Genetic aspects of milk coagulation properties in Italian Holstein cows.

The aim of this study was to estimate heritability of milk coagulation properties and their genetic correlations with protein contents for Holstein Friesian cattle breed. Data. A total of 1071 Italian Friesian cows from 34 herds in Northern Italy were sampled once during the period from January to July 2004. The milk samples came from the morning milking and were collected during the milk recording. Samples were analyzed, within maximum 3 hours from milking time (because they were without any preserving agent), for milk coagulation properties, milk 10 ITAL.J.ANIM.SCI. VOL. 4 (SUPPL. 2), 10-12, 2005 yield, fat and protein percentage, acidity (SH° 50), casein content and somatic cell count (SCC). The milk coagulation properties (MCP) were determined using a Computerized Renneting Meter (Polo Trade, Italy), allowing the milk samples to coagulate for a maximum time of 30 minutes, because, in cheese-making process for most cheese type, curd is usually cut 30 minutes after the addition of the clotting enzyme. The three MCP determined were milk coagulation time (R) in minutes, curd-firming time (K20) in minutes, and curd firmness (A30) in millimeters. The R parameter was the time from the addition of rennet to milk to the beginning of coagulation; K20 was the time from the beginning of coagulation to the moment the width of the curve was 20 mm; A30 was the width of the curve 30 minutes after the addition of rennet. The milk samples that did not form curd in 30 minutes were defined as non-coagulated (NC) samples. Due to failed coagulation process, 107 samples were excluded so, finally, 964 samples were available for statistical analysis. Pedigree information was provided by the Italian Holstein-Friesian Breeders Association (ANAFI, Cremona, Italy). In conclusion, data from this study showed that heritability for MCP were moderate, suggesting that selection for improving milk rennet-coagulation ability might be effective. Further researches to estimate genetic parameters between MCP, production traits, casein content and milk protein polymorphism should be considered, especially to evaluate the opportunity to integrate milk recording system with additional traits related to milk rennet-coagulation ability, in order to create a possible selection index for cheese production in Italian Holstein Friesian breed.