Energy Requirement of Dairy Cows In lactating dairy cows, it has been shown that energy is utilized for maintenance, lactation and pregnancy with approximately equal efficiency 60 – 70% with an average of 64.4% Lactation BW gain Energy balance Maintenane Reqt 112 kcal ME Or 73.5 kcal NE/kg.75 ME intake As a result, the energy requirements for all expressions are expressed as one term, NEl

Maintenance requirement Energy requirements Maintenance requirement Related to body surface area or metabolic body size Maintenance reqt. = .073 Mcal/kg.75 Because this value was determined in cattle in metabolism stalls, a 10% activity allowance was included 2001 says Maintenance reqt. For NEl = .08 Mcal/kg.75 Example 650 kg cow Maintenace reqt. for Nel = .08 x 650.75 = 10.3 Mcal Activity allowance Normally the 10% activity allowance is adequate Additional energy is needed for grazing animals Walking Adjustment = .00045 Mcal Nel/kg BW/ horizontal km Example 650 kg x 4 km x .00045 = 1.17 Mcal Eating Adjustment = .0012 Mcal Nel/kg BW (Assumes 60% of diet is pasture) 650 kg x .0012 Mcal/kg BW = .78 Mcal Factors like cow nutrient reqt., herbage allowance, herbage height, herbage quality, and terrain used by beef NRC weren’t used in dairy NRC

Walking on hilly terrain ARC Adjustment = .03 Mcal NEl /kg BW/vertical km 2001 Dairy NRC defines a hilly pasture as one in which the cattle move 200 m of vertical distance daily Therefore, NRC use an adjustment of .03 x .2 = .006 Mcal/kg BW Example 650 kg cow x .006 Mcal NEl/kg BW = 3.9 Mcal NEl % increase in maintenance Flat, close to parlor Hilly, far from parlor good pasture good pasture Horizontal movement 2.8 11.4 Eating 7.6 7.6 Terrain - 37.9 10.4 56.9

Environmental adjustments Cold stress Because lactating cows have high heat production, the 2001 NRC felt that it was not necessary to adjust the nutrient requirements for cold DM digestibility will decrease 1.8% units for each 10oC reduction in temperature below 20oC 1989 NRC recommended that total Nel allowance be increased by 8% in cold weather, but 2001 NRC made no recommendation Heat stress Degree NEl cost, Mcal/day % increase in maintenance Mild .7 7 Severe 2.4 25 Needs Panting Metabolic changes Can’t be quantitated enough to develop an equation

Pregnancy requirement Energy requirement increases from day 190 to 279 of pregnancy Efficiency of ME use for pregnancy is quite low, 14% Energy requirement NEl (Mcal/d) = [(.00318 x D - .0352) x (CBW/45)]/(.14 x .64) Day = Day of gestation CBW = Calf birth weight in kg Example Day NEl Mcal/d % increase in maintenance 190 6.09 59.2 230 7.45 72.4 270 8.82 85.6

Growth for 1st and 2nd calf heifers Mature shrunk BW (MSBW) = .96 x MW SBW = .96 x current BW Standard reference BW (SRW) = 478/MSBW Equivalent shrunk BW (ESBW) = (SBW –CW) x SRW/MSBW Where CW = conceptus weight Equivalent empty BW = .891 x ESBW Equivalent empty BW gain = .956 x ADG RE required = .0635 x EEBW.75 x EEBWG1.097 Example Mature weight 650 kg Gain RE Mcal/d Maintenance % increase 1st calf gaining .4 kg/d 1.82 9.02 20.1 2nd calf gaining .2 kg/d .90 9.58 9.4

Lactation requirement NEl = .0929 x Fat% + .0347 x CP% + .0395 x lactose% Simply added to maintenance Theoretical efficiency for synthesis of milk components Efficiency Milk fat 81 Milk protein 89 Lactose 77 Dietary ME to milk energy 64 There is little variation in the efficiency of ME use over a broad range of diets Mcal/kg DM ME to milk energy, % 2 60.8 2.6 63.0 3.0 64.0 The utilization of ME for milk production and body tissue is subject to little variation Variation in ME content accounts for 88% of the variation in NE Total efficiency of ME use can not be regulated practically But partitioning of energy between milk and body tissue is diet dependent

Solutions to early lactation energy deficiency Because peak lactation occurs 6 to 8 weeks into lactation and peak feed intake occurs 8 to 12 weeks into lactation, it’s difficult to meet both the energy requirements and fiber requirements of high producing cows Solutions Limit maximum amount of grain to meet the fiber requirement and make up for the energy deficit at other periods of the lactation cycle Cows in good condition (but not overly fat) can safely lose up to 100 kg body tissue (15% of BW) during the first 70 days of lactation

Calculation of energy from weight loss Calculation of shrunk BW (SBW) = .96 x BW Calculation of BCS on a 9 point basis (BCS(9)) = ((Dairy BCS – 1) x 2) + 1 Empty BW at CS5 on a 9 point scale = (SBW x .851)/CSFx Factors CSF1 = .726 CSF2 = .794 CSF3 = .863 CSF4 = .931 CSF5 = 1.00 CSF6 = 1.069 CSF7 = 1.137 CSF8 = 1.206 CSF9 = 1.274 Calculation of empty BW at CSx EBWx = CSFx x CS5BW Calculation of fat weight at CSx Proportion of fat at CSx = Afx = .037683 x BCS9 Weight of fat at CSx = TFx = EBWx x Afx Calculation of protein weight at CSx Proportion of protein at CSx =Apx = .200886 - .0066762xBCS9 Weight of protien at CSx = TPx = EBWx x Apx Tissue energy reserve at CSx= ERx = (9 x TFx) + (5.55 x TPx) Energy available from1 CS loss on a 5 point scale = NEl = .82 x (ERCS9 – ERCS9-2)

Stage of lactation ME to tissue Tissue to milk Total Efficiency of ME use for replacement of energy loss differs in relation to stage of lactation when stores are replaced Efficiency Stage of lactation ME to tissue Tissue to milk Total Late lactation 75 82 61.5 Dry 60 82 49.2 Energy cost for tissue replacement during lactation = (.644/.75) x (ERCS9+2 + ERCS9) Energy cost for tissue replacement during dry period = (.644/.60) x (ERCS9+2 + ERCS9) It is preferable to replace body energy stores during late lactation as opposed to the dry period. Additional advantages to putting weight on during late lactation Easier to feed grain to lactating cows Because intake is higher, its easier to feed extra grain will not decrease forage intake.

Example How much 4% fat-corrected milk can a 1450 cow produce from body tissue going from CS 3.5 to 2.5 on a dairy scale? FBW = 1450/2.2 = 659 kg SBW = 659 x .96 =632 kg BCS(9) = ((3.5 – 1) x 2) +1 = 6 BCS(9) = ((2.5 – 1) x 2) + 1 = 4 CSF6 = 1.069 CSF4 = .931 CS5EBW = 632 x .851/1.069 = 503.7 EBW6 = 503.7 x 1.069 = 538.4 EBW4 = 503.7 x .931 = 468.94 AF6 = .037683 x 6 = .2261 AF4 = .037683 x 4 = .1507 TF6 = 538.4 x .2261 = 121.73 TF4 = 468.94 x .1507 = 70.684 AP6 = .200886 - .0066762 x 6 = .1608 AP4 = .200886 - .0066762 x 4 = .1742 TP6 = 538.4 x .1608 = 86.59 TP4 = 468.94 x .1742 = 81.68 ER6 = (9.4 x 121.73) + (5.55 x 86.59) ER4 = (9.4 x 70.684) + (5.55 x 81.68) = 1624.84 = 1117.76 NEl mobilized, Mcal = .82 (1624.84 – 1117.76) = 415.80 Mcal Assuming 4% fat-corrected milk requires .74 Mcal NEl/kg then, Milk from tissue = 415.8/.74 = 561.9 kg Dietary energy needed to replace tissue in Late lactation = .644/.75 x (1624.84 – 1117.76) = 435.41 Mcal Dry period = .644/.60 x (1624.84 – 1117.76) = 544.87

Balancing the ration for maximum NDF intake on a % BW basis Allows more flexibility in forage to grain ratio Considers fiber contribution from grain byproducts Assumes that cows consume NDF at 1.2% of BW But because of a .1% standard deviation, Mertens recommends using 1.1% of BW. Example Assume a 1500 cow She will require 1500 x .011 = 16.5 lb NDF If DMI = 2.8% BW, then % NDF in diet = 39.3% of DM If DMI = 3.2% BW, then %NDF in diet = 34.3% of DM If DMI = 3.6% BW, then %NDF in diet = 30.5% of DM If DMI = 4% BW, then %NDF in diet = 27.5% of DM 75% of NDF should come from forages Do not allow dietary NDF to drop below 25% In addition, the nonfiber carbohydrate should be between 30 and 40% of the dietary DM Too low will cause inadequate microbial synthesis Too high will cause milk fat depression or acidosis

Increase the energy concentration of the grain with fat and, thereby, cows will be able to consume adequate forage NRC recommendations Limit added at to 3 to 4 % of diet (600 – 700 gm) Since normal diet contains 3% fat, total dietary fat should be limited to 6 – 7% of DM Lactation response to fat is curvilinear with maximum milk yield occuring at 16% of ME from fat (600 – 700 gm) Advantages of fat supplementation Can maintain a higher proportion of forage in the diet Fat test may be elevated Particularly if ruminally protected fats are fed Milk fat depression may occur after use Fats increase dietary energy without increasing the heat increment May improve reproduction Mechanism Decreases insulin and increase progesterone which increases follicle size and number Decreases prostaglandin 52 alpha increases persistence of corpus luteum May decrease first service conception if fat increases milk production

Problems with fat supplementation Milk fat depression Particularly a problem if unsaturated or unprotected fats are fed Particularly a problem if low fiber diets are fed Milk protein depression Milk protein % = 101.1 - .6381x + .0141x2 where x = total dietary fat Related to increase in milk production Negative effects of fat on milk protein may be replaced by supplementing nicotinic acid (12 gm/d) or ruminally undegraded amino acids Decreased feed intake Mechanism Decreased gut motility Decreased palatability Oxidation of fat in liver Decreased cellulose digestion Dependent on type of fat Ca salts of fatty acids decrease DMI by 2.5% /each 1% CaLFA added Unprotected fats reduced DMI by 1.25% /each 1% fat added Saturated fats do not reduce feed intake Oilseeds reduce feed intake quadratically with minimal intake at 2% fat Decreasd digestion of Ca and Mg If fat added, Ca and Mg should be added to diet If unsaturated fat is added, Ca and Mg should be increased by 20 to 30%

Problems with added fats may be minimized by Feeding fats that are inert in the rumen Feeding in small amounts several times per day Feeding fats in total mixed rations rather than as individual components Choice of fat Innertness Decreased solubility increases inertness Saturated fats are more inert than polyunsaturated fats Ca salts of fatty acids are more inert than free oils Whole oil seeds are more inert than free oils Protein needs If no protein is needed, use tallow If undegradable protein is needed, use heated soybeans If degradable protein is needed, use raw soybeans or cottonseed Fiber needs If fiber is needed, feed whole cottonseed Because of gossypol, feed no more than 8 lb cottonseed/day Price Timing of fat feeding Because fat reduces feed intake, fat supplementation is of little value for the first 5 to 7 weeks of lactation Fat supplementation should be terminated early enough to prevent the cows from becoming excessively fat (BCS > 3.5)

Increase the proportion of concentrates in the diet and supplement the diet with: Buffers Increases rumen pH decreasing production of Trans-10 (18:1) FA and increases Acetate/Propionate Buffers include sodium bicarbonate, sodium sesquicarbonate, magnesium oxide, and potassium carbonate Most useful when diet is deficient in effective fiber or the animal is undergoing the transition from a high forage diet to a high grain diet. Tend to be unpalatable and short-term responses Undegraded choline

Nutrient repartitioning Bovine somatotropin Effects Increases milk production Dairy NRC says at 5 to 50 mg/d, milk production will increase by 3 to 6 kg/day Monsanto data said that production would increase by 16% from day 60 to 312 post-partum Increases feed and water intake Major factor responsible for increased milk Takes 3 to 5 weeks to develop Increases feed efficiency Effect of increased milk production diluting the effects of maintenance No effect on nutrient utilization per se. Decreases milk protein percentage Increases mobilization of tissue reserves Increases metabolic rate and body heat production Increases heart rate and cardiac output Increases milk production to the mammary gland Affects reproduction Reduces rebreeding rate Increases twinning rate, particularly in heifers Increases mastitis and somatic cell count

Factors affecting response to bst Genetic merit Nutritional status Feed as a high producing cow Cows should have access to feed for 20 hr/day Management Inject 500 mg bst-Zn every 14 days beginning 9 weeks into lactation Do not give to cows in poor condition

Problems associated with energy intake by dairy cows Milk fat depression Causes Shortage of energy plus utilization of body fat Cows are thin, ketosis prone and high producing cows Can be corrected by increasing dietary energy level or feed intake Milk fat depression syndrome Decreased forage to concentrate ratio and/or supplementing polyunsaturated fatty acids increase production of trans-10(18:1) fatty acids will inhibit mammary fatty acid synthesis Factors Inadequate effective NDF Excessive carbohydrate energy (> 40% NFC) Inadequate particle size (Forage harvested or ground at < ¼” theoretical length of chop; 75^ of NDF must come from forage) Excess unsaturuated fatty acids Dietary buffers will reduce problem

Ketosis-fatty acid liver In early lactation, energy must be mobilized from tissue reserves Excessive use of tissue energy Lack of OAA Lack of carnitine Lack of niacin Overcomes limit of triglyceride to be: transported from liver as VLDL oxidized in TCA cycle in liver Fat accumulates Acetyl-CoA in hepatocytes (Fatty liver) Acetoacetate B-OH-Butyrate Impairs gluconeogenisis Impairs feed intake Appear in milk Reduces glucose Increased milk fever Increased displaced abomasum Increased retained placenta Increased mastitis

Symptoms Metabolic profile Normal Ketosis (2-4 weeks PP) Blood mg% Glucose 52 28 Ketones 3 41 Plasma Free fatty acids 3 33 Triglycerides 14 8 Free cholesterol 29 15 Cholesterol esters 226 150 Phospholipids 174 82 Poor appetite Loss of body weight Gaunt and dull appearance Irregular rumen contractions May stagger or appear uncoordinated Milk production will decrease Complications DA, milk fever, retained placenta, and mastitis

Reduced intake at calving Intake decreases by 30% one to two days before calving and doesn’t return until one to two days after calving NRC equation DMI(%BW) = 1.97 - .75e.16t where t = Days pregnant – 280 Ketosis prevention Maximize intake immediately before calving Avoid abrupt change to high grain lactation diet at calving Feed balance ration Use high quality forages Avoid excessive fatness in cows Drench cows with propylene glycol (1L/day) for 1 week daily before calving Propylene glycol is metabolized to lactate that can be used for gluconeogenisis Supplement with nicotinic acid (6 – 12 g/d) Increases DMI Reduces lipolysis Recommendations Use in ketosis prone cows Use from 14 days prepartum to 120 days postpartum Use palatable carrier

Displaced abomasum Caused by the abomasum sliding to the left under the rumen after calving if the rumen fails to take up its normal space Factors Failure of rumen to take up space left as uterus retracts Omentum attached to the abomasum may have stretched Rumen atony Diet High grain diet in late gestation Decreased contractions Decreased intake causes less rumen volume Decreased intake causes less Ca intake and therefore contractions Inadequate forage in the diet Decreased muscle tone in GIT Decreased rumen mat results in less buffering and higher concentrations of VFAs

Reproductive difficulties Body condition loss, 1st 5 wk < .5 .5-1.0 > 1.0 Days to 1st ovulation 27 31 42 Days to 1st observed estrus 48 41 62 Days to 1st service 68 67 79 1st service conception, % 65 53 17 Services/conception 1.8 2.3 2.3 Pregnancy rate, % 94 95 100 Physiogical effects of negative energy balance Reduced secretion of luteinizing hormone LH amplitude, pg/ml = 339 + 25.3 x energy balance Increased number of small follicles (3 – 10 mm) Decreased number of large follicles (> 10 mm) Diam of largest follicle, mm = 9.24 + .56 x energy balance

Management Suggested CS range Calving 3 – 3.75 Have cows at appropriate condition Suggested CS range Calving 3 – 3.75 Peak milk yield 2.25 – 2.75 150 – 200 days of lactation 3 – 3.5 Dry period 3 – 3.5 Feed for high feed intake At equal energy balance, cows with highest feed intake and milk production have earliest estrus Fat supplementation Increases blood progesterone Increases follicle size Does not improve reproduction if fat causes increased milk production