RECENT ADVANCES IN LACTATION PHYSIOLOGY

Recent advances in lactation physiology have seen signifi­cant progress in understanding the molecular mechanisms underlying milk synthesis, regulation of milk composition, and mammary gland development.

1. Heat stress and its effect on dairy buffaloes: Various innovative measures like combination of fan and sprinklers together or wallowing the animal completely under the water/pools found to have increased production of milk as well as reproductive ability of animals. By combined way of using fan shade and sprinklers along with the supplementary like minerals, vitamins and antiox­idants was also led to increased milk production.

2. Thermotolerance and impact of heat stress in dairy cattle: Climate change exacerbates environ­mental challenges for livestock, particularly dairy cattle, by intensifying heat stress through more frequent hot days and heatwaves. Dairy cows, with their high metabolic heat load, are especially vulnerable. Heat stress disrupts various biological processes, leading to significant economic losses. To combat heat stress, cows employ physiological and cellular mechanisms that divert energy away from other functions, impacting milk production, reproduction, and health. Selecting thermotoler- ant dairy cattle becomes imperative. Strategies include reducing milk production, crossbreeding with heat-tolerant breeds, selecting based on phys­iological traits, and enhancing immune responses. Each approach has its merits and drawbacks, all detailed in the literature. This review explores the multifaceted issues surrounding heat stress in dairy cattle and evaluates proposed selection strat­egies for thermotolerance (Cartwright, Shannon L. et al. 2023).

3. Contribution on dairy production in one health perspective: Taking enough care and precision on the dairy production by providing proper nutri­ents and environment to the animal concerned to reduce the stressful environment such as heat stress during climate change.

4. Microbiomes of milk and udder in correlation: Many study highlighted the variability in results regarding the characterization of the microbiota in bovine milk. While other studies had charac­terized the microbiota of teat skin, teat canal, and milk samples, there was still no consensus on the existence and function of a core com­mensal microbiota in bovine milk. Additionally, the idea of dysbiosis (microbial imbalance) as a causal factor in udder health issues was still speculative. One consistent finding by Ruegg (2022) was that milk contained a low biomass of microbial DNA. However, there was a pressing need for standardization of methods and replica­tion of experiments to enhance understanding in this emerging field.

5. Microbiome-mammary gland interactions: McGuire, M.K., et al. (2017) found that the micro­biome of the mammary gland and its influence on lactation performance and milk composition are areas of growing research interest, highlighting the importance of the gut-mammary axis in lacta­tion physiology.

6. Epigenetic regulation of lactation: The interac­tion between the microbiome of the mammary gland and lactation performance, as well as milk composition, has been an increasingly studied area, emphasizing the significance of the gut­mammary axis in lactation physiology as observed by Lemay, D.G., et al. (2013).

7. Nutrigenomics and milk composition: Bach, A. (2018) mentioned that progress in nutrigenomics has provided insights into how maternal nutrition during lactation impacts the composition of milk and the health of offspring, guiding the develop­ment of optimal dietary strategies to enhance milk quality.

8. Role of hormones and signaling pathways: Ongoing research into hormonal regulation and intracellular signaling pathways involved in mammary gland development and lactation has revealed potential targets for improving both the quantity and quality of milk production.

9. Painless or non-ivasive method of tracking the thermal condition of the animals for produc­tion: Sejian, V et al. (2022) summarized various non-invasive methods used to measure heat stress response in farm animals, focusing on behavioral and physiological changes. Technologies for mea­suring cortisol from hair, feces, urine, saliva, and milk offer valuable insights into heat stress lev­els. Infrared thermography facilities can accu­rately gauge animal surface temperatures, aiding in assessing climate resilience. GPS and GNSS applications help understand behavioral changes in grazing animals during heat stress. Emerging techniques like sensors and machine learning show promise but require further development for broader use. These advancements could inform policymakers in developing strategies to sustain livestock production in a changing climate.

10. Genomic selection for lactation traits: Advances in genomic technologies and bioinformatics have facilitated the discovery of genetic markers asso­ciated with lactation performance, enabling more precise selection methods to enhance milk yield and quality in dairy animals Van Raden (2008).

11. Mammary stem cells and regeneration: Research has made strides in understanding mam­mary stem cell populations and their role in mam­mary gland regeneration and lactation persistence. (Wang, D., et al. 2020).

12. Role of exosomes in milk: Chen, X., et al. (2021) said that exosomes, small extracellular vesicles secreted in milk, have emerged as important mediators of intercellular communication in the mammary gland and are implicated in milk qual­ity and neonatal development.

13. Maternal stress and milk composition: Studies have investigated the impact of maternal stressors on milk composition and its implications for off­spring health and development, highlighting the complex interplay between maternal physiology and lactation outcomes reported by Prosser, C.

14. Sustaining longer lactation cycle: Throughout history, farmers have been advised to maintain a one-year calving interval to optimize milk yield peaks, yet this led to increased risks of diseases and disorders due to frequent drying-off, calv­ing, and lactation cycles. Extending the voluntary waiting period (VWP) between inseminations was identified as a solution to mitigate these chal­lenges, reducing the frequency of calving events and benefiting cow health, fertility, and reduc­ing labor and surplus calf numbers. Concerns arose about prolonged lactation periods, such as decreased milk yield in late lactation and potential cow fattening, impacting herd economics. Limited knowledge existed about subsequent lactation performance and calf outcomes with extended lactations. Responses of dairy cows to extended VWP varied depending on individual character­istics like parity, milk yield, and body condition. Customized strategies based on individual cow traits emerged as a potential future approach to select high-producing cows with consistent lacta­tion curves, thus reducing risks of fattening and milk yield reduction while minimizing challeng­ing calving eventsvan Knegsel et al. (2022).

15. Non-coding RNAs in milk: Non-coding RNAs, including microRNAs and long non-coding RNAs, present in milk have been shown to regulate gene expression in the neonate and may have implica­tions for milk functionality and offspring health.

16. Environmental exposures and milk quality: Ly, A., et al. (2023) explored the effects of envi­ronmental contaminants and pollutants on milk quality, including the presence of toxins and their impact on human health through breastfeeding.

17. Extending life of dairy cows as producer: The sustainability of milk production on farms is closely tied to the longevity of dairy cows, refer­ring to their productive lifespan. Longevity is a complex aspect influenced by various factors, lack­ing a standardized definition or measurement.

18. Mastitis and lacatting animals: Mastitis is the most common disease in dairy cows, impact­ing their welfare and farm profits. Since mod­ern dairy farming began, efforts to minimize mastitis have been ongoing. This paper reviews advances in mastitis detection, management, and prevention since 1917. Initially, research focused on understanding bacteria causing intramam­mary infections, particularly Streptococcus aga­lactiae and Staphylococcus aureus. Successful control programs emerged by identifying infec­tion mechanisms, clinical states, screening tests, and pathogen-specific traits. Control strategies shifted to preventing new infections and reduc­ing infection duration, incorporating teat dip­ping, hygienic milking, and strategic antibiotic therapy. Researchers now address mastitis from environmental pathogens and define antimicrobial usage for animal welfare. While significant prog­ress has been made, evolving herd structures and stricter standards ensure ongoing mastitis research remains crucial.

These recent advances provide valuable insights into vari­ous aspects of lactation physiology, contributing to our understanding of milk production, composition, and the health outcomes for both the cow and offspring.

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