F. Wittwer et al., SCREENING OF PROTEIN METABOLIC UNBALANCE BY BULK MILK UREA DETERMINATION IN DAIRY HERDS, Archivos de medicina veterinaria, 25(2), 1993, pp. 165-172
Bulk milk urea concentration, similar to mean serum urea, has been use
d as an indicator of the protein-energy balance intake in dairy cows.
Accordingly, to determine the association between blood and milk urea
values the herd blood urea concentration (mean of 7 lactating cows) an
d bulk milk urea concentration (tank or churn milk samples) were deter
mined in 21 dairy herds. Besides, to determine reference values, seaso
nal and herd variance, and the frequency of herds with abnormal values
, bulk milk samples were obtained monthly during 1 year from 82 suppli
ers at two dairy plants in the South of Chile. Mean bulk urea concentr
ations (6.2 +/- 2.0 mmol/l) was similar to mean herd blood urea value
(6.2 +/- 2.0 mmol/l) and a significant association between these param
eters was found (r = 0.9477; p < 0.01). Mean urea concentration in the
milk samples obtained during a year from 82 herds was 4.9 +/- 1.2 mmo
l/l, with a reference range of 2.5 to. 7.4 mmol/l. No differences were
found between samples obtained from tanks or churns (p > 0.05). The h
ighest values were found during autum and spring, and the lowest durin
g summer. The annual coefficient of variation (CV) ranged from 13% to
47%, showing a high seasonal variation. The between herds CV was also
high, ranging from 20% to 31%. Of the 82 herds, 27% showed abnormal va
lues in two or more opportunities. 5.4% of the samples had urea values
above the reference values specially during spring, and 3.8% were bel
ow the reference values mainly during summer. According to these resul
ts, bulk milk urea concentrations render information similar to herd b
lood urea values, and present high seasonal and herd variations. Also,
there was a high frequency of herds with nutritional unbalance of pro
tein-energy.