Beef Cattle Nutrition and Feeding
Frequently Asked Questions
Feeding Cottonseed Meal to Developing Bulls
Seedstock producers enter bulls into an on-farm development program to
collect post-weaning performance information and develop bulls to breeding age
for clientele. Development programs range from forage-based programs with
supplementation to high-concentrate diets that allow bulls to express their
genetic potential for growth over a shorter period of time. Breeders
developing bulls on a high-concentrate diet should be concerned with ingredient
selection.
The most commonly questioned ingredient in bull development rations is
cottonseed meal. Cottonseed contains a pigment known as gossypol that interferes
with reproduction in males. The main concern with cottonseed and cottonseed meal
is with the concentration of free (unbound) gossypol.
Potential Dangers of Cottonseed Meal
A study published in the
Journal of Animal Science in 1998 showed that feeding cottonseed meal to
bulls at a rate that delivered 6.4 milligrams (mg) per pound of body weight
daily from 6 to 16 months of age delayed puberty in 50% of the bulls through the
end of the study, decreased sperm production by 30% in the bulls that could be
collected, and reduced the percentage of live sperm by 47%.
The goal of the study was to maintain a consumption of 6 mg/lb BW daily of
free gossypol. This level has been found to cause reproductive problems in
bulls. Unfortunately, the study did not evaluate the carryover effects into the
reproductive rates in the cow herd.
To achieve the level of free gossypol intake observed in the study, bulls
were required at the beginning of the study to consume 6 pounds per day of a 67%
cottonseed meal supplement. By the end of the study, bulls were consuming 13
pounds of supplement that contained 80% cottonseed meal. Overall, bulls consumed
4 to 10.6 pounds daily of cottonseed meal from the beginning to the end of the
study, and the free gossypol content of the cottonseed meal was approximately
0.12%. This level of gossypol in the cottonseed meal is within the typically
reported value for solvent and expeller extracted cottonseed meal.
Advances in Cottonseed Milling May Mean Safer Meal
Traditionally, we’ve been educated that free gossypol can cause a problem in
bulls, but changes in cottonseed milling practices during the late ‘80s and
early ‘90s were promoted to greatly reduce the free gossypol content of
cottonseed meal. As a result, the
Journal of Animal Science study was initially developed for a practice
that has gradually migrated over into an unquestionably safe practice.
To defend the practice, a laboratory that routinely analyzes for gossypol was
contacted to determine the typical free gossypol concentration of the samples
they’ve analyzed. Surprisingly, free gossypol was being observed in the range of
0.4 to 0.6% in cottonseed meal, far greater than the 0.1% that was expected.
In comparison to the above study, a typical high-concentrate bull ration for
650 pound bulls may contain 20% roughage (hay or cottonseed hulls), corn, and
cottonseed meal. A formulation to provide 14% protein (dry matter basis) will
contain approximately 14% cottonseed meal. At this rate, a 650-pound bull would
consume 2.3 pounds cottonseed meal daily if dry matter intake were 2˝ % of body
weight. This level of cottonseed meal intake is nearly half of that observed in
the study cited above and falls below the 3 to 5 pound maximal level of
cottonseed meal generally recommended for this age group.
Gossypol content of cottonseed meal, however, varies depending on the source,
and based on the laboratory observations discussed earlier, may more likely
contain 0.5% free gossypol instead of 0.1%. Consumption of 2.3 pounds cottonseed
meal daily that contains 0.5% free gossypol would supply approximately 8 mg/lb
BW daily, which is greater than the level observed to cause negative effects on
reproductive development and function cited in the study mentioned earlier.
Recommendations for Using – and Limiting – Cottonseed Meal
The generally cited recommendation for limiting cottonseed meal in the diet
for young developing bulls is based on a maximum of 150 ppm free gossypol in the
diet. If the available cottonseed meal contains 0.5% free gossypol, then
cottonseed meal consumption would need to be limited to 0.5 pounds daily, far
less than the 3 to 4 pound recommendation.
Upon gathering data for this article, the conclusion is that making the
decision to feed cottonseed meal to growing bulls should be approached with
precaution and preplanning.
The first decision is to determine whether bulls are going to be supplemented or
fed a complete ration. When supplemented (<1 lb/d), it is less likely that
cottonseed meal, even at 0.5% free gossypol, will result in severe reproductive
problems. First, gossypol intake is much lower under this condition, and
secondly, the rate of passage of the diet will likely be slower than with a
high-concentrate diet. Free gossypol has the potential to become bound to other
nutrients (proteins, minerals) in the rumen.
If planning for a complete ration, do a lot of homework. Determine what mill
is processing the cottonseed meal and the level of free gossypol commonly
observed. Manufacturers should be able to provide information about amounts of
free gossypol in their products. Otherwise, without having a good knowledge
of the gossypol content of the available cottonseed meal, alternative protein
feeds such as soybean meal or higher protein by-products should be used. In
the previously discussed study, Vitamin E (4000 IU per day) was reported to
reverse effects of free gossypol when gossypol was consumed at 6 mg per pound
body weight daily.
Bull buyers should be aware of the gossypol concern. Always ask about the
diet used to develop bulls, and never purchase a young bull without a breeding
soundness examination completed by a veterinarian. Just because cottonseed meal
was a component of the ration doesn’t mean the bulls are reproductively unsound.
For more information on gossypol and rations for developing bulls, visit with
your local county Extension office or consulting nutritionist.
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Nutrition and Feeding Frequently Asked Questions
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