2004

1. 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) • 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 Total and direct effect of DD on fertility LIFETIME ANALYSIS DD maximizing LM, by parity • 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 • 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 • 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 2004 • 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. • 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 • SUBSEQUENT LACTATION ANALYSES • Solutions for DD by subsequent lactation yield 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. • Long DD is detrimental for fat (blue) and protein (red) % • SCS (yellow) is benefited by a long dry period in subsequent lactation • 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