Abstract
Simple SummaryFodder beet (FB) is widely used in grazing dairy systems of New Zealand to support early- and late-lactation milk production, however, the large fraction of water-soluble carbohydrate present in FB bulbs presents a risk of subacute and acute ruminal acidosis. Despite widespread use of FB across New Zealand, the incidence of ruminal acidosis using industry-recommended methods of feeding FB has not been investigated. This study analyzed the time-dependent changes to rumen fermentation, apparent dry matter intake, milk production, milk composition and plasma amino acid concentration of grazing dairy cows supplemented with moderate amounts (40% of dry matter intake) of FB during early lactation. Our findings indicate that incidence of subacute ruminal acidosis due to FB is greater than currently realized, as 25% of cows developed severe subacute ruminal acidosis following transition to target FB allocation (40% of daily intake). Across all cows, FB reduced rumen pH, feed conversion efficiency and was not advantageous to milk production. These results suggest methods for adapting cows to a diet containing FB require further evaluation to reduce the risk of subacute ruminal acidosis (SARA) experienced by individuals within the herd.In a cross-over design, eight rumen cannulated dairy cows were used to explore the industry-recommended method for dietary transition to fodder beet (FB: Beta vulgaris L.) on changes to rumen fermentation and pH, milk production, dry matter intake (DMI) and the risk of subacute ruminal acidosis (SARA) during early lactation. Cows were split into two groups and individually allocated a ryegrass (Lolium Perenne L.) and white clover (Trifolium repens L.) diet (HO) or the same herbage supplemented with 6 kg DM/cow of harvested fodder beet bulbs (FBH). Dietary adaptation occurred over 20 days consisting of: stage 1: gradual transition to target FB intake (days 1–12, +0.5 kg DM of FB/d); stage 2: acclimatization (days 13–17) and stage 3: post-adaption sampling (days 18–20). Response variables were analyzed as a factorial arrangement of diet and stage of adaption using a combination of ANOVA and generalized linear mixed modelling. Dietary proportion of FB represented 22, (stage 1), 32 (stage 2) and 38% (stage 3) of daily DMI. One cow during each period developed SARA from FB and the duration of low pH increased with FBH compared to the HO treatment (p < 0.01). Rumen concentrations of lactic and butyric acid increased with FBH but concentrations of acetate, propionate and total volatile fatty acids (VFA) declined by 9.3% at day 20, compared to the HO treatment (p < 0.01). Treatments did not affect milk production but total DMI with supplemented cows increased during the final stage of adaptation and feed conversion efficiency (FCE kg milk/kg DM) declined with the FBH treatment. The occurrence of SARA in 25% of animals fed FB suggest it is a high-risk supplement to animal health and further evaluation of industry-recommended methods for feeding FB at the individual- and herd-scale are needed.
Highlights
New Zealand dairy farms have come to rely on fodder beet to increase body condition scores (BCS)within a short 6–8-week timeframe over the winter dry cow period
Previous research suggests that there is limited advantage to milk production when fodder beet (FB) is fed to grazing dairy cows [4,5,6], which may indicate that FB increases the substitution rate and reduces the milk response to the supplement when compared with alternative supplements such as pasture silage or cereal grains [7,8]
One cow in the first period developed subacute ruminal acidosis (SARA) on day 10 of adaption, and her FB allocation was reduced to 3 kg DM, which was maintained until the end of the experiment
Summary
New Zealand dairy farms have come to rely on fodder beet to increase body condition scores (BCS)within a short 6–8-week timeframe over the winter dry cow period. The popularity of fodder beet (FB) is driven by the potential to obtain large yields (>20 t dry matter: DM/ha) of high metabolizable energy bulbs (~12 MJ ME) that are ~90% utilized when grazed in situ [1,2,3]. Previous research suggests that there is limited advantage to milk production when FB is fed to grazing dairy cows [4,5,6], which may indicate that FB increases the substitution rate (kg DM herbage/kg DM FB) and reduces the milk response to the supplement (kg milk/kg DM supplement) when compared with alternative supplements such as pasture silage or cereal grains [7,8]. The low milk response to FB may indicate impaired rumen function, as FB bulbs contain small amounts of fiber (
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