No abstract

Milk coagulation, especially in small ruminant species, is often hard to evaluate, as coagulation traits are normally considered individually and several factors related to udder health might distort yield calculation. Due to the lack of studies about these factors, our objective was to determine milk coagulation efficiency (CE) and its determinants using a deterministic technical efficiency approach, an ordinary least square regression model, and ANOVA. Milk from 300 Manchega ewes was collected and analyzed for composition, milk coagulation properties, and hygienic quality. The study results indicate that the estimated CE in Manchega ewes was 0.69, implying an important proportion of the animals produce poorly coagulating milk. The results of the ordinary least square regression model and ANOVA revealed that the main factor causing inefficiency was the initial pH of milk. Crude protein, casein and plasmin activity had moderate effects on CE, and, finally, other factors such as freezing point depression, somatic cell count, colony-forming units, and fat concentration had minor effects.

The global production of sheep milk is growing, and the main industrial use of sheep milk is cheese making. The Spanish Churra sheep breed is one of the most important native dairy breeds in Spain. The present study aimed to estimate genetic parameters for a wide range of traits influencing the cheese-making ability of Churra sheep milk. Using a total of 1,049 Churra ewes, we studied the following cheese-making traits: 4 traits related to milk coagulation properties (rennet coagulation time, curd-firming time, and curd firmness at 30 and 60 min after addition of rennet), 2 traits related to cheese yield (individual laboratory cheese yield and individual laboratory dried curd yield), and 3 traits measuring curd firmness over time (maximum curd firmness, time to attain maximum curd firmness, and syneresis). In addition, a list of milk traits, including the native pH of the milk and several milk production and composition traits (milk yield; the fat, protein, and dried extract percentages; and the somatic cell count), were also analyzed for the studied animals. After discarding the noncoagulating samples (only 3.7%), data of 1,010 ewes were analyzed with multiple-trait animal models by using the restricted maximum likelihood method to estimate (co)variance components, heritabilities, and genetic correlations. In general, the heritability estimates were low to moderate, ranging from 0.08 (for the individual laboratory dried curd yield trait) to 0.42 (for the fat percentage trait). High genetic correlations were found within pairs of related traits (i.e., 0.93 between fat and dried extract percentages, −0.93 between the log of the curd-firming time and curd firmness at 30 min, 0.70 between individual laboratory cheese yield and individual laboratory dried curd yield, and −0.94 between time to attain maximum curd firmness and syneresis). Considering all the information provided here, we suggest that in addition to the current consideration of the protein percentage trait for improving cheese yield traits, the inclusion of the pH of milk as a measured trait in the Churra dairy breeding program would represent an efficient strategy for improving the cheese-making ability of milk from this breed.

In Spain, ewe milk is mainly used for cheesemaking, and farming systems have traditionally been based on the use of autochthonous breeds. However, in recent years, the progressive introduction of highly productive foreign breeds in Spanish farms has led to an increasing interest in the characterization of dairy sheep breeds to evaluate whether genetic selection schemes should focus on productivity or milk technological aptitude. The purpose of this work was to explore milk composition and coagulation to classify 4 of the main dairy sheep breeds used in Spain. This study included 832 individual ewe milk samples from the breeds Manchega, Assaf, Merino de Grazalema, and Merino de Los Pedroches. Samples were analyzed for native pH, composition (fat, protein, lactose, and total solids), coagulation properties, and individual laboratory curd yield. An indicator of coagulation efficiency was also determined. Canonical discriminant analysis was performed to establish differences and similarities among breeds based on the measured variables. In addition, cluster analysis was performed to study and quantify the concrete relationships among the discriminated groups. Discriminant analysis proved to be a powerful tool to accurately draw distinctions between breeds. In all cases, discrimination among breeds was evident and the 4 breeds could be easily differentiated. Cluster analysis showed greater similarity between Merino de Grazalema and Assaf compared with the other breeds, and F-statistics indicated a higher discriminating ability for the variables related to milk composition. However, Merino de Grazalema and Manchega were difficult to separate according to milk composition, but the coagulation process differenced them clearly. Coagulation also evidenced similarities between Manchega and Merino de Los Pedroches, although the latter was revealed to be the most different breed of all 4, which could lay the ground for its differentiation as an independent breed in the Official Catalogue of Spanish Livestock Breeds.

Yeasts are always present in any type of cheese, as well as in the factories where it is produced. However, the role of the yeast community in the cheese making process, as well as the routes of contamination used by yeast species to contaminate milk from the dairy farm environment, are not well known. The objectives of this study were to broaden the knowledge of the dominant yeast community in Manchega sheep’s milk and to assess the contamination routes of the yeast species depending on the farm practices. Milk, teat surface (collected from ten ewes per farm), feed, and air (collected in milking parlours and livestock housing) samples were collected from 12 typical farms in Castilla-La Mancha, Spain with differences in farming practices, and the yeast species were identified using DNA sequencing methods. To evaluate whether certain farming practices have an effect on the distribution of species of yeast in the milk samples, a mixed model was used. The results showed that most of the dominant yeast species (mainly belonging to the genus Candida) found in milk were also found in the other samples, indicating a microbial transfer from the farm environment to the milk. Furthermore, the statistical model showed that factors influencing yeast counts in milk were the presence of yeasts in the milking parlour, the use of silage, and the frequency of acid treatment for cleaning the milking machines. In conclusion, milk contamination from the yeast species present in the dairy farm environment is related to certain farming practices such as the use of silage and the daily use of acid in the cleaning of the milking machines, which favours the presence of desirable microbiota in milk.