D.R. Mertens

Manure nutrient excretion by Jersey and Holstein cows.

The objective of this study was to evaluate feces, urine, and N excretion by Jersey and Holstein cows. Sixteen multiparous cows (n=8 per breed) were fed 2 experimental rations at calving in a switchback experimental design. Diets were 50% forage and based on corn meal (control) or whole cottonseed. Half the cows in each breed started on the control diet and half started on the whole cottonseed diet. Cows were switched to the other diet at 60 d in milk and switched back to their original diet at 165 d in milk. Pairs of cows were moved into open-circuit respiration chambers on d 49, 154, and 271 of lactation for 7-d measurement periods. While in the chambers, total collection of feed refusals, milk, recovered hair, feces, and urine was conducted. No effect of the interaction of diet and breed was observed for measures of nutrient digestibility and manure excretion. Total daily manure excretion was lower in Jersey cows than in Holstein cows, with reductions generally proportional to changes in feed intake. Jersey cows consumed 29% less feed and excreted 33% less wet feces and 28% less urine than Holstein cows. Intake, fecal, and urinary N were reduced by 29, 33, and 24%, respectively, in Jersey cows compared with Holstein cows. Equations from American Society of Agricultural and Biological Engineers underpredicted observed values for all manure measures evaluated (urine, manure solids, N, wet manure), and breed bias was observed in equations predicting excretion of urine, N, and wet manure. Although these equations include animal and dietary factors, intercepts of regression of observed values on predicted values differed between Holsteins and Jerseys for those 3 measures. No breed bias was observed in the prediction of manure solids excretion, however, making that equation equally appropriate for Jerseys and Holsteins. The effect of breed on manure and nutrient excretion has significant nutrient management implications.

Technical note: effect of sample processing procedures on measurement of starch in corn silage and corn grain.

Methods for processing feedstuffs before analysis can affect analytical results. Effects of drying temperature (corn silage), preservation method (corn grain), and grinding method (corn silage and grain) on starch analysis values were evaluated. Corn silage samples dried at 55 or 105 degrees C and grain samples dried at 55 degrees C were ground to pass the 1-mm screen of an abrasion mill or cutting mill and analyzed for free glucose and starch corrected for free glucose. Starch analyses were performed in triplicate to assess the effect of treatment on precision of starch determination. Drying at 105 degrees C decreased free glucose and tended to decrease starch detected in silage. Decreased free glucose and starch values in silages dried at 105 degrees C may have been caused by the destruction of glucose and production of Maillard products through nonenzymatic browning. Maillard products with reducing activity could potentially interfere with the glucose oxidase-peroxidase glucose detection method used. Compared with the cutting mill, grinding samples through the abrasion mill increased the precision of starch measures in silage, likely due to the effect of the finer particle size produced by the abrasion mill allowing more accurate subsampling of a more homogeneous matrix. Starch values were greater for grain ground with an abrasion mill than with a cutting mill, with the difference greater for dry-rolled than for high-moisture corn. For starch analysis of corn silage and corn grain, drying at lower temperatures (55 degrees C) in forced-air ovens and grinding through the 1-mm screen of an abrasion mill or its equivalent is recommended.