F . Buckley et al. Livestock Production Science 64 2000 107 –119
111 Table 1
Chemical composition of grass, grass silage and concentrate offered over the 3 years Grass
Grass silage Concentrate
a
S.D. Silage 1
Silage 2 Conc. 1
Conc. 2 S.D.
S.D. S.D.
S.D. DM
– –
195 25.2
294 88.6
875 0.6
880 4.2
pH –
– 3.7
0.00 4.3
0.56 –
– –
– Composition of dry matter g kg
Organic matter digestibility 824
33.7 –
– –
– –
– –
– Dry matter digestibility
– –
759 35.8
803 27.0
– –
– –
Crude protein 209
32.4 159
11.0 198
27.2 201
0.6 169
6.1 Crude fibre
– –
– –
– –
84 13.6
108 11.9
Modified acid detergent fibre 208
21.3 314
42.6 262
57.7 –
– –
– NCGD
– –
– –
– –
822 8.5
841 2.5
Oil –
– –
– –
– 53
3.0 30
3.5 Ash
– –
77 0.6
88 8.3
74 2.7
87 2.1
a
S.D., standard deviation. Table 2
The effect of cow genetic merit on pre- and post-grazing sward surface heights cm over the 3 years
a
HG MG
S.E.D. Sig.
Pre-grazing sward surface heights 20.0
20.0 0.35
NS Post-grazing sward surface heights
6.6 6.7
0.10 NS
a
S.E.D., standard error of difference; NS, not significant P ,0.05.
3. Results the silage offered while indoors and during periods
of grass shortage throughout the grazing season, 3.1. Sward measurements
respectively. Concentrate 1 and 2 refer to the con- centrate offered up until mid-April and the remainder
Table 1 shows the average chemical composition of the year, respectively.
of the grass, grass silage and concentrate offered Table 2 shows that the herbage allocated to both
over the 3 years of the study. Silage 1 and 2 refer to genotypes was of similar pre-grazing height and that
Table 3 The effect of cow genetic merit on milk production over three lactations
First lactation Second lactation
Third lactation 26 weeks Significance
a
HG MG
S.E.D. HG
MG S.E.D.
HG MG
S.E.D. 1st
2nd 3rd
Yieldskg cow Milk
6441 5496
119.1 7779
6862 131.5
6199 5499
148.0 SCM
5895 5286
110.6 7209
6482 120.9
5548 5147
128.7 Fat
241 222
5.5 302
274 6.2
228 217
5.9 Protein
222 193
4.4 264
235 4.2
206 185
4.4 Lactose
299 260
5.37 356
317 6.1
283 256
7.1 Composition g kg
Fat 37.5
40.6 0.82
39.0 40.2
0.74 36.9
39.6 0.74
NS Protein
34.4 35.3
0.40 34.1
34.3 0.30
33.3 33.7
0.33 NS
NS Lactose
46.5 47.4
0.24 45.8
46.2 0.25
45.7 46.6
0.31 NS
a
S.E.D., standard error of difference; NS, not significant P ,0.05; P,0.05; P,0.01; P,0.001.
112 F
. Buckley et al. Livestock Production Science 64 2000 107 –119
both genotypes grazed to similar intensity over the quality grass on a daily basis over the 3 years
grazing season. The area allocated to the HG cows Stakelum and Dillon, 1990.
was on average 5 to 6 greater than that allocated the MG cows to achieve similar post-grazing heights.
3.2. Milk yield and composition Both the chemical analysis of the herbage and the
post-grazing sward surface height suggest that the Table 3 shows the effect of cow genetic merit on
cows had access to adequate quantities of high milk production during first, second and third lacta-
Fig. 1. Effect of cow genetic merit ———, HG; - - -, MG on the seasonality of milk production by week of lactation for first, second and third lactations 26 weeks.
F . Buckley et al. Livestock Production Science 64 2000 107 –119
113
tion. The HG cows produced significantly higher HG cows had a significantly P
,0.01 higher SDMI yields of milk, solids corrected milk SCM Tyrrell
during the non-lactating period Table 5. In very and Reid, 1965, fat, protein and lactose during all
early lactation when offered grass silage ad libitum three lactations. With the exception of the second
plus 7.9 kg DM of concentrates daily there was no lactation the MG cows produced milk of significantly
difference in SDMI between the HG and MG cows higher fat and lactose concentrations. There was no
Table 5. However, with a separate group of cows effect of cow genetic merit on protein concentration.
that were turned out to pasture in very early lactation Estimated total lactation milk yields kg as third
and offered 4.4 kg DM concentrates daily the HG lactation animals would have been 8758 and 7610
cows had significantly P ,0.05 higher GDMI
for the HG and MG cows, respectively Farrell, Table 5.
1998. This corresponds to a difference in total lactation yield kg between the genetic groups of
3.4. Live weight and condition score 948, 917 and 1148 for first, second and third
lactations, respectively. Table 6 shows the effect of cow genetic merit on
Fig. 1 shows the milk production profiles for the live weight and condition score at different stages of
HG and MG cows during the first, second and third lactation when cows were in their first, second and
lactations. Peak milk production was 28.1 and 23.9 third lactation. Cow genetic merit had no significant
kg day at week 8 of lactation, 34.9 and 30.6 kg day effect on live weight at any stage during first, second
at week 9 of lactation and 39.4 and 34.9 kg day at or third lactation with the exception of the start of
week 6 of lactation for the HG and MG cows during the second lactation when the HG cows had a
the first, second and third lactations, respectively. significantly P
,0.05 higher live weight. The MG cows had significantly P
,0.001 higher condition 3.3. DM intake estimates
score at all stages of lactation while as first, second and third lactation. Figs. 3 and 4 show the lactation
Table 4 shows the effect of genetic merit on profiles for live weight and condition score averaged
GDMI and TDMI for the intake estimates taken on over first, second and third lactation 26 weeks. The
all cows during the grazing season as first, second average live weight change from weeks 1 to 4, 4 to 8
and third lactation. The average lactation stage when and 8 to 12 of lactation were
20.80 and 20.65, the intake estimates were obtained were 164, 161
20.33 and 20.26, and 0.06 and 0.06 for the HG and and 114 days into lactation in the first, second and
MG cows, respectively, over the three lactations. third lactation, respectively. The individual TDMI
However, none of the differences observed between estimates over the three lactations are shown in Fig.
the two genotypes were significant. The HG cows 2. The HG cows had significantly P
,0.001 higher had significantly P
,0.05 greater condition score GDMI and TDMI when compared to the MG cows
change averaged across the three lactations from in the first, second and third lactations Table 4. The
weeks 1 to 4 20.14 vs. 20.09 and weeks 4 to 8
Table 4 The effect of cow genetic merit on intake kg cow day of grass dry matter GDMI and total dry matter TDMI over three lactations
Lactation no. Days in milk
Intake Cow genetic merit
Significance
a
HG MG
S.E.D. 1
164 GDMI
14.4 13.7
0.17 TDMI
16.0 15.3
0.17 2
161 GDMI
19.3 17.9
0.17 TDMI
20.5 19.1
0.17 3
114 GDMI
18.0 16.4
0.22 TDMI
20.2 18.6
0.22
a
S.E.D., standard error of difference. P
,0.001.
114 F
. Buckley et al. Livestock Production Science 64 2000 107 –119
Fig. 2. Effect of cow genetic merit ♦, HG; j, MG on DM intake TDMI for first, second and third lactation at different stages of
lactation.
F . Buckley et al. Livestock Production Science 64 2000 107 –119
115 Table 5
The effect of cow genetic merit on intake kg cow day of silage dry matter SDMI, grass dry matter GDMI and total dry matter TDMI Lactation no.
Days in milk Intake
Cow genetic merit Significance
a
HG MG
S.E.D. 2
– SDMI
13.2 12.1
0.21 3
25 SDMI
10.3 10.1
0.40 NS
TDMI 18.1
18.0 0.40
NS 3
34 GDMI
17.2 15.7
0.62 TDMI
21.5 20.0
0.62
a
S.E.D., standard error of difference; NS, not significant P ,0.05; P,0.05; P,0.01.
Table 6 Live weight and condition score of high HG and medium MG genetic merit over three lactations first, second and third
First lactation Second lactation
Third lactation 26 weeks Significance
a
HG MG
S.E.D. HG
MG S.E.D.
HG MG
S.E.D. 1st
2nd 3rd
Live weight kg Pre-calving
592 585
8.0 650
634 8.4
714 705
12.9 NS
NS Week 1
522 518
8.9 572
563 8.1
616 611
11.0 NS
NS NS
Week 8 491
490 7.6
536 538
8.5 591
589 10.0
NS NS
NS End of lactation
549 560
8.8 631
649 11.4
– –
– NS
NS –
Condition score Pre-calving
2.79 3.25
0.069 3.04
3.38 0.067
3.09 3.63
0.086 Week 8
2.35 2.77
0.066 2.44
2.92 0.069
2.42 3.19
0.102 End of lactation
2.52 2.97
0.074 2.75
3.35 0.078
– –
– –
a
S.E.D., standard error of difference; NS, not significant P ,0.05; P,0.05; P,0.001.
Fig. 3. Effect of cow genetic merit ———, HG; - - -, MG on live weight by week of lactation averaged over the three lactations.
116 F
. Buckley et al. Livestock Production Science 64 2000 107 –119
Fig. 4. Effect of cow genetic merit ———, HG; - - -, MG on condition score by week of lactation averaged over the three lactations.
20.12 vs. 20.07 of lactation when compared to and Ireland
.0.85 genetic correlation but a consid- the MG cows. The averaged live weight gain kg
erable scaling effect between the two countries. This day between first and second, and between second
scaling effect indicated that grass-based feeding and third lactation was significantly P
,0.01 higher systems like those in Ireland reduce the ability of the
11.20 vs. 10.91 for the HG cows when compared animal to exploit its full genetic advantage. In the
to the MG cows. present study there was no interaction between cow
genetic merit and feeding system for any of the performance traits measured Buckley, 1999. The
4. Discussion difference in milk production observed between the
