M.H. Poore

The acreage of cotton grown in North Carolina has increased in recent years, increasing the supply of whole cottonseed available to cattlemen. In three of the last four years, whole cottonseed has been avail able at less than $100/ton FOB gins, which is well below the actual value of it's nutrients of about $140/ton. Cottonseed is also conveniently handled and requires no processing, making it a very desirable feed that has been rapidly adopted. Because most cow calf producers using whole cottonseed also want to feed it to their replacement heifers, and because of the growing stocker sector in the state, we have received many questions regarding the optimal use of whole cottonseed for growing cattle. Several previous studies conducted have suggested that cottonseed should be limited to less than 15% of diet dry matter, but additional information is needed to strengthen this recommendation.

Cotton textile mill waste is short fiber cotton resulting from the processing of raw cotton into yarn. This is another alternative feed available to North Carolina cattlemen that is available in some areas, but again, information on which to base feeding recommendations is limited. This trial was conducted to evaluate the effect of altering the level of whole cottonseed in sorghum silage-based diets with or without the cotton fiber added. This design allowed not only the evaluation of cottonseed level and cotton fiber, but also whether the type of fiber present in the diet would alter the influence of cottonseed.

Materials and Methods
Sixty M-1 Angus heifers purchased from North Carolina Graded Feeder Calf Sales were used in the 84-day trial. They were fed total mixed rations through Calan feeding gates at the Butner Beef Cattle Field Laboratory during the winter of 1992-1993. The diets contained on a dry matter basis either 67% sorghum silage and 33% concentrate or 47% sorghum silage, 20% cotton fiber, and 33% concentrate. Soybean meal, ground corn, and whole cottonseed were included in the concentrates such that each type of diet had either 0, 6, 12, 18 or 24% whole cottonseed , giving a total of 10 different diets and six heifers per individual diet. Diets were formulated to meet protein and mineral requirements, and were predicted to provide 2 lb/day gain.

Shrunk weights were obtained on the heifers at the beginning and at the end of the trial to determine gain. Initial weight of the heifers was 541 lb, and feed intake was monitored daily. Near the mid point of the trial, rumen samples were withdrawn by stomach tube 2 hours after the morning feeding to evaluate ruminal ammonia and VFA levels, and blood samples were obtained at the same time to evaluate blood urea nitrogen levels.

Results and Discussion
There were few interactions between whole cottonseed level and the addition of cotton fiber, so only main effects are reported here. The main effects of cottonseed level and cotton fiber on growth, intake, ruminal ammonia and blood urea nitrogen are shown in Table 1, while ruminal VFA level and proportions are shown in Table 2. Dry matter intake and average daily gain were not influenced, while feed efficiency was improved when 20% cotton fiber was substituted for sorghum silage. Blood urea nitrogen was decreased and ruminal ammonia was increased indicating that there was some effect of the cotton fiber on ruminal nitrogen metabolism. Ruminal VFA were also influenced by the cotton fiber in that total VFA was higher, and the proportion of propionate, isobutyrate, butyrate, and isovalerate were lower in diets with cotton fiber. This result indicates that while the textile mill waste may influence the ruminal environment, it has great potential as a feed, and appears to have a nutritional value similar to sorghum silage.

Increasing cottonseed level linearly decreased dry matter intake and average daily gain of the heifers with what appeared to be a break between the 12 and 18% levels. Feed efficiency was not effected by cottonseed level. At the highest level of whole cottonseed, heifers fell well short of the rate of gain needed to meet the target weight for breeding. The reason for this negative effect of cottonseed is not clear but could be due to several factors. The oil present in the cottonseed could have negative effects on ruminal function, but earlier studies have indicated that even the fat content of the 24% cottonseed diets should not have caused a problem. Another possibility is that the toxin gossypol present in cottonseed could have been involved. The cottonseed used contained 1.15% total gossypol, a substantially higher level than reported for cottonseed produced in other areas of the country. The level of gossypol consumed by the heifers in the 24% cottonseed diet (18.4 grams/head/day) was near the level known to cause some subclinical toxicity, but depressed feed intake and growth rate have not been reported at this level. Additional research is being conducted to understand the reason for this reduction in feed intake and growth rate. It is recommended that due to the importance of obtaining predictable perfor mance in developing heifers and stocker cattle, cotton seed should be limited to 15% of the diet, or about 2.5 lb/head/day.

Cotton textile mill waste substituted for sorghum silage had no negative effect on performance of these heifers, indicating that it has potential as a feed ingredient in this type of diet. Increasing whole cottonseed decreased gain in diets with or without cotton fiber. The break appeared to occur between 12 and 18% whole cottonseed, and this supports the recommendation of limiting whole cottonseed to 15% of the diet for growing cattle.

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