Traditionally the growth of calves and heifers has been tracked using tables and/or graphs where the goal for weight was based on the age of the heifer. This system of benchmarking growth is based on the assumption that the mature bodyweight of all cows is equal. In reality the variation in body weight of full grown cows is significant. For example, mature Holstein cows can range in body weight from 1,300 to 2,000 lbs! So to assume that at 6, 9, 12, or 18 months of age that a heifer that will grow to be 1,300 lbs. should have the same body weight as one of her pen mates that will weigh 2,000 lbs. when she is full grown is illogical.
A better system of evaluating a heifer’s weight relative to her age is to benchmark her current weight against her estimated mature body weight. A reasonable goal is to reach 85% of her mature weight at first calving. To reach this goal a heifer needs to be 55% of mature weight at conception. This system of evaluating heifer body weight is referred to as the Targeted Growth System (TGS). The table below shows benchmark weights based on the TGS.
| Desired Body Weights for Heifers using Targeted Growth System | ||||||
| Target as % | Mature Body Weight, lbs. | |||||
| Age, Months | Mature Weight | 900 | 1200 | 1500 | 1800 | 2100 |
| 13 | 55 | 495 | 660 | 825 | 990 | 1155 |
| 22 | 85 | 765 | 1020 | 1275 | 1530 | 1785 |
Note: The target weight at 22 months is the weight of a fresh heifer and not the weight of a pregnant heifer.
The range of mature body weights in the table may seem extreme but the TGS logic can be applied to any dairy breed large or small as well as to heifers with significant variation in genetic potential for mature body size. One of the advantages of using the targeted growth system is that the principal can be applied to any dairy cow regardless of her breed. If a heifer’s mature body weight can be estimated, then accurate predictions of her target body weight at breeding and calving are easy to obtain.
Farms that adopt the TGS can then determine the appropriate age for weight at first calving. Researchers at Penn State evaluated records from over 100,000 Holstein heifers to determine how age at first impacted first lactation milk production. The graph below shows the results.
Data from DHI processing centers show the average age of first calving is 26 months of age with a range of 17 to 45 months! Targets for age at first calving of 17 or 45 months are extreme and probably not realistic goals. The graph shows that Holstein heifers calving between 21 and 23 months of age have the highest level of milk production during their first lactation; providing evidence that a target age of 22 months of age is optimum. To achieve this goal, a heifer needs to conceive on average at 13 months of age. For these reasons, heifers need to reach 55% of mature body weight by 13 months of age.
The TGS is a valuable tool to help dairymen manage the growth of their heifers so that they enter the milking herd at 22 months of age. This system allows each dairy to customize the target weights they want to hit by 13 months of age based on the genetics potential for mature body weight of the cattle in their herd.
The ideal method of determining the weight of heifers is to use a livestock scale to precisely measure body weight. However, in many situations using a scale may not be practical. Heart girth can also be used to estimate body weight. Weight tapes can be purchased for this purpose, or heart girth can be measured with a flexible, non-elastic tape. Weight estimates can then be made using a table that converts heart circumference to an estimate of body weight. Frequent measurement of heifer weights provides information that can be used to alter the nutrition and/or management of heifers. One of the more practical systems of weighing heifers is to weigh and record individual heifer weights when they are restrained for vaccination, breeding, and pregnancy examination.
Are you currently monitoring growth in your heifers? What methods do you find works best for estimating weights?
If you’re not yet monitoring heifer growth then you may be missing an opportunity to maximize the profit potential of your heifers by using the Targeted Growth System. Take time to review the target weights your heifers should be reaching at 13 months of age. Then contact your ANC Consultant to discuss how you can fine tune your heifer program to reach these goals!
Source: Agri-Nutrition Consulting
