Bioavailability of aflatoxin B1 and ochratoxin A, but not fumonisin B1 or deoxynivalenol, is increased in starch-induced low ruminal pH in nonlactating dairy cows.

High-production dairy and beef systems require diets rich in starch. This practice may induce ruminal acidosis and also increase exposure to mycotoxins because starches in starch-rich diets are the main vehicles of mycotoxin contamination. The aim of this study was to investigate the effects of low ruminal pH on the bioavailability of 4 major mycotoxins [i.e., aflatoxin B1 (AFB1), ochratoxin A (OTA), deoxynivalenol (DON), and fumonisin B1 (FB1)]. Eight nonlactating dairy cows fitted with rumen cannulas were used in a double crossover experiment. The trial was divided into 4 periods with 2 periods per crossover. Cows were divided into 2 groups receiving a low (15% dry matter basis) and high-starch diet (30.8%) with and without live yeast supplementation (1×1010 cfu per cow) in the first and second crossover, respectively. At the end of each period, cows received a single dose of mycotoxin-contaminated feed containing 0.05, 0.2, 0.24, and 0.56mg of AFB1, OTA, DON, and FB1 per kg of feed, respectively. The fecal and urinary excretion of mycotoxins and their metabolites was monitored for up to 48h postdosing. As expected, ruminal pH decreased in cows fed the high-starch diet. The high-starch diet increased the bioavailability of OTA and AFB1. Urinary excretion of OTA 24h after mycotoxin administration increased 3-fold in the high-starch diet, correlated with lower fecal excretion. Similarly, a decrease in fecal excretion of AFB1 was accompanied by an increase in urinary excretion of its major metabolite, aflatoxin M1, 48h after mycotoxin administration. In contrast to AFB1 and OTA, the bioavailability of DON and FB1 remained unchanged. Yeast supplementation had no effect on the excretion balance of these 2 mycotoxins. In conclusion, these results show that high-starch diets increased the bioavailability of OTA and AFB1, most probably through the lowering effect on ruminal pH. This greater bioavailability potentially increases the toxic effects of these mycotoxins.

Screening tests of the protein quality of grain legumes for poultry production.

Three screening tests for protein quality, modified limiting amino acid score (MLAAS), net weight gain (NWG) and net protein ratio (NPR), were compared. Two experiments using young broiler chickens were conducted in a temperature-controlled room at 28.5 +/- 0.5 degrees with no adaptation to cages and diets, or at 31 +/- 0.5 degrees with 2 d adaptation to cages and diets. Nine isoenergetic diets containing nominally 100 g crude protein/kg supplied by legume meals and one isoenergetic N-free diet were randomly allocated to chicks in single cages in each side of a four-tier battery brooder. Each dietary treatment had eight replicates. The chickens had access ad lib. to diet and drinking water throughout a 14 d observation period. Body weight and feed were measured at the start on day 7 and at the end on day 21. The results indicated that keeping the chickens at 31 +/- 0.5 degrees and giving them a 2 d adaptation period decreased the variability of chickens' responses to each treatment. MLAAS, NWG and NPR methods could distinguish legume proteins of high, medium and low feed values. MLAAS correlated well with NWG (r 0.90; P < 0.001) and NPR (r 0.78; P < 0.01) in evaluating the protein quality of grain legumes used as sole sources of protein for meat chickens. However, MLAAS did not predict the exact order of NWG and NPR. Growth was limited because dietary methionine, the first limiting amino acid, provided only 27.6-55.2% of the recommended proportion in the protein. Although the results should be interpreted cautiously since a small sample size was used, it was concluded that the MLAAS calculation could be used as a reasonable estimate of the relative protein quality of most grain legumes, but that NWG and NPR were better methods as they detected limiting factors other than limiting amino acids in raw and processed legumes.