R .C. Dobos et al. Livestock Production Science 63 2000 235 –243
239
and freeze dried for the determination of moisture. effects were each heifer within each month of
Freeze dried aliquots also were used to determine lactation. The variance component estimation meth-
lipid content Folch et al., 1957 and amount of dry od was restricted maximum likelihood REML and
fat free tissue DFFT. Duplicate samples of DFFT the type of covariance matrix was compound sym-
were used to determine the amount of DNA Martin metry.
et al., 1972, hydroxyproline Bergman and Loxley, 1963 and nitrogen in the udder. The hydroxyproline
value was converted to collagen using a factor of
3. Results
7.14, assuming 300 000 collagen g mole. 3.1. Pre-pubertal heifer growth, age and LW at
2.8. Statistical analyses slaughter
Liveweight gain during the pre-pubertal feeding Influence of dietary CP and REP concentration on
period was determined from linear regression analy- pre-pubertal growth and age and LW at slaughter is
sis of LW against age. Differences in mammary summarised in Table 3. Pre-pubertal LWG was
development between diets and dietary concentra- influenced P
5 0.05 by dietary CP concentration, tions of CP and REP were compared by analysis of
such that heifers consuming the high-CP diets grew co-variance with initial LW and age and LW and age
at a faster rate 952 and 990 g per d compared with at slaughter as covariates. Covariates not contribut-
those heifers that consumed the low-CP diet 918 g ing to the source of variation were removed. Differ-
per d. However, pre-pubertal LWG was not in- ences in udder dimensions measured during lactation
fluenced P 5 0.23 by dietary REP concentration. At
were compared by analysis of covariance with days slaughter, LW averaged 364.6 kg across diets, with
in milk as a covariate. Monthly milk, protein and fat the least square mean LW of the heifers that had
yields were analysed using a mixed model split-plot consumed diet A being 30 kg heavier compared to
in time repeated measures analysis with calving date those heifers that consumed diets B and C P
5 and LW at calving as covariates. The fixed effects
0.09. However, LW at slaughter was not influenced were diet by month of lactation, while the random
by either dietary CP or REP concentration. Age at
Table 3 Least square means and contrasts for initial age and liveweight, age and liveweight at slaughter, and liveweight gain of pre-pubertal heifers
reared on diets varying in crude protein and undegradable protein
a
Diet Contrast
A B
C SED
Diet Low-CP vs.
Low-REP vs. high-CP
high-REP ——————— P ——————
All heifers N
21 21
21 Initial LW kg
114 115
122 5.7
0.31 0.38
0.82 Initial age d
160.3 160.5
156.1 10.1
0.89 0.82
0.66 LWG g per d
918 952
990 50.6
0.09 0.05
0.23 Slaughter heifers
N 6
6 6
Initial LW kg 115
126 128
13.2 0.59
0.32 0.88
Initial age d 137.3
166.5 159.8
14.8 0.15
0.06 0.66
LW at slaughter kg 386
352 356
20.4 0.22
0.09 0.87
Age at slaughter d 492.0
502.5 471.2
18.0 0.24
0.75 0.10
LWG g per d 924
972 944
67.4 0.80
0.62 0.98
a
Diet A 5 high-energy, low-CP, high-REP; Diet B 5 high-energy, high-CP, low-REP; Diet C high-energy, high-CP, high-REP.
SED 5 Standard error of difference for diet only; LW 5 liveweight; LWG 5 liveweight gain from 5–10 months; N 5 number of heifers.
240 R
.C. Dobos et al. Livestock Production Science 63 2000 235 –243
slaughter was not influenced by either dietary CP or mary gland development is shown in Table 4. At
REP concentration. slaughter, heifers that consumed diet B during the
pre-pubertal period had heavier dry udder weights 3.2. Pre-pubertal mammary gland development
P 5 0.01, tended to have more fat P 5 0.08 and
more secretory tissue area P 5 0.07 in the dry
3.2.1. Influence of dietary CP concentration diet udder than those heifers that consumed diet C 820
2
A vs . diets B and C
vs. 519 g; 636 vs. 420 g; 64.2 vs. 39.9 m . Other The influence of dietary CP concentration on pre-
mammary gland components were not different P .
pubertal mammary gland development is shown in 0.05, see Table 4.
Table 4. At slaughter, heifers that consumed diet A during the pre-pubertal period had more P
, 0.001 3.3. Influence of dietary CP and REP
area of fat tissue and a higher P 5 0.002 ratio of fat
concentration on first lactation production to secretory tissue in their mammary glands com-
pared to those that consumed diets B and C. Other The influence of pre-pubertal dietary CP and REP
mammary gland components were not different P .
concentration on age and LW at calving, first lacta- 0.05, see Table 4.
tion production and udder dimensions is shown in Table 5. The average pre-calving age and LW across
3.2.2. Influence of dietary REP concentration diet diets was 26.1 months and 524.6 kg, respectively.
B vs . C
Heifers that consumed diet A were, on average, the The influence of dietary REP concentration at the
lightest at calving 517.8 kg compared to those same dietary CP concentration on pre-pubertal mam-
heifers that consumed either diet B 531.4 kg or diet
Table 4 Least square means and contrasts for components of mammary glands of heifers raised on diets varying in crude protein and undegradable
protein
a
Diet Contrast
A B
C SED
Diet Low-CP vs.
Low-REP vs. high-CP
high-REP ——————— P ———————
N 6
6 6
Trimmed wet udder weight g 2044
1903 1553
252.4 0.16
0.15 0.17
Trimmed dry udder weight g 741
820 519
116.4 0.04
0.43 0.01
Composition of dry udder g
DFFT 269
296 288
97.8 0.96
0.71 0.94
Protein 81
113 76
33.9 0.53
0.61 0.31
Fat 692
636 420
123.6 0.09
0.16 0.08
Ash 7.5
9.2 10.7
2.5 0.43
0.25 0.51
Composition of DFFT g
Protein 211
250 245
82.1 0.86
0.60 0.93
DNA 3.7
5.5 6.8
2.1 0.34
0.18 0.60
Protein DNA 57.0
52.9 45.0
9.7 0.47
0.33 0.43
Collagen in DFFT 34.3
34.5 32.0
1.7 0.21
0.45 0.16
2
Fat tissue area m 74.9
42.7 24.1
11.8 0.002
, 0.001 0.14
2
Secretory tissue area m 53.4
64.2 39.9
12.4 0.18
0.90 0.07
Ratio fat secretory tissue 1.6
0.69 0.61
0.29 0.007
0.002 0.77
a
Diet A 5 high-energy, low-CP, high-REP; Diet B 5 high-energy, high-CP, low-REP; Diet C 5 high-energy, high-CP, high-REP.
SED 5 Standard error of difference for diet only; N 5 number of heifers slaughtered; DFFT 5 dry fat free tissue; CP 5 crude protein;
REP 5 undegradable protein.
R .C. Dobos et al. Livestock Production Science 63 2000 235 –243
241 Table 5
Least square means, SED and contrasts for age and LW at first calving, and first lactation production of heifers raised on diets varying in crude protein and undegradable protein
a
Diet Contrast
A B
C SED
Diet Low-CP vs.
Low-REP vs. high-CP
high-REP —————— P ——————
N 15
13 11
Calving LW kg 518
531 525
12.8 0.29
0.36 0.59
Calving age months 26.3
26.0 26.1
0.50 0.56
0.61 0.77
Milk l per d 18.8
17.8 19.4
0.63 0.55
0.66 0.37
Protein kg per d 0.61
0.57 0.65
0.05 0.11
0.40 0.08
Fat kg per d 0.70
0.73 0.78
0.07 0.86
0.58 0.99
Udder circumference cm 129.8
125.3 127.3
5.3 0.66
0.40 0.65
Udder length cm 64.6
65.0 66.5
2.9 0.81
0.68 0.67
Udder breadth cm 73.5
72.0 73.7
3.0 0.80
0.73 0.54
a
Diet A 5 high-energy, low-CP, high-REP; Diet B 5 high-energy, high-CP, low-REP; Diet C 5 high-energy, high-CP, high-REP.
SED 5 Standard error of difference for diet only; REP 5 undegradable protein; N 5 number of heifers; LW 5 liveweight.
C 524.6 kg. However, age and LW at calving were consumed pre-pubertal diets of high-energy, high-CP,
not influenced P . 0.05 by either pre-pubertal
low-REP. Pre-pubertal dietary REP concentration did dietary CP or REP concentration.
not influence first lactation production, although The average daily first lactation milk, protein and
there was a tendency for more daily protein to be fat yields across diets was 18.6 l, 0.61 and 0.73 kg,
produced when pre-pubertal dietary REP concen- respectively. Daily first lactation milk, protein and
tration was increased. fat yields were not influenced by pre-pubertal dietary
Our lactation results for pre-pubertal dietary CP CP concentration. Pre-pubertal dietary REP concen-
concentration are in contrast to those of Pirlo et al. tration did not influence daily first lactation milk and
1997, who found an increase in daily first lactation fat yields but daily protein yield tended to be greater
milk production of 1.6 kg when heifers were fed a P
5 0.08 in those heifers that had consumed diet C high-CP diet 110 NRC, 1989 compared to a
compared to those that consumed diet B during low-CP diet 90 NRC, 1989 at similar high pre-
pre-puberty. Udder dimensions measured during first pubertal LWG. The comparison of pre-pubertal
lactation were not influenced P . 0.05 by either
dietary REP concentration in our study indicated that pre-pubertal dietary CP or REP concentration.
the high-REP diet compared with the low-REP diet produced similar lactation results to those of Pirlo et
al. 1997. Since they did not study dietary REP
4. Discussion concentration, their increase in milk and protein may
