|Olmos Colmenero, J|
Submitted to: Journal of Dairy Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/15/2006
Publication Date: 3/1/2007
Citation: Brito, A.F., Broderick, G.A., Olmos Colmenero, J.J., Reynal, S.M. 2007. Effects of feeding formate-treated alfalfa silage or red clover silage on omasal flow of nutrients and microbial protein synthesis in lactating dairy cows. Journal of Dairy Science. 90:1392-1404. Interpretive Summary: A large proportion of the protein in alfalfa is broken down in the silo to nonprotein nitrogen (NPN). This form of nitrogen may be used less efficiently than intact protein. Nonprotein nitrogen formation may lead to increased urinary nitrogen excretion, which can contribute to environmental pollution. Treating ensiled crops with formic acid is widely used in Europe to reduce NPN formation; we found that formic acid-treatment of ensiled alfalfa increased protein yield and reduced urinary nitrogen excretion when that silage was fed to dairy cows. An enzyme naturally present in red clover results in low NPN silage when it is ensiled. Therefore, it seemed possible that red clover silage might be better for dairy cows than alfalfa silage. However, most of the cows protein needs come from protein formed by microbes living in the rumen, the first compartment of the cows stomach and rumen microbes can live and grow using NPN to meet at least part of their needs. The rest of protein that the dairy cow uses comes from dietary protein escaping breakdown by these rumen microbes. We wanted to determine how feeding these silages with different amounts of NPN affected the cow’s protein supply flowing out of the rumen. To accomplish this, we fed 8 dairy cows diets containing one of these 4 silages: 1) normal alfalfa silage, 2) alfalfa silage treated with a solution containing formic acid, 3) red clover silage with the same amount of fiber as the alfalfa, or 4) red clover silage with the same amount of protein as the alfalfa. All of the cows had rumen cannulas (holes made into their rumens by veterinarians using surgery) so digesta flowing out of the rumen could be sampled to measure the protein coming from the microbes and the diet. The cows ate more feed on the 2 alfalfa diets. Although cows fed either red clover silage had more dietary protein escaping the rumen, the amounts of microbial protein and total protein flowing out of the rumen were greater on either alfalfa silage. Also, there were no differences between regular alfalfa silage and the formic acid-treated alfalfa silage, and between the 2 red clover silages. This means that the lowering the NPN in silage, whether as a result of the red clover enzyme or the acid-treatment, did not improve the protein nutrition of the dairy cows in this experiment. This research means that the rumen microbes are able to produce enough protein from silage NPN to make up for at least some of the protein breakdown in the silo. Dairy farmers will be able to use this information when feeding alfalfa silage containing high levels of NPN. Also, there appears to be no advantage in milk production for dairy farmers to feed their cows red clover silage with low NPN rather than alfalfa silage.
Technical Abstract: Eight ruminally cannulated Holstein cows that were part of a larger lactation trial were blocked by days in milk and randomly assigned to replicated 4 x 4 Latin squares to quantify effects of nonprotein N (NPN) content of alfalfa silage (AS) and red clover silage (RCS) on omasal nutrient flows. Diets, fed as total mixed rations, contained 50% dry matter from control AS (CAS), ammonium tetraformate-treated AS (TAS), late maturity RCS (RCS1), or early maturity RCS (RCS2). The CAS, TAS, and RCS2 diets had 36% high-moisture shelled corn and 3% solvent soybean mean and the RCS1 diet had 31% high-moisture shelled corn and 9% solvent soybean mean. All diets contained 10% corn silage, 27% neutral detergent fiber, and 17-18% crude protein. Silages differed in NPN and acid detergent insoluble N (% of total N): 50 and 4% (CAS); 45 and 3% (TAS); 27 and 8% (RCS1); 29 and 4% (RCS2). Omasal flow of microbial nonammonia N (NAN), measured using 15N, averaged 69 g/d higher on cows fed AS versus RCS but no differences were observed within AS or RCS diets. Rumen-degraded protein was higher on AS; however, dietary NAN flow at the omasum was 34% higher on RCS. The NRC (2001) model predicted microbial NAN flows that averaged 26% less than those measured using 15N. Except for Arg, omasal flows of individual AA, branched-chain AA, non-essential AA, essential AA, and total AA did not differ in cows fed AS versus RCS. Within AS diets, no differences in omasal flows of any AA fractions were observed. However, omasal flows of Asp, Ser, Glu, Cys, Val, Ile, Tyr, Lys, non-essential AA, and total AA all were higher in cows fed RCS1 versus cows fed RCS2. In this trial, there was no advantage to reducing NPN content of hay-crop silage. Feeding AS diets gave rise to greater supply of rumen-degraded protein and microbial NAN than feeding RCS diets, and also resulted in improved milk yield in a companion study.