Annual rhythms of feed intake and milk production in the western United States and relationships to management strategies

Document Type


Publication Date



American Dairy Science Association


Journal of Dairy Science




Suppl. 1






nnual rhythm, milk synthesis, yearly pattern


Milk yield (MY) and milk components follow a repeatable yearly cosine function. Generally, in the US MY peaks in mid-April and reaches a nadir in mid-October, whereas milk fat concentration (FAT) and protein concentration (PRO) peak near January 1 and reach nadir near July 1. We have J. Dairy Sci. 103 (Suppl. 1) 91 previously demonstrated that these rhythms differ across regions of the US, with MY having greater amplitude in the Southeast and Southwest US, and FAT and PRO having greater amplitude in the Upper Midwest and northeast. However, we have not characterized these rhythms in the Western US, and little is known about how annual rhythms vary among different management systems. This experiment used 129,530 monthly milk production and feed intake records collected from 2006 to 2019 from 332 herds throughout California, the Pacific Northwest, the Southwest, the Rocky Mountains and the Upper Midwest. We examined the effects of region, breed, housing type (freestall vs. loose), and milking frequency (2x/d vs. 3x/d) on annual rhythms of dry matter intake (DMI), MY and FAT and PRO by fitting monthly production records to the linear form of cosine functions with a 12-mo period in SAS 9.4. Dry matter intake fit a 12-mo rhythm in all regions except the Rocky Mountains (P < 0.01) and peaked between Feb 24 and Mar 22. The greatest amplitude of the DMI rhythm occurred in the Southwest (2.4 kg). Milk yield fit an annual rhythm in all regions (P < 0.01) and had a greater amplitude in the Southwest and California compared with the Pacific Northwest, Rocky Mountains and Upper Midwest (P < 0.05). Milk yield fit a 12-mo rhythm regardless of breed (P < 0.01), but the amplitude of the rhythm was greater for Holsteins than Jerseys or Crossbreds (P < 0.05). Relative to freestalls, cows on loose housing had 22%, 63%, and 57% greater amplitudes of MY, FAT, and PRO rhythms, respectively (P < 0.05). Milking frequency did not affect the annual rhythms of MY, FAT, or PRO (P > 0.10). In conclusion, milk and components in the Western US follow annual rhythms that are impacted by latitude similar to previous reports, and are also modified by housing system.