ABSTRACT
Ninety-three intensively managed, mature ewes were followed through three lactations to study effects and interrelationships of postweaning fast, prophylactic antibiotic injection, number of lactations and breed on subclinical mastitis, milk production and milk composition. Animals used in a 2 x 2 factorial design were allotted to treatment combinations of 1) postweaning 72 h fast or no fast, and 2) 1 x 10(6) units of procaine penicillin or sham i.m. injection at weaning. Treatments were implemented at weaning in yr 1; each ewe received the same treatment in each of the subsequent 2 yr of the study. Breeds included Finnish Landrace (F), Dorset (D), Rambouillet (R), Finnish Landrace x Dorset (FD) and Barbados Blackbelly x Dorset (BD). Milk production was greatest for D, followed by BD, FD, R and F during yr 1 (P less than .01) and overall (P less than .05). Milk production data were not collected in yr 2, but similar results were obtained in yr 3, except that the R and F exchanged rank positions. Milk composition was affected by breed. Breeds differed (P less than .05) in percentage lactose, fat and total nonfat solids in yr 1 and differed (P less than .01) in percentage lactose, fat, solids and protein across the 2 yr. A breed difference (P less than .05) was observed for incidence of mastitis at 3 wk postpartum and at weaning. Milk production was negatively correlated with incidence of mastitis (r = -.22, P less than .05). Milk production was improved (P less than .05) by a 72-h postweaning fast.(ABSTRACT TRUNCATED AT 250 WORDS)
