2015-06-182015-05http://hdl.handle.net/2346/62275The objectives of first study were to determine the digestibilities of nutrients as well as investigate the nitrogen retention of calves fed different planes of milk replacer nutrition during the first week of life. Twelve Jersey calves were blocked by BW at birth and randomly assigned to high plane of nutrition (HPN) or low plane of nutrition (LPN) treatments. The HPN calves were offered 20g DM/kg BW of a 28% CP and 20% fat milk replacer. The LPN calves were fed 14.5g DM/kg BW of a 20% CP and 20% fat milk replacer. All calves were given 3 L of pooled colostrum within 1 hour of birth after which they were assigned to treatments. Calves were given 1 day to adapt to treatment, accordingly, calves were 30 to 36 hours old at the start of data collection. The study was divided into two 72 hour periods. Total collection of feces occurred over each 72 hour period and total urine was collected for the last 24 hours of each period. Peripheral blood samples were collected at the beginning and end of each period and analyzed plasma glucose and urea nitrogen concentrations. Fecal scores were greater (P=0.004) for HPN calves during both periods; however, there was no difference (P≥0.253) in the dry matter percentage of feces. There were no differences (P≥0.239) between treatments in either digestible or metabolizable energy efficiencies, which averaged 92 and 83% for HPN and LPN, respectively. There was a treatment x period interaction (P=0.038) for the percentage of intake nitrogen retained, as HPN calves had greater percentage of intake nitrogen retained during period 1 (88.0 vs 78.7 ± 1.79; P=0.004), but was not different from calves fed the LPN during period 2 (85.3 vs 85.0 ± 1.79; P=0.904). Therefore these data indicate that neonatal calves have the capability to digest and absorb the additional nutrients with a higher plane of nutrition during the first week of postnatal life. The additional energy and amino nitrogen absorbed by calves fed the higher plane of nutrition were incorporated into lean tissue growth with a great efficiency. The objective of second study was to evaluate the effects of plane of milk replacer nutrition on the resistance to an opportunistic enteric challenge with Citrobacter freundii at 10 days of life. Twenty colostrum-fed Jersey calves were blocked by BW at birth and randomly assigned to either a high plane of nutrition (HPN) or low plane of nutrition (LPN) treatment. The LPN calves were fed 400 and 450 g DM/d of a 20% CP and 20% fat milk replacer during the 1st week and the remainder of the study, respectively. The HPN calves were fed 600 and 700 g DM/d of a 28% CP and 20% fat milk replacer during the 1st week and the remainder of the study, respectively. All calves were challenged orally with 1 x 108 colony forming units of a stationary phase culture of Citrobacter freundii at day 10. Fecal scores were recorded throughout the study and rectal temperatures were recorded daily immediately before and after the challenge. Fecal samples and plasma from peripheral blood samples were collected stored at -80oC at day 10, 12, 14, 16, 18, 20, 22, and 24 until further analysis. Fecal samples were analyzed for dry matter percentage and plasma was analyze for concentrations of urea nitrogen, glucose, and haptoglobin. All calves were harvested at day 24 and ileum tissue samples were analyzed for morphology. Water intakes were greater for the HPN calves before the enteric challenge (P≤0.062) and increased to a greater extent after the challenge (P≤0.021). Fecal scores were also greater among HPN calves (2.52 vs 2.04 ± 0.07; P=0.001); however, there was no difference in dry matter percentage of feces between treatments (19.9 vs 21.9 ± 1.34%; P=0.291). There was a difference in the dry matter percentage of feces scored as a fecal score 3 between the HPN and LPN calves (20.2 vs 16.3 ± 0.965%; P=0.006). Rectal temperatures were greater among the HPN calves (P=0.024). In addition, the HPN calves had numerically greater peak plasma haptoglobin concentrations after the challenge (511 vs 266 ± 108.0 μg/mL; P=0.118) and tended to have a greater total mucosal height of the distal ileum (921 vs 752 ± 59.1 μm; P=0.059). Therefore these data indicate that calves fed a HPN during the neonatal period have a mildly greater acute phase response to an opportunistic bacterial enteric infection and it may be associated with a greater mucosal surface area of the distal ileum. Furthermore, these data reiterate that fecal scores should not be the only measure of enteric health, especially when evaluating the effects of planes of nutrition.application/pdfengCalfDigestibilityDiseaseHealthNutritionThesisUnrestricted.