We determined the effects of calf milk replacers containing 0, 5, or 10% bovine plasma protein (PP), either without or with the supplemental amino acids (AA) Ile and Thr, on growth and health of male Holstein calves (n = 104) for 56 d. Milk replacers were formulated to contain 22% crude protein (CP), 20% fat, and 2.0% Lys. Milk replacers (12.5% solids) were fed at a rate of 1.5% of body weight (BW) on a dry matter basis during wk 1 and 1.75% of BW beginning on d 8. Starter was introduced on d 36 so that effects of PP and AA balance in milk replacers could be isolated. Intake, respiratory scores, and fecal scores were measured daily. Body weight and stature were measured weekly and blood serum samples were obtained during wk 4. Treatments had no effects on intakes of dry matter, CP, or metabolizable energy. During wk 6 and 8, BW was less as PP inclusion increased without AA supplementation compared with the other treatments. In wk 7, calves fed the higher level of PP without AA had lower BW than calves fed either the lower level of PP without supplemented AA or the higher inclusion of PP with supplemented AA. Average daily gain and gain:feed were lowest for calves fed the higher inclusion of PP without supplemented AA; heart girth in wk 7 was smallest for those calves. During the first 21 d, occurrence of scours was greater in calves fed the control milk replacer than in calves fed milk replacers containing the higher inclusion of PP either without or with supplemental AA. Occurrence of scours was also greater for the lower inclusion of PP compared with the higher inclusion of PP when AA were supplemented. Throughout the 56-d experiment, the chance of antibiotic treatment was greater for calves fed the control milk replacer than for all other treatments except the higher inclusion of PP without supplemental AA. Additionally, chance of antibiotic treatment was greater for the higher inclusion of PP without supplemental AA than for other milk replacers with PP. Calves fed treatments with the higher inclusion of PP had fewer days of scours than the controls. All milk replacers with PP, except the milk replacer containing higher PP without supplemental AA, had fewer days of treatment with antibiotics compared to the all-milk control. Inclusion of PP provided similar performance and improved health as long as milk replacers were balanced for Ile and Thr.

Glucagon-like peptide 2 (GLP-2) is a peptide released by the lower gut that has potent trophic and restorative effects on the intestinal epithelium. Two experiments were conducted to assess the effects of feeding rate and either metabolizable or nonmetabolizable glucose supplementation on GLP-2 concentrations in plasma and intestinal development in Holstein calves. In the first experiment, 48 newborn calves were assigned to 12 treatments (n=4) corresponding to the factorial combination of 4 milk feeding amounts [1.75, 1.32, 0.88, and 0.44% of body weight (BW) as dry matter (DM)] and 3 oral supplementation treatments (nonsupplemented, glucose-supplemented, and 3-O-methyl glucose-supplemented). In the second experiment 30 newborn calves (n=10) were fed milk at a fixed rate of 1.75% of BW as DM and assigned to the same glucose supplementation treatments used in experiment 1 to investigate effects on intestinal development. In the first experiment, we found a saturating response of plasma GLP-2 to increasing feeding levels. The feeding rate at which 50% of the maximal GLP-2 release occurred was estimated to be 0.53% of BW as DM or 30.3% of the maximum feeding rate (1.75% of BW as DM), whereas maximal secretion was estimated to be about 98.6 pmol/L. In turn, feeding 75, 50, or 25% of the maximal feeding rate (i.e., 1.75% BW as DM) resulted in plasma GLP-2 concentrations 87, 72, and 49% of that in fully fed calves, respectively. Neither metabolizable nor nonmetabolizable glucose supplementation affected GLP-2 secretion and no interaction with feed intake level was detected. In the second experiment, no effect of glucose supplementation was observed on intestinal growth, mucosal cell proliferation, or expression of genes related to the actions of GLP-2. Nonetheless, we observed that a pool of genes of the GLP-2 signaling pathway was more abundantly and coordinately regulated in the colon than in the ileum of these animals, indicating an opportunity for dietary induction of the peptide in this organ. In conclusion, during this experiment, plasma GLP-2 concentrations responded in a diminishing return fashion to milk intake but not to glucose supplementation, even at milk consumption levels of only 0.4% of BW as DM.

We measured the effects of milk replacers containing 0, 33, 66, or 100% of the total replaceable whey protein as bovine plasma protein (PP), without or with Ile supplementation, on the intake, growth, and health of 124 male Holstein calves for 35d. Milk replacers were formulated to contain 18% crude protein and 20% fat, with contents of Lys and Met equalized. When fed to calves at 1.5% of body weight (dry matter basis) under thermoneutral conditions, diets were predicted to allow average daily gains of 0.55kg/d based on metabolizable energy or 0.40kg/d based on apparent digestible protein. Protein supply was more limiting than energy so that differences in protein use could be detected. Dry matter intakes decreased with increased PP, irrespective of Ile supplementation. Final body weights decreased linearly with increasing PP, regardless of Ile supplementation. Average daily gain tended to be affected in a quadratic manner as PP increased, either with or without Ile supplementation; average daily gain and gain-feed ratio were greatest for calves fed diets containing 33% PP and lowest for calves fed 100% PP. The analyzed Lys content in the milk replacers was variable compared with formulated values, and this may have affected growth results. However, the gain-Lys ratio was affected by an interaction of the linear effect of increasing PP with Ile supplementation: it decreased with increasing PP but was improved by supplementation with Ile for calves fed 100% PP. Body measurements decreased with increasing PP inclusion; only decreased heart girth was reversed with Ile supplementation. The lowest and highest inclusion of PP, regardless of Ile supplementation, decreased the occurrence of scours compared with the control diet (all whey protein). Calves fed the lowest and highest PP without Ile supplementation also had fewer total days of scours in the first 21d. In addition, calves fed 100% PP without supplementation of Ile had fewer days of medication compared with the control diet. Even at the highest PP inclusion, average daily gain was minimally affected if Ile was supplemented. Growth rates, gain-feed ratio, and gain-Lys ratio were decreased at higher PP inclusion, but Ile overcame part of the reduction in gain-Lys ratio for 100% PP. Additional titration studies will have to be conducted to determine optimal PP inclusion rates, with a focus on supplementation of potentially limiting essential AA, as well as effects at higher growth rates.