Date of Award

1988

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

First Advisor

R. W. Adkinson

Abstract

Cows diagnosed as having clinical mastitis and from two sire selection lines were compared to assess differences in somatic cell count scores, duration of clinical episode and number of antibiotic treatments applied. The effect of various environmental factors and type traits on somatic cell count score (SCCS) and on duration of episode was investigated and amount and cost of discarded milk was calculated. Data consisted of multiple observations on cows diagnosed as clinically infected at least once during a lactation. Single trait (ST) cows were daughters of sires selected based on predicted differences for milk. Multiple trait (MT) cows were daughters of sires selected based on an index of milk, fat and type. Single trait cows had significantly lower SCCS, had longer clinical episodes and received more antibiotic treatments than MT cows. Least squares mean estimates for SCCS were 1.71 for the ST line and 4.86 for the MT line. Means for days of discarded milk were 16.70 days for the ST line and 7.80 days for the MT line. Estimate for number of treatments were 24.58 for the ST line and 13.44 for the MT line. These differences increased across generations. Results indicated that slower milking cows tended to have lower SCCS, longer episodes and receive more antibiotic treatments. Cows with larger udders before milking had shorter episodes and received less treatments. Cows with larger udders after milking had longer episodes and required more treatments. Taller cows and cows with high udders had higher SCCS and shorter episodes. Single trait cows had significantly more milk discarded due to antibiotic treatment than MT cows. Means for amount of discarded milk for the ST and MT lines were 360.81 kg and 250.99 kg, respectively. The ST line was, however, significantly higher for milk production even after deducting milk losses. Amount of discarded milk was negatively associated with size of udder area before milking, udder height and wither height and positively associated with size of udder area after milking and machine time. Use of some mastitis traits in selection and culling decisions may be necessary.

Pages

211

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