Neonatal Bull Calves Research Articles

Maternal heat stress reduces body and organ growth in calves: Relationship to immune status

Late-gestation heat stress of dairy cows reduces fetal growth and influences postnatal performance and immune status of the offspring. Our first objective was to evaluate the effect of in utero heat stress on overall fetal and organ growth, particularly organs associated with immune function. The second objective was to examine the cellular mechanism of altered passive immunity in neonatal bull calves after in utero heat stress. Specifically, we examined the rate of apoptosis of intestinal cells early in life, as it is associated with gut closure. Dams were dried off approximately 45 d before expected calving and randomly assigned to 1 of 2 treatments: heat stress (HT) or cooling (CL). During the dry period all cows were housed under shade in a freestall barn, where the pen for CL cows was equipped with active cooling, including water soakers and fans, whereas the pen for HT cows had no soakers or fans. Using rectal temperature and respiration rate as indicators, heat stress was severe. Average rectal temperature in HT cows was 39.3°C compared with 39.0°C in CL cows, and HT cows had a respiration rate of 66.7 breaths/min compared with 43.2 breaths/min for CL cows. Bull calves (n = 30) were immediately separated from their dams at birth, weighed, and then killed before colostrum feeding (n = 5/treatment; d 0) or at 1 or 2 d of age following colostrum feeding (n = 5/treatment per day). After slaughter, the small intestine was removed and weighed, and samples from the jejunum were fixed for immunohistochemistry. Birth weight of bulls from HT dams was 1.1 kg lower than that of bulls from CL dams. Thymus, spleen, and heart weights of HT bulls were lower relative to those of CL bulls, whereas liver weight of HT bulls tended to be lower relative to that of CL bulls. Jejunal cell apoptosis decreased with age in both HT and CL calves after birth, mirroring gut closure. However, in utero heat stress increased the apoptotic rate in the jejunum, particularly at birth. We conclude that the chronic exposure to heat strain of HT compared with CL dams in late gestation significantly affected fetal growth and immune tissue development, which may be associated with reduced immune function in early life. Also, late-gestation heat stress increased calves' intestinal apoptosis in the first 2 d of life, which might explain the decreased IgG uptake and limited passive immune competence observed in previous studies.

Neonatal lipopolysaccharide exposure does not diminish the innate immune response to a subsequent lipopolysaccharide challenge in Holstein bull calves

The innate immune response following experimental mastitis is quite variable between individual dairy cattle. An inflammatory response that minimizes collateral damage to the mammary gland while still effectively resolving the infection following pathogen exposure is beneficial to dairy producers. The ability of a lipopolysaccharide (LPS) exposure in early life to generate a low-responding phenotype and thus reduce the inflammatory response to a later-life LPS challenge was investigated in neonatal bull calves. Ten Holstein bull calves were randomly assigned to either an early life LPS (ELL) group (n=5) or an early life saline (ELS) group (n=5). At 7d of age, calves received either LPS or saline, and at 32d of age, all calves were challenged with an intravenous dose of LPS to determine the effect of the early life treatment (LPS or saline) on the immune response generated toward a subsequent LPS challenge. Dermal fibroblast and monocyte-derived macrophage cultures from each calf were established at age 20 and 27d, respectively, to model sustained effects from the early life LPS exposure on gene expression and protein production of components within the LPS response pathway. The ELL calves had greater levels of plasma IL-6 and tumor necrosis factor-α than the ELS calves following the early life LPS or saline treatments. However, levels of these 2 immune markers were similar between ELL and ELS calves when both groups were subsequently challenged with LPS. A comparison of the in vitro LPS responses of the ELL and ELS calves revealed similar patterns of protein production and gene expression following an LPS challenge of both dermal fibroblast and monocyte-derived macrophage cultures established from the treatment groups. Whereas an early life exposure to LPS did not result in a dampened inflammatory response toward a later LPS challenge in these neonatal bull calves, the potential that exposure to inflammation or stress in early life or in utero can create an offspring with a low-responding phenotype as an adult is intriguing and has been documented in rodents. Further work is needed to determine if an inflammatory exposure in utero in a dairy animal would result in a low-responding innate immune phenotype.

The role of signaling pathways on proliferation and self-renewal of cultured bovine primitive germ cells.

Gonocytes are primitive male germ cells residing in the neonatal testes and are unipotent in nature, but also have pluripotent stem cell ability in mice under appropriate culture conditions. This study was performed to elucidate the molecular mechanisms of self-renewal and survival of cultured bovine gonocytes. Gonocytes were isolated from neonatal bull calves and were cultured in DMEM/F12 supplemented with 15 % knock-out serum replacement (KSR) and glial cell-derived neurotrophic factor (GDNF). Cells were analyzed six days after culturing for cell-signaling molecular markers. Colony formation was observed 3-4 days after being cultured. Addition of GDNF enhanced mitogen-activated protein kinase 1/2 (MAPK1/2) phosphorylation and activated the MAPK signaling pathway. Inhibition of MAPK signaling reduced cell proliferation and abolished colony formation. However, inhibition of phosphoinositide 3-kinase-AKT (PI3K-AKT) signaling, a dominant pathway for self-renewal of mouse germ cells, did not show any effects on cultured bovine gonocytes. Expression of cell cycle-related regulators cyclin D2 and cyclin-dependent kinase 2 (CDK2) was downregulated with inhibition of MAPK signaling. These results indicate activation of MAPK plays a critical role in self-renewal and survival of bovine gonocytes via cyclin D1 and CDK2.

Influence of Bovine Antiserum (Bo-Bac 2X) Injection on Colostral Immunoglobulin G Absorption in Neonatal Dairy Calves

On the background of positive survival data from farms in Mississippi, treating calves with antiserum injection in addition to normal colostrum administration, the objective of the present study was to evaluate the influence of a single subcutaneously administered bovine antiserum injection (0.031g of IgG/kg of body weight) and pooled colostrum administration on efficiency of Ig absorption and on 24-h plasma IgG concentration in neonatal bull calves. Twenty-nine male dairy calves (21 Holsteins and 8 Jerseys) were assigned randomly at parturition to receive one of four treatments: 1) colostrum (n=9), 2) colostrum and bovine antiserum injection (n=7), 3) milk replacer (n=5), or 4) milk replacer and bovine antiserum injection (n=8). At birth, calves either did or did not receive an injection of bovine antiserum and were fed pooled colostrum or milk replacer (Holsteins, 3.8 L; Jerseys, 1.9 L) via an esophageal feeder. Blood was collected immediately before administration of the colostrum or milk replacer, then again at 24 and 48h postpartum. Immunoglobulin G concentrations of colostrum, milk replacer, antiserum, and plasma were monitored by single radial immunodiffusion. Colostrum administration and injection of bovine antiserum each increased plasma Ig concentration at 24h posttreatment. In addition, antiserum injection increased the apparent efficiency of absorption of colostral Ig by 42% over that for calves fed colostrum alone. The increase in plasma IgG for antiserum-treated calves exceeded the total amount of IgG administered in the antiserum injection; hence, this increase appeared to be the result of an increase in total absorption of colostral IgG, or possibly antiserum injection somehow triggered active synthesis of IgG. Injection of antiserum might possibly serve as a beneficial adjunct to a colostrum management program by enhancing the acquisition of passive immunity from colostral sources.

Ruminal Metabolic Development in Calves Weaned Conventionally or Early

Eight neonatal bull calves were rumen fistulated and assigned to one of two weaning programs to study the effect of diet and weaning age on ruminal metabolic development. All calves were fed colostrum until 3 d of age and milk until weaning. Calves in the early weaning program were fed milk and a highly palatable, prestarter diet until they consumed 227 g/d and then a mixture of 227g of prestarter and all the starter diet they would eat. Calves in this group were weaned at 4 wk of age. Calves in the conventional weaning program were fed milk and a starter diet and weaned at 6 wk of age. Eight ruminal samples were collected over 12h from each calf at 1, 4, 8, and 12 wk of age. Ruminal fluid samples were analyzed for pH, VFA, NH3 N, and L(+)- lactate and D(−)-lactate concentrations. Calves weaned early had lower ruminal pH, higher total VFA concentration, and higher molar proportion of butyrate than conventionally weaned calves. Ruminal NH3 N and lactate concentrations were not significantly affected by the weaning program, although lactate tended to be higher in calves weaned early. Ruminal VFA concentration increased and NH3N concentration decreased with increased feed consumption by calves in both groups. Molar proportions of acetate, isobutyrate, and isovalerate decreased, and those of propionate increased with age in both groups. Apparently, ruminal metabolic development, as evidenced by changes in fermentation products, was faster in calves weaned early than in calves weaned conventionally.