Occurrence of neonatal and postnatal mortality in range beef cattle. II. Factors contributing to calf death.

Results are summarized of necropsy findings from 798 calves lost from birth to weaning over a 15-yr period. Autopsies determined cause of death and ascertained anatomical normalcy of the skeletal, musculature and organ systems and functinal status of the lungs. Of the 798 calves, 77.7% were anatomically normal and 22.3% were abnormal (P < 0.01) and 75.0% of the total deaths of abnormal calves occurred by Day 2 postpartum. Birth weights of normal calves averaged 4.2 kg heavier (P < 0.05) than that of abnormal calves. Internal hydrocephalus was identified and confirmed heritable as a lethal recessive trait. The number of calves lost from dystocia (406 calves, 50.9%) exceeded losses from all other causes (392 calves, 49.1%). Lung status was determined for 492 calves dying at birth, with 39.6 and 60.4% having functional and nonfunctional lungs, respectively (P < 0.01). Diseases, mainly scours and pneumonia, ranked second in importance as cause of death (12.8%), followed by exposure-chilling (5.6%) due to cold and wet conditions. Abnormalities observed included heart anomalies (24 calves), hydrocephalus (38 calves) and a missing segment of the caudal gut (8 calves). Multiple congenital malformations were found in 15 calves with findings similar to those resulting from maternal consumption of toxins from poison hemlock (Conium maculatum) during gestation. Twelve calves died from peritonitis resulting from a perforated abomasal ulcer caused by accumulated hair. Of the 373 dystocia deaths in anatomically normal calves, 121 (32.4%) involved abnormal presentation, with calves involved in backward or breech presentation accounting for 62.0% of the losses from abnormal presentation. Calves experiencing hiplock or retained forelimb were heavier (P < 0.05) than calves presented in normal, back-ward or breech positions. Dystocia scores were assigned to 253 calves dying at parturition. Percentage losses within score were 52.6, 6.7, 30.8 and 9.9 (P < 0.05) and birth weights were 33.9, 36.1, 39.2 and 37.4 kg (P < 0.05) for scores of 1, 2, 3 and 4, respectively.