Nitrogen balance of dairy cows divergent for milk urea nitrogen consuming either plantain or perennial ryegrass

Authors: MARSHALL, CAMERON - Lincoln University - New Zealand; Beck, Matthew; GARRETT, KONAGH - Lincoln University - New Zealand; BARRELL, GRAHAM - Lincoln University - New Zealand; AL-MARASHDEH, OMAR - Lincoln University - Australia; GREGORINI, PABLO - Lincoln University - New Zealand

Submitted to: Animals
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/20/2021
Publication Date: 8/22/2021
Citation: Marshall, C.J., Beck, M.R., Garrett, K., Barrell, G.K., Al-Marashdeh, O., Gregorini, P. 2021. Nitrogen balance of dairy cows divergent for milk urea nitrogen consuming either plantain or perennial ryegrass. Animals. 11(8). Article 2464. https://doi.org/10.3390/ani11082464.
DOI: https://doi.org/10.3390/ani11082464

Interpretive Summary: The excretion of nitrogen in urine by cattle poses considerable environmental concerns associated with leaching and greenhouse gas emissions. A dairy cow’s milk urea nitrogen concentration has been identified as a strong indicator of urine nitrogen excretion. A breeding value has been established for milk urea nitrogen concentrations. However, the relationship between the breeding value and absolute urine nitrogen excretion amounts by grazing dairy cows and ruminal microbial efficiencies have not been established. As such, scientists from ARS in Bushland, Texas, in conjunction with scientists at the Lincoln University (Lincoln, New Zealand) conducted a metabolism study using cows divergent for a milk urea nitrogen breeding value. It was determined that cows with a low milk urea nitrogen breeding value had a 28% reduction in urinary nitrogen excretion per urination event and had 16% greater microbial crude protein production relative to cows with a high milk urea nitrogen breeding value. These results suggest that dairy cows can be selected based on phenotypic differences in their milk urea nitrogen concentrations to reduce environmental impacts while increasing ruminal production of microbes, which may be associated with greater production.

Technical Abstract: Inefficient nitrogen (N) use from pastoral dairy production systems has resulted in environmental degradation, as a result of excessive concentrations of urinary N excretion leaching into waterways and N2O emissions from urination events into the atmosphere. The objectives of this study were to measure and evaluate the total N balance of lactating dairy cows selected for milk urea N concentration breeding values (MUNBVs) consuming either a 100% perennial ryegrass (Lolium perenne L.) or 100% plantain (Plantago lanceolata L.) diet. Sixteen multiparous lactating Holstein Friesian × Jersey cows divergent for MUNBV were housed in metabolism crates for 72 h, where intake and excretions were collected and measured. No effect of MUNBV was detected for total N excretion; however, different excretion characteristics were detected, per urination event. Low MUNBV cows had a 28% reduction in the concentration of urinary urea nitrogen (g/event) compared to high MUNBV cows when consuming a ryegrass diet. Cows consuming plantain regardless of their MUNBV value had a 62% and 48% reduction in urinary urea nitrogen (g/event) compared to high and low MUNBV cows consuming ryegrass, respectively. Cows consuming plantain also partitioned more N into feces. These results suggest that breeding for low MUNBV cows on ryegrass diets and the use of a plantain diet will reduce urinary urea nitrogen loading rates and therefore estimated nitrate leaching values, thus reducing the environmental impact of pastoral dairy production systems.