Dry period length in US Jerseys: characterization and effects on performance

Area of Science:

• Animal Science
• Dairy Science
• Reproductive Management

Background:

• The dry period is crucial for mammary gland regeneration and preparing cows for subsequent lactation.
• Optimizing dry period length (DD) is essential for dairy cow productivity and health, particularly in high-producing breeds like Jerseys.
• Previous research has indicated varying optimal dry periods, but breed-specific data, especially for Jerseys, is needed.

Purpose of the Study:

• To characterize dry period lengths in US Jersey cows.
• To determine the effects of varying dry period lengths (DD) on subsequent lactation milk, fat, and protein yields, somatic cell score (SCS), and days open (DO).
• To identify the optimal dry period length that maximizes yield across lactations for Jersey cows.

Main Methods:

• Utilized Dairy Herd Improvement Association (DHIA) field data from US Jersey cows calving between 1997 and 2004.
• Analyzed 123,032 records from 73,797 cows across 808 herds.
• Employed a statistical model including herd-year, calving details, previous lactation records, age, and DD as a categorical variable, with pre-adjusted cow effects.

Main Results:

• Jersey milk, fat, and protein yields were maximized with 61 to 65 DD in the subsequent lactation.
• Dry periods of 30 days or less significantly reduced production, while short dry periods (<30 days) improved fat and protein percentages and reduced DO.
• Jersey cows experienced a substantial increase in SCS with dry periods of 30 days or less (10% for ≤20 DD, 4.6% for 21-30 DD).

Conclusions:

• Dry periods of 45 to 70 days are recommended to maximize yields across adjacent lactations for Jersey cows.
• Producers should avoid dry periods shorter than 45 days due to significant production losses and negative impacts on SCS.
• Long dry periods exceeding 70 days are also detrimental, proving more costly to total yield than very short dry periods (<30 days).