Effect of a 2-step probiotic program on digestive health and performance of Holstein heifer calves.

Managing the composition of the bacterial communities in the digestive tract with the use of probiotics that enhance protective microflora could result in positive effects on health and performance of calves. The objective of this study was to evaluate a 2-step probiotic program (added to colostrum and milk) on the digestive health and growth of preweaning Holstein heifers. A randomized clinical trial was conducted from July to October 2020 in a calf rearing facility in Colorado. Calves were housed in pairs sharing the same treatment in 2 polyethylene hutches within a common area of 4.50 m2. A total of 232 calves were enrolled at birth and randomly allocated into 2 treatment groups [control (CTR) = 116; treatment (PB) = 116] and followed until weaning (64 ± 3 d). Treatment consisted of 2 formulations of a multistrain bacterial-based probiotic added in colostrum (PBF1) and milk (PBF2). Treatment calves received 2 g of PBF1 added to each colostrum feeding, and 1 g of PBF2 added to the milk at the morning feeding 3 times per week up to weaning. Calf weight was collected at birth, at 30 d of age, and at weaning. Serum total protein was determined at age 3 ± 1 d and a health assessment was completed 3 times per week. Statistical analyses were performed using SAS, with calf considered the experimental unit clustered by housing pair. Cox proportional hazard analysis and time to event analysis were used to compare time to the first diarrhea event and time to recovery between treatment groups. The total number of diarrhea events and culling were assessed by Poisson regression and logistic regression analysis, respectively. Linear regression was performed to evaluate differences in average daily gain by treatment group. Overall, the mean (± standard error) temperature humidity index (THI) was 75 (± 0.44) units during the study period, which resulted in continuous exposure to heat stress in the day hours. No difference between treatment groups was observed in serum total protein. The overall incidence of diarrhea was 96.6% (CTR = 99%, PB = 95%); no differences were determined in the hazard of a first diarrhea episode or in the median time to the first diarrhea event (11 d in both groups). Similarly, no differences were found in the likelihood of recovery or in the median time to recovery from diarrhea (7 d in both groups). Likewise, treatment group was not associated with the number of diarrhea events, mean (± standard error, g/d) average daily gain from birth to weaning [CTR = 562.5 (13.9); PB = 570.8 (13.5)], or with the odds of culling. The most prevalent pathogen isolated from feces was Clostridium, which tended to be more frequent in CTR calves than PB calves. In conclusion, the probiotic program did not affect the incidence of enteric disease or the growth of preweaning heifer calves.

Use of milk electrical conductivity for the differentiation of mastitis causing pathogens in Holstein cows.

Mastitis is one of the most prevalent and costly diseases in dairy cattle. Key components for adequate mastitis control are the detection of early stages of infection, as well as the selection of appropriate management interventions and therapies based on the causal pathogens associated with the infection. The objective was to characterize the pattern of electrical conductivity (EC) in milk during intramammary infection, considering specific mastitis-causing pathogen groups involvement. Cows (n = 200) identified by an in-line mastitis detection system with a positive deviation ≥15% in the manufacturer's proprietary algorithm for EC (high electrical conductivity (HEC)) were considered cases and enrolled in the study at the subsequent milking. One control (CON) cow, within normal ranges for EC, was matched to each case. A composite milk sample was collected aseptically from each cow for bacteriological culture. Milk yield (MY) and EC were recorded for each milking during ±7 days relative to enrollment. Milk cultures were categorized into gram positive (GP), gram negative (GN), other (OTH) and no growth (NOG). Data were submitted for repeated-measures analysis with EC as the dependent variable and EC status at day -1, bacteriological culture category, parity number, stage of lactation and days relative to sampling as main independent variables. Average (± standard error (SE)) EC was greater in HEC than in CON cows (12.5 ± 0.5 v. 10.8 ± 0.5 mS/cm) on the day of identification (day -1). Milk yield on day -1 was greater in CON than in HEC (37.6 ± 5.1 v. 33.5 ± 5.2 kg). For practical management purposes, average EC on day -1 was similar for the different bacteriological culture categories: 11.4 ± 0.6, 11.7 ± 0.5, 12.3 ± 0.8 and 11.7 ± 0.5 mS/cm in GN, GP, OTH and NOG, respectively. Parity number was only associated with day -1 EC in HEC group, with the greatest EC values in parity 3 (12.3 ± 0.3 mS/cm), followed by parity 2 (11.9 ± 0.2 mS/cm), parity >3 (11.6 ± 0.5 mS/cm) and primiparous cows (11.2 ± 0.2 mS/cm). An effect on EC for the interaction of day relative to identification by pathogen gram category was observed. The same interaction effect was observed on daily MY. Overall, the level of variation for MY and EC between- and within-cows was substantial, and as indicated by the model diagnostic procedures, the magnitude of the variance in the cows in the CON group resulted in deviations from normality in the residuals. We concluded that characteristic temporal patterns in EC and MY in particular pathogen groups may provide indications for differentiation of groups of mastitis-causing pathogens. Further research to build detection models including EC, MY and cow-level factors is required for accurate differentiation.