Effect of grazing management on herbage protein concentration, milk production and nitrogen excretion of dairy cows in mid‐lactation

Abstract

The objective of this experiment was to use diurnal and temporal changes in herbage composition to create two pasture diets with contrasting ratios of water‐soluble carbohydrate (WSC) and crude protein (CP) and compare milk production and nitrogen‐use efficiency (NUE) of dairy cows. A grazing experiment using thirty‐six mid‐lactation Friesian x Jersey cows was conducted in late spring in Canterbury, New Zealand. Cows were offered mixed perennial ryegrass and white clover pastures either in the morning after a short 19‐day regrowth interval (SR AM) or in the afternoon after a long 35‐day regrowth interval (LR PM). Pasture treatments resulted in lower pasture mass and greater herbage CP concentration (187 vs. 171 g kg−1 DM) in the SR AM compared with the LR PM but did not affect WSC (169 g kg−1 DM) or the ratio of WSC/CP (1·0 g g−1). Cows had similar apparent DM (17·5 kg DM cow−1 d−1) and N (501 g N cow−1 d−1) intake for both treatments. Compared with SR AM cows, LR PM cows had lower milk (18·5 vs. 21·2 kg cow−1 d−1), milk protein (0·69 vs. 0·81 kg cow−1 d−1) and milk solids (1·72 and 1·89 kg cow−1 d−1) yield. Urinary N concentration was increased in SR AM, but estimated N excretion and NUE for milk were similar for both treatments. Further studies are required to determine the effect of feeding times on diurnal variation in urine volume and N concentration under grazing to predict urination events with highest leaching risk.

Nitrogen leaching losses from lysimeters containing winter kale: the effects of urinary N rate and DCD application

“…In grazed pasture systems, pasture crude protein levels are often well in excess of animal crude protein requirements, leading to higher urinary N concentrations (Litherland & Lambert 2007). Work by Miller et al (2012) reported daily N excretion rates from cows grazing kale to be notably lower than those grazing pasture (Pacheco et al 2010;Bryant et al 2013). Further work on determining urinary N concentrations from dairy cows grazing winter forage crops is required to better understand typical N loading rates of cow urine deposits in grazed winter forage crop systems to avoid an over-estimation or under-estimation of paddockscale leaching losses.…”

Pre-Grazing Herbage Mass Affects Grazing Behavior, Herbage Disappearance, and the Residual Nutritive Value of a Pasture during the First Grazing Session

“…In several studies where significant effects of HM on the productive performance of cows were observed [8,18,27], it is feasible to observe that, when comparing high and low HM, the differences between treatments in the pre-grazing ADF content are in the range of 40 to 60 g/kg, values higher than those observed in our study. The HHM treatment was generated by delaying the regrowth period before the start of the study in relation to the regrowth period of MHM (+15 days of regrowth), which may influence fiber concentration in the pasture and, consequently, its digestibility [2,28]. However, the higher content of pre-grazing ADF and during the first 120 min of the first GS in HHM did not affect the concentration of DOMD, as fiber digestibility in a vegetative leafy spring pasture is high (>800 g/kg) and therefore an increase in ADF does not necessarily result in lower DOMD [29].…”

The Challenge of the Urine Patch for Managing Nitrogen in Grazed Pasture Systems

“…Urine N concentration also varies with animal reproductive status, season, and time of day Betteridge et al, 1986;Hoogendoorn et al, 2010;Bryant et al, 2013). Methods for estimating urine N concentration are "spot" sampling (Hoogendoorn et al, 2010), urine sensors (Betteridge et al, 2010b), and modeling based on intake of N; sodium and potassium (Bannink et al, 1999).…”

“…Methods for estimating urine N concentration are "spot" sampling (Hoogendoorn et al, 2010), urine sensors (Betteridge et al, 2010b), and modeling based on intake of N; sodium and potassium (Bannink et al, 1999). Bryant et al (2013) recognized the need for caution when interpreting urine N concentration from spot sampling, Table 1 Characteristics of urine patches deposited by dairy and beef cattle, sheep, and deer grazing predominantly pasture-based diets. Of the range of studies reported in Haynes and Williams (1993b) Clark et al…”

“…As N intake increases, the proportion of urinary N present as urea increases (Topps and Elliott, 1967;Petersen et al, 1998), from as low as 25% in a sheep diet with low protein, to 90% for cows grazing heavily fertilized, high N-containing grass . The proportion of total N in urine as urea has been shown to be higher in the morning than evening (Petersen et al, 1998;Bryant et al, 2013). Urine composition has also been shown to influence N transformation processes (Clough et al, 2003b;Decau et al, 2004;Petersen et al, 2004;van Groenigen et al, 2005a).…”