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

Environmental degradation has been attributed to inefficient nitrogen utilization from pastoral dairy production systems. This 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, which would help inform strategic management decisions. 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 as ways to reduce environmental impact. 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 selected as low for MUNBV consistently had a 65.2-kg lower urinary urea nitrogen (UUN) load (kg/ha) than high MUNBV cows for all hours of the day when consuming RG. The association between lower urinary urea loading rates and less N leaching implies a reduced environmental impact from low MUNBV cows consuming RG. When cows consumed PL, regardless of MUNBV, they had on average a 137.5-kg (UUN/ha) lower loading rate compared with high MUNBV cows on RG and a 72.2-kg (UUN/ha) lower loading rate compared with low MUNBV cows consuming RG across the day. Cows on PL also exhibited a different diel pattern of UUN load compared with cows consuming RG. Differences in the diel pattern of N excreted in feces were also detected based on MUNBV and by diet, with low MUNBV cows excreting on average 3.06 g more N in feces per event for the majority of the day compared with high MUNBV cows when consuming RG. Lower UUN loading rates and more N excreted in feces indicate 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 environmental impact compared with RG.

Rumen function and grazing behavior of early-lactation dairy cows supplemented with fodder beet.

Fodder beet (FB) is a source of readily fermentable carbohydrate that can mitigate early spring herbage deficits and correct the negative energy balance experienced during early lactation in pastoral dairy systems of New Zealand. However, the low-fiber and high-soluble carbohydrate content of both FB bulb and spring herbage are factors that promote subacute ruminal acidosis, impairing rumen function and limiting the marginal milk production response to supplement. In a crossover experiment, 8 Holstein Friesian × Jersey early-lactation dairy cows were used to test the effect of supplementing 16 kg of dry matter (DM) of a grazed perennial ryegrass herbage with 6 kg of DM/d of FB bulb (FBH) versus herbage only (HO) on changes in rumen function and grazing behavior. Following 20 d of adaptation to diets, DM disappearance (%) of FB bulb (FBH cows only) and herbage were measured in sacco, separately. Cows were fasted overnight, and the ruminal contents were bailed the following morning (~0930 h) again to determine the pool size of volatile fatty acids, ammonia, and particle size of digesta, as well as to estimate the rate of ruminal outflow and degradation of neutral detergent fiber. The FBH diet did not alter DM intake, milk yield, or milk solid (fat + protein) production compared with HO. Supplementation of herbage with FB reduced ruminal pH compared with HO between ~0800 h and 1300 h each day. During each period, 1 cow experienced severe subacute ruminal acidosis (pH <5.6 for >180 min/d) during final adaptation to the target FB allocation. The FBH diet reduced the ruminal pool of acetate and ammonia, but increased the ruminal pool of butyrate and lactate compared with HO. When fed FB, rumination and grazing time increased and grazing intensity declined compared with cows fed HO. Despite increased rumination, the comminution of large particles declined 28% between the first and second rumen bailing when cows were fed FB, and in sacco DM disappearance of perennial ryegrass declined 18% compared with cows fed HO. These results indicate that grazing dairy cows supplemented with FB (40% of daily intake) increase rumination and mastication intensity to counteract reduced ruminal degradation of ryegrass herbage due to low ruminal fluid pH.

Evaluation of PEETER V1.0 urine sensors for measuring individual urination behavior of dairy cows.

Due to environmental concerns around N leaching and NO2 emissions from intensive pastoral dairying systems, there has been an increase in research focused on mitigation strategies and on-animal technologies to evaluate urination behavior of grazing dairy cows. Nitrogen leaching and NO2 emissions are associated with urine nitrogen loading onto pasture, which is a function of urine nitrogen concentration and urine volume per urination event. The PEETER V1.0 urine sensor (Lincoln University, Christchurch, New Zealand) is a promising on-animal measurement technology; however, it has yet to be validated in vivo. The objective of this work was to validate the PEETER V1.0 urine sensor's estimations of individual urination events (i.e., urine volume). We fitted 15 Holstein-Friesian × Jersey lactating dairy cows (506 ± 35 kg of live weight, body condition score of 3.75 ± 0.25, and 150.4 ± 20.7 d in milk) with individual PEETER V1.0 sensors and placed them in metabolism crates for 72 h. Every urination event (n = 480) was collected manually and compared with the urine volume estimated by the PEETER V1.0 sensor to determine precision and accuracy using Lin's concordance correlation coefficient (CCC). The CCC is calculated as a function of the Pearson's correlation (precision) and bias correction factor (Cb; Cb = 1 is perfect), and it demonstrates how far the values of the 2 methods are from perfect agreement (accuracy; i.e., a 45° line). The mean urination event volume (mean ± standard deviation) was 2.7 ± 0.94 and 2.6 ± 0.92 L for the actual and PEETER V1.0 sensor, respectively. The PEETER V1.0 sensor showed excellent precision (r = 0.90) with near-perfect accuracy (Cb = 1.00), and the CCC value was high (CCC = 0.90), indicating excellent agreement. Based on these results, the PEETER V1.0 urine sensor provides estimates that are precise and accurate. We conclude that the PEETER V1.0 sensor can be used to evaluate urination behavior of grazing dairy cows.

Grazing dairy cows with low milk urea nitrogen breeding values excrete less urinary urea nitrogen.

There is an increasing pressure on temperate pastoral dairy production systems to reduce environmental impacts, coming from the inefficient use of N by cows in the form of excessive urinary N excretion and subsequent N leaching to the waterways and NO2 emissions to the atmosphere, these impacts have spurred research into various mitigation strategies, which have so far overlooked animal-based solutions. The objectives of this study were first, to investigate the relationship between MUN breeding values (MUNBV) and urinary urea N (UUN) concentrations and total excretion in grazing dairy cows; and secondly, to evaluate such a potential relationship in the context of different sward compositions and stage of lactation. Forty-eight multiparous, lactating Holstein-Friesian dairy cows genetically divergent for MUNBV were strip-grazed on either a ryegrass-white clover (24 cows) or ryegrass, white clover and plantain sward (24 cows), during both early and late lactation. Cows were fitted with Lincoln University PEETER sensors to evaluate urination behaviour by measuring frequency and volume of urination, as well as daily urine excretion. Urine and faeces were sampled for urea N content. Milk yield and composition were measured for individual cows in both periods. There was a positive relationship between MUNBV and MUN (R2 = 0.67, P ≤ 0.05), with MUN decreasing 1.61 ± 0.19 mg/dL per unit decrease in MUNBV across both sward types and stages of lactation. Urinary urea N concentration decreased 0.67 ± 0.27 g/L (R2 = 0.46, P ≤ 0.05) per unit decrease of MUNBV, with no effect on urine volume or frequency (number of urination events per day), which resulted in a 165.3 g/d difference in UUN excretion between the animal with the highest and the lowest MUNBV. At the same milk yield, percentage of protein in milk increased by 0.09 ± 0.03 (R2 = 0.61, P ≤ 0.05,) per unit decrease in MUNBV. Our results suggest that breeding and selecting for dairy cows with low MUNBV can reduce urinary urea N deposition onto pasture and consequently the negative environmental impact of pastoral dairy production systems in temperate grasslands. Moreover, reducing MUNBV of dairy cows can potentially increase farm profitability due to greater partitioning of N to milk in the form of protein.

Structure of neurolysin reveals a deep channel that limits substrate access.

The zinc metallopeptidase neurolysin is shown by x-ray crystallography to have large structural elements erected over the active site region that allow substrate access only through a deep narrow channel. This architecture accounts for specialization of this neuropeptidase to small bioactive peptide substrates without bulky secondary and tertiary structures. In addition, modeling studies indicate that the length of a substrate N-terminal to the site of hydrolysis is restricted to approximately 10 residues by the limited size of the active site cavity. Some structural elements of neurolysin, including a five-stranded beta-sheet and the two active site helices, are conserved with other metallopeptidases. The connecting loop regions of these elements, however, are much extended in neurolysin, and they, together with other open coil elements, line the active site cavity. These potentially flexible elements may account for the ability of the enzyme to cleave a variety of sequences.