Recent research has revealed potential advantages of feeding an elevated plane of nutrition to calves during the preweaning period. However, calves fed more nutrients preweaning may be more susceptible to depressed growth and weaning stress during the transition from liquid to solid feed. The objective of this study was to investigate the relationship between the age of weaning and feed intake, and its influence on growth, gastrointestinal development, and behavioral indicators in dairy calves fed an elevated plane of nutrition during the preweaning period. To meet this objective, 20 female Holstein calves were randomly assigned at birth to be weaned at 6 or 8 wk. Milk replacer (mixed at 150 g/L) was offered at 1.2 kg/calf per day in 2 meals until a 1-wk step-down, when meals were reduced by 50% 1 wk before weaning. Daily starter, chopped oat straw, water intake, and weekly body weights were measured until d 70 of life. To assess digestive tract development, rumen fluid, fecal, and blood samples were taken before and after weaning (d 35, 49, and 63) and analyzed for ruminal short-chain fatty acids, blood β-hydroxybutyrate, and fecal starch, respectively. Behavioral indicators of weaning stress, including vocalizing and non-nutritive oral behavior, were measured by visual observation for 1 h, 3 times per week, before the second feeding of the day during the period from 2 wk before weaning to 2 wk after weaning. The calves weaned at 8 wk compared with 6 wk had higher average daily gain for the week preweaning (0.79±0.09 vs. 0.34±0.10 kg/d) and postweaning (1.05±0.09 vs. 0.35±0.11 kg/d), and were heavier at d 70 (99.9±1.81 vs. 91.0±2.26 kg). From 5 to 8 wk of age, starter and water intakes were lower in calves weaned at 8 wk of age. However, overall starter intake did not differ during the last week of the experiment. Furthermore, calves weaned at 8 wk compared with 6 wk had higher starter intake for 1 wk preweaning (1.36±0.13 vs. 0.40±0.08 kg/d) and postweaning (2.51±0.20 vs. 1.16±0.15 kg/d). In both treatments, weaning increased ruminal short-chain fatty acids, blood β-hydroxybutyrate, and fecal starch, yet the differences between the week before and after weaning were greater for calves weaned at 6 wk compared with those weaned at 8 wk. Treatment × week relative to weaning interactions indicated that several behaviors varied between early- and later-weaned calves during the week before weaning; calves weaned at 6 wk tended to exhibit 75% more non-nutritive oral behavior and spent 55% less time ruminating, and 36% less time lying compared with calves weaned at 8 wk. Under the conditions of this study, the results suggest that calves fed an elevated plane of nutrition preweaning have higher starter intakes and average daily gain during the weaning period when weaning is extended from 6 to 8 wk of age.

Recent research suggests that circulating β-hydroxybutyrate (BHB) levels may be a meaningful indicator of grain intake and rumen development in pre-ruminant calves. As such, BHB levels may be a surrogate measure of rumen function to contribute to minimal weaning stress during the transition from liquid to solid feed. The primary objective of this study was to determine the optimal cut-point of circulating BHB levels that would be predictive of sufficient grain intake and rumen development for a successful transition from liquid to solid feed at the time of weaning. An additional objective was to validate the Precision Xtra (Abbott Diabetes Care, Abingdon, UK) calf-side test for determination of BHB in whole blood in calves around weaning, as compared with the gold standard laboratory method. A total of 20 Holstein female calves were randomly assigned at birth to be weaned at 6 wk (n=10) or 8 wk (n=10) of age. Milk replacer (mixed at 150 g/L) was offered at 1.2kg/calf per d in 2 meals until a 1-wk step down, when milk meals were reduced by 50% 1 wk before weaning. Daily measurements included the intakes of starter grain, chopped straw, and water. Weekly measurements included body weight and blood BHB, until 70 d of life. To assess digestive tract development, rumen fluid samples were taken before and after weaning (d 35, 49, and 63) and analyzed for ruminal short-chain fatty acids. Whole blood was collected by jugular venipuncture, and BHB was determined by the Precision Xtra test at calf-side. In addition, serum was separated from a clotted sample, frozen, and stored until laboratory analysis was performed. Laboratory BHB results were correlated with both the Precision Xtra test (r=0.95) and starter intake over 1 d (r=0.89), a 3-d average (r=0.90), and a 7-d average (r=0.90). Additionally, laboratory BHB results were associated with total ruminal volatile fatty acids (r=0.82), ruminal butyrate (r=0.77), and body weight (r=0.69). A receiver operating characteristic curve was created to plot the true positive rate against the false positive rate at 10μmol/L BHB intervals to determine the optimal cut-point of circulating BHB that is predictive of an average starter intake of 1,000 g/d over a 3-d period. The optimal combination of sensitivity (95.7%) and specificity (96.1%) was at 100µmol of BHB/L of blood. A value of 0.2 mmol/L on the Precision Xtra test yielded a sensitivity and specificity of 84.0 and 97.2%, respectively, over the 3-d average period of starter intake. These results show considerable promise for use of the Precision Xtra whole blood BHB test in the decision-making process of determining sufficient starter grain intake and rumen development for a successful transition from liquid to solid feed, and indicate that this test conducted at calf-side is highly accurate.

A B S T R A C TDiarrhea, resulting from gastrointestinal infection by pathogens, is a common cause of the high mortality and morbidity of neonatal calves. The objective of this study was to evaluate the effects of supplementing a yeast product in milk replacer (MR) on growth and health of calves, and on fecal populations of some targeted microorganisms related to calf health and growth (i.e., total bacteria, Escherichia coli, Clostridium cluster XIVa, Faecalibacterium prausnitzii and Bifidobacterium spp.). We hypothesized that feeding a Saccharomyces cerevisiae var boulardii (SCB) product would improve gastrointestinal health and growth performance of calves. Forty-two Holstein bull calves (42.6 ± 0.77 kg at birth) were randomly assigned on day 2 of age to either a control or SCB treatment. The SCB was supplemented in MR and fed at 5 g/d per head to supply 10 billion colony-forming units per day. All calves received high quality colostrum (> 50 mg/mL of immunoglobulin G) during the first 24 h of life, and were fed with 8 L MR (150 g/L mixed with 40°C water) daily from day 2-35, and 4 L daily from day 35-42. Calves were also fed calf starter ad libitum from day 7-56. Daily MR and starter offered and refused, daily fecal scores, nasal scores, ear scores, and weekly body weight of calves were recorded. Fecal samples were collected on day 7, 35 and 56 after the first feeding of that day for microbial targets analysis. Overall, there is no serious disease challenge for all the calves during the entire experimental period. No differences were observed in MR intake, starter intake, metabolizable energy (ME) intake, average daily gain, ME intake to gain ratio, fecal score, nasal score, eye score or any targeted microorganisms between treatments throughout the experiment. These results suggest that supplementing SCB in MR has no additive effects on animal growth or fecal biomarkers of gut health when calves do not show deteriorated health status.