Variation in cheese making properties of milk from dairy cows: focus on animal status, farming system and crossbreeding

Approximate 80% of world milk production comes from cows and nearly 40% of the total cow milk is processed into cheese. Thus, cheese making properties of cow’s milk have received great interest from global cheese industry. In last decades, many scientific researches have investigated the factors able to affect the cheese making properties of milk. Among these, particular attention has been given to composition, handling, storage and pretreatment of milk, such as standardization and pasteurization, and to equipment and technology used to process milk into cheese. Also breeds of cows and specific characteristics of the animals, such as parity, days in milk and herds, have been investigated by several authors. Conversely, less is known about the effects of animal metabolic status on cheese-making properties of milk. Similarly, the relationships between the cheese-making properties of milk with different management strategies of dairy cows, such as specific farming systems, or the use of crossbreeding schemes need to be further investigated. Therefore, the present PhD thesis aimed to investigate the effects of rumen acidity status, that of summer transhumance dairying system and the implications of adopting specific schemes of crossbreeding on milk coagulation properties and cheese-making traits of dairy cows. In the present thesis, cheese-related traits of milk from individual cows were assessed by focusing on rumen acidity status (chapter 1), summer transhumance farming system (chapter 2) and crossbreeding (chapter 3 and chapter 4) effects on the milk composition, coagulation properties (single point milk coagulation traits and curd firming equation parameters), and cheese yield and nutrient recoveries in the curd. In addition, the quality (chemical components, rheological traits and sensory attributes) of cheese made from the milk of crossbred cows and purebred Holstein was also assessed (chapter 4). More precisely, the goal of the first chapter was to investigate whether the rumen acidity status affects rumination time (RT), and the yield, composition and coagulation properties of milk (MCP), considering also cheese yield (CY) and milk nutrient recoveries in curd (REC). The increase in milk yield achieved in recent decades by the dairy sector has been sustained by feeding dairy cows with more concentrates and less forage. The use of high grain rations in dairy cows is related to an increase in rumen acidity. For this study, one hundred early-lactating Holstein cows with no clinical signs of disease and fed total mixed rations were used. Rumen fluid was collected once from each cow by rumenocentesis to determine pH and volatile fatty acid (VFA) content. The cows were classified according to the quartile of rumen acidity (QRA), a factor defined by multivariate analysis and associated with VFA and pH. Rumen fluid pH averaged 5.61 in the first quartile and 6.42 in the fourth, and total VFA content increased linearly with increasing rumen acidity. In addition, RT increased as rumen acidity increased, but only in the daily time interval from 08:00 to 12:00. Milk yield linearly decreased as rumen acidity increased, whereas QRA did not affect pH, fat or the protein content of milk. Furthermore, the MCP, assessed by lactodynamograph, and CY were unaffected by QRA. It is suggested that differences in rumen acidity have little influence on the nutrient content, coagulation properties and CY of milk. The second chapter aimed to investigate the effects of summer transhumance of dairy cows to alpine pastures on body condition, milk yield and composition, coagulation properties, cheese yield and nutrient recoveries in curd. Summer transhumances of dairy cows to mountain pasture are widespread dairy farming system practiced in many European countries. In this study, total 12 multiparous Brown Swiss cows from lowland permanent farm (PF) were divided in two equal groups where one group remained at the PF and the other group was transferred to the alpine mountain pastures (ALP; 1860 m above sea level) from July to September. From June to October (once in a month), daily milk yield and body condition score (BCS) were recorded, and individual milk samples (n = 60, 2000 mL each) were collected for assessing milk composition, MCP, CY and REC traits. Compared with PF, ALP cows had a reduced milk yield and BCS, which was maintained on return to the PF, with greater fat and lower protein contents of milk. MCP, CY and REC traits were same for both groups of animals. Summer transhumance did not alter the cheese making efficiency of milk but depressed milk yield and consequently daily cheese yield, which was nearly 2 kg/d, lower for the ALP than the PF cows and was only partially recovered after returning to the PF in autumn. The objective of the third chapter was to investigate the effects of long term systematic application of rotational crossbreeding on milk technological properties and cheese yield. Crossbreeding is a strategy to counter the declining fertility, resilience and longevity of purebred Holstein (Ho) cows. However, little is known of the effects of long-term systematic rotational crossbreeding on milk technological properties and cheese yield. In this study we compared the milk composition, coagulation properties and individual cheese yields of 468 purebred Ho and 648 crossbred (CR) cows obtained from two 3-breed rotational crossbreeding systems using Viking Red (VR), Montbéliarde (Mo) and Ho sires over 4 generations. Individual milk samples were collected once from 1116 primiparous and multiparous cows kept in two dairy herds, raised for the production of Grana Padano (high milk yield, total mixed ration based on corn silage) and Parmigiano Reggiano cheese (moderate milk yield, only dry feeds). In both herds, a 3-breed rotational mating system was used, in which Ho cows were first inseminated with VR, whereas Mo and Ho semen was used in the subsequent generations. In one herd, the sequence Mo-VR-Ho was also used. Individual milk samples were analyzed for milk composition, single-point MCP, and parameters for modeling curd-firming over time, whereas CY and REC traits were assessed through a laboratory cheese-making procedure. Compared with Ho, CR cows produced 5.8% less milk, with comparable fat but greater protein and casein contents, and lower lactose contents and somatic cell scores (SCS). Milk from CR cows reached a curd firmness of 20 mm more quickly, and exhibited greater curd firmness at 30, 45 and 60 min from rennet addition. Ho and CR cows yielded milk with very similar CY and REC traits. The milk fat content, SCS, curd firmness traits and CY of CR cows relative to the Ho cows differed in the two herds, and the favorable effects on the CR cows were more evident in the herd with the greatest milk yield and the worst MCP traits. Crossbred cows of the four generations performed similarly, with the exception of the better MCP of the milk from F1 CR cows. The two rotational systems using different sire-breed sequences also performed similarly. In summary, both rotational crossbreeding programs exhibited some advantage over the Ho purebred breeding system in terms of milk composition and MCP, but not CY. Future research is needed to investigate the interactions between crossbreeding schemes and dairy systems. The fourth chapter focuses mainly on rheological, chemical and sensory properties of cheese made from milk obtained by purebred Ho and 3-breed rotational CR cows. Four generations of CR cows (F1 to F4) obtained using semen from VR, Mo and Ho sires were considered. A total of 120 individual milk samples (Ho: 40; CR: 80, 20 for each generation) were collected from evening milking in 6 different sessions of 20 cows each. Samples consisted on 2000 mL of raw full-fat milk, and they were refrigerated after collection and processed the subsequent day for assessing milk composition, casein micelle size, fat globule size, milk coagulation properties, fresh cheese yield and milk nutrient recoveries in the curd and model cheese preparation. The casein micelle and fat globule size in milk were measured by laser light scattering using Mastersizer 2000. The prepared cheeses, weighing 157.6 ± 23.2 g after 70 d of ripening, were evaluated for ripening loss, chemical, rheological and sensory attributes. Rheological properties include the instrumental color assessment, through a Minolta colorimeter, and the texture analysis, through a TA.XTplus texture analyzer. Sensory analysis was performed by 6 panelists, which assessed cheese samples (score: low, 1 to high, 10) for five main sensory attributes related to appearance (color), smell intensity, flavor intensity, taste attributes (sweet, salt, sour, bitter and umami), and texture characteristics (elasticity, firmness and moisture). Results show that, compared with the milk from purebred Ho cows that from CR cows had greater contents of protein and casein and lower contents of lactose and somatic cell score. Moreover, milk from CR cows had smaller average casein micelle size compared to milk from Ho cows, with comparable, although tendentially smaller, fat globule size (d43, d32). Also, milk from CR cows showed shorter time to reach a curd firmness of 20 mm and greater curd firmness at 45 and 60 min after rennet addition. Milk from CR and Ho cows exhibited similar cheese yield and milk nutrient recovery traits. In addition, the weight, chemical composition, rheological (color, hardness, cohesiveness, elasticity index and chewiness) and sensory attributes of individual model cheeses were comparable for Ho and CR cows. Among crossbred cows, VR sired crossbred cows displayed a positive effect on milk composition (protein and casein), curd firming properties, CY and REC traits and weight of cheese for fresh and ripened condition, whereas Mo sired crossbred cows had opposite trends for these traits. This study indicates that 3 breed rotational crossbreeding scheme did not exert any negative effect in cheese making properties and cheese attributes and seems to adapt to farming systems particularly focused toward cheese production. The knowledge of this research provides new insights in factors affecting cheese making properties which have significant importance for farmer and cheese industry point of view.