Diurnal Concentration of Urinary Nitrogen and Rumen Ammonia Are Modified by Timing and Mass of Herbage Allocation

Abstract

Simple SummaryLow nitrogen use efficiency in grazing dairy cows leads to high urinary N excretion, which contributes to greenhouse gases emission. This problem has been associated with high N and low energy intake, increasing rumen ammonia (NH3) concentration, and thereby, increasing urinary N excretion. Under this situation, it is important to discover nutritional and grazing management strategies that allow reduced urine N excretion in the pasture. This study evaluated whether changes in time of herbage allocation and herbage mass modify the diurnal pattern of urinary nitrogen (N) concentration and ruminal NH3 of lactating dairy cows. We found that the combination of time of herbage allocation and herbage mass modified rumen NH3 production and urinary N concentration. Results suggest that maintaining cows in the holding pen at the milking parlor for two hours after morning and afternoon milking could allow collection of urine from cows in the slurry pit during peak N concentration, returning cows to the pasture at a time of day when urinary N concentration is decreased.AbstractThe objective of this work was to evaluate whether changes in time of herbage allocation and herbage mass (HM) (low (L) or medium (M)) modify the diurnal pattern of urinary nitrogen (N) concentration and ruminal ammonia (NH3) of lactating dairy cows. Four Holstein-Friesian cows fitted with rumen cannula were randomly allocated to one of four treatments: 1) low herbage mass in the morning (L-AM) (Access to new herbage allocation after morning milking with a herbage mass (HM) of 2000 kg DM/ha); 2) low herbage mass in the afternoon (L-PM) (Access to new herbage allocation after afternoon milking with a HM of 2000 kg DM/ha); 3) medium herbage mass in the morning (M-AM) (Access to new herbage allocation after morning milking with a HM of 3000 kg DM/ha); and 4) medium herbage mass in the afternoon (M-PM) (Access to new herbage allocation after afternoon milking with a HM of 3000 kg DM/ha). A four by four Latin Square design with four treatments, four cows, and four experimental periods was used to evaluate treatment effects. Rumen NH3 concentration was greater for L-AM compared to L-PM and M-PM at 13:00 and 16:00 h. Urine urea and N concentrations were lower for M-AM compared to L-AM. Urine N concentration was greater for L-AM than other treatments at 10:00 hours and greater for M-PM compared to M-AM at 16:00 hours. Results suggest that maintaining the cows in the holding pen at the milking parlor for two hours after morning grass silage supplementation for L-AM and for two hours after afternoon grass silage supplementation for M-PM, could allow collection of urine from cows at the holding pen and storage of urine in the slurry pit during the time of peak N concentration, returning cows to the pasture at a time of day when urinary N concentration is decreased.

Urine and fecal excretion patterns of dairy cows divergent for milk urea nitrogen breeding values consuming either a plantain or ryegrass diet

“…Similar peaks in concentration have been reported previously for grazing dairy cows by Cosgrove et al (2017) and Beltran et al (2019). The pattern of UUN excretion from cows consuming the RG diet can be associated with the time it takes for protein in the feed to be catabolized and converted to NH 3 in the rumen (Ueda et al, 2016), absorbed into the blood and detoxified by ureagenesis in the liver, and then excreted in urine (Olmos Colmenero and Broderick, 2006;Cosgrove et al, 2017;Beltran et al, 2019). As the UUN concentration is related to rumen NH 3 concentration, a difference in rumen NH 3 based on MUNBV in cows fed a ryegrass diet would be expected; however, prior studies have reported no differences in rumen NH 3 concentrations by MUNBV (Marshall et al, 2020(Marshall et al, , 2021a.…”

“…Cows of both high and low MUNBV consuming the RG diet exhibited a peak in UUN concentration 2 to 3 h after feed allocation. Similar peaks in concentration have been reported previously for grazing dairy cows by Cosgrove et al (2017) and Beltran et al (2019). The pattern of UUN excretion from cows consuming the RG diet can be associated with the time it takes for protein in the feed to be catabolized and converted to NH 3 in the rumen (Ueda et al, 2016), absorbed into the blood and detoxified by ureagenesis in the liver, and then excreted in urine (Olmos Colmenero and Broderick, 2006;Cosgrove et al, 2017;Beltran et al, 2019).…”

The Replacement of Ground Corn with Sugar Beet in the Diet of Pasture-Fed Lactating Dairy Cows and Its Effect on Productive Performance and Rumen Metabolism

“…The greater urinary N excretion is in part a consequence of greater concentrations of NH 3 in the rumen. Once NH 3 is produced by ruminal bacteria, it can be used to build microbial protein (energy-dependent process) or be transported to the liver (low energy availability in the rumen) to be converted into urea; then, it may be excreted through the urine [ 55 , 56 , 57 ] or recycled into the rumen along with saliva [ 42 ]. Nitrogen excretion through the urine and dung are important in terms of environmental pollution because they are an important N source for N 2 O emissions in pasture-based livestock systems, a powerful greenhouse gas whose global warming potential (GWP) is greater than CO 2 and CH 4 [ 58 ].…”

Nitrogen Use Efficiency and Partitioning of Dairy Heifers Grazing Perennial Ryegrass (Lolium perenne L.) or Pasture Brome (Bromus valdivianus Phil.) Swards during Spring

“…According to Ueda et al [45], when N intake is increased, NH 3 -N utilization by ruminal microbes can be improved when the supply of readily fermentable carbohydrates in the rumen is increased. Heifers grazing Bv had a high N intake, while their energy intake (ME and WSC) was similar to that of heifers grazing Lp; therefore, the excess of N was converted to NH 3 by ruminal bacteria [46], as a result of the imbalance in the supply of energy and protein in the rumen, which is supported by the greater N intake and lower WSC:CP ratio of Bv.…”