The objective of this trial was to investigate the effects of partial replacement of sorghum silage and soybean meal with whole cottonseed on microbial protein synthesis and efficiency and nitrogen metabolism in lactating Holstein cows receiving forage cactus based diets. Five animals were randomly assigned to a 5 × 5 Latin square design and were fed diets containing (% of DM): 0.0, 6.25, 12.50, 18.75, and 25.00% of whole cottonseed. Inclusion of whole cottonseed in the diet did not affect microbial nitrogen and microbial protein synthesis, which averaged 295.08 and 1844.27 g/day, respectively. Microbial protein synthesis and microbial nitrogen efficiency decreased linearly by 0.30 and 1.43 g per each 1% inclusion of whole cottonseed in the diet. Urinary urea and concentration of urea and urea-N in plasma and milk were not affected by increasing the levels of dietary whole cottonseed. It can be concluded that the inclusion of up to 25% of whole cottonseed (% of diet DM) had no detrimental effects on microbial protein synthesis and N utilization in lactating cows fed forage cactus based diets.
creatinine; purine derivatives; spot sampling; semi-arid