COW HEAL ▶▶▶TH


A balanced diet is key for a healthy rumen


The rumen is the most influential site of digestion, and microbial fermentation provides much of the energy needed to maintain body condition, pregnancy and lactation. Feeding the rumen microbes and stabilising the rumen environment is therefore key.


BY DR HELEN WARREN, EUROPEAN TECHNICAL MANAGER FOR RUMINANTS, ALLTECH T


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1 Heifers 30 Cows ▶ DAIRY GLOBAL | Volume 5, No. 4, 2018 All lactations Control Yea-Sacc


he rumen ecosystem is made up of four groups of microbes: bacteria, protozoa, fungi and archaea. There also exist some bacteriophages, mycoplas- mas and archaeophages (Tapio et al., 2017). In


terms of numbers, bacteria are by far the most abundant (Kim et al., 2011) at 1010–1011 cells/ml, followed by archaea (106–108 cells/ml), protozoa (105 cells/ml) and fungi (103–105 cells/ml). Bacteria comprise around two thirds of the rumen microbial biomass, with protozoa mak- ing up to 50% (Tymensen et al., 2012) due mainly to their size. This microbial ecosystem generates sources of energy, nitrogen and other nutrients via the breakdown of dietary ingredients. Volatile fatty acids (VFA) are the end-product of bacterial fermentation of carbohydrates and are absorbed across the rumen wall as the primary energy source for the ruminant. It is well-established that diets high in soluble car- bohydrates (starch and sugar) can lead to over-production of


Figure 1 - Effect of dietary inclusion of live yeast on feed efficiency (kg FECM/kg DMI) in Holstein dairy cows (adapted from Steingass et al., 2007).


VFA, particularly propionate and lactate, and also, ultimately, to a drop in rumen pH and sub-acute acidosis (SARA) and/or acute acidosis. Cellulolytic bacteria operate within a narrow pH range (above 6.0; Russell and Wilson, 1996) and can only survive for a relatively short time below this range before their growth and activity are compromised. Thus, fibre diges- tion is inhibited if rumen pH remains low for long periods. Sub-acute ruminal acidosis is a complex metabolic condition in the cow involving low ruminal pH for prolonged periods of time. It has been referred to as a pH drop below 5.5 for an ex- tended time (Plaizier, 2008). There is no consensus threshold pH value that is a definitive diagnosis of this syndrome, and SARA is not simply an acidic rumen environment but also highly dependent on the rumen VFA. Thus, it is not only a pH-dependent pathology, it is also the result of changes in the microbial population secondary to the type of diet fed (Calsamiglia, 2010).


Diet should be balanced Rumen bacteria have varying requirements for protein sources. The fibre digesters have an almost exclusive require- ment for soluble nitrogen, i.e., ammonia. For the microbes to effectively use this nitrogen source, they require energy, and this energy is provided in the form of fermentable carbohy- drates. Synchrony between soluble nitrogen and energy sup- ply has long been the subject of ruminant diet formulation in many sectors, with the aim of avoiding periods of excess or deficiency in nitrogen supply. Even with total mixed ration (TMR) feeding, there are periods of excess followed by peri- ods of deficiency of rumen ammonia levels. This is particular- ly evident when the diet is supplemented with urea. Excess rumen ammonia is wasteful and can lead to elevated blood urea nitrogen (BUN) and, subsequently, milk urea nitrogen (MUN) levels. An oversupply of rumen ammonia can also de- rive from overfeeding dietary protein. Diets are still often be- ing formulated to 18 or 19% crude protein, even though re- cent research has demonstrated that, provided the diet is correctly balanced, this is unnecessary and can have a detri- mental effect on performance. The deamination and metab- olism of excess protein results in an energy cost to the ani- mal that could exacerbate situations like negative energy balance (NEB) in fresh cows. Increasing NEB in fresh cows can also impact circulating progesterone levels, resulting in


Feed efficiency (kg FECM/kg DMI)


PHOTO: SHUTTERSTOCK


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