Objective: To report on spontaneous clinical and subclinical acidosis in a large dairy herd, to evaluate the diets and feeding strategies involved, and to report on measures of rumen function in the cows affected.
Design: A Gippsland dairy herd was sampled as part of a wider randomised cross-sectional study that examined the prevalence, risk factors for, and effects of, acidosis on rumen function of dairy cattle. Three herds on the farm were involved in the study: the transition herd (cows 3 weeks prior to calving), the very fresh lactating herd (1 < days in milk < 10, herd 1) and the fresh lactating herd (10 < days in milk < 120, herd 2) including a small lame herd fed separately. The transition cows were fed 2 kg dry matter triticale per cow per day and hay with an estimated total dry matter intake of 4.8 kg per cow per day. The lactating cow diet included 6.75 kg dry matter triticale per cow per day with total concentrate fed being 8.1 kg dry matter per cow per day in the milking parlour. Silage, lucerne cubes, hay and pasture (herd 2 only) was also fed to the lactating cows with the estimated total dry matter intake for cows in herds 1 and 2 being 13.7 kg and 20.8 kg per cow per day respectively. Three primiparous and five multiparous cows in early lactation (< 100 days in milk) were randomly selected from each of two lactating herds: herds 1 and 2. Rumen fluid was sampled from each cow by both rumenocentesis and stomach tube. The rumenocentesis samples were tested for pH at the time of sampling. Stomach tube samples were frozen and subsequently tested for volatile fatty acid, ammonia, and D- and L-lactate concentration.
Results: In the very fresh herd, there was a high prevalence of severe lameness and scouring, coupled with a mean rumen pH 5.67, low mean total volatile fatty acid concentration 71.0 mM and high mean concentrations of L- and D-lactate, (7.71 mM and 7.31 mM), respectively. Cows in the fresh herd had moderate signs of scouring and lameness. A lame herd comprising approximately 50 cows separated from the fresh herd was also present on the farm. The mean rumen pH of the fresh herd was 5.74 and mean rumen concentrations of volatile fatty acids, ammonia, L- and D-lactate were within ranges considered normal.
Conclusions: The transition diet failed to supply sufficient energy and protein for maintenance of cows of this live weight in late gestation. The diet fed to the very fresh herd was low in effective fibre and contained an excessive content of non-structural carbohydrate in the form of processed, rapidly fermentable grain. The sudden change from the transition diet to the diet fed to the very fresh herd probably also precipitated the outbreak of acidosis. This case report provides unique detail, including information on diets and rumen parameters, of an outbreak of acidosis in a pasture-fed herd.