Nutrition, urea and SCC in sheep’s milk: interesting relationships
Animal nutrition greatly influences milk composition, which can be controlled to improve its milk characteristics for human nutrition. However, it is also true that milk composition is an excellent indicator of the animal’s nutritional status. Some changes in macro-components can also be related to the animal’s immune response.
Some insights into the relationships between nutrition and somatic cells in milk were recently presented in a paper in the journal “Small Ruminant Research” by the Animal Science Section of the University of Sassari, Italy.
The true protein of milk, the synthesis of which is under high genetic control, is much less influenced by animal nutrition than milk fat.
In contrast, the non-protein nitrogen fraction of milk is primarily influenced by nutritional factors.
The solubility and degradability of dietary protein and energy availability in the rumen can particularly influence milk urea.
Milk urea concentration is known to be a good indicator of protein excesses and deficiencies in the ration but also of energy metabolism, whereby low urea levels are associated with fermentable carbohydrate deficiency in the rumen (Giovanetti et al., 2019).
Urea concentration in milk is also associated with adverse effects on health, reproductive performance, and immune response in dairy ewes. It is particularly interesting to note that urea concentration in milk is inversely associated with somatic cell count (SCC) in ewes and cows.
Surprisingly, when urea concentrations of Sarda sheep milk analyzed by the Farmers Regional Laboratory in Sardinia (today LAORE LAB; more than 150,000 milk samples in 2017) were correlated with milk composition parameters, a robust negative relationship between urea and CCS was observed.
Furthermore, data on milk production and composition of 72 ewes fed dry unifeed (with a constant protein content of 16.5 percent on SS fed from parturition to 165 days of lactation; Atzori et al., 2019) were specifically analyzed.
Urea was negatively associated with SCC (r = -0.57; P < 0.001), and this was independent of milk production. In ewes that produced more than 1.0 L/day of milk, urea values above 43 mg/dL were associated with values below 500,000 SCC/mL.
Indeed, milk production only partially explains the effect of the lactation stage on milk SCC content, and this result agrees with previous evidence reporte...
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