Problems of calf rearing in connection with their mortality and optimal growth: A review

Development of a multivariable prediction model to identify dairy calves too young to be transported to auction markets in Canada using simple physical examination and body weight

Calves born on Eastern Canadian dairy farms that are not kept in the herds are traditionally sold through auction markets and are raised for meat purposes such as veal calves. Since February 2020, a new Canadian federal regulation has forbidden calves <9 d old to be sold through auction markets. However, in the absence of a real-time birth registry consultation system, it would be of interest to look for predictors that could be associated with age to allow identification of calves too young to be transported. In the current retrospective cross-sectional study, 1,178 calves with a declared birth date (411 calves aged <9 d old; 34.9%) were assessed in 2 large Québec auction sites. Easy-to-record covariates [body weight (BW), breed phenotype, and presence of an umbilical cord remnant] as well as other clinical signs (umbilical swelling, enlargement, umbilical pain, wet umbilicus, skin tent, sunken eyes, ocular and nasal secretion, and hide cleanliness) were assessed. Two logistic regression models using age as a dichotomous dependent variable (<9 d old vs ≥9 d old) were built. The first model (model 1) considered all covariates, which were selected after univariable analyses and a backward stepwise selection process, whereas a more pragmatic model (model 2) only included the 3 easy-to-record variables (i.e., BW, breed, umbilical cord). Both models had similar accuracy to detect calves <9 d old (sensitivity of 38.4 and 37.5%, and specificity of 85.7 and 84.6% for model 1 and 2, respectively). Model 2 was subsequently more specifically studied as it employs a faster and easier assessment. Decision thresholds were tested for their robustness based on misclassification cost term (MCT) analysis with various prevalence of calves <9 d old and various costs of false-negative:false-positive ratio. Despite statistical significance, model accuracy, even if refined with MCT analysis, was limited at the individual level, showing the limits of using physical signs and BW or their combination as a reliable proxy of age. The sensitivity of these models to find calves <9 d old was not to be used for monitoring compliance with the Canadian federal regulation. The relatively high model specificity may help to use this model as a rule-in test (i.e., targeting positive calves for further investigation) rather than a rule-out test (due to its low sensitivity).

A Cross-sectional Study of Reproductive Performance of Smallholder Dairy Cows in Coastal Tanzania

A retrospective cross-sectional study was conducted on 200 randomly selected smallholder farms from a mixed dairy farming system in Tanga, Tanzania, between January and April 1999. We estimated the frequency and determinants of long calving interval (LCI), retention of fetal membrane (RFM), dystocia, and abortion in smallholder crossbred cattle and explored birth trends. The mean calving interval was 500 days and birth rate was 65 per 100 cow-years. Dystocia was reported to affect 58% of calvings, and 17.2% of animals suffered RFM. Using mixed effect models, the variables associated with LCI, RFM and dystocia were breed, level of exotic blood and condition score. Zebu breeding was associated with LCI (odds ratio (OR) = 2.3, p = 0.041) and Friesian breeding with lower odds for RF (OR = 0.26, p = 0.020). Animals with higher levels of exotic blood had lower odds for evidence of dystocia (OR = 0.45, p = 0.021). Evidence of dystocia was significantly associated with poor condition score (p = -1.10, p = 0.001). Our observations suggest that LCIs are common in smallholder dairy farms in this region and a likely source of economic loss. Dystocia, RFM, poor condition score and mineral deficiency were common problems and were possibly linked to LCI.

Comparison of calf housing types and tympanic temperature rhythms in Holstein calves

During fall, 30 Holstein calves were randomly assigned to three housing treatments from birth to weaning: conventional wooden hutches, enclosed molded polyethylene domes, and thermomolded opaque polymer hutches with ridge-top ventilation systems. The wooden and polymer hutches had outdoor pens. Fifteen calves, 5 in each housing type, were fitted with portable data loggers to record ambient (calf microclimate) and tympanic temperatures. Additional data collected included weekly girth, BW, and feed intake; blood samples were collected within 24 h of birth and at weaning (8 wk); and behavioral observations were made at 1, 4, and 7 wk of age. Polyethylene domes had the warmest microclimate, followed by wooden and polymer hutches. Feed intake, growth measurements, blood physiology, and behavior were unaffected by housing type. Diurnal tympanic temperature rhythms of neonatal dairy calves in this study were monophasic: maximums were at 1200 to 1700 h, and minimums were at 0600 to 0900 h. Computed fractal dimensions of tympanic temperature by week indicated a gradual diminishing of stress as the calves became older and acclimated to their environment. This objective characterization provides a basis for further evaluation of physiological stress and a means of improving environmental management.

Animal health and management and their impact on economic efficiency

Relationships between animal health and economic efficiency were examined using data from genetic investigations and management studies. Genetic investigations have indicated that cows bred for high production do require more health care, but that increased costs for health care negate only a small fraction of the greater returns from cows that are genetically superior for yield traits. These same studies have identified age of cow and stage of lactation as important sources of variation in health care costs. Health care costs increase with age and are highest at parturition and immediately thereafter, and decrease to much lower levels as lactation progresses. Animal health issues considered from a management perspective were macro-environment (climate, housing, facilities), nutrition-reproduction complex, replacement management, mastitis and udder health, and herd health preventive medicine programs. Most advances in management of animal health were beneficial, but some are economical only for large herds. Improvement of udder health through continued and expanded research on milking procedures and equipment design is an area of unusual promise. Additional research appears needed to cope with stress and fatigue to legs and feet in modern facilities. Preventive medicine programs become more cost effective as herds become larger and should be used by a larger percentage of dairy producers. The economic efficiency of many management practices is uncertain due to a paucity of data. Animal scientists should plan to incorporate economic comparisons into much more of their research.