Holstein cattle have been selectively bred for their high milk production. The seed of the cotton plant, Gossypium spp. is a good source of fibre, protein and carbohydrate. To improve milk production, whole cottonseed or cottonseed meal can be added to livestock feed. Cottonseed meal is cottonseed that has been processed by grinding. [Figure 2.1] Free gossypol is a toxin found in cotton seeds. Some of this free gossypol binds to protein to form bound gossypol. This occurs during cottonseed meal production and in the rumen (forestomach) of the cow during microorganism fermentation. Free gossypol is easily absorbed. Bound gossypol is absorbed less easily and is not toxic. An investigation was carried out on the effect of different dry-matter diets on lactating (milk-producing) Holstein cows: • 30 healthy cows were fed on the same cottonseed-free diet for 14 days. • The cows were then divided equally into five groups, A to E, and fed on one of five experimental diets for 42 days. • The quantity of milk produced each day was recorded. • The cows had no visible signs of illness during the 42 days. For each diet, Table 2.1 shows: • the cottonseed content and total gossypol (free and bound) content • the mean daily dry matter taken in during feeding (intake) • the mean daily lactation performance (milk yield). [Table 2.1] SE = standard error | group | description of dry matter diet | cottonseed content/percentage of dry matter | total gossypol in diet/mg kg⁻¹ | dry matter intake kg d⁻¹ SE = 1.4 | milk yield/kg d⁻¹ SE = 1.3 | |-------|--------------------------------------------|----------------------------|-----------------------------|---------------------------------|---------------------------| | | | whole cottonseed | cottonseed meal | | | | A | cottonseed replaced by soybean meal | 0 | 0 | 0 | 24.8 | 27.6 | | B | whole cottonseed | 15.0 | 0 | 1039.7 | 23.6 | 29.7 | | C | cottonseed meal | 0 | 7.0 | 900.1 | 23.2 | 27.9 | | D | mixed 1 (whole cottonseed and cottonseed meal) | 7.5 | 3.5 | 959.7 | 22.6 | 28.7 | | E | mixed 2 (whole cottonseed and cottonseed meal) | 15.0 | 7.0 | 1922.0 | 24.0 | 32.6 | The differences in the dry matter intake for groups A to E were not statistically significant.