Graduate Thesis Or Dissertation
 

Interrelationships among characteristics of body form and milk production in dairy cattle

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  • Evaluations of body form and measures of milk production were recorded for 188 Holstein lactations and 77 Jersey lactations in the Oregon State University Dairy Herds. Components of body form included general appearance, dairy character, body capacity, and mammary system and 34 sub-components of these four traits plus body weight and wither height. Subjective components of body form were scored by two judges at approximately 30 days post-partum independent of age and previous score. Measures of milk production included actual and mature equivalent yields of milk, fat, and SNF, and percentages of fat and SNF plus peak yield, persistency of milk yield, solids-corrected milk, and test-day yields of milk for the first six months of lactation. Age at parturition and estimated breeding value were also included in this study. Sub-components of body form were quite effective in explaining the variation in the four major components. General appearance, dairy character, body capacity, and mammary system had R² values of .84, .94, .95, and .95, and .82, .95, .94, and .96, respectively for Holsteins and Jerseys. Correlations among the sub-components of dairy character and of body capacity were quite strong, ranging from .49 to .96 for both breeds. Correlations among the sub-components of general appearance were lowest and the most variable of the four major components (-.08 to .91). Correlations among components of mammary system were intermediate. Path coefficients indicated that the sub-components with the most effect on overall score for general appearance were stature, feet and legs, and rump or its components. Sub-components of dairy character had about equal effects on overall score for dairy character except that scores for pins and hide had the least influence. Scores for overall body capacity were influenced the greatest by depth of barrel. In scoring mammary system the most emphasis was placed on fore udder, followed by rear udder and score for teats. Final score was most influenced by scores for mammary system. It was found that the relative emphasis as indicated by path coefficient analyses was strongly affected by the variability of the traits involved. The effect of age was found to be significant in this study making interpretation of the correlations more difficult. Dairy character, body capacity, body weight, and wither height all increased with age. General appearance and final score were less affected by age. Scores for mammary system decreased with advancing age. Milk yield was correlated .99 with SNF yield. Milk yield with fat yield (.92 in Holsteins and .94 in Jerseys) were higher than previously reported. Age had no significant effect on percent fat but caused a decrease in percent SNF with advancing age. Correlations of most of the components of body form with milk yield were rather low. Dairy character was correlated .46 and .15 with actual milk yield in Holsteins and Jerseys, respectively. Adjusting the milk, fat, and SNF to mature equivalents or adjusting milk to a common energy basis were not effective in increasing the correlations of body form with milk production. Dairy character was correlated .43 and -.09 with peak yield and persistency, respectively for Holstein and .26 and .01, respectively for Jerseys. Measures of body size (body capacity, body weight, and wither height) were more highly correlated with peak production than with other measures of milk production. Their respective correlations with peak yield for Holsteins and Jerseys were .25 and .17 for body capacity, .39 and .41 for body weight, and .32 and .25 for wither height. The corresponding correlations of these components with persistency were -.07 and -.01 for body capacity, -.33 and -.23 for body weight and -.23 and -.08 for wither height.
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