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Table 1: Effect of active live yeast on milk production and feed efficiency (Source: Schothorst Feed Research, 2014)


Control


Fat-corrected milk yield (FCM, kg/day)


Butterfat production (kg/day)


Feed efficiency (kg FCM/ kg DMI)


1 Vistacell at 4g/cow/day 2 Vistacell AB = Vistacell at 4g/cow/d + Acid Buf at 88g/cow/day


“The result was a 4% rise in milk fat production from 1.58 to 1.65 kg/ day and a 3% improvement in overall feed conversion efficiency – in terms of kg fat-corrected milk yield per kg dry matter intake – from 1.60 to 1.65,” explains Dr McIlmoyle (see Table 1). “However, such results rely heavily on yeast efficacy, so as


well as ensuring rumen pH is already close to ideal, it’s important to understand the other factors that determine yeast performance. Put simply, not all yeasts are the same, and not all yeasts will reliably and consistently produce a worthwhile return on investment (ROI).”


Understanding yeast differences The most basic yeasts are those which deliver only prebiotic effects, being dead yeast cultures or extracts that contain very few, if any, viable yeast cells. These can bind with pathogens and act as a food source for beneficial microbes within the rumen, but have no activity themselves, which can limit their impact on the rumen environment. In contrast, live yeast remain active after ingestion, and it’s these


live cells that use up excess oxygen and compete for sugars in the rumen as they continue to be metabolically active. Early generation yeasts of this type were typically byproducts of the baking industry, but the latest strains to be introduced have been specifically selected and screened for beneficial effects and survival within the rumen. “Dead yeasts will have some impact, helping lower the risk of


acidosis and reduce the pathogenic load in the rumen and lower gut,” Dr McIlmoyle states. “For example, even cell wall fragments of the Saccharomyces cerevisiae yeast have been shown to bind to pathogens and mycotoxins, whilst also stimulating lactic acid bacteria and the animal’s immune system. “And although intact versions of such yeasts, even if hydrolysed,


can also act as a source of nutrition and metabolites for beneficial rumen microbes, they’re still much less effective than probiotic active live yeasts.”


Differentiating live yeasts And when it comes to assessing the performance of these active yeasts, there are additional factors that need to be considered,


37.1 1.46 1.59


Yeast only 1


38.6 1.58 1.60


Yeast plus conditioner 2


38.9 1.65 1.65


       


      “However, CFU count really is just part of the equation,” he


adds. “Unless the yeast is in a form that can withstand storage, feed manufacture, delivery and ingestion, and remain viable in the rumen, then much of that yeast value can be lost before it has time to act. “The traditional ‘noodle’ form of active yeast is now being


replaced by more tightly packed structures such as round ‘beads’ that offer greater CFU counts with better oxygen scavenging properties and longer shelf life (minimum 12 months). The result is a far more consistent delivery of the necessary number of active yeast cells to produce good results in the rumen.”


“Combining the right strain of active yeast with an effective dose in the rumen is the key to releasing the full potential value yeasts can offer”


Rumen stability is another factor that can vary considerably,


with survivability levels after 24 hours in the rumen ranging from lows of 15% to as high as 37%, depending on the particular yeast chosen. And from a practical perspective, it’s also important to realise that not all active yeasts have multi-species registration, with some requiring multiple products to be stocked to cover the full range of livestock species. “Combining the right strain of active yeast with an effective dose


in the rumen is the key to releasing the full potential value yeasts can offer. The result is a three-pronged approach ‒ reducing detrimental microbial populations, optimising the rumen environment, and directly supporting beneficial microbial activity ‒ that will maximise FCE gains.”


FEED COMPOUNDER MAY/JUNE 2018 PAGE 27  


highlights Dr McIlmoyle. The number of colony forming units (CFU) contained in a single ‘dose’ of yeast, for example, is critical to performance in the rumen (see Figure 3), and can range from as low as 10 billion up to 50 billion CFU in commercial yeast products.


Figure 3: Relationship between active yeast dosage and rumen volatile fatty acid (VFA) production (Source: Desnoyers et al., 2009)


   


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