Essential oil supplementation in milk replacers: short- and long-term impacts on feed efficiency, the faecal microbiota and the plasma metabolome in dairy calves.

Early supplementation with oregano essential oil (EO) in milk replacer (MR) may improve growth, immune responses, the microbiota and the metabolome in dairy calves during pre-weaning and in adulthood. Sixteen female dairy calves (3 days of age) were divided in two groups (n = 8/group): the control group (no EO) and the EO group (0.23 ml of EO in MR during 45 days). After weaning, calves were kept in a feedlot and fed ad libitum. The animals were weighed, and blood and faecal samples were collected on days 3 (T0), 45 (T1) and 370 (T2) to measure the biochemical profile and characterise peripheral blood mononuclear cells (PBMCs; CD4+, CD8+, CD14+, CD21+ and WC1+), the metabolome and microbiota composition. The EO group only had greater average daily weight gain during the suckling (EO supplementation) period (P = 0.030). The EO group showed higher average CD14+ population (monocytes) values, a lower abundance of Ruminococcaceae UCG-014, Faecalibacterium, Blautia and Alloprevotella and increased abundances of Allistipes and Akkermansia. The modification of some metabolites in plasma, such as butyric acid, 3-indole-propionic acid and succinic acid, particularly at T1, are consistent with intestinal microbiota changes. The data suggest that early EO supplementation increases feed efficiency only during the suckling period with notable changes in the microbiota and plasma metabolome; however, not all of these changes can be considered desirable from a gut health point of view. Additional research studies is required to demonstrate that EOs are a viable natural alternative to antibiotics for improving calf growth performance and health.

Starter protein content and supplemental soybean oil or hydrogenated palm fatty acids in Holstein dairy calves: growth performance, protozoa population, and nitrogen utilization efficiency.

The study hypothesized that a 24% protein starter diet supplemented with inert fat (palm fatty acids; PLFs) instead of triglyceride-rich soybean oil (SBO) would promote the growth of dairy calves. The effects of different protein contents (20 vs 24% CP) and fat sources (SBO vs PLF at 2.5% DM) on growth, digestibility, blood metabolites, rumen protozoa and urinary nitrogen in dairy calves were investigated. A total of 52 female dairy calves (mean age 3 days and BW 40.7 kg) were allocated to the following treatments in a completely randomized design: (1) 20% CP starter diet supplemented with SBO (20CP-SBO), (2) 20% CP starter diet supplemented with PLF (20CP-PLF), (3) 24% CP starter diet supplemented with SBO (24CP-SBO), and (4) 24% CP starter diet supplemented with PLF (24CP-PLF). Calves were weaned on day 53, and the study ended on day 73. The 24CP diets enhanced starter feed intake, average daily gain (ADG), withers height, hip width, organic matter (OM) digestibility, and preweaning blood glucose compared to the 20CP diets. In contrast, SBO supplementation reduced feed intake, ADG, withers height, OM and CP digestibility, and pre- and postweaning blood glucose and beta-hydroxybutyrate levels, while increasing preweaning aspartate aminotransferase, compared to PLF. SBO supplementation led to lower urinary excretion of purine derivatives and microbial protein synthesis postweaning, and a reduction in protozoa population both pre- and postweaning. Calves fed PLF had higher starter intake than those fed SBO, regardless of the diet being 20CP or 24CP. Calves fed the 24CP-PLF diet had the highest ADG, while calves fed the 20CP-SBO diet had the lowest ADG. Calves fed the 20CP-SBO diet had lower feed efficiency than calves fed the other diets during the preweaning period and throughout the experimental period. Calves fed the 24CP-PLF diet had higher hip heights at weaning and on day 73 than calves fed the other diets. Calves fed the 20CP-SBO diet had lower neutral detergent fiber digestibility than calves fed the other diets. Calves fed the 24CP-SBO diet had higher postweaning blood urea nitrogen concentration than calves fed the other diets. Feeding the 20CP-SBO diet to dairy calves decreased urinary allantoin excretion and rumen microbial protein synthesis but increased urinary nitrogen excretion during the preweaning period. Our results suggest that PLF is more suitable than SBO in calf diets, especially when calves fed 24% CP, possibly due to improved nutrient digestibility.

Ultrasound characterization of mammary gland development in heifer calves fed at two different levels until weaning.

Ultrasound technologies allow for a non-invasive assessment of mammary gland (MG) development, the differentiation between the tissue types of the MG, and the evaluation of changes in its composition. This study aimed to work out a detailed description of the different stages of MG development that are visually discernible by ultrasonography for providing a template to classify the different structures. With this basis, the qualitative categorization of the developmental stage, as well as further quantitative assessments via pixel densities in the structures of interest, should be facilitated. Ultrasonic images were acquired from all four quarters of 37 German Holstein heifer calves fed either at a high feeding level of milk replacer (MR; 14% solids) at 10 L/day (1.4 kg MR/day; HI, n = 18) or at a restrictive low level of 5.7 L/day (0.8 kg MR/day; RES, n = 19) until linear weaning from week 13 to 14 of life. Ultrasound MG scans were performed first in week 3 of life, fortnightly from week 8-16, and in week 20 of life, in standing position, of each quarter, using a B-mode ultrasound device equipped with a linear probe (18 MHz). The developmental stages of the mammary gland parenchyma (PAR), visible in ultrasound images, obtained over 20 weeks of life, were categorized, described, and drawn by hand. On this basis, a template for classifying the visible categories of mammary PAR development and its surrounding tissue (SURR), and for measuring their pixel brightness was created thus providing an ultrasonographic atlas of the developing bovine MG, describing 11 categories. The ultrasound images were further classified by PAR structure, and pixel brightness was measured in PAR and SURR by using ImageJ Fiji. The difference in pixel brightness between PAR and SURR, the delta (Δ) pixel value was calculated. With increasing age, higher atlas categories of PAR developmental stages were shown. Pixel values, i.e. the brightness of PAR, its SURR, and Δ pixel value changed with age but were neither affected by the feeding group nor by a group × time interaction. With progressing PAR development, its pixel brightness increased from week 10 to 20 of life, i.e., the PAR became more hyperechoic since it spread and grew into its SURR. The atlas can serve as a template for the categorization and qualitative assessment of MG structures and for the quantitative assessment of PAR's development by measuring pixel brightness. With our study, we could show the structural development in PAR as well as in SURR in MG simultaneously in early life and confirm the spreading of PAR into its SURR by ultrasound scanning.