|Valadares, R F - UNIV FED DE VICOSA-BRAZIL|
|Valadares Filho, S C - UNIV FED DE VICOSA-BRAZIL|
|Clayton, M K - UNIV OF WISCONSIN-MADISON|
Submitted to: Journal of Dairy Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: May 11, 1999
Publication Date: N/A
Interpretive Summary: Alfalfa silage is one of the most common forages fed to dairy cows in the U.S.; however, when alfalfa is put in the silo, more than half of its protein is broken down to nonprotein nitrogen. Utilization of nonprotein nitrogen is stimulated by feeding extra energy in the form of grains such as high moisture corn. However, if too much grain is fed, dairy cows suffer from "acid stomach" because excessive acid is produced during digestion in the rumen (the first compartment of the cow's stomach). Dairy cows require forage fiber in their diets to prevent over-production of acid formation in the rumen; however, the optimum balance between alfalfa silage and high moisture corn is unknown. The objective of this trial was to find the best level of grain (high moisture corn) to feed with forage (alfalfa silage) to get the greatest production of milk and milk components. A total of 24 dairy cows were fed four diets: 1) 20% grain and 80% alfalfa silage, 2) 35% grain and 65% alfalfa silage, 3) 50% grain and 50% alfalfa silage, or 4) 65% grain and 35% alfalfa silage. These diets also were balanced for protein. Amount of milk and milk components produced by cows fed each diet was measured and a mathematical method used to identify the grain level that gave maximum yield. Cows produced the most milk fat when the diet contained 43% grain and produced the most milk at 57% grain but yield of milk protein and milk sugar was still increasing at 65% grain (the highest level fed in the trial). Thus, the "optimum" grain level differs for producing different milk components. Farmers can use this information to determine how much grain to feed with alfalfa silage to get maximum yield of milk and milk fat. However, recommendations can not yet be made about alfalfa silage and grain feeding for maximum protein yield.
Technical Abstract: Twenty-four multiparous dairy cows, including eight with ruminal cannulae, were blocked by days in milk and assigned to treatment sequences in one of six 4X4 Latin squares with 21-d periods. Diets were formulated from alfalfa silage plus a concentrate mix based on ground high moisture ear corn, solvent soybean meal and urea. Diets fed in the trial contained (dry matter rbasis): 1) 20% concentrate, 80% alfalfa silage, 2) 35% concentrate, 65% alfalfa silage, 3) 50% concentrate, 50% alfalfa silage, or 4) 65% concentrate, 35% alfalfa silage. Diets were isonitrogenous with NPN at 43% of total N. Total urine collection was made using indwelling Folley catheters for 24-h during each period. Urinary creatinine excretion averaged 29.0 mg/kg BW/d. [There were significant quadratic effects on total urinary excretion of allantoin, uric acid, and purine derivatives (allantoin plus uric acid), and on ruminal synthesis of microbial N (estimated from purine derivatives)]. The maximum response occurred about 48% dietary concentrate. Daily urinary excretion was estimated using spot urine samples from creatinine concentration and the mean daily creatinine excretion. Daily excretion of allantoin, uric acid and purine derivatives estimated from spot urine sampling followed the same pattern as that observed using total collection. Milk allantoin secretion increased linearly with concentrate level and accounted for 4.2 to 5.7% of the total purine derivative excretion. It was concluded that spot urine sampling will yield satisfactory estimates of purine derivative excretion when creatinine is used to quantify urine volume. Maximal microbial yield was observed at 48% dietary concentrate, suggesting this was the optimal level needed to maximize utilization of dietary NPN from alfalfa silage and other sources.