Rumen digesta and products of fermentation in cows fed varying proportions of fodder beet (Beta vulgaris) with fresh pasture or silage or straw

Abstract

Context Fodder beet (FB) is a popular feed for dairy cows in temperate climates due to its high yields, high digestibility, low nitrogen (N) content in the dry matter (DM) and convenience of feeding (grazing in situ). However, the risk of ruminal acidosis requires research to design feeding regimes that capture these benefits without compromising animal health. Aims To understand aspects of rumen function when FB is offered in conditions representative of practical feeding in temperate pastoral systems. Methods Two indoor experiments were undertaken; one with cows in late lactation fed fresh perennial ryegrass with three proportions of FB (0, 0.23 and 0.45) and another with non-lactating cows fed pasture silage with 0.65 FB or barley straw with 0.86 FB. Measurements included rumen pH, short-chain fatty acid (SCFA) and ammonia concentrations determined at 2-h intervals, as well as daily individual cow intakes, estimates of microbial growth and rumen dynamics. Key results The inclusion of 0, 0.23 and 0.45 FB with fresh pasture in the did not affect daily DM intakes (~14.6 kg), milk yield (~10.7 kg), microbial synthesis (129 g of N/d) or fractional outflow rates of digesta (0.16/h; 11.2 L/h) of lactating cows. The non-lactating cow ration comprising 0.86 FB with straw was inappropriate and resulted in low intakes and insufficient dietary N. Microbial growth was approximately one-third of that in cows fed pasture silage with 0.65 FB. The ruminal pH reached lower values in all treatments where FB was offered. Rumen ammonia concentrations averaged 4.4 mmol/L in cows fed pasture but was sometimes undetectable in lactating cows fed 0.45 FB and in non-lactating cows. The amount of FB in the diet affected the extent of the circadian changes in molar proportions of SCFA. Conclusions Based on the results presented here, feeding fresh FB to dairy cows should not exceed ~0.4 of their DMI with pasture (late lactation), or ~0.6 of their intake with silage (non-lactating). Implications These findings could support evidence-based recommendations for FB use, considering its effects on aspects of rumen function, such as microbial protein synthesis and pH.

Supplementation of Spring Pasture with Harvested Fodder Beet Bulb Alters Rumen Fermentation and Increases Risk of Subacute Ruminal Acidosis during Early Lactation

“…Despite greater apparent DMI, cows fed FBH experienced lower concentrations of total VFA, as both concentrations of acetate and propionate declined when compared to cows fed HO. Although Pacheco, et al [6] also reported a lower concentration of acetate from cows when FB was fed as 23% or 45% of DMI, differences were not as large as those observed in the current study. Reduction in total VFA concentration has only been reported for non-lactating dairy cows fed large amounts of FB (>60% DMI) [6].…”

“…Both FBH and HO diets resulted in rumen pH that was lower than previously reported for housed cows fed increasing proportions of FB and herbage [6]. The continuous measurement of rumen pH in the current experiment should be more accurate and warrant more regular measurements than every 2 h as practiced in [6,30]. Zebeli, et al [16] and Mertens [50] suggest that the duration of low rumen pH also increases when the NDF and physically effective NDF (i.e., stimulates chewing and secretion of saliva) content of herbage is less than 42%.…”

“…Rumen pH was reduced following consumption of FB in the morning; however, rumen pH of cows fed the HO diet was also low and variable (Table 4). Both FBH and HO diets resulted in rumen pH that was lower than previously reported for housed cows fed increasing proportions of FB and herbage [6]. The continuous measurement of rumen pH in the current experiment should be more accurate and warrant more regular measurements than every 2 h as practiced in [6,30].…”

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

“…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).…”

Commercial practice of out-wintering dairy heifers in Great Britain

“…Despite straw being readily available in GB, its low use in the current survey contrasts with that in Canterbury, NZ, where straw was reported to be frequently fed to dry cows (Edwards et al 2017). Straw is high in functional fibre, but recent research suggests that it is not suitable as a supplement with fodder beet (Waghorn et al 2018, Pacheco et al 2020.…”