Digestion and nitrogen excretion by Holstein–Friesian cows in late lactation offered ryegrass-based pasture supplemented with fodder beet

Abstract

Recent changes in New Zealand dairying have included incorporation of fodder beet (FB) into rations. The present trial explored the impact of substituting different proportions of ryegrass-based pasture with FB for cows fed ad libitum in late lactation. The objective was to measure effects of FB on intake, digestion and urinary nitrogen (N) excretion using 16 Holstein–Friesian cows with a permanent rumen fistula. Before the 9-day indoor measurement period, cows were adapted to feeding 0%, 20%, 40% or 60% FB (bulbs and tops) with medium quality ryegrass-based pasture (191 g CP and 517 g neutral detergent fibre (aNDF)/kg DM; DM digestibility 0.634) over 2 weeks. However, it became apparent that a diet of 60% FB was detrimental to cow health, with two cows developing acidosis. The allocation of FB was reduced and the actual intakes were 23% and 45% of DM intake during the trial. Feeding FB substantially reduced N intake and urinary N excretion. The lower level (23%) of FB resulted in greater DM digestibility, albeit with a small reduction in N and aNDF digestibility. However, the higher level (45%) of FB reduced N and aNDF digestibility by 7.1 and 12.1 percentage units respectively, relative to pasture. Daily creatinine excretion was lower than published measurements from cattle fed dry diets, and circadian variation in urinary N:creatinine ratios suggests a need for caution when attempting to predict daily urinary N excretion from spot samples.

Modelling feeding strategies to improve milk production, rumen function and discomfort of the early lactation dairy cow supplemented with fodder beet

“…However, the substantial increase of lactic acid concentration, reduced DMI and milk production indicate that MINDY experienced SARA when fed 7FB and that rumen conditions were sub-optimal when 4FB was fed. Moderate allocations of FB (<40% inclusion) have previously been reported as 'safe' for late-lactation dairy cows (Dalley et al, 2019;Waghorn et al, 2019). Discrepancies between latelactation studies and the current data set may be a consequence of cows being more susceptible to low pH during the post-partum transitioning period (Penner et al, 2007), but further in vivo studies are required to verify this finding.…”

“…Replacing starch with sugar reduces the supply of glucogenic precursors, which may limit milk response from supplement (Evans and Messerschmidt, 2017). FB may further limit milk production by reducing gross energy (GE) intake as Waghorn et al (2019) reported GE values for FB bulb was less than pasture (16.3 v. 18.7 kJ/g DM).…”

“…Except for lower concentration of all VFA and a slight increase of propionate associated with increasing FBA, rumen fermentation profiles were similar across diets. Changes of fermentation profiles in response to sucrose or FB supplementation are variable, with some accounts of increased synthesis of butyric acid when starch is replaced with sucrose (Khalili and Huhtanen, 1991;Chamberlain et al, 1993) or FB is used to supplement herbage (Eriksson et al, 2004;Waghorn et al, 2019;Pacheco et al, 2020) although, Pacheco et al (2020) found propionate concentrations increased in response to FB supplementation. These responses reflect altered chemical composition of the diet as formation of propionate is increased with glucogenic precursors such as starch, whereas butyrate reflect greater dietary sugar content, due to FB (Oba, 2011).…”

Nitrogen leaching losses from fodder beet and kale crops grazed by dairy cows in southern SouthlandNitrogen leaching losses from fodder beet and kale crops grazed by dairy cows in southern Southland

“…The 50% difference in N leached under FB in Trial 1 and 40% difference to date in Trial 2 (Figure 4) reflected the 40 to 45% reduction in N intakes estimated for the cows grazing FB in winter (Figure 2). This lower N intake in the winter-grazed FB treatment reflects its lower CP content (Table 2; Dalley et al 2017;Waghorn et al 2019) and consequently reduced N excretion. The leaching loss of 142 kg N ha -1 measured from the winter-grazed kale treatment in Trial 1 was particularly high when compared to previous measurements from brassica crops elsewhere in Southland (30-108 kg N ha -1 ; Monaghan et al 2013;Smith et al 2012) and may be at least partly attributable to the mineralisation of large amounts of soil organic N following the dry summer that preceded winter of Trial 1.…”

“…Harvested FB can also be stored for up to 3 months and fed out in spring as a supplement during early lactation (Gibbs et al 2015). In addition to its high yield potential, an advantage of FB is its relatively low Crude Protein (CP) content which can lower urinary nitrogen (UN) concentrations (Dalley et al 2017) and has the potential to reduce UN excretion when fed as a supplement to cows in late lactation (Dalley et al 2020;Waghorn et al 2019). Reduced UN excretion is expected to result in less N leaching over the winter grazing period (Malcolm et al 2016;De Ruiter et al 2019).…”