8th World Congress on Genetics Applied to Livestock Production, August 13-18, 2006, Belo Horizonte, MG, Brasil HEALTH, IMMUNE FUNCTION AND SURVIVAL OF HOLSTEIN AND CROSSBRED JERSEY X HOLSTEIN DAIRY CALVES K. A. Weigel, C. Maltecca, H. Khatib, V. R. Schutzkus, and P. C. Hoffman University of Wisconsin, 1675 Observatory Drive, Madison, WI, 53706, USA INTRODUCTION For many years, the superiority of the Holstein breed for milk production and the strong role of breed associations in developing selection policies have limited the use of crossbreeding in dairy cattle. However, trends in milk pricing favoring high fat and protein content, coupled with increasing concerns about health, fertility, and calving performance have led to greater interest in crossbreeding among commercial dairy producers. In a recent crossbreeding survey (Weigel and Barlass, 2003), dairy producers with crossbred cattle indicated improved survival rates among F 1 Holstein x Jersey calves and backcross (Holstein x Jersey) x Holstein calves, relative to their pure Holstein contemporaries. Furthermore, a preliminary study (Maltecca and Weigel, 2004) on a commercial farm reported significantly (P < 0.05) higher serum protein and IgG levels in F 1 Jersey x Holstein calves at 0 to 72 hr of age, relative to their Holstein contemporaries. In the same study, Holstein calves tended (P < 0.10) to have higher fecal consistency scores than F 1 Jersey x Holstein calves, reflecting a greater incidence of scours. The objective of this study was to assess differences in serum protein and IgG levels, scours, respiratory disease and perinatal and pre-weaning mortality between Holstein and backcross (Holstein x Jersey) x Holstein calves. MATERIALS AND METHODS Data collection. Crossbred calves were produced via backcross mating of randomly chosen lactating Holstein cows to randomly allocated young F 1 Holstein x Jersey sires (N = 7). The remaining lactating Holstein cows were randomly mated to young Holstein sires (N = 74) to produce experimental controls. Data were collected from November 2003 to December 2005. Calves were isolated from their dams immediately after birth and were not allowed to suckle maternal colostrum. Calves were weighed within 15 min of birth and were fed a single colostrum meal by nipple bottle with pooled, frozen colostrum from multiparous Holstein cows within 1 hr, at a rate of 7% of body weight. An esophageal feeder was used when calves refused to suckle. Fecal consistency scores and respiratory disease scores were measured on Monday, Wednesday, and Friday of each week. The former were measured on a 4-point ordinal scale (1 = normal, 2 = soft, 3 = runny, 4 = watery), while the latter were measured on a 5-point ordinal scale (1 = normal, 2 = runny nose, 3 = heavy breathing, 4 = moist cough, 5 = dry cough). Data for female calves were collected from birth through weaning, while data for male calves were collected from birth through 7 d of age, when these calves were sold from the farm. Therefore, mean and maximum fecal and respiratory scores were evaluated from birth to 7 d of age for male and female calves and from birth to weaning for female calves only. Perinatal and pre-weaning mortality data were recorded at 24 hr of age and 6 wk of age, respectively. Serum protein level and serum IgG level were evaluated as follows. Blood samples (5 ml) were collected at 24 to 72 hr of age by jugular venipuncture using evacuated tubes containing no anticoagulant. Serum was harvested from the blood via centrifugation and was frozen at –20°C until analysis. Serum protein was measured using a refractometer, while serum IgG was determined using a radial immunodiffusion assay. The IgG specific antiserum was incorporated into agarose gel; the sample antigen diffused into gel containing the antibody, and a ring of precipitation was formed, proportional in size to the concentration of the antigen. Statistical analyses. A general linear model was used to analyze traits measured on a continuous scale, including: mean fecal consistency score and respiratory disease score from