1. Abstr. M65
Test-day milk loss associated with elevated test-day somatic cell score
R.H. Miller, H.D. Norman, G.R. Wiggans, and J.R. Wright
Animal Improvement Programs Laboratory, Agricultural Research Service, USDA, Beltsville, MD
BACKGROUND
Estimated milk loss per unit increase in lactation mean SCS
135 kg during first parity
270 kg for parities 2-4
Raubertas and Shook, 1982, J. Dairy Sci. 65:419
DATA
Holstein test-day records from first and second calvings during 1995 through 2002
First 4 test days required for milk yield and SCS
First test day required to be <41 d after calving
RESULTS (cont.)
Partial regression of test-day milk yield (kg) on mean of prior and current test-day SCS:
Prior SCS most useful for predicting test-day milk yield during late lactation for parity 1 and on test day 4 for parity 2
Current SCS useful for predicting test-day milk yield regardless of test day or parity but more useful for parity 2
Partial regression of test-day milk yield (kg) on mean of prior test-day SCS (current test-day SCS not in model):
Prior SCS most useful for predicting test-day milk during late lactation for parity 1 and test-days 6 through 10 for parity 2
RESULTS (cont.)
Partial regression of standardized lactation milk yield (kg) on test-day SCS:
Test
day
Mean prior SCS
Current SCS
Parity 1
Parity 2
121
–0.142
–0.289
–0.235
–0.589 13
–0.155
–0.327
–0.216
–0.512 14
–0.163
–0.366
–0.252
–0.489 15
–0.197
–0.335
–0.260
–0.521 16
–0.249
–0.329
–0.255
–0.569 17
–0.284
–0.312
–0.246
–0.647 18
–0.295
–0.269
–0.291
–0.744 19
–0.346
–0.198
–0.286
–0.875 10
–0.302
0.021 (NS)
–0.401
–1.209
1Mean prior SCS = SCS on test day 1
Test
day
Parity 1
Parity 2
Coefficient
t-value 1
–54.6
–22.4
–61.4
–26.0 2
–40.9
–14.2
–32.3
–12.3 13
–31.4
–10.2
–25.3
–9.2 14
–15.3
–4.8
–16.9
–5.8 15
–9.4
–2.9
–13.7
–4.5 16
–7.2
–2.2
–18.2
–5.7 17
–0.7 (NS)
–0.2
–18.0
–5.5 18
–6.5 (NS)
–1.9
–21.5
–6.4 19
11.6
3.4
–20.8
–6.1 10
15.7
4.9
–45.3
–14.3
OBJECTIVES
Determine test-day milk loss associated with elevated SCS on current and previous test days
Determine lactation milk loss associated with elevated SCS on test days 1 through 10
RESULTS
Maximum mean SCS and highest frequency of peak SCS on test day 1 for parity 1 and on test day 10 for parity 2:
Mean milk yield on test day:
CONCLUSIONS
Test-day milk loss due to elevated SCS:
Greatest for current test day
Carryover effect for subsequent test days (nearly equal for parity 1, much less for parity 2)
Lactation milk loss due to elevated SCS:
Greatest for test-day 1 regardless of parity
Much greater for early lactation than for late lactation for parity 1
Substantial for all test days during parity 2 (especially early and late lactation)
Mastitis control most critical at calving or during early lactation for 1st-parity heifers and important throughout lactation for 2nd­parity cows
LEAST-SQUARE ANALYSES
Milk yield on test day n (n = 2, 3, …, 10) as dependent variable; corresponding test-day SCS and mean test-day SCS (1, 2, …, n–1) as independent variables
Nuisance effects: parity, calving year, regression on DIM on test day 1, regression on days open (test days 7 to 10 only)
Analysis within herd and cow
Corresponding analyses without regression on current test-day SCS
Corresponding analysis with standardized lactation (305-d, 2-times-a-day milking, mature- equivalent) milk yield as dependent variable and test-day SCS (n = 1, 2, … 10) as independent variables
Test day
Parity 1
Parity 2
Error df
121
–0.201
–0.581
214,526 13
–0.256
–0.664
213,672 14
–0.315
–0.711
212,927 15
–0.371
–0.713
203,369 16
–0.428
–0.746
196,010 17
–0.462
–0.784
176,296 18
–0.509
–0.797
171,801 19
–0.550
–0.805
165,397 10
–0.587
–0.780
143,748
1Mean prior SCS = SCS on test day 1