# Presentation: 065652

## OBJECTIVES

**OBJECTIVES**
- Determine the factors that affect dry period length
- Find the minimum dry period length needed to maintain performance in the subsequent lactation
- Determine dry period length, between each of the first 3 lactations, that maximizes lifetime production

**INTRODUCTION**
- Recent studies have indicated that reducing dry period to 30 d could be beneficial (Bachman, 2002)
- Dated studies support 40 to 60 d dry  (Coppock et al., 1974; Funk et al., 1987)

**MATERIALS & METHODS**
- Holstein cows calving from 01/01/1997 to 12/31/2003
- Herds on DHI test during the entire period
- Actual yield calculated by test-interval method using adjustment factors of Shook et al. (1980)
- Records were adjusted for cow effects
- Total of 774,168 records and 3632 herds
- Lactational analyses
- Model included herd-year (HY), year-state-month of calving, days dry (DD), age, and age2
- Traits examined were milk, fat, protein, days open (DO), fat %, protein %, and somatic cell score (SCS)
- Lifetime milk (LM) analysis
- LM accounts for loss of milk in previous lactation due to dry off and any detrimental effects on herd life

**REFERENCES**
- Bachman, K.C. 2002. Milk Production of dairy cows treated with estrogen at the onset of a short dry period. JDS 85:797-803.
- Coppock, C.E., R.W. Everett, R.P. Natzke, and H.R. Ainslie. 1974. Effect of dry period length on Holstein milk production and selected disorders at parturition. JDS 57:712-718.
- Funk, D.A., A.E. Freeman, and P.J. Berger. 1987. Effects of pervious days open, previous days dry, and present days open on lactation yield. JDS 70:2366-2373.
- Shook, G.E., L.P. Johnson, and F.N. Dickinson. Factors for improving accuracy of estimates of test-interval yield. DHI, USDA, July 1980. v. 56 (4) p. 9-24.

- Subsequent lactation yield maximized at 60 to 65 DD
- Short DD was more detrimental for parity 2 (blue)
- Fat and protein follow the same pattern

**SUBSEQUENT LACTATION ANALYSES**
**Solutions for DD by subsequent lactation yield**

**RESULTS**
**FACTORS AFFECTING DD**
- DO accounts for the most variation in DD
- Second highest is lactational milk
**Least square means for factors that affect DD**

|  |  | LSMean |  | SE |
| --- | --- | --- | --- | --- |
| Milk* |  |  |  |  |
|  | 1 | 64.26 | 0.35 |  |
|  | 2 | 59.53 | 0.35 |  |
|  | 3 | 55.94 | 0.35 |  |
| Days open* |  |  |  |  |
|  | 1 | 55.22 | 0.35 |  |
|  | 2 | 58.49 | 0.35 |  |
|  | 3 | 66.01 | 0.35 |  |
| SCS* |  |  |  |  |
|  | 1 | 59.26 | 0.35 |  |
|  | 2 | 60.06 | 0.35 |  |
|  | 3 | 60.41 | 0.35 |  |
| Lactation |  |  |  |  |
|  | 1 | 56.51 | 0.10 |  |
|  | 2 | 60.15 | 0.09 |  |
|  | 3 | 60.59 | 0.14 |  |
|  | 4 | 60.64 | 0.19 |  |
| *Categories were defined as: 1) lower third of data, 2) middle third of data, and 3) upper third of data. |  |  |  |  |

- Cows completing their first lactation (blue) benefited from a longer DD, relative to older cows
- Mature cows can successfully handle a 30-d dry period

**LIFETIME ANALYSIS**
**DD maximizing LM, by parity**

- The net effect (solid lines) of DD on fertility is that shorter DD results in fewer DO, but this advantage is entirely due to lower milk yield
- Direct effect (dotted lines) of short DD on fertility, independent of milk yield, is negative
**Second lactation effects of DD on fat %, protein %, and SCS **

**Total and direct effect of DD on fertility**

- Long DD is detrimental for fat (blue) and protein (red) %
- SCS (yellow) is benefited by a long dry period in subsequent lactation

**CONCLUSIONS**
- Production is maximized in the subsequent lactation with a dry period of 60 d, regardless of parity.
- However, LM is maximized by a 40-d dry period between first and second lactations, and 30 DD for lactations thereafter.
- Long dry periods appear to adversely affect fat and protein %.
- SCS in the subsequent lactation is improved by a long dry period.
- The net effect of a short dry period on fertility is beneficial. However, this is entirely due to lower milk yield associated with shorter DD. The direct effect of a short DD on DO is detrimental.