Omission of dry period and effects on the subsequent lactation curve and on milk quality around calving in Italian Holstein cows

Figures & data

Table 1 Chemical composition of the basal diets used during the experiment (AOAC, 2000).

Chemical composition		Pre-parturition			Post-partum^*
	CTR		CON
	-55 to -20 d	-20 to 0 d	-55 to -20 d	-20 to 0 d
DM, %	51.7	55.8	54.3	57.0	66.0
CP, % DM	11.6	12.5	12.3	13.0	15.3
Lipids, % DM	3.4	3.7	3.3	3.5	2.3
NDF, % DM	56.0	50.7	52.8	48.4	35.6
Starch, % DM	20.7	20.9	22.9	23.2	24.9
Net energy, MFU/kg DM	0.74	0.76	0.80	0.79	0.91

CTR= cows having a 55 d dry period; CON= cows of continuous lactation group; MFU= Milk Feed Units (INRA, 1988)

* Diets of CTR and CON cows were the same after calving.

Table 2 Results of mixed model ANOVA for test day milk yield in the lactation subsequent to CTR or CON treatments.

Source	DF	F	P
Lactation group (L)	1	3.76	0.08
Parity (P)	1	3.73	0.08
L×P	1	0.64	0.43
w1×L×P (Across & Within)^*	4	2116.32	< 0.001
w2×L×P (Across & Within)^*	4	521.44	< 0.001
Residual	4750	-	-

CTR= cows having a 55 d dry period; CON= cows of continuous lactation group.

* Across and within regression coefficients of Wilmink function for the lactation curve, where: w1= regression coefficient on DIM and w2= regression coefficient on exp-^0.05×DIMWilmink, 1997

Table 3 Within Lactation group (L), Parity (P) and interaction L×P estimated regression coefficients and standard error (SE) estimates for the Wilmink function used to describe the lactation curve.

Item	Regression coefficients^*
	w0		w1		w2
	coefficient	SE	coefficient	SE	coefficient	SE
Lactation group(L)
CTR	41.905	1.902	-0.067	0.001	-22.546	0.668
CON	36.893	1.749	-0.085	0.001	-17.246	0.601
Contrast for L	-	-	< 0.001	-	< 0.001	-
Parity (P)
Primiparous	36.903	1.646	-0.072	0.002	-21.058	0.719
Multiparous	41.894	1.992	-0.081	0.001	-18.733	0.539
Contrast for P	-	-	< 0.001	-	0.010	-
L×P
CTR-primiparous	40.443	3.010	-0.062	0.002	-24.597	1.106
CTR-multiparous	43.366	2.327	-0.073	0.001	-20.495	0.750
Contrast for P within CTR	-	-	< 0.001	-	0.002	-
CON-primiparous	33.363	2.611	-0.082	0.002	-17.520	0.920
CON-multiparous	40.423	3.329	-0.088	0.002	-16.972	0.773
Contrast for P within CON	-	-	0.017	-	0.649	-

* w0= intercept, w1= regression coefficient on DIM, w2 regressioncoefficient on exp^-0.05×DIM, (Wilmink, 1987). CTR= cows having a 55 d dry period; CON= cows of continuous lactation group.

Figure 1 Estimated shape of the lactation curve subsequent to a different lactation length treatment (CTR, continuous lines; CON, dotted lines) and parities (squares for Multiparous, ML, circles for Primiparous, PR). CTR=cows having a 55 d dry period; CON=cows of continuous lactation group.

Table 4 Characteristics of the lactation curves obtained from estimated regression coefficients of Wilmink function (Wilmink, 1987).

	305 Milk Yield (kg)	Peak DIM (d)	Yield at peak(kg)	Persistency^*
Lactation group (L)
CTR	9198	56	36.8	-62
CON	6957	46	31.3	-78
Parity (P)
Primiparous	7502	54	31.6	-66
Multiparous	8653	49	36.3	-74
L×P
CTR-primiparous	8976	60	35.5	-57
CTR-multiparous	9420	53	38.0	-67
CON-primiparous	6029	47	27.9	-75
CON-multiparous	7884	45	34.7	-81

CTR= cows having a 55 d dry period; CON= cows of continuous lactation group.

* Expressed in g/d and calculated as: (MY at 305 d-MY at peak)/(305-Peak DIM).

Table 5 Results of mixed model ANOVA for milk quality reported as values of F statistics.

Source	DF	Fat (%)	Protein (%)	Lactose (%)	MUN (mg/dL)	SCS
Lactation group (L)	1	0.10	0.03	3.23	0.44	1.82
Parity (P)	1	0.23	0.27	3.62	0.65	2.23
L×P	1	0.16	0.01	2.84	0.25	4.19
Sampling time (S)	11	2.12^*	16.98^***	15.39^***	1.33	8.63^***
L×S	8	0.83	0.97	1.46	1.27	1.00
P×S	11	0.96	0.52	1.58	0.28	0.87
L×P×S	8	0.70	0.34	0.82	1.87	1.05
Residual	98	-	-	-	-	-

* P<0.05;

** P<0.01;

*** P<;0.001.

SCS = 3 + log₂ (SCC/100,000).

Pattern of fat, protein and somatic cell score (SCS*) in milk in different lactation groups (CTR, continuous lines; CON, dotted lines) around calving. *SCS= 3+log₂ (SCC/100,000). CTR= cows having a 55 d dry period; CON=cows of continuous lactation group.

AOAC 2000 Official methods of analysis of AOAC international 17th ed. W. Horwitz Washington, DC, USA

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