Star Milling

Estimating Body Weight Of Growing Foals

This article will help you accurately estimate a foal's body weight, which will guide a proper feeding program.

Estimating body weight (BW) of foals can be a challenge unless you are fortunate to have access to a platform scale. A foal’s growth rate is very rapid in the beginning but as the foal becomes older his body weight gain per day will decrease. For example, during the first month of life a foal can gain more than 3 pounds each day compared to 2 – 2½ pounds per day between the ages of 2 – 3 months and around 1½ pounds per day during months 5 – 6. The weight tapes that were developed for adult horses are not very reliable for estimating a foal’s weight during these early and different stages of growth. The weight tapes start to be more reliable by 18 months of age.

The tables included in this section may provide some reasonable guidelines in estimating body weights of foals during growth. Tables 1 & 2 are summaries of body weight changes for Arabian colts and fillies that were collected in the early 1980’s. The data was collected by students at California State Polytechnic University - Pomona but was never published in a journal that would reach the scientific community. The university has an Arabian breeding program that is part of the outstanding Animal & Veterinary Sciences and Animal Health programs for Animal Technicians.

Note that the percent of mature body weights for the Arabian data (Tables 1 & 2) are similar to those published in The Horse by Dr. Warren Evans (1990), which is provided in Table 3. For example the percent (%) of mature body weights for 6, 12 & 18 months of age approximates 46, 67 and 79% respectively.

The % of mature body weights provided in The Horse (Table 3) provides reasonable guidelines in estimating body weights of foals during growth.

Table 1. Body Weight Changes for Arabian Females

Average Body Weight, lb

Months Birth 1 6 12 18 24 36 48
Average Body Weight, lb 87 178 454 657 783 884 967 971
Average Weight Gain, lb - 91 276 203 126 100 84 3
% of Mature Body 9 18 46 67 80 90 99 99

Table 2. Body Weight Changes for Arabian Males

Months Age in Months

Months Birth 1 6 12 18 24 36 48
Average Body Weight, lb 88 170 463 670 806 893 970 1005
Average Weight Gain, lb - 82 293 207 135 88 77 35
% of Mature Body 9 17 45 65 79 87 95 98

In Table 3 note that regardless of age or mature body weight, the percent of mature BW is basically the same. For example, the percent of mature body weight achieved at 8 months of age is about 54% regardless of the final mature weight of 900, 1100 or 1300 lb. From the data in this table a prediction of the mature body weight for the foal is required. Although this “best-guess” is a crude estimate, the BW is usually based on some knowledge of the breed, body-type, sire, dam and perhaps full and half-siblings. For example if the estimated mature body weight of a 8 month old foal was 1100 lbs, then the % of mature body weight is 55%. That is 55% of 1100 lbs equals 605 lbs (1100 lbs X 0.55) = 605 lbs).

Table 3. Percent of Mature BW during Growth

Age in Months 900 lbs Mature BW 1000 lbs Mature BW 1300 lbs Mature BW
% of Mature Body Weight
4 36% 36% 36%
6 46% 46% 45%
8 54% 55% 54%
10 61% 62% 61%
12 67% 67% 65%
14 71% 72% 69%
16 76% 76% 73%
18 79% 80% 77%

Source: The Horse by Dr. Warren Evans (1990)

What if you incorrectly estimate a foal’s body weight and end up feeding too little? No worries, because if you have developed skills in body condition scoring, you should be able to make that determination in a reasonable amount of time.

Table 4 provides actual body weight measurements from 2 – 18 months of age for different expected mature boat weights from 900 – 1300 lbs. For example if the expected mature body weight is estimated to be 1300 lbs and the growing youngster is 14 months of age then the estimated body weight at this age would be around 900 lbs.

Table 4. Estimating Foal’s BW (lb) during Growth

Age in Months 900 lbs Mature BW 1000 lbs Mature BW 1100 lbs Mature BW 1200 lbs Mature BW 1300 lbs Mature BW
Body Weight in Pounds (lbs)
2 230 260 290 300 330
4 325 360 400 432 465
6 415 460 510 540 585
8 485 550 600 648 700
10 545 620 680 732 790
12 600 670 740 780 850
14 640 760 840 876 950
16 680 760 840 876 950
18 710 800 880 924 1000

Source: The Horse by Dr. Warren Evans (1990)

A foal’s performance is significantly improved when fed a balanced growth formula that complements the forage portion of the diet. Integrity Mare & Foal, a pellet feed, is for growing foals up to 10 months of age. Integrity Growth, a texture feed, is for growing horses from 10 months to 3 years of age. These provide the optimal nutrition for these important phases a horse’s life cycle.

References
1. Unpublished data. Growth Measurements of Arabian Colts and Fillies. California Stat Polytechnic University, Pomona.
2. Evans, J.W., A. Borton, H. Hintz and L.D. Van Vleck. 1990. The Horse. W.H. Freeman Company, New York