| Predicting Horn Growth
By Malcolm A. Goodman
Texas Longhorn Journal Nov/Dec 1999
With the high interest in horn length in today’s market, horn evaluation is key for both buyers and sellers. When I saw the data in the Texas Longhorn Journal on the longest horned bulls and cows, I thought it would be of value to the Texas Longhorn industry to ploy and analyze the data. I had done something similar with horn data for animals in my herd.
While horn length and HMA (horns per month of age) are of interest, these measurements don’t allow a good comparison of horn growth at different ages. This is because horn growth, like weight gain, is fast in the early years and then levels off. So how can we evaluate whether an animal has good horn for its age? And what do we compare to?
For my herd, I plotted the horns versus age (Based on data measured) for all females, including heifers and calves, and found a nice smooth trend. A simple equation of the trendline through the statistical average of the data provided a means to easily calculate the “expected” horn for any female at any age. I could then compare the expected value with the actual value to see if the animal is above or below average and how much. The percent difference was calculated and used to compare and rank the cows in my herd. I did this for both horn and weight (also, for bulls and steers separately) and now monitor and update this information regularly in my Longhorn database.
The TLJ data not only provided a good statistical base across a wide age ranch (119 bull data points from 10 months to 13 years of age and 160 cow data points from 10 months to 21 years), but also provided the “Super Horned Bulls and Cows,” both young and old, for us to compare to. How do our animal’s horns, at their age, compare with these elite animals? What should I expect the horns to be six or twelve months from now?
From the date, 100 bulls and 159 cows had both date-of-birth and date-of-measurement, so I could calculate the exact age of the individual when the horns were measured. These points are plotted in Figures 1 and Figure 2, along with the trendlines. I did not cull any of the data; there are only a few outlier points. I tried both a logarithm fit and polynomial fit to the data, and the latter did best, even though the curves look like log plots. The data after four years for bulls, and seven years for cows, tends to dip in the middle, mainly because of the significant number of long-horned younger animals. So I used a separate linear fit after five years for bulls and after eight years for cows.
The trendline can be interpreted as a “horn growth line.” The mature horn length determined from the trend line equations, say at 20 years, can be used to calculate the percent of mature horn reached at any age, see Figure 3. This percentage then determines the multiplier factor for predicting the eventual horn at maturity, as demonstrated in the figure inset.
Some interesting observations:
- Bulls have fifty percent of their horn length at one year of age, seventy five percent after the second year, ninety percent after three years, and ninety-eight percent at five years old. Just double the horns at one year old to predict the adult horn length. And don’t expect much horn growth, if any, after five years (although there are obviously exceptions to every rule).
- For cows, horn growth is more gradual, but is still quite rapid in the early years. Cows grow forty-three percent of their adult length during the first year, sixty-six percent (or two-thirds) by two years of age, eighty percent at three years, and ninety-three percent when they turn five years old. So, just multiply the first year measurement by 2.3, or the second year measurement by 1.5, to estimate adult length.
- The data bubble at four years for bulls and at six to seven years for cows suggests that the trend lines for older animals in the future (5 to 10 years) will translate upward about five inches, i.e. more 70-inch horned bulls and 75-inch horned cows.
The comparative results are shown with the twenty-five bulls and cows ranked by the calculated percent difference between “actual” and “projected” horn length. Many of the bulls and cows ranked in the upper half are the younger animals. Of the top twenty bulls, eighteen are less than five years old and fifteen are less than three years old. However, the top ranked bull is six years old and also happens to be the longest-horned bull. But, based on “DIFF%” (the calculated percent difference), the second ranked bull is close behind and is only sixteen months old.
Of the top twenty cows, fifteen are less than five years old and thirteen are les than two years old, including the four heifers ranked at the top. Again, this strongly suggests that the longhorns of tomorrow will have even more than their super-horned sires and dams of today.
At this point, you may be asking, “Can I use these same multiplying factors to predict horn growth for my animals?” I tend to think so. Just as a one-year-old bull listed here with 35 inches of horn may reach 70 inches at maturity, your 25-inch yearling bull is just as likely to double his horn to 50 inches. It is important to remember that these results are statistical. On the average, these trends and results should hold true. Any given animal may do better or worse than the trendline average as exhibited in Figures 1 and Figure 2.
It would be useful to test these results with more data in the future. Breeders who have been measuring horn for a number of years can check these predictions now. Any breeder with at least one set of horn measurements for their herd, can develop their own herd trendlines to evaluate and compare the horn growth of different animals within their program. This horn growth line for your herd can then be used for future evaluation, as the age and horn length of each Texas Longhorn changes.