Dairy cows with different milk urea nitrogen breeding values display different grazing behaviours

Authors: MARSHALL, C - Lincoln University - New Zealand; Beck, Matthew; GARRETT, K - Lincoln University - New Zealand; FLEMING, A - Lincoln University - New Zealand; BARRELL, G - Lincoln University - New Zealand; AL-MARASHDEH, O - Lincoln University - New Zealand; GREGORINI, P - Lincoln University - New Zealand

Submitted to: Applied Animal Behaviour Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/23/2021
Publication Date: 8/24/2021
Citation: Marshall, C.J., Beck, M.R., Garrett, K., Fleming, A.E., Barrell, G.K., Al-Marashdeh, O., Gregorini, P. 2021. Dairy cows with different milk urea nitrogen breeding values display different grazing behaviours. Applied Animal Behaviour Science. 242. Article 105429. https://doi.org/10.1016/j.applanim.2021.105429.
DOI: https://doi.org/10.1016/j.applanim.2021.105429

Interpretive Summary: Urinary nitrogen excretion by cattle represents a significant source of environmental pollution through nitrate leaching and greenhouse gas emissions. Milk urea nitrogen concentration of dairy cows is a strong indicator of urine nitrogen excretion. There has been a breeding value established for milk urea nitrogen concentration. Recent research from ARS in Bushland, Texas, and Lincoln University (Lincoln, New Zealand) has demonstrated the ability of the milk urea nitrogen breeding value to identify animals that do excrete less urinary nitrogen and had greater ruminal microbial production. There is the possibility that these animals have phenotypic difference in milk urea nitrogen due to behavioral differences, yet this potential had not been explored. Accordingly, researchers from ARS in Bushland, Texas, and Lincoln University conducted an experiment to determine how the milk urea nitrogen breeding value was associated with grazing behavior of dairy cows. It was determined that cows with a low milk urea nitrogen breeding value had a different grazing behavior than cows with a high breeding value. The low milk urea nitrogen breeding value cows had greater chews per bite, which may have resulted in smaller particles entering the rumen, and therefore more incorporation of consumed nitrogen as microbes. These results may explain the previously reported lower urine nitrogen excretion and greater microbial production among cattle having low milk urea nitrogen breeding value. This information is of interest to other animal scientists, cattle breeders and farmers trying to better match nitrogen intake with its use to decrease fecal and urine output.

Technical Abstract: The objective of this study was to describe the diurnal pattern of grazing behavior of multi-parous dairy cows divergent for milk urea N breeding values (MUNBV) and the consistency of these differences across different sward compositions (perennial ryegrass [RG; Lolium perenne L.] or ryegrass with plantain [Plantago lanceolata L.; RGPL]) and stages of lactation (early and late lactation). Jaw movement recorders were fitted to 24 animals in early lactation and 16 cows in late lactation, in early lactation 12 cows were assigned to the ryegrass diet and 12 cows assigned to the plantain diet, in late lactation 8 cows were assigned to ryegrass with the remaining cows assigned to the plantain diet. For each diet half of the animals during both stages of lactation were classified as high for MUNBV and the other half as low for MUNBV. Low MUNBV animals had more mastications per bite over the day (P < 0.01) with a one-unit decrease in MUNBV result in 0.07 more bites per mastication during the first two grazing bouts, as well as differences in the temporal distribution of grazing bouts compared with high MUNBV cows. A one-unit decrease in MUNBV resulted in a 0.11 ± 0.02 increase in mastications per bite during the first grazing bout across both stages of lactation and sward composition. Ingestive behavior has a large impact on the physical features of ingesta and thereby rumen function. The results of this study indicate that dairy cows divergent for MUNBV grazing the same forage apply different grazing strategies in terms of oral processing of ingesta and diurnal meal pattern. These results present potential explanatory variables for phenotypical differences observed in dairy cows divergent for MUNBV.