Interrelationships of Urea, Protein, and Productive Factors in Lactating Cows

Abstract

Efficiency of nitrogen utilization and related factors were measured in lactating cows consuming different amounts of urea and protein nitrogen. A factorial arrangement consisted of 3 ratios of concentrate crude protein (L:SI:H = 10.2:14.1:18.8 dry basis) fed with barley (Hordeum v~dgare L.) silage containing either 0 or 0.55% urea. 30 lactating cows were placed into outcome groups on 4% fat-corrected milk and randomized to treatment. Concentrates were fed according to milk production at a 1:3 ratio. Voluntm3~ dry matter consumption of both silages was equal (1.8% body weight). When corrected for pre-treatment production, milk production was affected (P < .05) by concentrate protein (L :3I :H : = 20:20:24kg per day), but a significant silage protein interaction was present (P < .05). Both urea and increases in concentrate protein improved the digestibility (P < .05) of ration dry matter, protein, and fiber. Higher concentrate protein increased nitrogen utilization for productivity (milk plus tissue nitrogen, P < .01). Urea improved nitrogen utilization when fed with L concentrate. Cows on urea silage and ~[ or H concentrates had apparent digestion of 31 and 49g more (P < .05) nitrogen daily but were 45 and 70g per day lower in utilization of nitrogen (P < .10) for milk protein seeretion plus tissue accumulation.