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Modeling of off-feed periods caused by subacute acidosis in intensive lactating ruminants: application to goats.

Off-feed periods caused by subacute rumen acidosis are often observed in intensive ruminant production systems but appear in an unpredictable manner. The objectives of this paper were first, to study the influence of spontaneous off-feed periods due to bouts of acidosis on milk composition and on some rumen and blood parameters and second, to model the day-to-day variations in rumen pH, dry matter intake (DMI), and milk production during these bouts of acidosis. Twenty-five spontaneous off-feed periods were detected in an experiment performed in 18 mid-lactating goats fed a high concentrate diet over 11 wk. Dry matter intake, milk production, and rumen pH were measured daily during the experiment, which allowed us to model the day-to-day evolution of these 3 parameters during spontaneous bouts of acidosis. Bouts started with a very rapid pH decrease (1 d) followed by several days of relatively high rumen pH (>6.5) before recovery of preacidosis values. The pH decrease was followed by a decrease in DMI, reaching a nadir around 2 d after the start of the episode, and a milk yield decrease, reaching a nadir 3 d after the beginning of the episode. The high rumen pH was caused by the relatively small decrease in daily chewing time during the decrease in DMI. Therefore, chewing time per unit of DMI increased, which probably increased the buffer supply per unit of DMI. Dry matter intake and milk yield needed around 20 d to recover to preacidosis values. Energy balance also decreased during DMI and milk yield decreases but recovered more rapidly than DMI and milk yield. However, energy balance cumulated from the start of the bout of acidosis remained negative for more than 10 d. Milk composition and rumen and blood parameters were not measured daily and therefore could not be used in the modeling process. However, during off-feed periods, milk fat and protein contents were negatively correlated with DMI, whereas milk lactose content was positively correlated with DMI. Low DMI was also linked to low blood pH, bicarbonates, and low rumen volatile fatty acids but high levels of plasma nonesterified fatty acids. This indicates that rumen fermentation was reduced and body reserves were mobilized during bouts of acidosis. This analysis showed that spontaneous bouts of acidosis in intensively reared dairy ruminants can have a great influence on animal production and health over at least 3 wk, and can thus represent an important economic loss.