Gain

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Historically for seedstock cattle, body weight gain has been measured between weaning and yearling weights. However, depending on the intended use gain has had multiple trait definitions. In this article, we will assume that regardless of the trait definition the optimal application of animals' gain data is for the generation of EPDs. Because of the multiple sources of gain data, it is essential for organizations providing EPDs to record the characteristics of the source data. Additionally, care should be taken to appropriately include or exclude data for EPD production, because of the varying statistical characteristics of the types of gain measurements.

Gain between weaning and yearling

In its simplest form average daily gain (ADG) has been the total gain from weaning to yearling divided by the number of days between the two weights. Of course, it is important to account for environmental differences (e.g., contemporary groups) and other non-genetic factors such as the sex of the animal, the age of the dam, and the animal's age at weighing. Generally, average daily gain is a measurement of the average daily body weight change of an animal over a specified period of time. Average daily gain is calculated as follows: ADG (average daily gain) = (Final weight – Initial weight) / Days on test

It can also be expressed as a ratio as follows: ADGR (average daily gain ratio) = (ADG / Breed-test group average ADG) x 100

Initial and final weight data can be obtained as combinations of weights from specific testing periods (such as from feed intake tests), or from combinations of birth, weaning, yearling, mature, or harvest weights.

Gain from genetic evaluations

Several organizations publish EPDs for average daily gain. In all cases in North America, this is the average daily gain prediction for the period from weaning to yearling. It is simply calculated as,

$ADG={\frac {Yearling\,Wt\,EPD-Weaning\,Wt\,EPD}{160days}}$

It is important to note that in many North American genetic evaluations, including those of private organizations, the yearling weight EPD is calculated from a multiple-trait analysis that includes models for weaning weight and post-weaning 160-day gain. While not published as post-weaning gain EPDs, the few organizations that publish ADG EPDs produce them using the post-weaning 160-day gain EPDs from this multiple-trait analysis.

On-test Gain

In the past, when centralized bull testing was more common, gain during the test period was an essential component of those tests.

Feed intake and gain testing

Often feed intake tests will measure gain during the testing period in order to make an assessment of efficiency of feed utilization.

Table 1. Average correlation and regression coefficients between standard (70-day) and varying shortened test period lengths for on-test average daily gain (ADG) and metabolic mid-weight (MMWT). (adapted from ) )

Test Length	ADG Pearson Correlation	MMWT Pearson Correlation	ADG Regression	MMWT Regression
28 days	0.66	0.975	0.275	0.92
42 days	0.835	0.99	0.525	0.98
56 days	0.945	1	0.825	1.005

Partial body weights

[MIKE's INFO GOES HERE]

Feedlot gain

[Included here for completeness...]

Warm-up period recommendations

BIF recommends a warm-up or acclimation period of at least 21 days should be included in the gain test. The goal of the acclimation period is to reduce within contemporary group variation in feed intake due to non-genetic factors (e.g. pre-test environment) and to acclimate animals to both the test diet and the testing equipment. Animals should be transitioned from receiving to test diets gradually to minimize digestive system upset. Frequently these transitions will include moving animals from a primarily roughage-based receiving/backgrounding diet (either fed ad libitum or with restricted intake) to a higher energy, concentrate-based growing diet fed ad libitum. If calves entering a test have been previously transitioned to a diet that will be used in the formal feed intake test, then the acclimation period may be substantially reduced (by a week or more) to accommodate acclimation to the feed intake equipment only. However, users should be cautious that animals acclimated to a high concentrate diet are not restricted from that diet while training to prevent acidosis issues when they return to normal consumption levels.

Test diets

Diets used in feeding tests will vary according to animal type, animal gender, environmental constraints, feed ingredient availability, cost, and management. Therefore, data collection should be implemented such that diets can be adjusted insofar as possible to a common nutritional base. All animals within one test should be fed the same test diet, and the diet should be formulated to provide essential nutrients and sufficient energy to ensure the expression of animal differences for intake. The ingredient composition of the diet should be recorded, and the ingredient composition of the diet maintained throughout the test period. It is desirable for samples of diet ingredients or of the complete diet to be sent to a commercial laboratory for complete chemical analysis.

Diets used in tests with growing bulls should contain at least 2.4 Mcal ME/(kg DM). Diets used in tests with finishing steers should contain at least 2.9 Mcal ME/(kg DM). There is a growing number of reports in the scientific literature in which data from intake tests are adjusted to common energy content, mainly to increase across-test comparability. That is, statistical adjustment to a constant energy density requires recording of enough chemical composition data on the diet(s) to derive metabolizable energy (ME) in megacalories (Mcal) on a dry matter basis. Average daily intake and functions of intake data should be reported on a dry matter basis. Expression of daily feed intake values on a dry matter basis removes variability in the moisture content across a diversity of diets, and increases the comparability across multiple tests and studies. As-fed measurement of daily feed intake can be recorded as well, but for further data analyses, sufficient information must be supplied to convert feed intake to a dry matter (DM) basis.

Attribution

The contents of this article are a result of an ad hoc BIF committee with additions, from various authors including McNeil, Spangler, and Golden. This article is derivative of the original Guidlines wiki page Intake and Feed Efficiency.