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
have been due to the higher REP concentration in the Pre-pubertal diets of high-CP consumed by heifers
high-CP diet because of the higher intake of soybean to achieve LWG in excess of 900 g per d did
meal. influence mammary gland development, such that the
Capuco et al. 1995 found that pre-pubertal area of fat tissue and the ratio of fat to secretory
heifers grown in excess of 900 g per d and fed a tissue in these glands was decreased but did not
high-CP diet 22 CP had lighter mammary glands, affect first lactation daily milk, protein and fat yields.
less mammary fat and more total mammary DNA Further, pre-pubertal diets of high-energy, high-CP,
compared to those fed a low-CP diet 15 CP. Our high-REP decreased the weight of the dry gland and
study confirms this observation that high-CP diets tended to decrease the amount of fat and the area of
consumed during pre-puberty tended to reduce the secretory tissue compared to glands from heifers that
weight of mammary glands, as well as the area of fat
242 R
.C. Dobos et al. Livestock Production Science 63 2000 235 –243
tissue and ratio of fat to secretory tissue. Further Acknowledgements
reduction in mammary gland weight was observed in our study when pre-pubertal REP concentration at a
The authors wish to acknowledge the contribution high-CP concentration was increased.
of funding from the Commonwealth Department of The comparison of dietary REP concentrations at
Employment, Education, Training and Youth Affairs, the same dietary CP concentration, indicates that
NSW Dairy Corporation, NSW Dairy Farmers As- pre-pubertal heifers gaining in excess of 900 g per d
sociation, Elanco Animal Health Australia, Dairy had less developed mammary glands when REP was
Farmers Ltd., Australian Dairy Research and De- increased. However, these heifers were able to
velopment Corporation, Semex Australia Pty. Ltd., produce 1.6 l per d more milk than their herd-mates
Herd Improvers Australia Pty. Ltd., MillMaster consuming a low-REP pre-pubertal diet. This could
Feeds Ltd., Wrightsons Seeds Pty. Ltd., University of have been due to compensatory mammary growth
Sydney and NSW Agriculture. Thanks to Mr B. after mating and differences in body composition at
Rhees, Ms Y. Leischke-Mercer and Ms S. Plowman the start of calving. Capuco et al. 1995 have
for managing the heifers during the pre-calving stage discussed the concept of compensatory mammary
of the experiment and to Dr J. Gooden and his growth in terms of inhibition of either primary duct
dedicated staff at the University of Sydney MayFarm elongation or branching of ducts. Inhibition of
for heifer management during the lactation stage. mammary growth in their study appeared to occur at
a later stage of development ductular branching than in the study by Sejrsen et al. 1982. No
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5. Conclusion
