 12.0 1.9 12.0 1.9 12 1340 13.9 2.2 13.9 2.2 13.9 2.2 a Adapted from NRC, 1 996 b c Does not a ccount for i ncreased e nergy needs due to cold s tress Net e nergy for maintenance, Mcal/day d Crude protein, l b/day Young cows require higher quality feeds (more nutrient dense diets) than older cows at every stage of production because they are still growing, they do not have a complete set of mature teeth, and they lack the volume and capacity to eat as much as a mature cow. Table 3 shows the nutrient requirements of first- and second-calf heifers that have an expected mature weight of 1200 pounds. Nutrient requirements increase and decrease in a manner similar to those of mature cows as they move through their production cycle. Table 3. Daily Energy and Protein Requirements f or First and Second Calf Heifers a,b,c Months First Calf Heifers Second Calf Heifers CPe Since Heifer Wt. NEmd Heifer Wt. NEm CP Calving (lbs) Mcal lbs (lbs) Mcal lbs 0 ( calving) 1080 14.8 2.3 1235 14.3 2.2 1 970 14.1 2.3 1110 15.0 2.5 2 ( peak milk) 985 15.0 2.5 1110 16.0 2.8 3 1000 14.6 2.4 1120 15.4 2.6 4 1010 13.9 2.2 1125 14.4 2.4 5 1025 13.1 2.1 1130 13.5 2.2 6 1040 12.5 1.9 1140 12.7 2.0 7 ( weaning) 1060 9.4 1.5 1150 9.0 1.5 8 1080 9.7 1.5 1160 9.3 1.5 9 1105 10.3 1.6 1180 9.9 1.6 10 1140 11.2 1.7 1205 10.8 1.7 11 1180 12.5 1.9 1240 12.1 1.9 a Adapted from NRC, 1 996 b c Assumes a 1 200 l b mature c ow weight a t a BCS = 5 with moderate peak milk production (20 l b/day) Does not a ccount for i ncreased e nergy needs due t o c old s tress d Net e nergy for maintenance, Mcal/day e Crude protein, l b/day Table 4 shows the energy required to change one BCS in a mature, 1200 pound cow. The energy requirements are expressed in Mcal of Net Energy for Maintenance (NEm). Thin cows require less energy to gain one BCS than fatter cows because they are depositing more protein and water. Accretion of protein is energetically more efficient and requires less energy than accretion of fat (adipose), which is more energy dense. As fat cows gain weight and condition, they deposit proportionally less protein and more fat than their thinner counterparts. This can be seen in a comparison between a BCS 4 cow who requires a total of 158 Mcal of NEm above maintenance to change one condition score vs. a BCS 6 cow who requires 210 Mcal of NEm. Thumb rule 1: It takes about 80 pounds for a mature cow to change one (±) BCS. First-calf heifers, on the other hand, require about 150 pounds to increase one BCS. The difference in weight required to change one BCS can be explained by the fact that first-calf heifers must continue to grow before they can begin depositing body condition (fat). Table 4. Energy Required to Change a Mature 1200 l b, BCS 5 Cow One Condition Score a,b BCS 1 2 3 4 5 6 7 8 9 Approx. Shrunk Body Wt., l bs 880 960 1040 1120 1200 1280 1360 1440 1520 Mcal NEmc to Change 1 BCS 78 105 131 158 184 210 238 264 290 a Adapted from Purdue research published by Buskirk e t a l., 1 992 J . Anim. Sci. 7 0:3867-‐3 876. b c Feeding 1 l b of dry s helled c orn provides a pproximately 1 Mcal NE m Net e nergy for maintenance, Mcal/day Table 5 shows the nutrient requirements for growing heifer calves housed in a thermoneutral environment and not implanted. This table can be used to develop preconditioning, heifer development, and feedlot rations. It is consistent with the previous tables and uses a 1200 pound mature weight for heifers and a 1200 pound harvest weight for finished steers expected to grade USDA low choice. As animals increase in weight, the maintenance requirements for both energy (NEm) and crude protein increase. Similarly, as average daily gain of the calf increases, the net energy for gain (NEg) and protein requirements also increase. Table 5. Daily Energy and Protein Requirements for Growing and Finishing Cattle a,b,c Weight (lbs) 525 650 775 900 1025 1150 Gain lbs/day 1.0 1.8 2.5 3.3 4.0 1.0 1.8 2.5 3.3 4.0 1.0 1.8 2.5 3.3 4.0 1.0 1.8 2.5 3.3 4.0 1.0 1.8 2.5 3.3 4.0 1.0 1.8 2.5 3.3 4.0 NEmd Mcal/day 4.7 4.7 4.7 4.7 4.7 5.5 5.5 5.5 5.5 5.5 6.3 6.3 6.3 6.3 6.3 7.0 7.0 7.0 7.0 7.0 7.7 7.7 7.7 7.7 7.7 8.4 8.4 8.4 8.4 8.4 NEge Mcal/day 1.28 2.37 3.50 4.67 5.86 1.50 2.78 4.11 5.48 6.88 1.72 3.17 4.69 6.25 7.85 1.92 3.55 5.24 6.99 8.78 2.12 3.91 5.78 7.71 9.68 2.31 4.26 6.30 8.40 10.55 CPf lbs/day 1.22 1.55 1.87 2.18 2.49 1.36 1.69 2.01 2.32 2.62 1.49 1.82 2.13 2.43 2.73 1.57 1.86 2.14 2.40 2.66 1.65 1.91 2.15 2.38 2.60 1.72 1.95 2.16 2.36 2.54 a Adapted from NRC, 1 996 b c Assumes a nimals weigh 1 200 l bs when t hey reach l ow c hoice (Small) marbling Does not a ccount for i ncreased e nergy needs due t o c old s tress d Net e nergy for maintenance, Mcal/day e Net e nergy for gain, Mcal/day f Crude protein, l b/day Table 6 shows the energy and protein requirements for growing bulls with a mature weight of 2000 pounds. The requirements relate to weight and gain in a manner similar to those of growing and finishing calves. Table 6. Daily Energy ( NEg and NEg)and Protein ( CP) Requirements for Growing Bulls a,b,c Weight (lbs) 500 800 1100 1400 1700 2000 Gain lbs/day 0 1 2 3 4 0 1 2 3 4 0 1 2 3 4 0 1 2 3 4 0 1 2 3 4 0 1 2 3 4 NEmd Mcal/Day 5.2 5.2 5.2 5.2 5.2 7.4 7.4 7.4 7.4 7.4 9.4 9.4 9.4 9.4 9.4 11.2 11.2 11.2 11.2 11.2 13 13 13 13 13 14.6 14.6 14.6 14.6 14.6 NEge Mcal/day 0.00 1.23 2.64 4.12 5.65 0.00 1.76 3.76 5.86 8.04 0.00 2.23 4.77 7.45 10.21 0.00 2.67 5.72 8.92 12.23 0.00 3.09 6.61 10.32 14.15 0.00 3.49 7.47 11.66 15.98 CPf lbs/day 0.73 1.19 1.63 2.05 2.47 1.04 1.51 1.93 2.33 2.71 1.32 1.69 2.01 2.30 2.57 1.58 1.87 2.09 2.27 2.43 1.83 2.03 2.16 2.24 2.30 2.07 2.19 2.22 2.25 2.28 a Adapted from NRC, 1 996 b c Assumes a nimals weigh 2 000 l bs when t hey reach maturity with a BCS = 5 Does not a ccount for i ncreased e nergy needs due t o c old s tress d Net e nergy for maintenance, Mcal/day e Net e nergy for gain, Mcal/day f Crude protein, l b/day When forage quantity (supply) is low, alternative feeding strategies must be considered. Utilization of crop residues is a strategy that can reduce cost by increasing grazing days and reducing the amount of hay needed. Corn stalks can provide 30-60 days of grazing depending on soil types and rainfall. Dropped ears will be gleaned from the field first by cows, but today’s corn genetics and harvesting equipment are designed to minimize ear drop. Leaves and shucks are the highest quality forage parts of the plant and will be consumed next. As the time after grain harvest increases, however, forage quality decreases rapidly due to weathering. For moderately conditioned cows in the middle trimester of pregnancy, they may only need a good vitaminmineral supplement for the first 20-30 days of corn stalk grazing. After 30 days on stalks, however, a protein supplement is usually recommended to improve fiber digestibility and forage intake. The key to successful corn stalk grazing is to monitor cow body condition. If cows begin losing weight and condition, either more supplementation (protein and/or energy) is needed, or cows should be provided an alternative diet. Utilizing low quality forages (baled corn stalks, wheat straw or mature hay) as a primary forage resource can add significant cost to the ration because of harvest and supplementation costs compared to the nutrients provided. This is especially true when low quality forages are used in rations for animals that have higher nutrient requirements (growing/developing, late gestation and early lactation). To be most cost effective, low quality forages should be fed to animals with the lowest requirements, such as dry cows in mid-gestation after calves are weaned. Low quality forages are typically low in protein (3-7% crude protein) and require protein supplementation to optimize fiber digestion and dry matter intake. Supplementation. The only way to get an accurate assessment of forage quality is to have the forage analyzed for nutrient content. If forages are analyzed and it is determined that the available forage cannot meet the animal’s requirements, then a cost-effective supplementation strategy should be developed. A wide range of supplements can be used with existing forage to meet requirements for different production situations. Typically this means utilizing feeds that are high in one or more nutrient categories (energy, protein, vitamins, minerals) that are deficient in the forage. It should be noted that mineral and vitamin requirements are not altered significantly by cow BCS, but energy requirements are dramatically affected by BCS. Factors that affect supplement selection are nutrient content of the forage, nutrient profile of the supplement, cost and availability of supplement, as well as cow nutrient needs based on BCS and stage of production. Type of supplement will then be dictated by how much protein and energy supplementation is required per day to reach the desired performance level. If energy is the only limiting nutrient, high energy supplements such as corn grain, soybean hulls or wheat midds will usually be the most economical in the Cornbelt. If both energy and protein are required, then a co-product with a higher level of protein such as corn gluten feed, distiller’s grains or soybean meal could be considered. Balancing rations when forages are fed free-choice requires an estimate of dry matter intake (DMI). It should be noted that DMI is different than feed disappearance because cows often sort, soil, and waste forage when they have unlimited access. Once DMI is determined, the amount of nutrients can be calculated and a supplement can be formulated that will correct any deficiencies. Table 7 provides a guide to estimated DMI of forages as a percent of body weight when intake is not known. This table shows that dry, gestating beef cows eat less dry matter than lactating cows, DMI goes up as forage quality increases, and protein supplementation increases dry matter intake when the forage quality (low and average quality) does not provide enough protein to optimize rumen fermentation and forage digestion. In contrast, protein does not increase DMI when forages contain adequate protein (high quality). Energy supplementation at low levels does not increase DMI, regardless of forage quality. It is important to realize that these estimates of forage intake are not as accurate as measuring actual intake or as using the neutral detergent fiber (NDF) value from a forage analysis to predict intake. It should be noted that higher levels of supplementation, especially energy supplementation, can actually decrease DMI. Table 7. Estimated Dry Matter Intake As determined By Forage Quality (Percent Of Body Weight)a No Supplemented with Item Supplement Protein Energy Dry, Gestating Cow Low Quality Forage 1.5 1.8 1.5 Average Quality Forage 2.0 2.2 2.0 High Quality Forage 2.5 2.5 2.5 Lactating Cow Low Quality Forage 2.0 2.2 2.0 Average Quality Forage 2.3 2.5 2.3 High Quality Forage 2.7 2.7 2.7 a Example: 1290 lb, BCS 5 cow in late gestation consuming average quality hay, appropriately supplemented with protein, would consume about: 1290 x 0.22 = 28.4 lb of hay on a dry matter (DM) basis daily. That same BCS 5 cow just after calving would weigh approximately 1200 lb and would consume about: 1200 x .025 = 30 lb of average quality hay (DM matter basis) daily when appropriately supplemented with protein. The best single indicator of forage quality is neutral detergent fiber (NDF) and it can be used to predict dry matter intake. As the NDF percentage in a forage increases with advancing maturity, dry matter intake will generally decrease. Many laboratories analyze for acid detergent fiber (ADF), but the analysis may or may not include an NDF value unless requested. Cow weight varies during the year due to changes in body condition score, pregnancy, and gut fill. Normal weight fluctuations resulting from a change in body condition (above or below a BCS 5) do not significantly alter the cow’s ability (volume and capacity) to consume forage. Therefore, a BCS 4 cow weighing 1120 pounds, a BCS 5 cow weighing 1200 pounds, and a BCS 6 cow weighing 1280 pounds will all consume similar amounts of forage. Similarly, a 1200 pound cow in a BCS 5 just after calving will consume a similar amount of forage as a 1290 pound, BCS 5 cow during the eighth month of pregnancy. Therefore, when using the NDF value from a forage analysis to predict dry matter intake, the correct base weight for a cow is her weight shortly after calving when pregnancy does not impact her scale weight. Cow weight after calving should be adjusted to a BCS 5 using Thumb Rule 1. Limit feeding hay. Research at Purdue University has shown that limiting the time cows have access to large round bales to 1, 2, or 4 hours per day reduced forage disappearance by 72, 50, and 22%, respectively, compared to estimated free-choice hay intake. This reduced disappearance reflects both a reduction in hay intake and wastage. Limiting access time to large round bales may be a valuable tool for producers when hay prices are expensive relative to grain and co-product feeds. When properly supplemented to meet the requirements, cow performance should not be negatively impacted. The feed ingredients and level of nutrients needed to supplement the cows should be determined by the nutrient analysis of the forage, ingredient availability and cost, and the animal’s requirements. How-to-Calculate Conversion of dry matter (DM) to as-fed Dry matter is an important concept because the beef industry utilizes a number of feeds that have significantly different amounts of moisture. When balancing diets and determining how much an animal will eat, always use DM values and then convert the value to an as-fed basis for feeding. An easy way to visualize a dry matter to as-fed conversion is to imagine a cup of freeze dried coffee. The cup with dry coffee has weight and the coffee is very concentrated. This is a dry matter weight and a dry matter concentration of coffee. When water is added to the cup, two things happen; weight is added to the cup, and the coffee is diluted. The cup with water now has an as-fed weight and an as-fed concentration of coffee. The same thing happens with feeds when water is present. Water Example: Assume a sample of corn silage is analyzed for nutrient profile and the analysis comes back containing 35% dry matter (65% moisture) and 8% crude protein (CP) on a DM basis. Also assume that 17.5 pounds of DM per head daily needs to be fed. What would the CP content be if the DM was 35%, and how much silage needs to be fed on an as-fed basis? Thumb Rule 2: Always use the percent dry matter value of a feed (not the percent moisture value) when balancing diets and determining dry matter intake. Step 1. Convert CP from a DM basis to an as-fed basis. The crude protein value will be diluted (get smaller) when going from dry matter to asfed. By multiplying the CP value of a feed by a number smaller than 1.0, it will get smaller. In this example, there is 8% CP and 35% DM. Therefore, thinking of the DM value of the feed as a decimal (.35 = .35 lb of dry feed/lb of as-fed feed), instead of a percent (35%), the number is smaller than 1.0, and can be used as follows; 8% CP in corn silage (DM basis) x .35 = 2.8% CP in corn silage (as-fed basis) Step 2. Convert pounds of corn silage from a DM basis to an as-fed basis. The pounds of corn silage on a DM basis will increase as water is added to the feed. In this case, 17.5 pounds of corn silage on a DM basis needs to get bigger as it is converted to an as-fed basis. Therefore, if 17.5 is divided by a number smaller than 1.0, it will get bigger. In this example, the dry matter value of 35% converted to a decimal (.35 = .35 lb DM/lb of as-fed feed) can be used as follows; 17.5 lb silage (dry matter basis) ÷ .35 = 50 lb silage (as-fed basis) Conversion of as-fed to dry matter (DM) The freeze dried coffee example can also be used to visualize conversion of as-fed to dry matter. As before, the cup filled with freeze dried coffee plus water can be thought of as an as-fed feed. To convert to DM, think of removing all the water so that only dried coffee remains. The weight of the cup decreases, and the concentration of the coffee increases when changing from an as-fed to a DM basis. The same thing happens with feeds. Water Example: Assume a modified dry distiller’s grains with solubles (MDDGS) that contain 48% DM (52% moisture) and 14.5% CP on an as-fed basis. Assume that 9 pounds of MDDGS are being fed on an as-fed basis per head daily. What would the CP content be on a DM basis, and how much DM is being fed? Thumb Rule 3: Rations are almost always formulated on a dry matter (DM) basis in the beef industry because of the significant variation in water content of feeds that are used. In addition, feed intakes are more accurately estimated on a DM basis (vs. an as-fed basis). Step 1. Convert the CP from an as-fed to a DM basis. The example above showed that the CP value of the feed will be more concentrated (get larger) when going from as-fed to DM. Dividing the CP value of the feed on an as-fed basis by the DM value of the feed as a decimal (a number smaller than 1.0) will result in the number getting larger. In this example, there is 14.5% CP and 48% DM. Therefore, thinking of the DM value of the feed as a decimal (.48 = .48 lb of dry feed/lb of as-fed feed), instead of a percent (48%), the number is smaller than 1.0 and can be used as follows; 14.5% CP in MDDGS (as-fed basis) ÷ .48 = 30.2% CP in MDDGS (DM basis) Step 2. Convert the pounds of MDDGS from an as-fed basis to a DM basis. In this case, 9 pounds of MDDGS on an as-fed basis needs to get smaller as it is converted to a DM basis. Therefore, when 9 is multiplied by a number smaller than 1.0, it will get smaller. In this example, the dry matter value of 48% can be converted to a decimal (.48 = .48 lb DM/ lb of as-fed feed) and can be used as follows: 9 lb of MDDGS (as-fed basis) x .48 = 4.32 lb of MDDGS (DM basis) Dry matter intake (DMI) of a forage To balance forage-based diets, both the nutrient content of the forage and dry matter intake must be determined. These two factors can then be used to determine if the forage can supply the required nutrients, or if the diet needs to be fortified with a supplement. Neutral detergent fiber (NDF) is one of the best predictors of forage quality and dry matter intake. Thumb Rule 4: Dry matter intake (DMI) can be predicted using the NDF value(DM basis) from a forage analysis as follows: 120 ÷ %NDF of the forage = DMI as a percent of body weight Thumb Rule 5: When estimating forage intake, a cow’s weight should be adjusted to a BCS 5 (using Thumb Rule 1) and either a non-pregnant, or very early gestation scale weight. As pregnancy progresses, the products of conception (gravid uterus, fluids, and membranes) result in an increase in cow weight across the scale, but do not result in an increase in dry matter intake. Similarly, as cows add or lose weight based on change in body condition, their intake does not change significantly. Example: Assume a 1200-pound base-weight cow is consuming hay with an NDF value of 50% (DM basis) and a dry matter value of 88%. How much hay will this cow consume per day? Step 1. Determine daily DMI of this cow as a percent of body weight using Thumb Rule 4. 120 ÷ 50% NDF = DMI of 2.4% of body weight Step 2. Determine daily DMI in pounds of hay per day for this 1200 pound cow. Convert DMI as a percent of body weight to a decimal equivalent. 1200 lb cow x .024 = 28.8 lb of hay DMI/day (DM basis) Step 3. Convert daily DMI to an as-fed basis for feeding. 28.8 lb hay DMI/day ÷ .88 = 32.7 lb of hay/day (as-fed basis) Caution: Not all hay that is fed is actually consumed. Hay disappearance is a combination of hay intake plus waste due to sorting and soiling. Dry matter intake (DMI) of hay when daily access-time is limited There may be times when limiting forage intake and supplementation of the needed nutrients is cheaper than feeding hay free-choice. For example, a drought could cause hay prices to be high relative to that of grain and/or by-products, or when nutrient requirements are low and available high quality forage exceeds the nutrient requirements. Thumb Rule 6: When cows have limited access-time to forage, an equation developed from research conducted at Purdue University can be used to determine the amount of forage dry matter intake (DMI) that that will be consumed per day: Hay DMI (% of BW) = 0.30 x Hours access – (.02 x Hay NDF%) + 1.34, where NDF of the forage is on a DM basis. Example: Assume a group of 1200 pound base-weight, BCS 5 cows consuming hay that contains 50% NDF (DM basis) and 85% dry matter. Cows will be limited to 4 hours of access-time to large round bales each day. How much hay will a 1200 pound cow consume per day? Step1. Determine daily DMI of this cow, as a percent of her body weight, using Thumb Rule 6. 0.30 x 4 hr access-time – (.02 x 50% NDF) + 1.34 = DMI of 1.54% of body weight/day Step 2. Determine daily DMI in pounds per day for this 1200 pound cow. 1200 lb x .0154 = DMI of 18.5 lb/day of hay Note: In this example, these same cows would consume about 120 ÷ 50 = 2.4% of their body weight on a DM basis, or 1200 lb x .024 = 28.8 lb of hay DM per day, if they were allowed freechoice access to large round bales. In this limited access-time feeding example, the producer could expect to reduce the amount of hay consumed (not including differences that might also exist in waste) by almost 36% (28.8 – 18.5 ÷ 28.8 = 35.76%). Research at Purdue found that when cows have limited access time to large round bales each day, they waste less hay because they spend more time eating, and less time sorting than cows with 24 hour per day access. Step 3. Convert DMI to an as-fed basis for feeding. 18.5 lb of hay intake (DM basis) ÷ .85 = 21.8 lb of hay (as-fed) Protein supplementation when energy deficiencies are minimal Producers often must supplement low quality forages to meet the protein requirement of the cow herd. An example would be when mid-gestation cows are consuming low quality forages that contain less than 8% crude protein (corn stalks, wheat straw, mature grass hay). Thumb rule 7: When the CP concentration of the diet drops below 8% on a dry matter basis, the microbes in the rumen will not have enough nitrogen to optimize fiber digestion and dry matter intake. Thumb rule 8: CP requirements for cows in mid-gestation, late gestation, and early lactation, respectively, are 8 – 10 – 12% (DM basis). If the diets do not supply these levels of CP, then supplementation is justified. Example. Assume a herd of 1200 pound, BCS 5, non-lactating, mid-gestation beef cows have free-choice access to a low quality forage and a good quality commercial vitamin/mineral supplement. How much soybean meal (SBM) supplement is required per cow daily to meet their CP requirement? Table 8 shows the CP and NEm content of the feeds and this cow’s requirements. Table 8. Crude protein (CP) and net energy for maintenance (NEm) values. Dry matter basis Item CP, % NDF, % NEm, Mcal/lb Soybean meal, 44% 49.9 -.95 Low quality forage 4.0 66.7 .44 CP, lb NEm, Mcal/day a Cow requirements 1.6 -9.8 a From Table 2, month 9 of the production cycle, month 6 of pregnancy. Cow is a 1200 lb cow that now weighs 1240 lb due to pregnancy. Step 1. Make sure the vitamin and mineral requirements are met from the free-choice access to a good commercial vitamin/mineral mix. This example assumes the vitamin/mineral requirements are met. Step 2. Determine daily DMI as a percent of body weight using Thumb Rule 4. 120 ÷ 66.7 = DMI of 1.8% of body weight Step 3. Determine daily DMI in pounds per day for this 1200 pound cow. 1200 lb cows x .018 = 21.6 lb of low quality forage intake/day (DM basis) Step 4. Calculate how much protein and energy are provided per day by the forage. 21.6 lb x .04 lb protein/lb of low quality forage = .86 lb of protein intake from forage 21.6 lb x .44 Mcal NEm/lb of low quality forage = 9.5 Mcal NEm intake from forage Step 5. Calculate the daily deficiency in CP and energy. 1.6 lb of protein required - .86 lb of protein supplied by forage = 0.74 lb protein deficient 9.8 Mcal NEm required – 9.5 Mcal NEm supplied by forage = 0.3 Mcal NEm deficient Step 6. Calculate how much SBM is needed per cow daily to correct the protein deficiency. .74 lb CP deficient ÷ .499 lb CP/lb of SBM = 1.48 lb/day of SBM (DM basis) needed Note: Adding 1.48 lb of SBM daily (DM basis) will add energy to the diet which will result in a slight excess in energy compared to the requirement. This is not necessarily a bad thing. In this case, energy is over-fed by 1.1 Mcal NEm/d (calculated as 1.48 lb/d x .95 Mcal NEm/lb = 1.4 Mcal NEm per cow daily provided by SBM, and 1.4 Mcal NEm provided by supplementation – 0.3 Mcal NEm deficiency before supplementation = 1.1 Mcal NEm/d excess). Thumb rule 9: On a practical basis, assume a 90% dry matter value for feeds taken out of a bag or a bin. While this value may not be absolutely correct, it is usually pretty close and easy to remember. Step 7. Convert the DM value to an as-fed value for feeding using Thumb Rule 9 1.48 lb of SBM (DM basis) ÷ .90 = 1.65 lb of SBM (as-fed basis) per cow daily Calculating a supplement when both energy and protein are required. When rations are balanced for growing/developing cattle, young cows, and cows in either late gestation or early lactation; an energy deficiency will often exist after the protein requirement has been satisfied. In this case, a feed containing both high energy and protein, such as distiller’s grains plus soluble (DGS) or corn gluten feed (CGF), can be considered. These two feeds have the advantage over corn because their energy comes in the form of a highly digestible fiber instead of starch. When starch is added to a forage-based diet at levels above 0.3% of body weight on a dry matter basis, it can reduce digestibility of the forage component in the diet. This is called a negative associative effect. Thumb rule 10: The recommended upper limit of supplementation (DM basis) is 0.3% of body weight for corn, 0.5% of body weight for the corn co-products (DGS and CGF) and 1.0% for pelleted soybean hulls. Thumb rule 11: The calcium:phosphorus ratio must be considered when adding either distiller’s grains or corn gluten feed to the diet because they contain high levels of phosphorus. Many commercial feed companies offer a high calcium vitamin/mineral supplement to be fed with these corn co-products. Feed grade limestone can also be fed as a calcium source. The recommended Ca:P ratio of the total diet is at least 1.5:1. Example. Assume a first-calf, BCS 5 heifer weighing 1080 just after calving is consuming a low/moderate quality hay and provided a high quality, free-choice vitamin/mineral supplement. How much dry corn gluten feed is needed per day to meet the protein and energy requirements. Table 9 provides the crude protein and energy values for feeds and this cow’s requirements. Table 9. Crude protein (CP) and net energy for maintenance (NEm) values. Dry matter basis Item CP, % NDF, % NEm, Mcal/lb Low quality forage 9.0 54.5 .52 Dry distiller’s grains + 28.0 -.98 soluble Dry corn gluten feed 23.0 -.88 CP, lb NEm, Mcal/day a Cow requirements 2.3 -14.80 a From Table 3, month 0 of the production cycle just after calving. Step 1. Make sure the vitamin and mineral requirements are met from the free-choice access to a good commercial vitamin/mineral mix. In this example, we will assume the vitamin/mineral requirements are met. Step 2. Determine daily DMI in pounds per day for this 1200 pound cow using Thumb Rule 4 and the hay NDF value from Table 9. 120 ÷ 54.5 = 2.2% of her body weight (DM basis) 1080 lb first calf heifer x .022 = 23.76 lb of hay intake (DM basis) Step 3. Calculate how much protein and energy are provided per day from forage. 23.76 lb x .09 lb protein/lb of low quality forage = 2.14 lb of protein intake 23.76 lb x .52 Mcal NEm/lb of low quality forage = 12.35 Mcal NEm intake Step 4. Calculate the daily deficiency in CP and energy using the cow requirements listed in Table 9. 2.3 lb of protein required – 2.14 lb of protein supplied by forage = 0.16 lb protein deficient 14.8 Mcal NEm required – 12.35 Mcal NEm supplied by forage = 2.45 Mcal NEm deficient Step 5. Calculate how much dry CGF will be needed per cow daily to correct the energy deficiency using the NEm value for CGF in Table 9. 2.45 Mcal NEm deficient ÷ .88 Mcal NEm/lb of supplement = 2.78 lb of CFG (DM basis) needed per cow daily. Step 6. Check to make sure this level of supplementation meets the CP deficiency. 2.78 lb of CGF (DM basis) x .23 lb of CP/lb of feed = .64 lb of CP provided by CGF .64 lb of CP provided - .16 lb CP deficiency = .48 lb of CP excess. Note: Feeding 2.78 lb of CGF (DM basis) meets the energy needs of the cow and exceeds the protein requirement, but it does not exceed the recommended upper level of dietary corn coproduct inclusion (Thumb Rule 10) of 0.5% of body weight (.005 x 1080 lb heifer = 5.4 lb) on a DM basis. The excess protein will be used as an energy source and cows may increase slightly in weight and BCS. Step 7. Convert from a DM to an as-fed basis for feeding using Thumb Rule 9. 2.78 lb ÷ .90 = 3.08 lb of CFG needed per cow daily on an as-fed basis Cost per unit of protein Producers are often faced with deciding which protein source to use. Ease of supplementation (convenience factor) and cost per unit of protein are two factors that need to be considered. Freechoice supplements that come in the form of blocks or tubs are convenient, but they typically increase the cost of supplementation compared to other protein sources that have less manufacturing cost, such as wet or dry corn co-products, soybean meal, and alfalfa hay. The price used for each protein source needs to reflect the cost to deliver it to the cows. This means that cost of storage, transportation, and delivery to the bunk must to be included to accurately compare protein sources. Example. Assume that three protein sources are available to a cow-calf producer; soybean meal (SBM), wet corn gluten feed (WCGF), and dry distiller’s grains plus solubles (DDGS). The cost per ton, dry matter analysis, and crude protein content on a dry matter basis for these protein sources are shown in Table 10. Table 10. Supplemental feed cost and nutrient profile of selected protein sources. Item Soybean meal, 44% Wet corn gluten feed Dry distiller’s grains + solubles Cost, $/tona 300 40 120 Dry Matter, % 88 40 89 % CP, DM basis 50 23 28 a This cost is an as-fed basis and needs to reflect cost delivered to the feed bunk. Cost of transportation, storage and feeding (labor, equipment and spoilage) of high moisture feeds can be significantly different than dryer feeds. Step 1. Feed prices are typically expressed on an as-fed basis, but the CP analysis is typically reported on a DM basis, therefore, the first step is to determine pounds of DM in a ton. SBM: 2000 lb/ton x .88 lb of dry matter/lb of feed = 1760 lb of DM per ton WCFG: 2000 lb/ton x .40 lb of dry matter/lb of feed = 800 lb of DM per ton DDGS: 2000 lb/ton x .89 lb of dry matter/lb of feed = 1780 lb of DM per ton Step 2. Calculate the pounds of protein per ton. SBM: 1760 lb of DM/ton x .50 lb of protein/lb of DM = 880 lb of protein per ton WCGF: 800 lb of DM/ton x .23 lb of protein/lb of DM = 184 lb of protein per ton DDGS: 1780 lb of DM/ton x .28 lb of protein/lb of DM = 498 lb of protein per ton Step 3. Calculate the cost per unit ($/lb) of protein SBM: $300/ton ÷ 880 lb of protein/ton = $0.34/lb of protein WCGF: $40/ton ÷ 184 lb of protein/ton = $0.22/lb of protein DDGS: $120/ton ÷ 498 lb of protein/ton = $0.24/lb of protein Step 4. Determine which is the best option. The cheapest source of protein in this example is provided by WCGF. The primary disadvantage with this protein source, however, is that it has a shorter shelf-life than the two other protein sources used in this example. While price per pound of protein is slightly higher for the DDGS in this example, the final cost of supplementing cows could be cheaper if a portion of WCGF is discarded because of spoilage. Adjusting energy level in the diet for cold stress. During the winter, cold stress can be both a nutritional and management issue. Cows consuming low to moderate quality forages late in gestation, or during early lactation, may not be able to eat enough forage to meet the increased energy requirements caused by cold stress. Putting out another big round bale of low to moderate quality hay typically will not meet the cow’s increased energy requirements. The energy requirements of a cow increase in direct proportion to wind chill. If cows are housed in an open lot, their energy requirements are not based on thermometer temperature, but rather wind chill temperature. If wind breaks are provided, thermometer temperatures become more useful. Wind breaks may be more cost effective in the long term compared to the cost of supplementing expensive high energy feeds. Thumb rule 12: For each 10o F drop below a wind chill of 30o F, the energy requirements increase 13% for cows in good body condition with a dry, winter hair coat; and 30% for thin cows, or cows with a wet or summer hair coat. Example. Assume a 1200 lb base-weight , BCS 5 cow during the last trimester of gestation is in a -10o F wind chill environment. The cow has free choice access to moderate quality hay that analyzes 85% DM and a good quality commercial vitamin/mineral supplement. How much pelleted soybean hulls will be needed per day to meet this increased requirement? Table 11 shows the crude protein and energy values for the feeds and this cow’s requirements. Table 11. Crude protein (CP) and net energy for maintenance (NEm) values. Dry matter basis Item CP, % NDF, % NEm, Mcal/lb Moderate quality forage 11.7 54.5 .53 Pelleted soybean hulls 12.0 -.88 CP, lb NEm, Mcal/day a Cow requirements 2.3 -12.0 a From Table 2, scale weight of this 1200 lb, BCS 5 cow in late gestation is about 1290 lb. Step 1. Calculate the increase in energy required above maintenance (Table 11) for this cow under cold stress using Thumb Rule 12. A wind chill factor of -10 o F is 4 units of 10 below 30 o F, therefore: 4 x .13 = 52% increase in energy required above maintenance 12 Mcal NEm/day required x .52 increase = 6.24 Mcal NEm/day increase in energy needed above maintenance due to cold stress Step 2. Calculate the total energy required per day for this 1200 lb cow under cold stress. 12 Mcal NEm/day requirement + 6.24 NEm/day increase = 18.24 Mcal NEm/day Step 3. Calculate how much hay this cow would be expected to consume using Thumb Rule 4 and the 54.5% NDF forage analysis. Note: The crude protein (DM basis) in hay (11.7%) and soybean hulls (12%) both exceed 10% CP for cows in late gestation (Thumb Rule 8), therefore, no additional protein supplementation is needed. 120 ÷ 54.5 = DMI of 2.2% of her body weight/day 1200 lb x .022 = 26.4 lb of hay DM/day Step 4. Calculate how much energy this cow would be expected to consume per day. 26.4 lb of hay DM x .53 Mcal NEm/lb of hay = 13.99 Mcal/d Step 5. Calculate the deficiency in energy intake per day. 18.24 Mcal NEm required/day – 13.99 Mcal NEm/day provided by hay = 4.25 Mcal NEm deficient/day Step 6. Calculate the amount of a high energy feed needed to meet this deficiency using SBH. 4.25 Mcal NEm/day deficiency ÷ .88 Mcal NEm/lb in SBH = 4.83 lb SBH (DM basis) Caution: Corn (1.01 Mcal NEm/ lb) was an optional high energy feed, but the amount needed (4.25 ÷ 1.01 = 4.2 lb of corn) would exceed Thumb Rule 10 of 0.3% of body weight (1200 x .003 = 3.6 lb) on a DM basis. Step 7. Convert from a DM basis to an as-fed basis for feeding using Thumb Rule 9. 4.83 lb of SBH (DM basis) ÷.90 = 5.4 lb of SBH (as-fed basis) Adjusting energy in the diet to increase body condition. Thin cows require more energy than moderately conditioned cows to maintain body temperature and an acceptable level of productivity. It is possible to program cows to gain weight and body condition to reach a body condition score of 5 by a target date using Tables 2 and 4. Example. Assume a typical 1200 lb cow in a BCS 4 at the beginning of the last trimester of gestation consuming moderate quality forage with a goal of having this cow calve in a BCS 5 in 90 days. How much pelleted soybean hulls will be needed per day to meet this increased energy requirement? Table 10 shows the crude protein and energy values for the feeds and this cow’s maintenance requirements. Note: This BCS 4 cow would weight about 1180 lb at this point in the production cycle (Month 10, Table 1), but she should weigh about 1180 + 80 = 1260 if she was in a BCS 5 (Thumb Rule 1). She has the volume and capacity to eat like she was a 1200 lb, base-weight cow (Thumb Rule 5). Table 12. Crude protein (CP) and net energy for maintenance (NEm) values. Dry matter basis Item CP, % NDF, % NEm, Mcal/lb Moderate quality forage 10.7 54.5 .53 Pelleted soybean hulls 12.0 -.88 CP, lb NEm, Mcal/day a Cow requirements 1.9 -12.0 a From Table 2, month 11 of the production cycle, month 8 of pregnancy. Step 1. Calculate the energy required above the maintenance requirement per day for this cow to move from a BCS of 4 to 5 in 90 days using Table 4. It will take a total of 158 Mcal NEm above the maintenance energy requirement to change from a BCS 4 to a BCS 5, therefore: 158 Mcal NEm ÷ 90 days = 1.75 Mcal NEm/day to move one BCS in 90 days Step 2. Calculate the total energy required/day for this cow. 12 Mcal NEm/day required + 1.75 Mcal NEm/day = 13.75 Mcal NEm needed per day Step 3. Determine hay intake using the Thumb Rule 4 and the hay’s NDF value from Table 12. 120 ÷ 54.5% NDF = DMI of 2.2% of body weight/day 1200 lb cow x .022 = DMI of 26.4 lb/day of hay Step 4. Calculate how much energy will be consumed from the forage daily. 26.4 lb/day of hay dry matter x .46 Mcal NEm/lb = 12.14 Mcal NEm/day Step 5. Calculate the daily energy deficiency. 13.75 Mcal NEm required/day – 12.14 Mcal NEm provided by hay intake/day = 1.61 Mcal NEm/day deficient Step 6. Calculate the amount of SBH/day needed to balance the energy requirement. 1.61 Mcal NEm deficient/day ÷ .88 Mcal NEm/lb of SBH = 1.83 lb/day of SBH (DM basis) Step 7. Convert from a DM basis to an as-fed basis using Thumb Rule 9 for feeding. 1.83 lb/day of SBH (DM basis) ÷ .90 = 2.0 lb/day of SBH (as-fed basis) Caution: Thin cows should be identified shortly after weaning when the cow is in the middle third of gestation and the nutrient requirements are low. As cows progress into late pregnancy and on into lactation, it becomes more difficult to formulate practical and economical forage-based rations that will provide a significant increase in weight and BCS. A little supplementation when requirements are low, that can be fed in small quantities over a longer period of time, is more economical than trying to make large changes in a short period of time when requirements are high. References: Ammerman, C.B., D.H. Baker, and A.J. Lewis. 1995. Bioavailability of Nutrients for Animals. New York: Academic Press; National Research Council. 1998. Nutrient Requirements of Swine, 10th revised edition. Washington, D.C.: National Academy Press; Buskirk, D.D., R.P. Lemenager, and L.A. Horstman. 1992. Estimation of Net Energy Requirements (NEm and NE ) of Lactating Beef Cows. J. Anim. Sci. 70:3867-3876. Δ Hale, C. and K.C. Olson. Mineral Supplements for Beef Cattle. University of Missouri Extension. http://extension.missouri.edu/publications/DisplayPub.aspx?P=G2081 National Research Council (NRC). 1996. Nutrient Requirements of Beef Cattle: Seventh Revised Edition: Updated 2000. National Academy Press.
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