Date of Award:

5-2001

Document Type:

Thesis

Degree Name:

Master of Science (MS)

Department:

Animal, Dairy, and Veterinary Sciences

Committee Chair(s)

Allen J. Young

Committee

Allen J. Young

Committee

Howard R. Bingham

Committee

Ronald L. Boman

Committee

E. Bruce Godfrey

Abstract

Monthly individual cow DHIA test records (approximately 90,000) from 96 Holstein and Jersey herds from Utah, Idaho, and Montana were analyzed used the Mixed procedure in SAS to determine the relationships of milk production parameters to milk urea N (MUN). Records spanned two consecutive years ending December 2000. Means for Holsteins were 34.1 kg/d milk yield, 15.2 mg/dl MUN, 3.18% milk protein, 3.5% milk fat, and 280,000 somatic cell count. Mean MUN for Holsteins was lowest in fall (Oct.-Dec) and highest in winter and spring. Cows with highest milk protein percent (≥ 3.2%) had lowest MUN over all levels of milk yield. Means for Jerseys were 21.9 kg/d milk yield, 13.7 mg/dl MUN, 3.73% milk protein, 4.6% milk fat, and 329,000 SCC. Mean MUN for Jerseys was lowest in summer and fall (June-Dec), while cows with the highest protein % (≥ 3.8%) did not have significantly different MUN concentrations from groups with lower milk protein %. Mean MUN, by 30 DIM increments, followed a curvilinear shape, similar to a lactation curve. Models suggest that as MUN increases, pregnancy status decreases, especially in Jerseys. Mixed multivariate models showed that milk yield, protein %, month of test, and lactation number were significantly related to MUN concentration, with milk yield having the greatest effect on MUN variation for Holstein cows 979% of sum of squares) and lactation category contributing the most variation in Jerseys (34.1% of sum of squares). Nitrogen utilization and NRC equations predicted the amount of crude protein provided to cows based on milk production variables and MUN concentrations. Ration crude protein % exceeded requirements in some cases. The study data show that MUN may be associated with DHIA production variables and can be used to evaluate CP in rations. It is important to consider production variables, especially milk protein percent, when developing optimal MUN concentrations relative to nutrient requirements under western conditions.

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