In experiment one, week old Jersey bull calves (n=39) were assigned to one of four diets: 21/21 (n=8), 27/33 (n=8), 29/16 (n=9), MILK; or a baseline sacrifice group (n=6). Diets 21/21, 27/33, and 29/16 were milk replacers containing 21, 27, or 29% CP, and 21, 33, and 16% fat, respectively. Diet 21/21 was fed at 15% of BW. Diets 27/33, 29/16, and MILK supplied 180g CP/d. Calves were fed 4 wk. Weight, hip height, wither height, heart girth, and body length were measured weekly. Weekly plasma samples were analyzed for PUN, NEFA, and glucose. Calves were processed to estimate body composition. Feed efficiency and ADG were greatest for calves fed MILK, least for calves fed 21/21, and intermediate for calves fed 29/16 and 27/33. Calves fed 27/33 or MILK had the greatest gains of fat and percentage fat in the empty body. Body fat percentage of calves fed 29/16 or 21/21 was not changed by diet. Performance of calves fed 27/33 and 29/16 was similar except that calves fed 29/16 were leaner and calves fed 27/33 had a propensity for elevated NEFA. Feeding 180g of CP in the MR was beneficial to calf performance compared with diet 21/21.
In experiment two, tissues from a subset of calves [21/21 (n=4), 27/33 (n=5), 29/16 (n=5), MILK (n=3), baseline (n=2)] were scanned using dual energy x-ray absorptiometry to estimate mass, fat, CP, and ash. Liver, organ, and carcass mass by DXA were correlated to scale weights (R2= 0.99, 0.62, and 0.79, respectively). DXA was a poor predictor of percentage fat, CP, and ash (adjusted R2 <0.10).
Experiment three determined level of calf mortality in the United States; and identified opportunities to reduce mortality. Herds (n=88) were representative of the US Jersey population. Production averaged 7180 ± 757 kg milk annually. Herds averaged 199 births annually. Mortality was 5.0% from birth to 24 h (M24) of life and 6.7% from 24 h to 3 mo of life (M3). Level of mortality (M24) was highest in herds that calved on pasture. Lower levels of mortality (M3) were associated with use or maternity pens and earlier weaning.
