Urine and fecal excretion patterns of dairy cows divergent for milk urea nitrogen breeding values

Authors: MARSHALL, CAMERON - Lincoln University - New Zealand; Beck, Matthew; GARRETT, K - Lincoln University - New Zealand; BARRELL, GRAHAM - Lincoln University - New Zealand; AL-MARASHDEH, O - Lincoln University - New Zealand; GREGORINO, PABLO - Lincoln University - New Zealand

Submitted to: Journal of Dairy Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/31/2022
Publication Date: 3/10/2022
Citation: Marshall, C.J., Beck, M.R., Garrett, K., Barrell, G.K., Al-Marashdeh, O., Gregorino, P. 2022. Urine and fecal excretion patterns of dairy cows divergent for milk urea nitrogen breeding values. Journal of Dairy Science. 105(5):4218-4236. https://doi.org/10.3168/jds.2021-21490.
DOI: https://doi.org/10.3168/jds.2021-21490

Interpretive Summary: Urinary nitrogen excretion represents a significant source of environmental pollutants in pastoral dairy production systems. Nitrogen deposited on pasture from urination events is a source of nitrous oxide, which is a potent greenhouse gas, ammonia emissions, and nitrate leaching. These sources of pollutants are largely driven by the amount of nitrogen deposited at the urine patch level, so that excretion patterns are important when considering the environmental impacts of pastoral dairy systems. Previous research conducted by scientists from ARS (Bushland, Texas) and Lincoln University (Lincoln, New Zealand) illustrated that cows with a low milk urea nitrogen breeding value have reduced urinary nitrogen concentrations on a daily basis; however, there is a lack of information on the diurnal pattern for urinary nitrogen excretions for cows divergent for a milk urea nitrogen breeding value. Accordingly, scientists from ARS and Lincoln University conducted an experiment with cows that had low or high milk urea nitrogen breeding value to evaluate potential differences in diurnal patterns of urinary nitrogen excretions by capturing each individual urination and fecal events. When low milk urea nitrogen cows were fed a perennial ryegrass diet, they had consistently reduced urinary urea nitrogen concentrations and greater fecal nitrogen concentrations, independent of the time of day. These results suggest a reduced environmental impact of low milk urea nitrogen breeding value dairy cows, and demonstrate the viability of improved animal genetics in reducing environmental impacts from dairy production.

Technical Abstract: Environmental degradation has been attributed to the inefficient use of nitrogen (N) utilization from pastoral dairy production systems, degradation has especially been associated with the urine patch which has been identified as a key component of nitrate leaching to waterways. However, a lack of information exists regarding the pattern of urination events and individual urination characteristics across the day. The aim of this study was therefore to evaluate and report the patterns and characteristics of fecal and urination events throughout the day for cows divergent for milk urea nitrogen breeding values (MUNBV) on either a plantain (Plantago lanceolata L. [PL]) or ryegrass (Lolium perenne L. [RG]) diet. Sixteen multiparous lactating Holstein-Friesian × Jersey cows divergent for MUNBV were housed in metabolism crates for 72 h with all excretion events captured and analyzed. Cows considered low for MUNBV consistently had a 65.2 kg lower urinary urea nitrogen (UUN) load (kg/ha-1) than high MUNBV cows when consuming RG, low loading rates are associated with less N leaching and therefore environmental impact. When cows consumed PL, regardless of MUNBV, they had lower loading rates for UUN across the day, with a different diurnal pattern compared with cows consuming RG. Differences in the diurnal pattern of N excreted in feces was also detected based on MUNBV and by diet, with low MUNBV cows excreting more N in feces for the majority of the day at a varying rate compared with high MUNBV cows when consuming RG. Lower UUN loading rate and more N excreted in feces indicates a potentially lower environmental impact from low MUNBV cows when consuming RG compared with high MUNBV cows. The use of the PL diet also resulted in lower UUN loading rates and greater levels of N excreted in feces compared with RG, therefore also indicating its ability to reduce the environmental impact compared with RG. Differences in the diurnal excretion patterns for both urinary and fecal characteristics based on MUNBV indicate that differences may be occurring as a result of differential rumen function between cows considered divergent for MUNBV on both diets.