Some abstracts do not have video files because ASAS was denied recording rights.
1512
The timing of feed availability entrains the circadian rhythm of milk synthesis in dairy cattle
Dairy cows have well-recognized natural daily rhythms of feed intake and milk synthesis. However, little is known about the regulation of these circadian rhythms. Variation in feed intake throughout the day results in a daily pattern of nutrient absorption, which may entrain the rhythm of milk synthesis. The objective of this study was to investigate the effect of the timing of feed availability on the daily rhythm of milk synthesis. Sixteen cows were randomly assigned to one of two treatment sequences in a cross-over design. All cows were fed the same total mixed ration ad libitum for 16 h/d either during the day (DF) or the night (NF). Cows on the DF treatment had feed available from 0700 to 2300 h, while NF cows were offered feed from 1900 to 1100 h. Treatment periods were 17 days and cows were milked every 6 h the last 7 days of each period. Milk samples were collected at each milking on the final two days of each period and analyzed for fat, protein and milk urea nitrogen (MUN). Blood samples were collected on the final 3 d of each period to represent every 4 h over the day. Body temperature was monitored using vaginal temperature loggers. Data was analyzed as a cross-over design in Proc Mixed and by cosine analysis to determine the phase (time at peak) and amplitude (peak to mean) of daily rhythms. Milk yield, fat and protein yield, and fat, protein, and MUN concentration displayed 24 h rhythms. Treatment modified the rhythm of milk yield, protein yield, MUN, and fat, and protein concentration (P < 0.05). Briefly, milk yield and lactose concentration were phase delayed by approximately 4 h in NF cows (P < 0.05). The daily rhythms of fat, protein and MUN concentration of NF cows were phase advanced by 2, 10 and 3 h, respectively (P < 0.05). The rhythms of fat, protein and MUN concentration exhibited a greater amplitude in NF compared to DF. Blood glucose followed a daily rhythm that was not affected by the timing feed availability (P > 0.10). There was a daily rhythm of body temperature was phase advanced 4 h by NF (P < 0.05). The timing of feed availability modified the rhythm of milk synthesis and body temperature in dairy cattle, but did not modify the daily pattern of plasma glucose.
Keywords: Circadian rhythm, food entrainment, milk synthesis