The following article was published in the Texas Longhorn Journal in December 1999. Click on the blue links in the text to see the plots. Use the Interactive Calculation for an exact prediction or the Horn Prediction Table for a quick rough estimate.
Predicting Future Horn Growth
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 plot 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 it's age? And what do we compare to?
The TLJ data not only provided a good statistical base across a wide range (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 data, 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 Figure 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 a polynomial fit to the data, and the latter did best, even though the curves look like log plots.
The trendline can be interpreted as a "horn growth line". The mature horn length determined from the trendline 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:
1) 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 horn 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).
2) For cows, horn growth is more gradual, but it 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 the adult length.
3) The data bubble at four years for bulls and at six to seven years for cows suggests that the trendlines 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.
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 Figure 1 and Figure 2.
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