Short communication: Dietary protein restriction and conjugated linoleic acid supplementation in dairy cows affect milk composition, the cheese-making process, and cheese quality

摘要

We used 20 mid-lactating Holstein cows, housed in4 pens according to a Latin square design, to evaluatethe effects of dietary protein restriction (crude protein:12.3 vs. 15.0% dry matter) and conjugated linoleic acidsupplementation (CLA: 6.34 g/d of C18: 2cis -9 ,trans -11and 6.14 g/d of C18: 2trans -10 ,cis -12) on milk composition,coagulation, curd firming and syneresis modeling,and cheese yield and quality (96 small cheeses). Dietarycrude protein restriction, suggested as a way to reduceN excretion in farming, caused a reduction in milkprotein content (−4%,), milk casein (−3.8%), lactose(−1%), cheese soluble protein (−16.8%), and the cheesematuration index (−15%), and a correlated increasein cheese fat content (+7.5%) and the fat to proteinratio (+18%). A modest reduction (−0.9%) in milk fatrecovery in the curd did not affect cheese yield. Theaddition of CLA to the cows’ diet, suggested as a wayto improve N use efficiency and the nutritional valueof dairy products, caused substantial alterations to themilk composition, cheese-making process, and cheesequality. The CLA reduced the fat (−12.3%), protein(−2%), casein (−2.2%), lactose (−1.0), and total solids(−4%) contents of milk, tended to delay coagulation,and weakened curd firming. The CLA reduced thefresh cheese yield (−7.5%) and cheese solids (−8.2%)because of the lower nutrient content of the milk,but also because of a lower recovery of milk proteinin the curd (−0.9%) and lower total solids (−4.5%).It also reduced the fat content in the ripened cheese(−11.8%), as well as the fat to protein ratio (−19.4%)as a result of having increased the protein content(+9.3%). Last, it increased the lightness of the paste ofthe ripened cheeses (+3.3%), and especially the shearforce (+16.3%). Dietary crude protein restriction, andCLA addition in particular, substantially altered themilk composition, cheese-making process, and cheesequality, and therefore needs to be carefully evaluated.Further studies are required to shed light on the causesof these modifications.