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TIER 1: BASIC CHARACTERISATION FOR LIVESTOCK POPULATIONS

Basic characterisation for Tier 1 is likely to be sufficient for most animal species in most countries. For this approach it is good practice to collect the following livestock characterisation data to support the emissions

Livestock species and categories: A complete list of all livestock populations that have default emission factor values must be developed (e.g., dairy cows, other cattle, buffalo, sheep, goats, camels, llamas, alpacas, deer, horses, rabbits, mules and asses, swine, and poultry) if these categories are relevant to the country. More detailed categories should be used if the data are available. For example, more accurate emission estimates can be made if poultry populations are further subdivided (e.g., layers, broilers, turkeys, ducks, and other poultry), as the waste characteristics among these different populations varies significantly.

Annual population: If possible, inventory compilers should use population data from official national statistics or industry sources. Food and Agriculture Organisation (FAO) data can be used if national data are unavailable. Seasonal births or slaughters may cause the population size to expand or contract at different times of the year, which will require the population numbers to be adjusted accordingly. It is important to fully document the method used to estimate the annual population, including any adjustments to the original form of the population data as it was received from national statistical agencies or from other sources.

Annual average populations are estimated in various ways, depending on the available data and the nature of the animal population. In the case of static animal populations (e.g., dairy cows, breeding swine, layers), estimating the annual average population may be as simple as obtaining data related to one-time animal inventory data. However, estimating annual average populations for a growing population (e.g., meat animals, such as broilers, turkeys, beef cattle, and market swine) requires more evaluation. Most animals in these growing populations are alive for only part of a complete year. Animals should be included in the populations regardless if they were slaughtered for human consumption or die of natural causes. Equation 10.1 estimates the annual average of livestock population.

AAP = annual average population

NAPA = number of animals produced annually

Broiler chickens are typically grown approximately 60 days before slaughter. Estimating the average annual population as the number of birds grown and slaughtered over the course of a year would greatly overestimate the population, as it would assume each bird lived the equivalent of 365 days. Instead, one should estimate the average annual population as the number of animals grown divided by the number of growing cycles per year. For example, if broiler chickens are typically grown in flocks for 60 days, an operation could turn over approximately 6 flocks of chickens over the period of one year. Therefore, if the operation grew 60,000 chickens in a year, their average annual population would be 9,863 chickens. For this example the equation would be:

estimates:

Equation 10.1 Annual average population

Where:

Annual average population = 60 days • 60,000 / 365 days / yr = 9,863 chickens

Figure 10.1 Decision tree for livestock population characterisation

Figure 10.1 Decision tree for livestock population characterisation

Box 2

Note:

1: These categories include: CH4 Emission from Enteric Fermentation, CH4 Emission from Manure Management, and N2O Emission from Manure Management.

2: See Volume 1 Chapter 4, "Methodological Choice and Identification of Key Categories" (noting Section 4.1.2 on limited resources), for discussion of key categories and use of decision trees.

Dairy cows and milk production: The dairy cow population is estimated separately from other cattle (see Table 10.1). Dairy cows are defined in this method as mature cows that are producing milk in commercial quantities for human consumption. This definition corresponds to the dairy cow population reported in the FAO Production Yearbook. In some countries the dairy cow population is comprised of two well-defined segments: (i) high-producing (also called improved) breeds in commercial operations; and (ii) low-producing cows managed with traditional methods. These two segments can be combined, or can be evaluated separately by defining two dairy cow categories. However, the dairy cow category does not include cows kept principally to produce calves for meat or to provide draft power. Low productivity multi-purpose cows should be considered as other cattle.

Dairy buffalo may be categorized in a similar manner to dairy cows.

Data on the average milk production of dairy cows are also required. Milk production data are used in estimating an emission factor for enteric fermentation using the Tier 2 method. Country-specific data sources are preferred, but FAO data may also be used. These data are expressed in terms of kilograms of whole fresh milk produced per year per dairy cow. If two or more dairy cow categories are defined, the average milk production per cow is required for each category.

TIER 2: ENHANCED CHARACTERISATION FOR LIVESTOCK POPULATIONS

The Tier 2 livestock characterisation requires detailed information on:

• Definitions for livestock subcategories;

• Livestock population by subcategory, with consideration for estimation of annual population as per Tier 1; and

• Feed intake estimates for the typical animal in each subcategory.

The livestock population subcategories are defined to create relatively homogenous sub-groupings of animals. By dividing the population into these subcategories, country-specific variations in age structure and animal performance within the overall livestock population can be reflected.

The Tier 2 characterisation methodology seeks to define animals, animal productivity, diet quality and management circumstances to support a more accurate estimate of feed intake for use in estimating methane production from enteric fermentation. The same feed intake estimates should be used to provide harmonised estimates of manure and nitrogen excretion rates to improve the accuracy and consistency of CH4 and N2O emissions from manure management.

Definitions for livestock subcategories

It is good practice to classify livestock populations into subcategories for each species according to age, type of production, and sex. Representative livestock categories for doing this are shown in Table 10.1. Further subcategories are also possible:

• Cattle and buffalo populations should be classified into at least three main subcategories: mature dairy, other mature, and growing cattle. Depending on the level of detail in the emissions estimation method, subcategories can be further classified based on animal or feed characteristics. For example, growing / fattening cattle could be further subdivided into those cattle that are fed a high-grain diet and housed in dry lot vs. those cattle that are grown and finished solely on pasture.

• Subdivisions similar to those used for cattle and buffalo can be used to further segregate the sheep population in order to create subcategories with relatively homogenous characteristics. For example, growing lambs could be further segregated into lambs finished on pasture vs. lambs finished in a feedlot. The same approach applies to national goat herds.

• Subcategories of swine could be further segregated based on production conditions. For example, growing swine could be further subdivided into growing swine housed in intensive production facilities vs. swine that are grown under free-range conditions.

• Subcategories of poultry could be further segregated based on production conditions. For example, poultry could be divided on the basis of production under confined or free-range conditions.

For large countries or for countries with distinct regional differences, it may be useful to designate regions and then define categories within those regions. Regional subdivisions may be used to represent differences in climate, feeding systems, diet, and manure management. However, this further segregation is only useful if correspondingly detailed data are available on feeding and manure management system usage by these livestock categories.

Table 10.1

Representative livestock categories1,2

Main categories

Subcategories

Mature Dairy Cow or Mature Dairy Buffalo

• High-producing cows that have calved at least once and are used principally for milk production

• Low-producing cows that have calved at least once and are used principally for milk production

Other Mature Cattle or Mature Non-dairy Buffalo

Females:

• Cows used to produce offspring for meat

• Cows used for more than one production purpose: milk, meat, draft Males:

• Bulls used principally for breeding purposes

• Bullocks used principally for draft power

Growing Cattle or Growing Buffalo

• Calves pre-weaning

• Replacement dairy heifers

• Growing / fattening cattle or buffalo post-weaning

• Feedlot-fed cattle on diets containing > 90 % concentrates

Mature Ewes

• Breeding ewes for production of offspring and wool production

• Milking ewes where commercial milk production is the primary purpose

Other Mature Sheep (>1 year)

• No further sub-categorisation recommended

• Females

Mature Swine

• Sows in gestation

• Sows which have farrowed and are nursing young

• Boars that are used for breeding purposes

• Gilts that will be used for breeding purposes

• Growing boars that will be used for breeding purposes

Chickens

• Broiler chickens grown for producing meat

• Layer chickens for producing eggs, where manure is managed in dry systems (e.g., high-rise houses)

• Layer chickens for producing eggs, where manure is managed in wet systems (e.g., lagoons)

• Chickens under free-range conditions for egg or meat production

Turkeys

• Breeding turkeys in confinement systems

• Turkeys grown for producing meat in confinement systems

• Turkeys under free-range conditions for meat production

• Ducks grown for producing meat

• Fur bearing animals

• Geese

1 Source IPCC Expert Group

2 Emissions should only be considered for livestock species used to produce food, fodder or raw materials used for industrial processes.

For each of the representative animal categories defined, the following information is required:

• annual average population (number of livestock or poultry as per calculations for Tier 1);

• average daily feed intake (megajoules (MJ) per day and / or kg per day of dry matter); and

• methane conversion factor (percentage of feed energy converted to methane).

Generally, data on average daily feed intake are not available, particularly for grazing livestock. Consequently, the following general data should be collected for estimating the feed intake for each representative animal category:

• feeding situation: confined, grazing, pasture conditions;

• milk production per day (kg/day) and fat content (%)2;

• average amount of work performed per day (hours day-1);

• percentage of females that give birth in a year3;

• number of offspring; and

Feed intake estimates

Tier 2 emissions estimates require feed intakes for a representative animal in each subcategory. Feed intake is typically measured in terms of gross energy (e.g., megajoules (MJ) per day) or dry matter (e.g., kilograms (kg) per day). Dry matter is the amount of feed consumed (kg) after it has been corrected for the water content in the complete diet. For example, consumption of 10 kg of a diet that contains 70% dry matter would result in a dry matter intake of 7 kg. To support the enteric fermentation Tier 2 method for cattle, buffalo, and sheep (see Section 10.3), detailed data requirements and equations to estimate feed intake are included in guidance below. Constants in the equations have been combined to simplify overall equation formats. The remainder of this subsection presents the typical data requirements and equations used to estimate feed intake for cattle, buffalo, and sheep. Feed intake for other species can be estimated using similar country-specific methods appropriate for each.

For all estimates of feed intake, good practice is to:

• Collect data to describe the animal's typical diet and performance in each subcategory;

• Estimate feed intake from the animal performance and diet data for each subcategory.

In some cases, the equations may be applied on a seasonal basis, for example under conditions in which livestock gain weight in one season and lose weight in another. This approach may require a more refined variation of Tier 2 or more complex Tier 3 type methodology.

The following animal performance data are required for each animal subcategory to estimate feed intake for the subcategory:

• Weight (W), kg: Live-weight data should be collected for each animal subcategory. It is unrealistic to perform a complete census of live-weights, so live-weight data should be obtained from representative sample studies or statistical databases if these already exist. Comparing live-weight data with slaughter-weight data is a useful cross-check to assess whether the live-weight data are representative of country conditions. However, slaughter-weight data should not be used in place of live-weight data as it fails to account for the complete weight of the animal. Additionally, it should be noted that the relationship between live-weight and slaughter-weight varies with breed and body condition. For cattle, buffalo and

1 This may be assumed to be zero for mature animals.

2 Milk production data are required for dairy animals. These can be estimated for non-dairy animals providing milk to young, where data are available.

3 This is only relevant for mature females.

mature sheep, the yearly average weight for each animal category (e.g., mature beef cows) is needed. For young sheep, weights are needed at birth, weaning, one year of age or at slaughter if slaughter occurs within the year.

• Average weight gain per day (WG), kg day-1: Data on average weight gain are generally collected for feedlot animals and young growing animals. Mature animals are generally assumed to have no net weight gain or loss over an entire year. Mature animals frequently lose weight during the dry season or during temperature extremes and gain weight during the following season. However, increased emissions associated with this weight change are likely to be small. Reduced intakes and emissions associated with weight loss are largely balanced by increased intakes and emissions during the periods of gain in body weight.

• Mature weight (MW), kg: The mature weight of the adult animal of the inventoried group is required to define a growth pattern, including the feed and energy required for growth. For example, mature weight of a breed or category of cattle or buffalo is generally considered to be the body weight at which skeletal development is complete. The mature weight will vary among breeds and should reflect the animal's weight when in moderate body condition. This is termed 'reference weight' (ACC, 1990) or 'final shrunk body weight' (NRC, 1996). Estimates of mature weight are typically available from livestock specialists and producers.

• Average number of hours worked per day: For draft animals, the average number of hours worked per day must be determined.

• Feeding situation: The feeding situation that most accurately represents the animal subcategory must be determined using the definitions shown below (Table 10.5). If the feeding situation lies between the definitions, the feeding situation should be described in detail. This detailed information may be needed when calculating the enteric fermentation emissions, because interpolation between the feeding situations may be necessary to assign the most appropriate coefficient. Table 10.5 defines the feeding situations for cattle, buffalo, and sheep. For poultry and swine, the feeding situation is assumed to be under confinement conditions and consequently the activity coefficient (Ca )is assumed to be zero as under these conditions very little energy is expended in acquiring feed. Activity coefficients have not been developed for freeranging swine or poultry, but in most instances these livestock subcategories are likely to represent a small proportion of the national inventory.

• Mean winter temperature (°C): Detailed feed intake models consider ambient temperature, wind speed, hair and tissue insulation and the heat of fermentation (NRC, 2001; AAC, 1990) and are likely more appropriate in Tier 3 applications. A more general relationship adapted from North America data suggest adjusting the Cf of Equation 10.3 for maintenance requirements of open-lot fed cattle in colder climates according to the following equation (Johnson, 1986):

Equation 10.2

Coefficient for calculating net energy for maintenance Cfi (in _ cold) = Cf + 0.0048 • (20 - °C)

Where:

Cfj = a coefficient which varies for each animal category as shown in Table 10.4 (Coefficients for calculating NEm), MJ day-1 kg-1

°C = mean daily temperature during winter season

Considering the average temperature during winter months, net energy for maintenance (NEm) requirements may increase by as much as 30% in northern North America. This increase in feed use for maintenance is also likely associated with greater methane emissions.

• Average daily milk production (kg day-1): These data are for milking ewes, dairy cows and buffalo. The average daily production should be calculated by dividing the total annual production by 365, or reported as average daily production along with days of lactation per year, or estimated using seasonal production divided by number of days per season. If using seasonal production data, the emission factor must be developed for that seasonal period.

• Fat content (%): Average fat content of milk is required for lactating cows, buffalo, and sheep producing milk for human consumption.

• Percent of females that give birth in a year: This is collected only for mature cattle, buffalo, and sheep.

• Number of off spring produced per year: This is relevant to female livestock that have multiple births per year (e.g., ewes).

• Feed digestibility (DE%): The portion of gross energy (GE) in the feed not excreted in the faeces is known as digestible feed. The feed digestibility is commonly expressed as a percentage (%) of GE or TDN (total digestible nutrients). That percentage of feed that is not digested represents the % of dry matter intake that will be excreted as faeces. Typical digestibility values for a range of livestock classes and diet types are presented in Table 10.2 as a guideline. For ruminants, common ranges of feed digestibility are 45-55% for crop by-products and range lands; 55-75% for good pastures, good preserved forages, and grain supplemented forage-based diets; and 75-85% for grain-based diets fed in feedlots. Variations in diet digestibility results in major variations in the estimate of feed needed to meet animal requirements and consequently associated methane emissions and amounts of manure excreted. It is also important to note that digestibility, intake, and growth are co-dependent phenomena. For example, a low digestibility will lead to lower feed intake and consequently reduced growth. Conversely, feeds with high digestibility will often result in a higher feed intake and increased growth. A 10% error in estimating DE will be magnified to 12 to 20% when estimating methane emissions and even more (20 to 45%) for manure excretion (volatile solids).

Digestibility data should be based on measured values for the dominant feeds or forages being consumed by livestock with consideration for seasonal variation. In general, the digestibility of forages decreases with increasing maturity and is typically lowest during the dry season. Due to significant variation, digestibility coefficients should be obtained from local scientific data wherever possible. Although a complete census of digestibility is considered unrealistic, at a minimum digestibility data from research studies should be consulted. While developing the digestibility data, associated feed characteristic data should also be recorded when available, such as measured values for Neutral Detergent Fiber (NDF), Acid Detergent Fiber (ADF), crude protein, and the presence of anti-nutritional factors (e.g., alkaloids, phenolics, % ash). NDF and ADF are feed characteristics measured in the laboratory that are used to indicate the nutritive value of the feed for ruminant livestock. Determination of these values can enable DE to be predicted as defined in the recent dairy NRC (2001). The concentration of crude protein in the feed can be used in the process of estimating nitrogen excretion (Section 10.5.2).

• Average annual wool production per sheep (kg yr-1): The amount of wool produced in kilograms (after drying out but before scouring) is needed to estimate the amount of energy allocated for wool production.

Table 10.2

Representative feed digestibility for various livestock categories

Main categories

Class

Digestibility (DE%)

Swine

• Mature Swine - confinement

• Growing Swine - confinement

• Swine - free range

• 50 - 70% 1

Cattle and other ruminants

• Feedlot animals fed with > 90% concentrate diet;

• Pasture fed animals;

• Animals fed - low quality forage

• 45 - 55%

Poultry

• Broiler Chickens -confinement

• Layer Hens - confinement

• Turkeys - confinement

• Geese - confinement

• 80 - 90%

1 The range in digestibility of feed consumed by free-range swine and poultry is extremely variable due to the selective nature of these diets. Often it is likely that the amount of manure produced in these classes will be limited by the amount of feed available for consumption as opposed to its degree of digestibility. In instances where feed is not limiting and high quality feed sources are readily accessible for consumption, digestibility may approach values that are similar to those measured under confinement conditions.

Gross energy calculations

Animal performance and diet data are used to estimate feed intake, which is the amount of energy (MJ/day) an animal needs for maintenance and for activities such as growth, lactation, and pregnancy. For inventory compilers who have well-documented and recognised country-specific methods for estimating intake based on animal performance data, it is good practice to use the country-specific methods. The following section provides methods for estimating gross energy intake for the key ruminant categories of cattle, buffalo and sheep. The equations listed in Table 10.3 are used to derive this estimate. If no country-specific methods are available, intake should be calculated using the equations listed in Table 10.3. As shown in the table, separate equations are used to estimate net energy requirements for sheep as compared with cattle and buffalo. The equations used to calculate GE are as follows:

Table 10.3

Summary of the equations used to estimate daily gross energy intake for Cattle,

Buffalo and Sheep

Metabolic functions and other estimates

Equations for cattle and buffalo

Equations for sheep

Maintenance (NEm)

Equation 10.3

Equation 10.3

Activity (NEa)

Equation 10.4

Equation 10.5

Growth (NEg)

Equation 10.6

Equation 10.7

Lactation (NEl)*

Equation 10.8

Equations 10.9 and 10.10

Draft Power (NEwork)

Equation 10.11

NA

Wool Production (NEwool)

NA

Equation 10.12

Pregnancy (NEp)*

Equation 10.13

Equation 10.13

Ratio of net energy available in diet for maintenance to digestible energy consumed (REM)

Equation 10.14

Equation 10.14

Ratio of net energy available for growth in a diet to digestible energy consumed (REG)

Equation 10.15

Equation 10.15

Gross Energy

Equation 10.16

Equation 10.16

Source: Cattle and buffalo equations based on NRC (1996) and sheep based on AFRC (1993). NA means 'not applicable'.

* Applies only to the proportion of females that give birth.

Net energy for maintenance: (NEm ) is the net energy required for maintenance, which is the amount of energy needed to keep the animal in equilibrium where body energy is neither gained nor lost (Jurgen, 1988).

Equation 10.3 Net energy for maintenance

Where:

NEm = net energy required by the animal for maintenance, MJ day-1

Cf! = a coefficient which varies for each animal category as shown in Table 10.4 (Coefficients for calculating NEm), MJ day-1 kg-1

Weight = live-weight of animal, kg

Net energy for activity: (NEa) is the net energy for activity, or the energy needed for animals to obtain their food, water and shelter. It is based on its feeding situation rather than characteristics of the feed itself. As presented in Table 10.3, the equation for estimating NEa for cattle and buffalo is different from the equation used for sheep. Both equations are empirical with different definitions for the coefficient Ca.

Equation 10.4 Net energy for activity (for cattle and buffalo)

Where:

NEa = net energy for animal activity, MJ day-1

Ca = coefficient corresponding to animal's feeding situation (Table 10.5, Activity coefficients) NEm = net energy required by the animal for maintenance (Equation 10.3), MJ day-1

Equation 10.5 Net energy for activity (for sheep)

Where:

NEa = net energy for animal activity, MJ day-1

Ca = coefficient corresponding to animal's feeding situation (Table 10.5), MJ day-1 kg-1

weight = live-weight of animal, kg

For Equations 10.4 and 10.5, the coefficient Ca corresponds to a representative animal's feeding situation as described earlier. Values for Ca are shown in Table 10.5. If a mixture of these feeding situations occurs during the year, NEa must be weighted accordingly.

Table 10.4

Coefficients for calculating net energy for maintenance ( NEm )

Animal category

Cfi (MJ d-1 kg-1)

Comments

Cattle/Buffalo (non-lactating cows)

0.322

Cattle/Buffalo (lactating cows)

0.386

This value is 20% higher for maintenance during lactation

Cattle/Buffalo (bulls)

0.370

This value is 15% higher for maintenance of intact males

Sheep (lamb to 1 year)

0.236

This value can be increased by 15% for intact males

Sheep (older than 1 year)

0.217

This value can be increased by 15% for intact males.

Source: NRC (1996) and AFRC (1993).

Table 10.5

Activity coefficients corresponding to animal's feeding situation

Situation

Definition

Ca

Cattle and Buffalo (unit for Ca is dimensionless)

Stall

Animals are confined to a small area (i.e., tethered, pen, barn) with the result that they expend very little or no energy to acquire feed.

0.00

Pasture

Animals are confined in areas with sufficient forage requiring modest energy expense to acquire feed.

0.17

Grazing large areas

Animals graze in open range land or hilly terrain and expend significant energy to acquire feed.

0.36

Sheep (unit for Ca = MJ d-1 kg-1)

Housed ewes

Animals are confined due to pregnancy in final trimester (50 days).

0.0090

Grazing flat pasture

Animals walk up to 1000 meters per day and expend very little energy to acquire feed.

0.0107

Grazing hilly pasture

Animals walk up to 5,000 meters per day and expend significant energy to acquire feed.

0.0240

Housed fattening lambs

Animals are housed for fattening.

0.0067

Source: NRC (1996) and AFRC (1993).

Net energy for growth: (NEg) is the net energy needed for growth (i.e., weight gain). Equation 10.6 is based on NRC (1996). Equation 10.7 is based on Gibbs et al. (2002). Constants for conversion from calories to joules and live to shrunk and empty body weight have been incorporated into the equation.

Where:

NEg = net energy needed for growth, MJ day-1

BW = the average live body weight (BW) of the animals in the population, kg C = a coefficient with a value of 0.8 for females, 1.0 for castrates and 1.2 for bulls (NRC, 1996) MW = the mature live body weight of an adult female in moderate body condition, kg WG = the average daily weight gain of the animals in the population, kg day-1

Where:

NEg = net energy needed for growth, MJ day-1 WGlamb = the weight gain (BWf - BW,), kg yr-1 BWi = the live bodyweight at weaning, kg

BWf = the live bodyweight at 1-year old or at slaughter (live-weight) if slaughtered prior to 1 year of age, kg a, b = constants as described in Table 10.6.

Note that lambs will be weaned over a period of weeks as they supplement a milk diet with pasture feed or supplied feed. The time of weaning should be taken as the time at which they are dependent on milk for half their energy supply.

The NEg equation used for sheep includes two empirical constants (a and b) that vary by animal species/category (Table 10.6).

Table 10.6

Constants for use in calculating NEG for Sheep

Animal species/category

(MJ kg-1)

(MJ kg-2)

Intact males

2.5

0.35

Castrates

4.4

0.32

Females

2.1

0.45

Source: AFRC (1993).

Net energy for lactation: (NEi ) is the net energy for lactation. For cattle and buffalo the net energy for lactation is expressed as a function of the amount of milk produced and its fat content expressed as a percentage (e.g., 4%) (NRC, 1989):

Equation 10.8

Net energy for lactation (for beef cattle, dairy cattle and buffalo) NE1 = Milk • (l.47 + 0.40 • Fat)

Where:

NEl = net energy for lactation, MJ day-1

Milk = amount of milk produced, kg of milk day-1

Two methods for estimating the net energy required for lactation (NEl) are presented for sheep. The first method (Equation 10.9) is used when the amount of milk produced is known, and the second method (Equation 10.8) is used when the amount of milk produced is not known. Generally, milk production is known for ewes kept for commercial milk production, but it is not known for ewes that suckle their young to weaning. With a known amount of milk production, the total annual milk production is divided by 365 days to estimate the average daily milk production in kg/day (Equation 10.9). When milk production is not known, AFRC (1990) indicates that for a single birth, the milk yield is about 5 times the weight gain of the lamb. For multiple births, the total annual milk production can be estimated as five times the increase in combined weight gain of all lambs birthed by a single ewe. The daily average milk production is estimated by dividing the resulting estimate by 365 days as shown in Equation 10.10.

Equation 10.9

Net energy for lactation for sheep (milk production known)

Where:

NEl = net energy for lactation, MJ day-1

Milk = amount of milk produced, kg of milk day-1

EVmiik = the net energy required to produce 1 kg of milk. A default value of 4.6 MJ/kg (AFRC, 1993) can be used which corresponds to a milk fat content of 7% by weight

Where:

NEl = net energy for lactation, MJ day-1

WG wean = the weight gain of the lamb between birth and weaning, kg

EVmilk = the energy required to produce 1 kg of milk, MJ kg-1. A default value of 4.6 MJ kg-1 (AFRC, 1993) can be used.

Net energy for work: (NEwork ) is the net energy for work. It is used to estimate the energy required for draft power for cattle and buffalo. Various authors have summarised the energy intake requirements for providing draft power (e.g., Lawrence, 1985; Bamualim and Kartiarso, 1985; and Ibrahim, 1985). The strenuousness of the work performed by the animal influences the energy requirements, and consequently a wide range of energy requirements have been estimated. The values by Bamualim and Kartiarso show that about 10 percent of a day's NEm requirements are required per hour for typical work for draft animals. This value is used as follows:

Where:

NEwork = net energy for work, MJ day-1

NEm = net energy required by the animal for maintenance (Equation 10.3), MJ day-1 Hours = number of hours of work per day

Net energy for wool production: (NEwool ) is the average daily net energy required for sheep to produce a year of wool. The NEwool is calculated as follows:

Where:

NEwool = net energy required to produce wool, MJ day-1

EVwool = the energy value of each kg of wool produced (weighed after drying but before scouring), MJ kg-1. A default value of 24 MJ kg-1 (AFRC, 1993) can be used for this estimate.

Productionwool = annual wool production per sheep, kg yr-1

Net energy for pregnancy: (NEp) is the energy required for pregnancy. For cattle and buffalo, the total energy requirement for pregnancy for a 281-day gestation period averaged over an entire year is calculated as 10% of NEm. For sheep, the NEp requirement is similarly estimated for the 147-day gestation period, although the percentage varies with the number of lambs born (Table 10.7, Constant for Use in Calculating NEp in Equation 10.13). Equation 10.13 shows how these estimates are applied.

Equation 10.13 Net energy for pregnancy (for cattle/buffalo and sheep)

Where:

NEp = net energy required for pregnancy, MJ day-1 Cpregnancy = pregnancy coefficient (see Table 10.7)

NEm = net energy required by the animal for maintenance (Equation 10.3), MJ day-1

Table 10.7

Constants for use in calculating NEp in Equation 10.13

Animal category

^pregnancy

Cattle and Buffalo

0.10

Sheep

Single birth

0.077

Double birth (twins)

0.126

Triple birth or more (triplets)

0.150

Source: Estimate for cattle and buffalo developed from data in NRC (1996). Estimates for sheep developed from data in AFRC (1993), taking into account the inefficiency of energy conversion.

When using NEp to calculate GE for cattle and sheep, the NEp estimate must be weighted by the portion of the mature females that actually go through gestation in a year. For example, if 80% of the mature females in the animal category give birth in a year, then 80% of the NEp value would be used in the GE equation below.

To determine the proper coefficient for sheep, the portion of ewes that have single births, double births, and triple births is needed to estimate an average value for Cpregnancy. If these data are not available, the coefficient can be calculated as follows:

• If the number of lambs born in a year divided by the number of ewes that are pregnant in a year is less than or equal to 1.0, then the coefficient for single births can be used.

• If the number of lambs born in a year divided by the number of ewes that are pregnant in a year exceeds 1.0 and is less than 2.0, calculate the coefficient as follows:

Cpregnancy = [(0.126 • Double birth fraction) + (0.077 • Single birth fraction)]

Where:

Double birth fraction = [(lambs born / pregnant ewes) - 1] Single birth fraction = [1 - Double birth fraction]

Ratio of net energy available in diet for maintenance to digestible energy consumed (REM): For cattle, buffalo and sheep, the ratio of net energy available in a diet for maintenance to digestible energy consumed (REM ) is estimated using the following equation (Gibbs and Johnson, 1993):

Where:

REM = ratio of net energy available in a diet for maintenance to digestible energy consumed DE% = digestible energy expressed as a percentage of gross energy

Ratio of net energy available for growth in a diet to digestible energy consumed (REG): For cattle, buffalo and sheep the ratio of net energy available for growth (including wool growth) in a diet to digestible energy consumed (REG ) is estimated using the following equation (Gibbs and Johnson, 1993):

Where:

REG = ratio of net energy available for growth in a diet to digestible energy consumed DE% = digestible energy expressed as a percentage of gross energy

Gross energy, GE: As shown in Equation 10.16, GE requirement is derived based on the summed net energy requirements and the energy availability characteristics of the feed(s). Equation 10.16 represents good practice for calculating GE requirements for cattle and sheep using the results of the equations presented above.

In using Equation 10.16, only those terms relevant to each animal category are used (see Table 10.3).

Where:

GE = gross energy, MJ day-1

NEm = net energy required by the animal for maintenance (Equation 10.3), MJ day-1

NEa = net energy for animal activity (Equations 10.4 and 10.5), MJ day-1

NEi = net energy for lactation (Equations 10.8, 10.9, and 10.10), MJ day-1

NEwork = net energy for work (Equation 10.11), MJ day-1

NEp = net energy required for pregnancy (Equation 10.13), MJ day-1

REM = ratio of net energy available in a diet for maintenance to digestible energy consumed (Equation 10.14)

NEg = net energy needed for growth (Equations 10.6 and 10.7), MJ day-1

NEwool = net energy required to produce a year of wool (Equation 10.12), MJ day-1

REG = ratio of net energy available for growth in a diet to digestible energy consumed (Equation 10.15)

DE%= digestible energy expressed as a percentage of gross energy

Once the values for GE are calculated for each animal subcategory, the feed intake in units of kilograms of dry matter per day (kg day-1) should also be calculated. To convert from GE in energy units to dry matter intake (DMI), divide GE by the energy density of the feed. A default value of 18.45 MJ kg-1 of dry matter can be used if feed-specific information is not available. The resulting daily dry matter intake should be in the order of 2% to 3% of the body weight of the mature or growing animals. In high producing milk cows, intakes may exceed 4% of body weight.

Feed intake estimates using a simplified Tier 2 method

Prediction of DMI for cattle based on body weight and estimated dietary net energy concentration (NEma) or digestible energy values (DE%): It is also possible to predict dry matter intake for mature and growing cattle based on body weight of the animal and either the NEma concentration of the feed (NRC, 1996) or DE%. Dietary NEma concentration can range from 3.0 to 9.0 MJ kg-1 of dry matter. Typical values for high, moderate and low quality diets are presented in Table 10.8. These figures can also be used to estimate NEma values for mixed diets based on estimate of diet quality. For example, a mixed forage-grain diet could be assumed to have a NEma value similar to that of a high-quality forage diet. A mixed grain-straw diet could be assumed to have a NEma value similar to that of a moderate quality forage. Nutritionists within specific geographical areas should be able to provide advice with regard to the selection of NEma values that are more representative of locally fed diets.

Dry matter intake for growing and finishing cattle is estimated using the following equation:

Equation 10.17

Estimation of dry matter intake for growing and finishing cattle

DMI = BW0 75 •

(0.2444 • NEma - 0.0111 • NEma2 - 0.472)

_ NEma _

DMI = dry matter intake, kg day-1 BW = live body weight, kg

NEma = estimated dietary net energy concentration of diet or default values in Table 10.8, MJ kg-1 Dry matter intake for mature beef cattle is estimated using the following equation:

Equation 10.18a

Estimation of dry matter intake for mature beef cattle

DMI = BW075 •

(0.0119 • NEma 2 + 0.1938)

_ NEma _

DMI = dry matter intake, kg day-1 BW = live body weight, kg

NEma = estimated dietary net energy concentration of diet or default values given in Table 10.8, MJ kg-1

For mature dairy cows consuming low quality, often tropical forages, the following alternative equation for estimating dry matter intake based on DE% can be used (NRC, 1989):

Equation 10.18b

Estimation of dry matter intake for mature dairy cows

" f(5.4 • BW^ "

DMI =

[ 500 J

100 J_

DMI = dry matter intake, kg day-1 BW = live body weight, kg

DE%= digestible energy expressed as a percentage of gross energy (typically 45-55% for low quality forages)

Equations 10.17, 10.18a, and 10.18b provide a good check to the main Tier 2 method to predict feed intake. They can be viewed as asking 'what is an expected intake for a given diet quality?' and used to independently predict DMI from BW and diet quality (NEma or DE%). In contrast, the main Tier 2 method predicts DMI based on how much feed must be consumed to meet estimated requirements (i.e., NEm and NEg) and does not consider the biological capacity of the animal to in fact consume the predicted quantity of feed. Consequently, the simplified Tier 2 method can be used to confirm that DMI values derived from the main Tier 2 method are biologically realistic. These estimates are also subject to the cross check that dry matter intake should be in the order of 2% to 3% of the bodyweight of the mature or growing animals.

Table 10.8

Examples of NEMA content of typical diets fed to Cattle for estimation of DRY MATTER INTAKE IN EQUATIONS 10.17 AND 10.18

Diet type

NEma (MJ (kg dry matter)-1)

High grain diet > 90%

7.5 - S.5

High quality forage (e.g., vegetative legumes & grasses )

6.5 - 7.5

Moderate quality forage (e.g., mid season legume & grasses)

5.5 - 6.5

Low quality forage (e.g., straws, mature grasses)

3.5 - 5.5

Source: Estimates obtained from predictive models in NRC (1996), NEma can also be estimated using the equation: NEma = REM x 18.45 x DE% / 100.

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