| dc.description.abstract | This study was carried out to determine the effects of lactation number and period on udder traits in Jersey cows, and also the relationship between udder traits, milk yield and its composition, and subclinical mastitis. For that purpose, 53 Jersey cows with different numbers of lactations and lactation periods were selected. The udder traits of the Jersey cows, as well as their milk fat, protein, lactose and dry matter contents, and milk freezing-point, were measured. Subclinical mastitis was also assessed by using the California Mastitis Test (CMT) and somatic cell count (SCC). The effects of lactation number and period on teat height above ground (THAG) (P < 0.01) and right rear teat length (RRTL) (P < 0.05) were significant. Furthermore, the effects of RRTL on daily milk yield, and the effects of rear udder height (RUH) on milk fat, lactose ratio and freezing point (P < 0.05), were significant. There was a negative phenotypic correlation between THAG and lactation number (P < 0.01), and also lactation period, milk fat content and milk dry matter content (P < 0.05). Right front teat length (RFTL) was positively correlated with lactation number but negatively correlated with the milk lactose content and freezing point (P < 0.05). There was also a positive correlation between RRTL and lactation number and period, milk yield per day and 305-day milk yield (P < 0.05). Front udder attachment (FUA) and udder circumference (UC) were negatively, phenotypically correlated with the milk lactose content (P < 0.05). According to the CMT criteria, the differences between cows with mastitis and healthy cows for THAG, RFTL and UC were significant (P < 0.05). Increases in both lactation number and period were associated with a decrease in THAG and an increase in RRTL. An increase of RRTL was also associated with increases in daily and 305-day milk yield. In conclusion, particular emphasis should be placed on RRTL and THAG when dairy cows are selected on the basis of linear type assessment. Furthermore, an increased risk of mastitis in dairy cows as the udder gets closer to the ground, long front teats and large UC, should be taken into consideration in breeding programs. | en_US |
