The Effect of Increasing Urea Intake in the Lactating Dairy Cow on Follicular Dynamics and Ovulation

Abstract

A considerable number of calves is born prematurely. Morbidity and mortality of preterm calves are higher than of calves born at normal term. Besides insufficient functioning of the lungs, immaturities of the gastrointestinal tract (GIT) and of endocrine control of metabolism are thought to contribute to health problems. Because corresponding studies are lacking in preterm calves, we have tested the hypothesis that there are differences in maturation at birth and in response to feeding for 8 d of the GIT and of metabolic and endocrine traits between term and preterm calves. Fourteen calves were born on d 275 of gestation, i.e. 42 ± 3 h after dams were injected 0.5 mg prostaglandin F 2α and 5 mg Flumethason, and were slaughtered either on d 1 (GrPS, n=7) or on d 8 (GrPF, n=7) of life. Another 14 calves, serving as control, were spontanously born after normal lengths of pregnancy (290 ± 2 d) and were slaughtered either on d 1 (GrNS, n=7) before first feeding or on d 8 (GrNF, n=7) of life. The 8 d old preterm and term calves were fed colostrum and then mature milk. Blood samples were taken from jugular veins to measure blood gases, hematologic, metabolic and endocrine traits. Histomorphometrical analyses of duodenum, jejunum, ileum and colon were performed on slides stained with hematoxilin and eosin. Cell proliferation was based on counting crypt cells which (following injection of 500 µg 5-bromo-2`-deoxyuridine 1 h before slaughter) had incorporated this substance into DNA and relative to unlabeled epithelial cells and as relative to the length of the mucosal epithelial layer. Apoptotic cells were visualized based on terminal transferase 3' end labelling by fluorescence microscopy. Results: The pH was lower (P<0.05) in GrPS than in GrPF. Mean pCO 2 tended to be higher (P<0.05) in GrPS versus GrNS, and tended to be higher (P<0.1) in GrPS than in GrPF. There were no group differences in pO 2 , base excess, HCO 3 , TCO 2 , and sO 2 . Haematological traits were always in physiological range and barely differed between term and preterm calves. Blood plasma concentrations of metabolites (protein, immunoglobulin G, albumin, urea, creatinine, nonesterified fatty acids, triglycerides, cholesterol, glucose, lactate) and hormones (growth hormone, insulin-like growth factor-1, 3.5.3'-triiodothyronine and thyroxine, cortisol, insulin, glucagon) and patterns of postnatal changes in preterm calves were in the same range as in calves born at normal term. In jejunum villus circumferences, areas and heights were greater (P<0.001) in GrNS than in GrNF and GrPS. Villus circumferences and villus heights in ileum were greater (P<0.05) in GrNS than in GrNF. Crypt depths in duodenum, jejunum, ileum and colon were greater (P<0.001) in GrNF than in GrNS and GrPF. Villus circumferences, areas and heights were greatest in jejunum, whereas colon had the greatest crypt depths. Number of BrdU-labeled cells in duodenum and jejunum were higher (P<0.05) in GrNF than in GrNS. Number of BrdU-labeled cells in duodenum and number of BrdUlabeled cells...