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High interindividual variation in growth performance is commonly observed in veal calf production and appears to depend on milk replacer (MR) composition. Our first objective was to examine whether variation in growth performance in healthy veal calves can be predicted from early life characterization of these calves. Our second objective was to determine whether these predictions differ between calves that are fed a high- or low-lactose MR in later life. A total of 180 male Holstein-Friesian calves arrived at the facilities at 17 ± 3.4 d of age, and blood samples were collected before the first feeding. Subsequently, calves were characterized in the following 9 wk (period 1) using targeted challenges related to traits within each of 5 categories: feeding motivation, digestion, postabsorptive metabolism, behavior and stress, and immunology. In period 2 (wk 10–26), 130 calves were equally divided over 2 MR treatments: a control MR that contained lactose as the only carbohydrate source and a low-lactose MR in which 51% of the lactose was isocalorically replaced by glucose, fructose, and glycerol (2:1:2 ratio). Relations between early life characteristics and growth performance in later life were assessed in 117 clinically healthy calves. Average daily gain (ADG) in period 2 tended to be greater for control calves (1,292 ± 111 g/d) than for calves receiving the low-lactose MR (1,267 ± 103 g/d). Observations in period 1 were clustered per category using principal component analysis, and the resulting principal components were used to predict performance in period 2 using multiple regression procedures. Variation in observations in period 1 predicted 17% of variation in ADG in period 2. However, this was mainly related to variation in solid feed refusals. When ADG was adjusted to equal solid feed intake, only 7% of the variation in standardized ADG in period 2, in fact reflecting feed efficiency, could be explained by early life measurements. This indicates that >90% of the variation in feed efficiency in later life could not be explained by early life characterization of the calves. It is speculated that variation in health status explains a substantial portion of variation in feed efficiency in later life. Significant relations between fasting plasma glucose concentrations, fecal pH, drinking speed, and plasma natural antibodies in early life (i.e., not exposed to the lactose replacer) and feed efficiency in later life depended on MR composition. These measurements are therefore potential tools for screening calves in early life on their ability to cope with MR varying in lactose content. [ABSTRACT FROM AUTHOR]

Effects of solid feed (SF) level and roughage-to-concentrate (R:C) ratio on ruminal drinking and passage kinetics of milk replacer, concentrate, and roughage were studied in veal calves. In total, 80 male Holstein-Friesian calves (45 ± 0.2 kg of body weight) were divided over 16 pens (5 calves per pen). Pens were randomly assigned to either a low (LSF) or a high (HSF) SF level and to 1 of 2 R:C ratios: 20:80 or 50:50 on a dry matter (DM) basis. Roughage was composed of 50% corn silage and 50% chopped wheat straw on a DM basis. At 27 wk of age, measurements were conducted in 32 calves. During the measurement period, SF intake was 1.2 kg of DM/d for LSF and 3.0 kg of DM/d for HSF, and milk replacer intake averaged 2.3 kg of DM/d for LSF and 1.3 kg of DM/d for HSF. To estimate passage kinetics of milk replacer, concentrate, and straw, indigestible markers (CoEDTA, hexatriacontane C36, Cr-neutral detergent fiber) were supplied with the feed as a single dose 4, 24, and 48 h before assessment of their quantitative recovery in the rumen, abomasum, small intestine, and large intestine. Rumen Co recovery averaged 20% of the last milk replacer meal. Recoveries of Co remained largely unaffected by SF level and R:C ratio. The R:C ratio did not affect rumen recovery of C36 or Cr. Rumen fractional passage rate of concentrate was estimated from recovery of C36 in the rumen and increased from 3.3%/h for LSF to 4.9%/h for HSF. Rumen fractional passage rate of straw was estimated from Cr recovery in the rumen and increased from 1.3%/h for LSF to 1.7%/h for HSF. An increase in SF level was accompanied by an increase in fresh and dry rumen contents. In HSF calves, pH decreased and VFA concentrations increased with increasing concentrate proportion, indicating increased fermentation. The ratio between Cr and C36 was similar in the small and large intestine, indicating that passage of concentrate and straw is mainly determined by rumen and abomasum emptying. In conclusion, increasing SF level introduces large variation in passage kinetics of dietary components, predominantly in the rumen compartment. The SF level, rather than the R:C ratio, influences rumen recovery of concentrate and roughage. Our data provide insight in passage kinetics of milk (Co representing the milk replacer) and SF (Cr and C36 representing roughage and concentrate, respectively) and may contribute to the development of feed evaluation models for calves fed milk and SF. [ABSTRACT FROM AUTHOR]

We aimed to investigate the feeding values of milk replacer (MR), roughage, and concentrates for veal calves in a paired-gain setting, thus avoiding any prior assumptions in feeding values and major differences in nutrient intakes. One hundred sixty male Holstein-Friesian calves at 2 wk of age and 45 ± 0.2 kg of body weight (BW) were included in the experiment. Calves were allocated to pens (5 calves per pen) and pens were randomly assigned to 1 of 4 solid feed (SF) levels: SF1, SF2, SF3, or SF4, respectively, and to 1 of 2 roughage-to-concentrate (R:C) ratios: 20:80 or 50:50. An adaptation period from wk 1 to 10 preceded the experimental period (wk 11 to 27). Total dry matter (DM) intake from SF was targeted to reach 20, 100, 180, and 260 kg of DM for SF1 to SF4, respectively, during the 16-wk experimental period, and increased with preplanned, equal weekly increments. Roughage was composed of 50% corn silage and 50% chopped wheat straw based on DM. The quantity of MR provided was adjusted every 2 wk based on BW to achieve similar targeted rates of carcass gain across treatments. The reduction in MR provided (in kg of DM) to realize equal rates of carcass gain with inclusion of SF (in kg of DM) differed between the R:C ratio of 50:50 (0.41 kg of MR/kg of SF) and the R:C ratio of 20:80 (0.52 kg of MR/kg of SF). As carcass gain unintentionally increased with SF intake, the paired-gain objective was not fully achieved. When adjusted for realized rates of carcass gain, calves fed an R:C ratio of 20:80 still required 10% less MR than calves fed an R:C ratio of 50:50 for equal rates of carcass gain, indicating that the utilization of SF for gain increased with concentrate inclusion. Averaged for the 16-wk experimental period, the feeding value of MR relative to that of concentrates and roughages was close to that predicted based on their respective digestible energy contents. Nevertheless, the feeding value of SF relative to that of MR increased substantially with age. Therefore, additivity in feeding values of these ration components cannot be assumed. The results of the current study may contribute to the development of new concepts for formulation of veal calf diets with substantial amounts of SF. [ABSTRACT FROM AUTHOR]

Veal calves at the age of 4 to 6 mo often experience problems with glucose homeostasis, as indicated by postprandial hyperglycemia, hyperinsulinemia, and insulin resistance. It is not clear to what extent the ontogenetic development of calves or the feeding strategy [e.g., prolonged milk replacer (MR) feeding] contribute to this pathology. The objective of this study was therefore to analyze effects of MR feeding, weaning, and supplementation of short-chain fructo-oligosaccharides (FOS) on the development of glucose homeostasis and insulin sensitivity in calves during the first 3 mo of life. Thirty male Holstein-Friesian calves (18 ± 0.7 d of age) were assigned to 1 of 3 dietary treatments: the control (CON) group received MR only, the FOS group received MR with the addition of short-chain FOS, and the solid feed (SF) group was progressively weaned to SF. The CON and FOS calves received an amount of MR, which gradually increased (from 400 to 1,400 g/d) during the 71-d trial period. For the SF calves, the amount of MR increased from 400 to 850 g/d at d 30, and then gradually decreased, until completely weaned to only SF at d 63. The change in whole body insulin sensitivity was assessed by intravenous glucose tolerance tests. Milk tolerance tests were performed twice to assess changes in postprandial blood glucose, insulin, and nonesterified fatty acid responses. Whole-body insulin sensitivity was high at the start (16.7 ± 1.6 × 10-4 [μU/mL]-1), but decreased with age to 4.2 ± 0.6 × 10-4 [μU/mL]-1 at the end of the trial. The decrease in insulin sensitivity was most pronounced (~70%) between d 8 and 29 of the trial. Dietary treatments did not affect the decrease in insulin sensitivity. For CON and FOS calves, the postprandial insulin response was 3-fold higher at the end of the trial than at the start, whereas the glucose response remained similar. The SF calves, however, showed pronounced hyperglycemia and hyperinsulinemia at the end of the trial, although weaning did not affect insulin sensitivity. We conclude that whole body insulin sensitivity decreases by 75% in calves during the first 3 mo of life. Weaning or supplementation of short-chain FOS does not affect this age-related decline in insulin sensitivity. Glucose homeostasis is not affected by supplementation of short-chain FOS in young calves, whereas postprandial responses of glucose and insulin to a MR meal strongly increase after weaning. [ABSTRACT FROM AUTHOR]

Calf milk replacers contain 40 to 50% lactose. Fluctuating dairy prices are a major economic incentive to replace lactose from milk replacers by alternative energy sources. Our objective was, therefore, to determine the effects of replacement of lactose with glucose, fructose, or glycerol on energy and protein metabolism in veal calves. Forty male Holstein-Friesian calves (114 ± 2.4 kg) were fed milk replacer containing 46% lactose (CON) or 31% lactose and 15% of glucose (GLUC), fructose (FRUC), or glycerol (GLYC). Solid feed was provided at 10 g of dry matter (DM)/kg of metabolic body weight (BW0.75) per day. After an adaptation of 48 d, individual calves were harnessed, placed in metabolic cages, and housed in pairs in respiration chambers. Apparent total-tract disappearance of DM, energy, and N and complete energy and N balances were measured. The GLUC, FRUC, and GLYC calves received a single dose of 1.5 g of [U-13C]glucose, [U-13C]fructose, or [U-13C]glycerol, respectively, with their milk replacer at 0630 h and exhaled 13CO2 and 13C excretion with feces was measured. Apparent total-tract disappearance was decreased by 2.2% for DM, 3.2% for energy, and 4.2% for N in FRUC compared with CON calves. Energy and N retention did not differ between treatments, and averaged 299 ± 16 kJ/kg of BW0.75 per day and 0.79 ± 0.04 g/kg of BW0.75 per day, respectively, although FRUC calves retained numerically less N (13%) than other calves. Recovery of 13C isotopes as 13CO2 did not differ between treatments and averaged 72 ± 1.6%. The time at which the maximum rate of 13CO2 production was reached was more than 3 h delayed for FRUC calves, which may be explained by a conversion of fructose into other substrates before being oxidized. Recovery of 13C in feces was greater for FRUC calves (7.7 ± 0.59%) than for GLUC (1.0 ± 0.27%) and GLYC calves (0.5 ± 0.04%), indicating incomplete absorption of fructose from the small intestine resulting in fructose excretion or fermentation. In conclusion, energy and N retention was not affected when replacing >30% of the lactose with glucose, fructose, or glycerol. Increased fecal losses of DM, energy, and N were found in FRUC calves compared with CON, GLUC, and GLYC calves. Postabsorptive losses occurred with the urine for glucose and glycerol, which caused a lower respiratory quotient for GLUC calves during the night. Fructose was oxidized more slowly than glucose and glycerol, probably as a result of conversion into other substrates before oxidation. [ABSTRACT FROM AUTHOR]