COLOSTRUM QUALITY AND ASSOCIATED FACTORS IN CROSSBRED DAIRY COWS IN AN ORGANIZED GOVERNMENT DAIRY FARM IN BANGLADESH

Abstract

Newborn calves are born agammaglobulinemic lacking circulating antibodies and rely entirely on colostrum to obtain early immune protection. Therefore, supplementing good quality colostrum is crucial for the successful transfer of passive immunity (TPI) in newborn calves. However, there is limited evidence from Bangladesh evaluating colostrum quality and its impact on TPI in the first month of life, particularly under intensive dairy farming conditions. Therefore, this study aimed to estimate the a) colostrum quality, b) association of colostrum quality with milk composition and udder health parameters, c) underlying cow- and calf-level risk factors impacting colostrum quality and calf health, d) prevalence of intramammary infection (IMI) causing pathogens in composite milk, and e) prevalence of Escherichia coli and cefotaxime-resistant E. coli between cows and their neoborn calves over time. A five-month cohort study was conducted on an organized commercial dairy farm with fifty-seven cows followed from calving to 30 days postpartum. Composite milk samples (n=392) were collected from each cow on days 1–5, 15, and 30 (day 1 considered colostrum). The composite milk samples were tested using digital (DR) (MISCO DD-3®, USA) and optical (OR) (ATAGO®, Japan) Brix refractometers, analyzed for milk composition, somatic cell count, and examined for bacterial identification. Milk composition (fat, protein, lactose, and solids-not-fat [SNF]) and somatic cell count (SCC) were determined using Ekomilk Horizon Unlimited® and DeLaval Somatic Cell Counter®. Rectal swabs were collected from the cows (n=278) and their calves (n=235) on days 1, 3, 5, 15, and 30 for bacterial culture. Additionally, 2 mL blood samples (n=114) were collected from cows and their newborn calves within 12–24 hours postpartum to assess TPI using calf serum total protein. As data were not normally distributed (Shapiro–Wilk test), pairwise correlations were evaluated using Spearman’s rank correlation (P ≤ 0.05). A strong positive correlation was observed between the digital and optical refractometers across all sampling days (r = 0.73–0.96; P < 0.001), indicating that either method can be reliably used for realtime assessment on-farm. On day 1, the 25th percentile of colostrum quality was 12.6% (DR) and 12.0% (OR), while the 75th percentile was 29.9% (DR) and 29.0% (OR). For serum total protein (TP) on day 1, the 25th percentile was 6.6 g/dL in cows and 5.7 g/dL in calves, whereas the 75th percentile was 7.4 g/dL in cows and 6.5 g/dL in calves. Interestingly, fifty cows (50 out of 55; 91%) produced good-quality colostrum (Brix ≥ 22% equivalent to 50g/L IgG); xvi however, only 30 calves (30 out of 54; 56%) achieved successful TPI (calf serum protein > 5.2 g/dL), indicating that underlying factors beyond colostrum quality likely influenced immunoglobulin absorption in the newborn calves. Importantly, the volume of colostrum yield in the first milking had a negative impact on colostrum quality (β= -0.2; P < 0.001). In contrast, calf birth weight had a negative impact on success of TPI (β= -0.5; P= 0.004) indicating larger calves might need a higher volume of good quality colostrum than were supplemented. Additionally, a high incidence rate of calf diarrhea (46.9%) was observed in the selected calves. It was found that calves with failure of TPI was four times more likely to develop calf diarrhea than calves with successful TPI (OR= 4.1; P= 0.05). Brix values (DR) were consistently positively related with milk protein and solids-not-fat (SNF) across sampling days, and showed strong correlations with lactose from day-2 onwards. Overall, 228 composite milk samples were culture-positive, with non-aureus staphylococci comprising 48% of IMI, followed by streptococcus-like organisms, Streptococcus spp., Staphylococcus aureus, and non-specific gram-negative bacteria. A high prevalence of cefotaxime-resistant E. coli in calves (46%) than cows (19%) was detected, suggesting potential risks of environmental or calf to calf transmission of pathogens and antimicrobial resistance concerns. In conclusion, this study findings support that routine on-farm colostrum quality testing, administration of adequate colostrum volume adjusted for calf birth weight and strengthened farm hygiene practices to improve passive immunity transfer and reduce early-life risk for diarrhea in newborn calves.