Sensor-captured modifications in cow behaviour under subacute ruminal acidosis
Résumé
High-energy diets increase the risk of Sub-Acute Ruminal Acidosis (SARA) in
ruminants. The behaviour of ruminants is modified under SARA however the impact on
behaviour of a high-energy diet and those of SARA per se are often confounded. We
aimed at distinguishing the effects of the diet and of SARA on cow behaviour. We fed
28 Holstein cows a low-starch diet (low starch diet, 10.5% starch) or a high-starch diet
(high starch diet, 31.5% starch). Control cows (n = 14) received the low starch diet for
60 days, Challenge cows (n = 14) received the same diet except for a 2-week period
during which they received the high starch diet and the 10 preceding days to ensure
the transition between diets. We monitored ruminal pH and activity of cows thanks to
sensors, dry matter intake (DMI), and milk yield of each cow on a daily basis. The
SARA status was defined according to the relative decrease in ruminal pH and to pH
variability. High starch diet induced SARA more often than low starch diet (81% days
when cows received high starch diet vs. 8% when they received low starch diet. High
starch diet also decreased milk yield and made cows spending less time eating but
eating more quickly (Challenge vs. Control cows during the challenge period: milk
yield, 20.0 vs. 18.2 L/d; % time spent eating, 22.5 vs. 27.6; eating rate, 77.1 vs. 69.6 g
DMI/min; P (diet x period) < 0.001 in all cases). A decrease in milk yield, a decrease in
the time spent eating and an increase in eating rate were also observed to a lesser
extent in cows experiencing SARA during the transition or the challenge periods, no
matter the diet (Challenge and Control cows: milk yield, - 0.5 and -0.3 L/d, P(SARA) =
0.03; % time spent eating, - 1.4 and - 0.84, P(SARA) = 0.02; eating rate, +4.9 and +3.2
g DMI/min, P(SARA) = 0.06; P (SARA x diet) > 0.50). In conclusion, an increase in
eating rate, especially combined with a decrease in milk yield should alert farmers to
the risk of ruminal acidosis.
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