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.

Review: Markers and proxies to monitor ruminal function and feed efficiency in young ruminants.

Developing the rumen's capacity to utilise recalcitrant and low-value feed resources is important for ruminant production systems. Early-life nutrition and management practices have been shown to influence development of the rumen in young animals with long-term consequences on their performance. Therefore, there has been increasing interest to understand ruminal development and function in young ruminants to improve feed efficiency, health, welfare, and performance of both young and adult ruminants. However, due to the small size, rapid morphological changes and low initial microbial populations of the rumen, it is difficult to study ruminal function in young ruminants without major invasive approaches or slaughter studies. In this review, we discuss the usefulness of a range of proxies and markers to monitor ruminal function and nitrogen use efficiency (a major part of feed efficiency) in young ruminants. Breath sulphide and methane emissions showed the greatest potential as simple markers of a developing microbiota in young ruminants. However, there is only limited evidence for robust indicators of feed efficiency at this stage. The use of nitrogen isotopic discrimination based on plasma samples appeared to be the most promising proxy for feed efficiency in young ruminants. More research is needed to explore and refine potential proxies and markers to indicate ruminal function and feed efficiency in young ruminants, particularly for neonatal ruminants.

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.

Effect of time of maize silage supplementation on herbage intake, milk production, and nitrogen excretion of grazing dairy cows.

The objective of this study was to evaluate the effect of feeding maize silage at different times before a short grazing bout on dry matter (DM) intake, milk production, and N excretion of dairy cows. Thirty-six Friesian × Jersey crossbred lactating dairy cows were blocked in 9groups of 4 cows by milk solids (sum of protein and fat) production (1.26±0.25kg/d), body weight (466±65kg), body condition score (4±0.48), and days in milk (197±15). Groups were then randomly assigned to 1 of 3 replicates of 3 treatments: control; herbage only, supplemented with 3kg of DM/cow of maize silage after morning milking approximately 9h before pasture allocation (9BH); and supplemented with 3kg of DM/cow of maize silage before afternoon milking approximately 2h before pasture allocation (2BH). Herbage allowance (above the ground level) was 22kg of DM/cow per day for all groups of cows. Cows were allocated to pasture from 1530 to 2030 h. Maize silage DM intake did not differ between treatments, averaging 3kg of DM/cow per day. Herbage DM intake was greater for control than 2BH and 9BH, and greater for 9BH than 2BH (11.1, 10.1, and 10.9kg of DM/cow per day for control, 2BH, and 9BH, respectively). The substitution rate (kilograms of herbage DM per kilograms of maize silage DM) was greater for 2BH (0.47) than 9BH (0.19). Milk solids production was similar between treatments (overall mean 1.2kg/cow per day). Body weight loss tended to be less for supplemented than control cows (-0.95, -0.44, and -0.58kg/cow per day for control, 2BH, and 9BH, respectively). Nitrogen concentration in urine was not affected by supplementation or time of supplementation, but estimated urinary N excretion tended to be greater for control than supplemented cows when urinary N excretion estimated using plasma or milk urea N. At the time of herbage meal, nonesterified fatty acid concentration was greater for control than supplemented cows and greater for 9BH than 2BH (0.58, 0.14, and 0.26mmol/L for control, 2BH, and 9BH, respectively). Timing of maize silage supplementation relative to a short and intensive herbage meal can reduce the substitution rate and increase herbage DM intake of grazing dairy cows.