Herd turnover rate reexamined: a tool for improving profitability, welfare, and sustainability.

Longevity and herd turnover rate are becoming common topics of discussion as the dairy industry strives for continuous improvement in efficiency, profitability, animal welfare, and environmental sustainability. Having the most productive animal fill each slot on a dairy makes strategic replacement and the resulting herd turnover an important tool for producers. Dairy operations can be considered to have slots available to be occupied by cows. The number of slots available is governed by dairy characteristics including parlor size and facility design. With sustainability and profitability goals, producers should aim to fill each slot with the most productive animal. The advantages of a modest surplus of replacement heifers allowing for a higher herd turnover rate are examined and shown to improve herd profitability, enhance welfare, and reduce environmental impact. A model assuming constant demand for dairy foods is presented with increased herd turnover rate leading to more milk production per cow and reduced enteric methane emissions. This analysis demonstrates that all else being equal, raising more replacements (having a relatively higher herd turnover rate and decreased herd-level longevity) improves sustainability compared to management aimed at lower herd turnover rates. Understanding the drivers of herd turnover in dairy production has important implications for the components of one health: animal well-being, food production, and environmental stewardship. The present work examines one tool toward this goal, while the companion Currents in One Health by Nguyen et al, JAVMA, January 2023, takes a broader view of many aspects of dairy sustainability.

Dairy production sustainability through a one-health lens.

Dairy production provides high-quality, healthful nutrients to people on a planet soon to be inhabited by over 9 billion people. In doing so, it is ever more important to continuously improve the care of dairy animals, safeguard the environment we all share, and reliably produce nutritious food while maintaining the economic viability of the people working in dairy agriculture. In this paper, we review some associations between dairy consumption and human health along with the many interconnections between people, dairy animals, plants, and our shared environment. Understanding these relationships is an example of one health at work. In the US, total dairy consumption is at its highest point in the last 50 years, while many objective measures of cow health (eg, subclinical mastitis) have never been better since they have been recorded. Further, indications of food safety such as violative antibiotic residues in milk have never been lower. Dairy foods provide essential nutrients such as protein, vitamin B12, and calcium, while there is also evidence that they are protective against chronic conditions such as cardiovascular disease. Finally, the environmental footprint of dairy production in the US, as measured by metrics such as carbon dioxide-equivalent emissions intensity per unit of dairy nutrient, is the lowest it has ever been. The companion Currents in One Health by Nguyen et al, AJVR, January 2023, discusses some additional animal welfare and environmental impact implications of modern dairy production management in detail.

Temporal kinetics of bovine mammary IgG secretion into colostrum and transition milk.

Neonatal calf survival and health is predominantly dependent on sufficient consumption of immunoglobulin G (IgG) and the resulting transfer of passive immunity (TPI). In this study, we investigate the potential for continued IgG secretion and temporal kinetics of mammary IgG output in sequential milkings performed at 0, 4, 16, 28, 40, and 52 hr postcalving in Holstein dairy cows. For colostrum (0 hr), we also scrutinize the relationships between IgG concentration, volume, refractometer readings (˚Bx values, Brix) and concentration of sugars (lactose and glucose). Mammary transcripts postpartum (0 hr) indicated that active IgG secretion continues beyond the first milking (colostrum; n = 4 to 5). IgG measurements at the different timepoints indicated that colostrum represents only 25.1% of the total IgG produced across the 6 sequential milking timepoints, with a substantial 48.9% being secreted into transition milk over the next 3 timepoints (4-, 6-, and 28-hr) combined. The differences on the basis of IgG concentrations across 0-, 4-, and 16-hr milking timepoints were not statistically significant (P = 0.1522; n = 9). For colostrum, volume remained highly variable, even with induced let-down prior to milking (n = 27). Nonetheless, colostrum IgG secretion was significantly co-regulated with volume (R2 = 0.915; P < 0.001; n = 18), an association that was stronger than that measured for lactose (R2 = 0.803; P < 0.001; n = 18) and glucose (R2 = 0.467; P = 0.002; n = 17). Comparing colostrum ˚Bx values to absolute IgG concentrations showed no correlation (R2 = 0.127; P = 0.07; n = 27); biochemical separation of colostrum components indicated that both proteins and nonprotein solutes could affect ˚Bx values (P < 0.0001 for both; n = 5). This suggests that ˚Bx values do not reasonably indicate IgG concentration to serve as a measure of "colostrum quality." Additionally, our finding that early transition milk (4-, 6-, and 28-hr) can contribute substantially more IgG than colostrum forces a rethink of existing feeding paradigms and means to maximize TPI in calves. Collectively, our results reveal the remarkable value of early transition milk and caveats to colostrum assessments that could advance application in enhancing neonatal calf health.