E. T. Lyatuu
M. L. Eastridge 1
The Ohio State University Department of Animal Sciences
Twelve Holstein dairy herds in Ohio were visited once, and 25% of the lactating cows in each herd were randomly selected for data collection. Blood and milk were sampled approximately four hours postfeeding. Many of the feeds and feed mixtures used on the farms were sampled and analyzed for chemical composition. Nutritional factors were found to be more important than genetics in accounting for variations in milk production, milk composition, milk urea nitrogen, and plasma urea nitrogen values. Nutrient intake was observed to provide better correlation estimates on these variables than nutrient content in diets. Milk protein yield was more responsive to dietary differences than milk protein percentage. The interaction between intakes of neutral detergent fiber (NDF) and nonfiber carbohydrates (NFC) was the most important factor accounting for the variation in milk protein yield, explaining 58% of the variation. The mean plasma urea nitrogen (PUN) concentration (13.4 ± 0.2 mg/dl) was higher than mean milk urea nitrogen (MUN) concentration (12.4 ± 0.2 mg/dl). The regression of milk urea nitrogen on plasma urea nitrogen resulted in the following relationship: MUN = 3.62 + (0.65 x PUN) (R2 = 0.73). Further regression analysis showed that both plasma and milk urea nitrogen concentrations were affected by ration composition and intakes of various dietary components. Dietary intake of crude protein (CP) was found to explain 16% of the variation observed in milk urea nitrogen concentration, while the squared term for fatty acid (FA) intake explained 11% of the variation. The concentrations of urea nitrogen in milk and plasma can be used to monitor feeding programs on dairy farms and thus used to improve management of the nutrition program. This provides another tool to dairy farmers for minimizing feed costs while maximizing production.
1For more information, contact at: The Ohio State University, 221B Animal Science Building, 2029 Fyffe Road, Columbus, OH 43210-1095; 614-688-3059; fax: 614-292-1515; e-mail: eastridge.1@osu.edu