Aflatoxins are poisonous carcinogens produced by fungi, mainly Aspergillus flavus and Aspergillus parasiticus. Aflatoxins can contaminate a variety of livestock feeds and cause enormous economic losses, estimated at between US$52.1 and US$1.68 billion annually for the U.S. corn industry alone. In addition, aflatoxin can be transferred from the diet to the milk of cows as aflatoxin M1 (AFM1), posing a significant human health hazard. In dairy cows, sheep and goats, chronic exposure to dietary aflatoxin can reduce milk production, impair reproduction and liver function, compromise immune function, and increase susceptibility to diseases; hence, strategies to lower aflatoxin contamination of feeds and to prevent or reduce the transfer of the toxin to milk are required for safeguarding animal and human health and improving the safety of dairy products and profitability of the dairy industry. This article provides an overview of the toxicity of aflatoxin to ruminant livestock, its occurrence in livestock feeds, and the effectiveness of different strategies for preventing and mitigating aflatoxin contamination of feeds.

The study objective was to evaluate the effects of sustained reduction of enteric methane (CH₄) emissions with dietary supplementation of the inhibitor 3-nitrooxypropanol (NOP) on growth rate and feed conversion efficiency of growing and finishing beef cattle. Eighty-four crossbred steers were used in a 238-d feeding study and fed a backgrounding diet for the first 105 d (backgrounding phase) and transition diets for 28 d followed by a finishing diet for 105 d (finishing phase) with 3 doses of NOP (0, 100, and 200 mg/kg DM). The experiment was a completely randomized design using 21 pens (4 cattle/pen) with 7 pens per treatment. When cattle were fed the backgrounding diet, pen DMI was reduced (P < 0.01) whereas G:F tended to improve (P = 0.06) with increasing dose of NOP supplementation. During the finishing phase, DMI (P = 0.06) and ADG (P = 0.07) tended to decrease with increasing dose of NOP supplementation. Although both levels of NOP were effective in reducing CH₄ emissions from the backgrounding diet (P < 0.01), only NOP supplemented at the highest dose was effective in reducing total CH₄ emissions from the finishing diet (P < 0.01). Methane yield (g/kg DMI) was reduced whereas hydrogen emissions were increased at the highest dose of NOP supplementation with both backgrounding and finishing diets (P < 0.01). Overall, these results demonstrate efficacy of NOP in reducing enteric CH₄ emissions from cattle fed backgrounding and finishing diets, and these effects were negated once NOP supplementation was discontinued.

Objective. To summarize the recent studies on effect of conjugated linoleic acid (CLA) on hepatic steatosis and hepatic and adipose lipid metabolism highlighting the potential regulatory mechanisms.Methods. Sixty-four published experiments were summarized in whichtrans-10,cis-12 CLA was fed either alone or in combination with other CLA isomers to mice, rats, hamsters, and humans were compared.Summary and Conclusions. Dietarytrans-10,cis-12 CLA induces a severe hepatic steatosis in mice with a more muted response in other species. Regardless of species, when hepatic steatosis was present, a concurrent decrease in body adiposity was observed, suggesting that hepatic lipid accumulation is a result of uptake of mobilized fatty acids (FA) from adipose tissue and the liver's inability to sufficiently increase FA oxidation and export of synthesized triglycerides. The potential role of liver FA composition, insulin secretion and sensitivity, adipokine, and inflammatory responses are discussed as potential mechanisms behind CLA-induced hepatic steatosis.

A meta-analysis of 158 peer-reviewed articles was conducted to examine effects of inoculation with Lactobacillus buchneri (LB)-based inoculants (LBB) that did or did not include homolactic or obligate heterolactic bacteria on silage fermentation and aerobic stability. A complementary meta-analysis of 12 articles examined LBB inoculation effects on dairy cow performance. Raw mean differences between inoculant and control treatment means weighted by inverse variance were compared with a hierarchical effects model that included robust variance estimation. Meta-regression and subgrouping analysis were used to identify effects of covariates including forage type, application rate (≤104, 105, 106, or ≥ 107 cfu/g as fed), bacteria type (LB vs. LB plus other bacteria), enzyme inclusion, ensiling duration, and silo type (laboratory or farm scale). Inoculation with LBB increased acetate (62%), 1, 2 propanediol (364%) and propionate (30%) concentration and aerobic stability (73.8%) and reduced lactate concentration (7.2%), yeast counts (7-fold) and mold counts (3-fold). Feeding inoculated silage did not affect milk yield, dry matter intake, and feed efficiency in lactating dairy cows. However, forage type, inoculant composition, and dose effects on silage quality measures were evident. Inoculation with LBB increased aerobic stability of all silages except tropical grasses. Adding obligate homolactic or facultative heterolactic bacteria to LB prevented the small increase in DM losses caused by LB alone. The 105 and 106 cfu/g rates were most effective at minimizing DM losses while aerobic stability was only increased with 105, 106, and ≥ 107 cfu/g rates. Inoculation with LBB increased acetate concentration, reduced yeast counts and improved aerobic stability but did not improve dairy cow performance.

Previous reports on milk protein responses to AA supplementation focused on Lys and Met concentrations expressed as a percentage of metabolizable protein, not the amounts of AA supplied. The objective of this study was to quantify the milk protein yield (MPY; g/d) response in studies in which Met or Lys was supplied either by postruminal infusion or in a rumen-protected form. A meta-analysis using a logistic regression model fitted using nonlinear mixed model procedures was performed on results from 23 published studies involving postruminal supplementation of Lys (18 experiments) and Met (35 experiments) in lactating dairy cows. Variance caused by study effect was removed by designation of individual study as subject within the random component within the nonlinear model. Milk protein responses to supplemental Met decreased from 16 to 4 g of milk protein per gram of metabolizable Met intake as Met intake varied from 25 to 70 g per cow per day. Similarly, milk protein responses to supplemental Lys decreased from 5.0 to 3.2 g of milk protein per gram of metabolizable Lys intake as Lys intake varied from 80 to 203 g per cow per day. Assuming Met and Lys concentrations of 2.76 and 7.63 g/100 g of milk protein, respectively, the implied marginal efficiencies of metabolizable AA use for MPY decreased from 44 to 12% for Met and from 39 to 25% for Lys over the range of metabolizable AA intakes. Although the estimated efficiencies were low compared with previous estimates, a low marginal efficiency of amino acid utilization would be expected when amino acid supply is at or near to the animal's requirement, as was the case in these experiments. This suggests that current models that assume both a constant MPY response and constant AA utilization efficiency are inadequate. Models that assume a constant efficiency of AA use will overestimate production responses to individual AA supply, especially when high amounts of metabolizable AA are fed.

The study addressed the importance of yeast (Saccharomyces cerevisiae) viability for reducing the incidence of subacute ruminal acidosis (SARA) and improving total tract nutrient digestibility in beef heifers. Six ruminally cannulated beef heifers (680 ± 50 kg BW) were used in a replicated 3 × 3 Latin square design and were fed a diet consisting of 40% barley silage, 10% chopped grass hay, and 50% barley grain-based concentrate (DM basis). Treatments were 1) no yeast (Control), 2) active dried yeast (ADY; 4 g providing 10¹⁰ cfu/g; AB Vista, Marlborough, UK), and 3) killed dried yeast (KDY; 4 g autoclaved ADY). The treatments were directly dosed via the ruminal cannula daily at the time of feeding. The periods consisted of 2 wk of adaptation (d 1 to 14) and 7 d of measurements (d 15 to 21). Ruminal pH was continuously measured (d 15 to 21) using an indwelling system. Ruminal contents were sampled on d 15 and 17 at 0, 3, 6, 9, and 12 h after feeding. Total tract nutrient digestibility was measured using an external marker (YbCl₃) from d 15 to 19. No treatment difference was observed for DMI (P = 0.86). Yeast supplementation (ADY and KDY) tended to increase total tract digestibility of starch (P = 0.07) whereas no effects were observed on digestibility of other nutrients. Both ADY and KDY elevated minimum (P < 0.01) and mean ruminal pH (P = 0.02) whereas no effects were observed on maximum pH (P = 0.12). Irrespective of its viability, yeast supplementation was effective in reducing time that ruminal pH was below 5.8 (P < 0.01) and 5.6 (P < 0.01). No treatment differences were observed for the ruminal VFA profile and lactate concentration. No treatment differences were observed on the relative population size of Streptococcus bovis, Fibrobacter succinogenes, and Megasphaera elsdenii (P > 0.10); however, the proportion of Ruminococcus flavefaciens in solid fraction of digesta was greater with KDY (P = 0.05). The study demonstrates the positive effects of yeast, irrespective of its viability, in reducing the severity of SARA. However, further studies are required to evaluate the importance of yeast viability for other dietary conditions, particularly when the risk of acidosis is high. Copyright © 2014. American Society of Animal Science .