Beef Cattle Live Animal Weights

Beef Cattle Recording: Specific recommendations for data collection The collection of live animal weights is critical to the analysis of productivity in the beef herd. Typical weights collected by producers are birth, weaning and yearling weights. It is important that these weights are collected consistently to ensure an informative analysis. Animals are typically weighed using suspension scales or electronic load cells. It is important to ensure that the weighing equipment particularly mobile scales are suitably located on a level surface. Scales should be regularly calibrated to ensure the accuracy of the recorded data. As a minimum, a scale that measures to an accuracy of 1kg/2lb should be used for birth weights and 2kg/5lb for later weights.

When weighing cattle several aspects must be considered. Birth weights are typically recorded on suspension scales. It is imperative that the calf is completely off the ground and is not obstructed in any way. It is best if the scale is mounted on a stand so that an accurate measure can be recorded. For weighing cattle on platform or suspension scales it is necessary that the scales are checked regularly for obstructions and that they are cleaned and balanced frequently.

Birth weight

Birth weight is the major contributor to dystocia in cattle. Therefore, collecting and analysing birth weight information is useful for many beef breeding programs. Birth weights should be collected within 48 hours of birth. Data that should be collected at birth include: Dam ID; Calf ID; birth date; birth weight; date of weighing and calving ease score. The calf should be dry and should be allowed to nurse the cow.

Weaning weight

Weaning weights are important to beef producers for several reasons. Weaning weights are an indication of the productivity of the dam and the genetic potential of the calf for pre-weaning growth. Weaning weights serve as the initial weight for determining post-weaning growth. Additionally, many producers market their calves at weaning based on the calves’ weights; therefore, weaning weights can have a significant influence on farm income. Genetic evaluations account for the environmental contribution to weaning weight and separate maternal and growth genetic components. Weaning weights should be collected at the time the calf is weaned. All calves in the contemporary group should be weighed at the same time. The age of the calf at this time may vary depending on the country of origin. For correct adjustment purposes the average age of the calves should be as close as possible to the age adjustment standard for that country or accepted management system. For example, the weaning adjustment age in the United States is 205 days of age, therefore, it is recommended that weaning weights should be taken when the average age of the calves is close to 205 days. If weights are taken at ages considerably different from this age the adjusted weights will not be as accurate.

Post-weaning growth

Weaning weights typically serve as the initial weight and yearling weights serve as the end-point for evaluating post-weaning growth. In situations where official weaning weights are collected prior to actual removal of the calf from the dam, the initial weight should be collected at the time of removal. Genetic evaluation of post-weaning growth may be reported different. This will either be reported as post-weaning growth or as yearling weight (which is typically the genetic value for weaning weight plus the genetic value for post-weaning growth). In either case the maternal component that influences the trait is accounted for so that the evaluation is on growth potential. Final weights for post weaning growth are traditionally taken as close to 365 days as possible. However, there are exceptions depending on country and management systems. For example, in the United States there are three accepted ages for yearling weights: 365 days; 452 days; and 550 days. Post-weaning weights should be collected when the average age of the calves is close to the appropriate age. All calves in the contemporary group should be weighed at the same time.

Finish weights

Collected live finish weights at time of harvest or slaughter is often used as the sale weight and is also critical to assessing dressing percentages. Determining the appropriate time to harvest animals and collect finished weights varies greatly depending on the country and expected utilization of the carcass. For genetic evaluation purposes these weights will be adjusted to a consistent end-point (i.e. age, fat thickness, etc.). Empty weights (no feed or water for minimum 12 hours) should be taken at time of harvest. A scale that measures in increments of 2 kg or 5 lb, or less, should be used for finished weights.

Test weights

Initial and final test weights to compute growth rate may be either full or shrunk (empty) weights. If full weights are utilized, initial and final weights should be an average of weights taken on two consecutive days to minimize fill effects. Otherwise, a single weight after a 12-hour shrink (no feed or water) is adequate. Weights may be collected at various points during the test to ensure that appropriate gains are being achieved. A scale that measures in increments of 2 kg or 5 lb, or less, should be used for test weights.

Chest girth circumference as a predictor of growth

In certain beef cattle management systems, where live weight cannot be recorded directly, chest circumference of animals may be recorded as indicator trait for growth rate in beef performance recording.

Chest girth can be recorded using a measuring tape; alternatively, it is possible to record chest girth using dedicated devices that can predict chest girth from the processing of digital images of the animal. Such devices must be composed by a digital - optical part that is in charge to take digital images of the animal and by a software that must interpret digital images and, using dedicated software, produce animal's chest girth estimate.

The device precision in chest girth estimation must be periodically verified by field calibrations where the average difference between tape and predicted chest girth should not exceed 2,5% of tape chest girth.

Live weight, a direct beef performance trait, can be estimated from chest circumference using a transformation formula that includes both:

1. The age of the animal, and
2. Its chest circumference.

The age of the animal is calculated as the difference in days between date of recording and animal’s birth date. Transformation formulas may be specific to breed and sex.

It is suggested that use be made of transformation formulas derived from sufficiently large datasets where both chest circumference and live weight were recorded on the same animal, and collected on animals at different ages. Where transformation formula derived from a multiple regression approach are used then the relative R2 should be at least 0.90. Where chest circumference data is used to estimate live weight, it is recommended:

1. That the recorded trait of chest circumference is specified, and that the appropriate units (centimetres, inches, meters, etc.) are specified.
2. That the actual chest circumference is recorded.
3. That chest circumference is stored in the central database and used to estimate live weight using appropriate and approved conversion formulae.
4. That estimated live weight derived from chest circumference together with original chest circumference be recorded together on the database.
5. That a code be recorded on the database with the animal record to indicate the procedure used to estimate growth from the chest measurement.

Adjusted growths and weights

Weights are recorded as raw weights together with the weighing date. In order to make live weights comparable among animals of the same breed and sex, and to allow data and information exchanges among countries, it is common practice to express live weights adjusted to specific reference ages. For instance, live weight at 365 days of age of the animal (“yearling weight”) makes it possible to rank animals of same breed, sex or herd for their growth aptitude.

Reference ages are defined according to specific breeding events; for instance, 200 days of age refers to weaning of the calves. Weights at reference age are important because they allow comparative analyses for animals in different environments and countries. Usually, recording activity in a herd requires weights on all the animals that are present in that day to be recorded. It may not be possible to make the required measurements on the exact date required. If for example the yearling weight is to be recorded, but only monthly, bimonthly or tri-monthly weightings are technically possible, the expected weight at day 365 can only be calculated using an adjustment procedure and will be stored as a ‘calculated trait’.

When a recorded trait such as live weight is standardized for a given age, the resulting adjusted weight becomes a calculated or derived trait, which is a function of the recorded weight and of the age of the animal. Thus, ‘weight’ is a directly recorded trait, while ‘weight at 200 days’ will be a calculated trait. For the international exchange of data, a standardization of time intervals is strongly recommended, and each national organization should define reference ages for its beef cattle breeds. When storing such weights, it is necessary to specify that these are calculated traits derived from raw data.

Live weight measurements, both from direct (scale) recording and from transformation of biometric measures (e.g., chest circumference) are of primary importance in monitoring an animal’s growth. As already mentioned, weights are recorded as raw weights together with the weighing date and can be adjusted to the reference age of choice. However, such data can be used to calculate other traits that can more easily provide information on the growth potential of the animal.

This type of data refers to live growth rate in a specific time interval and expresses the growth potential of an animal in a specific time period. While live weight specifies an animal’s weight in a single day, growth traits can refer to two weights recorded on two dates and describes an animal’s growth performance in the specific period. The resulting information can be useful for management and comparison among animal growth potentials at differing stages of growth.

Growth traits are of primary importance in beef breeding and the beef industry since growth is highly correlated to the economic value of retail product. These traits are usually expressed as daily gain in g per day. These growth traits are calculated traits and can be divided into two categories:

1. Growth rate from birth to a specific age such as 365 days.
2. Growth rate between defined periods in the animal’s life.

Recommendation for weight correction to standardized age

The usual method for calculating standard age weight is based on determining average daily gain between two weight recordings; then, assuming growth to be linear between the recordings, estimate live weight increase from the day of first recording and reference day and add it to weight on first recording. It is preferable that the age to which weight is being adjusted occurs between two successive recordings. If this is not possible, an extrapolation is possible if age at last recording falls within a specific time interval from the standard age. The time interval has to be determined by each recording organization based on recording frequencies.

Calculation method

Different situations can occur:

1. Where with the exception of birth weight, there is only one weight record available after birth:
   
   1. let $A_{R}$ be reference age
   2. let $W_{R}$ be weight at reference age
   3. let $D_{B}$ be birth date
   4. let $D_{t}$ be recording date t
   5. let $W_{B}$ be birth weight
   6. let $W_{t}$ be recorded weight at date t
   7. let $A_{t}$ be age of animal at recording date ( $=D_{t}-D_{B}$)

   If $A_{R}>A_{t}$

   $W_{R}={\frac {W_{t}-W_{B}}{A_{t}}}\times A_{R}+W_{B}$

   Else ${\displaystyle }$

   $W_{R}={\frac {W_{t}-W_{B}}{A_{t}}}\times (A_{R}-A_{t})+W_{t}$

   
   

2. Where there is more than one weight recordings are carried out after the birth is recorded. The following formula refers to the case of two recordings (n = 2). The procedure can be applied to any number n of recordings, noting that the reference age in this case should be comprised of the age intervals from two successive recordings, or, if this is not possible, should be closest to the last available record. The age range tolerance or limitation values should be specified by the recording organization, based on recording frequencies etc.
   • let $R_{A}$ be reference age
   • let $R_{W}$ be weight at reference age
   • let $D_{B}$ be birth date
   • let $D_{t-1}$ be recording date 1
   • let $D_{t-2}$ be recording date 2
   • let $W_{t-1}$ be recorded weight at date 1
   • let $W_{t-2}$ be recorded weight at date 2
   • let $A_{t-1}$ be age of animal at recording date 1 ( $=D_{t-1}-D_{B}$)
   • let $A_{t-2}$ be age of animal at recording date 2 ( $=D_{t-2}-D_{B}$)

   If $R_{A}<A_{t-1}$

   $R_{W}={\frac {W_{t-2}-W_{t-1}}{A_{t-2}-A_{t-1}}}\times (A_{t-1}-R_{A})+W_{t-1}$

   Else if $A_{t-1}<R_{A}<A_{t-2}$

   $R_{W}={\frac {W_{t-2}-W_{t-1}}{A_{t-2}-A_{t-1}}}\times (R_{A}-A_{t-1})+W_{t-1}$

   Else if $R_{A}>A_{t-2}$

   $R_{W}={\frac {W_{t-2}-W_{t-1}}{A_{t-2}-A_{t-1}}}\times (R_{A}-A_{t-2})+W_{t-2}$

3. In suckler herds participating in birth to weaning recording scheme, where the reference performance trait is weight adjusted for 200 days, the recommended calculation method is as follows:
   • let $A_{t}$ be the age at weighing in days
   • let $W_{t}$ be the weight in kilograms
   • let $W_{B}$ be the recorded birth weight or a breed standard,
   then reference performance is calculated as:

   $R_{W}={\frac {W_{t}-W_{B}}{A_{t}}}\times 200+W_{B}$

4. Where it is necessary to extrapolate to an age outside the lower and higher recording ages, a maximum allowable interval should be specified between the standard adjustment age and the available recording ages. This interval can be related to animal’s breed sex and growth potential in the period under consideration. Intervals greater than such threshold should not be used. For example, it may be decided that weight at 365 days can only be calculated if records are within a time period of ± 45 days. Useful weights to calculate 365 days weight should then only be recorded in the age range 320 and 410 days of age. Considering the variation in these parameters throughout recording schemes, the decision of threshold period for determining weight at standard age for each breed is left to member countries. Generally, computational method used are standard linear interpolations. However, if threshold periods are very large, a non-linear standardization may also be necessary within a recording scheme. For the international exchange, it is recommended that raw weights and dates of recording be provided as a minimum.

Recommendation for growth traits calculation

A number of weight gains definitions can be defined:

1. Average daily weight gain: This is total live weight increase between two weight recordings, divided by the number of days between the two weighing records. The trait is expressed in grams per day.
2. Live weight gain per day of age: Given a specific weight record, taken at a specific age of the animal, and given an actual or default birth weight of an animal, a live weight gain from birth may be calculated. For the calculation of this trait, birth weight and birth date of the animal should be mandatory data. In the case of missing or invalid birth weights the average birth weight for the breed and sex can be used. The trait is expressed in grams per day.
3. Net weight gain per day of age: This is the commercial carcass weight divided by days of age at slaughter. Birth date is mandatory in order to calculate age at slaughter. Net gain is expressed in grams per day. It is important to record the trim specification of the carcass as this can vary significantly.

The above-mentioned performance traits are calculated from a combination of recorded traits (weight recording and corresponding dates). This type of trait can be derived both from raw recorded data and from adjusted weights

Calculation method

Refer to current ICAR guidelines for the method.

1. Suckler herds from birth to weaning Weight gain may be calculated as follows:
   • let $WW$ be the corrected live weight at weaning, expressed in kilograms
   • let $BW$ be the birth weight, expressed in kilograms
   • let $A_{W}$ be the age at weaning, expressed in days
   Then, weight gain from birth to weaning is calculated as:

   ${\frac {(WW-BW)\times 1000}{A_{W}}}$

   and is expressed in grams per day.

2. Test stations The reference performance trait in test stations is average daily weight gain:
   • let $A_{S}$ be the age at test start, expressed in days
   • let $A_{F}$ be the age at test end, expressed in days
   • let $SW$ be the live weight at test start, expressed in kilograms
   • let $FW$ be the live weight at end of test, expressed in kilograms
   Then, average daily weight gain is calculated as:

   ${\frac {(FW-SW)\times 1000}{A_{F}-A_{S}}}$

   and is expressed in grams per day.

   
   

3. Finishing herds after weaning to slaughter The reference performance trait is average daily weight gain.
   • let n weight recordings be performed during the period
   • let $A_{n-1}$ be the age at weight recording n-1, expressed in days
   • let $A_{n}$ be the age at weight recording n, expressed in days
   • let $W_{n-1}$ be the live weight at weight recording n-1, expressed in kilograms
   • let $W_{n}$ be the live weight at weight recording n, expressed in kilograms
   Then, average daily weight gain is calculated as:

   ${\frac {(W_{n-1}-W_{n})\times 1000}{A_{n-1}-A_{n}}}$

   and is expressed in grams per day.