NUTRITIONAL AND ENVIRONMENTAL FACTORS REGULATING BIOLOGICAL RHYTHMS OF MILK SYNTHESIS IN DAIRY CATTLE
Open Access
- Author:
- Salfer, Isaac
- Graduate Program:
- Animal Science
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- May 02, 2019
- Committee Members:
- Kevin John Harvatine, Dissertation Advisor/Co-Advisor
Kevin John Harvatine, Committee Chair/Co-Chair
Paul Allen Bartell, Committee Member
William Burton Staniar, Committee Member
Connie Jo Rogers, Outside Member - Keywords:
- Biological rhythm
milk synthesis
daily rhythm
annual rhythm
circadian
dairy cattle
food entrainment - Abstract:
- Dairy cows exhibit well-characterized daily patterns of feed intake and milk synthesis. These patterns may represent circadian rhythms, endogenous repeating cycles of approximately 24 h that govern most physiological processes. Circadian rhythms are controlled by a set of ‘clock’ transcription factors that oscillate over 24 h and govern gene expression across the day. There is an increasing body of evidence demonstrating a role of nutrient intake in modifying circadian rhythms in peripheral tissues. However, this effect has not been well-characterized in dairy cattle. In addition to a daily rhythms of milk synthesis, dairy cows display seasonal changes of milk production that are not well understood. The objective of this dissertation was to examine the factors affecting daily and annual rhythms of milk synthesis. Specifically, we wanted to examine the effects of nutrient intake on the daily rhythms of milk synthesis, and the relationships between cow-level and environmental factors and the annual rhythms of milk production. To accomplish these objectives, 6 experiments were conducted, with the first 4 examining the role of nutrient intake on the daily rhythms of milk synthesis, and the final 2 characterizing factors influencing annual rhythms of milk production. First, the effect of time-restricted feeding on the daily patterns of milk synthesis and plasma hormones and metabolites was examined in an experiment where feed was temporally restricted to cows for 16 h/d either during the day (0700 to 2300 h) or at night (1900 to 1100 h). This experiment demonstrated that night restricted feeding shifted the peak of milk yield from morning to evening, while shifting the peak of milk fat and protein concentration from evening to morning. Moreover, the daily rhythms of plasma glucose, nonesterified fatty acids, plasma urea nitrogen, and insulin were shifted about 8 h by night-restricted feeding. The objective of the second experiment was to investigate if the changes in daily patterns of milk synthesis during time-restricted feeding were caused by changes in the molecular circadian clock of the mammary gland. This experiment compared a control group with feed available continuously to cows under night-restricted feeding (feed available for 16 h/d from 2000 h to 1200 h). Results demonstrated that night-restricted feeding altered the daily rhythms of expression of clock genes circadian locomoter output cycles kaput, cryptochrome 1 and REV-ERBα, suggesting that nutrients entrain the molecular circadian clock of the mammary gland. The final two experiments examined the role of specific nutrients on the daily rhythms of milk synthesis. In one experiment, a high C18:1 oil was abomasally infused either 24 h/d or for 8 h during the day (0900 to 1700 h) or the night (from 2100 to 0500). Day-infusion increased the amplitudes of milk and milk fat and protein yield while reducing the amplitudes of milk fat and protein concentration. However, treatment had little influence on the phase of the rhythms, suggesting that the timing of fatty acid infusion did not entrain the mammary clock. In the other experiment, sodium caseinate solution was abomasally infused either 24 h/d or for 8 h during the day (0900 to 1700 h) or the night (from 2100 to 0500). Night-infusion induced a daily rhythm of milk yield, but no rhythm was present during continuous or daytime infusion. Infusion of sodium caseinate during the day reduced the amplitude of fat concentration and increased the amplitude of protein concentration, while night-infusion decreased the amplitude of protein concentration. Treatment had little effect on the time at peak of the rhythm, suggesting that the mammary circadian clock was not entrained to the time of protein infusion. Furthermore, night-infusion shifted the peak of the nonesterified fatty acid rhythm from morning to evening. The final 2 experiments characterized factors influencing the annual rhythms of milk synthesis. First, annual rhythms of milk fat and protein concentration were compared among regions of the United States using monthly averages of Federal Milk Marketing Orders. The annual rhythms had greater amplitudes in northern regions compared to southern regions suggesting that they are related to photoperiod. In the same report, the effect of cow-level factors on annual rhythms of milk, fat, and protein yield, and milk fat and protein concentration were examined using data from 11 dairy herds in Pennsylvania. Rhythms were consistent regardless of herd, lactation number, and genotype, suggesting that they are highly conserved among individual cows. Finally, annual rhythms of milk, fat and protein yield and milk fat and protein concentration were studied using dataset obtained from Dairy Records Management Systems and, relationships between annual rhythms of production and daylength, change in daylength, and environmental temperature were determined. Annual rhythms differed between northern and southern states, with northern states having greater amplitudes of milk fat and protein concentration and southern states having greater amplitudes of milk yield. Moreover, the rhythms of milk fat and protein concentration were highly correlated with absolute daylength, while the rhythm of milk yield was highly correlated with the change in daylength, suggesting that they are controlled through two separate oscillatory mechanisms. In conclusion, the daily rhythms of milk synthesis are modified by the time of feeding and this effect appears mediated by the molecular circadian clock. The timing of both fatty acids and protein affect the robustness of milk synthesis rhythms, without large effects on their time of peak. Finally, yearly patterns of milk production appear to constitute an annual rhythm, with the rhythms of fat and protein concentration being entrained by daylength and the rhythm of milk yield being entrained by the change in daylength.