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The effect of dietary protein level during the pre-pubertal period of growth on mammary gland development and subsequent milk production in Friesian heifers
Livestock Production Science 63 (2000) 235–243 www.elsevier.com / locate / livprodsci
The effect of dietary protein level during the pre-pubertal period of growth on mammary gland development and subsequent milk production in Friesian heifers a, b b c d e R.C. Dobos *, K.S. Nandra , K. Riley , W.J. Fulkerson , I.J. Lean , R.C. Kellaway b
a NSW Agriculture Beef Centre, Armidale, NSW 2351, Australia NSW Agriculture, Elizabeth Macarthur Agricultural Institute, Camden, NSW 2570, Australia c NSW Agriculture, Wollongbar Agricultural Institute, Wollongbar, NSW 2477, Australia d Bovine Research Australasia, Camden, NSW 2570, Australia e Department of Animal Science, University of Sydney, Camden, NSW 2570, Australia
Received 3 December 1998; received in revised form 14 June 1999; accepted 19 July 1999
Abstract Sixty-three Friesian heifers were assigned to three different diets (21 per group) of 11 MJ ME per kg DM containing low crude protein (CP, 142 g CP per kg DM) with high rumen protected protein (REP, 270 g REP per kg CP) (diet A), high-CP (183 g CP per kg DM) with low-REP (133 g REP per kg CP) (diet B) and high-CP (182 g CP per kg DM) with high-REP (267 g REP per kg CP) (diet C) to obtain liveweight gains (LWG) of greater than 900 g per day between five and ten months of age in order to study the influence of dietary CP and REP concentration on mammary gland development and subsequent milk production. Six heifers per group were slaughtered at 16 months of age for evaluation of mammary glands. Pre-pubertal LWG was influenced by dietary CP concentration, such that heifers consuming diets B and C gained more than those consuming diet A (918 vs. 952 vs. 990 g per d). Dietary REP concentration did not influence pre-pubertal LWG. At slaughter, heifers consuming pre-pubertal diets with high-CP concentrations had less mammary fat tissue area and a lower ratio of fat to secretory tissue compared with those on the low-CP diet (74.9 vs. 42.7 vs. 24.1 m 2 ; 1.6 vs. 0.69 vs. 0.61). Heifers that consumed diet B during the pre-pubertal period had heavier dry udder weights, and tended to have more mammary fat and more secretory tissue area in the dry udder at slaughter than those heifers that consumed diet C (820 vs. 519 g; 636 vs. 420 g; 64.2 vs. 39.9 m 2 ). Age and LW at calving were not influenced by either dietary CP or REP concentration. Daily first lactation milk, protein and fat yields were not influenced by pre-pubertal dietary CP concentration. The REP concentration in the pre-pubertal diets did not influence daily milk and fat yields but heifers that consumed diet C produced 0.08 kg more daily protein than did heifers that had consumed diet B. 2000 Elsevier Science B.V. All rights reserved. Keywords: Heifers; Mammary gland development; Dietary protein; Rumen escape protein; Milk production
*Corresponding author. Tel.: 1 61-2-6770-1824; fax: 1 61-2-6770-1830. E-mail address: [email protected] (R.C. Dobos) 0301-6226 / 00 / $ – see front matter 2000 Elsevier Science B.V. All rights reserved. PII: S0301-6226( 99 )00137-2
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1. Introduction Dairy heifers grown to achieve liveweight gains (LWG) greater than 800 g per d before puberty have significantly reduced milk yields in some studies (Amir and Kali, 1974; Gardner et al., 1977; Little and Harrison, 1981; Sejrsen et al., 1982; Valentine et al., 1987; Waldo et al., 1989, but not in others (Capuco et al., 1988; van Amburgh and Galton, 1994; Capuco et al., 1995; Pirlo et al., 1997). This lack of consistency has been attributed to the different feeding standards used (Sejrsen, 1994), and also to diet composition (Kertz et al., 1987). Kertz et al. (1987) suggested that the lower milk yield because of high pre-pubertal LWG could be prevented by increasing the dietary crude protein (CP) concentration within this period. However, investigations conducted by van Amburgh and Gal¨ ton (1994) and Mantysaari et al. (1995) indicated no effect of dietary CP concentration on milk production and mammary gland development, respectively. Pirlo et al. (1997) investigated the effects of various levels of dietary energy and CP fed to Italian Friesian heifers between 100 and 300 kg liveweight on milk production during first lactation. Heifers consuming the diets with 110% recommended CP (NRC, 1989) at either 110% or 90% recommended (NRC, 1989) energy concentration had significantly higher protein concentrations in their milk. Although there was no influence of either dietary energy or CP on milk and fat yield, heifers that consumed the high-energy (110% NRC, 1989), low-CP (90% NRC, 1989) diet, produced 1.6 kg per d less milk than heifers that consumed the high-energy, high-CP (110% NRC, 1989) diet. Milk and fat yields were not influenced by dietary CP concentrations within the low-energy (90% NRC, 1989) diets. Pirlo et al. (1997) concluded that Italian Friesian heifers can tolerate LWG in excess of 800 g per d between dietary energy and CP concentrations of 90–110% recommendations (NRC, 1989). Mammary gland growth is reduced during the pre-pubertal period when high-energy diets are consumed to achieve early breeding ages (Sejrsen et al., 1982). Capuco et al. (1995) found that pre-pubertal heifers grown in excess of 900 g per d on a corn based diet (15% CP) had reduced mammary DNA and increased weight of gland and mammary fat
compared to heifers grown on an alfalfa based diet (22% CP). Milk production was not affected by either diet, LWG or LWG within diet. However, heifers on the high-CP diet produced 1.0 kg per d less fat-corrected milk, independent of pre-pubertal LWG. There is continuing pressure for dairy managers to reduce costs of production. Reducing age at first breeding is an option but there is a need to determine if diet composition can alleviate the negative effects of high LWG during the pre-pubertal period. Sejrsen and Foldager (1992) suggested that type of diet may not be important at lower LWG. They found no effect on mammary parenchyma of diets based on straw in heifers at low feeding levels. The objective of this experiment was to determine the effect of dietary protein concentration and amount of protein protected from rumen degradation (REP) within iso-energetic diets on mammary gland development and subsequent production of dairy heifers grown at LWG in excess of 900 g per d before puberty.
2. Materials and methods
2.1. Study location This experiment was conducted at NSW Agriculture’s Elizabeth Macarthur Agricultural Institute (EMAI), Camden (during the period from birth to three months gestation) and at the Dairy Research Foundation, University of Sydney, Camden (from three months of pregnancy to the completion of the first lactation). The experiment was approved by NSW Agriculture’s Animal Care and Ethics Committee at EMAI (94 / 12).
2.2. Pre-pubertal feeding period Sixty-three Friesian heifers were blocked by age and liveweight (LW) and randomly assigned within blocks to one of three treatment diets from five to ten months of age. Because heifers entered the experiment at two distinct periods, two subgroups per treatment diet (N 5 10 and N 5 11) were formed to avoid the interactions of social influences on diet
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intake. Heifers were kept and fed in feedlot type pens, with two pens per treatment. The ingredient and chemical composition of the pelleted diets fed to heifers within the pre-pubertal period is given in Table 1.
To ensure adequate fibre intake, sorghum (Sorghum sudanense) hay (8.060.1 MJ ME per kg DM; 8066.2 g CP per kg DM) was added to the pellets at a maximum of 30% by wet weight at each feeding. Total mixed diets were formulated to be iso-energetic but differed in level of CP and REP (Table 2). Each mixed diet was offered ad libitum at 1400 h and the consumption was calculated on a group basis at the end of each week. Heifers were weighed weekly from entry until the end of the pre-pubertal feeding period. Total intake of each mixed diet during the prepubertal feeding period was similar (P . 0.05) for all groups (12.7 vs. 12.4 vs. 12.3 t DM), with no evident ill-effects from consuming the treatment diets. Four heifers consuming diet C did not calve, as one was an inter-sex freemartin, one had an uterine torsion and two were not in-calf for unknown reasons.
Table 1 Ingredient and chemical composition of the three pelleted prepubertal diets Ingredients (kg per 100 kg)
Diet a A
Sorghum Wheat Millrun Meat meal Cottonseed meal Tallow Limestone Salt Enfield dairy premix Dicalcium phosphate Sodium bicarbonate Urea
36.39 0.00 50.06 0.00 8.00 1.55 2.20 1.00 0.75 0.00 0.00 0.00
Chemical composition ( g per kg DM) ME (MJ per kg DM) 11.00 Crude protein 139.80 Fat 507.00 Fibre 60.20 Calcium 9.10 Phosphorous 4.60
B 12.05 20.00 60.00 0.00 0.00 1.75 0.00 0.00 0.75 2.20 0.50 2.25
10.86 182.00 511.00 59.80 6.00 8.10
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C 26.46 0.00 55.99 4.85 11.75 0.00 0.00 0.00 0.20 0.25 0.50 0.00
2.3. Pre-pubertal diet analyses Weekly samples of each mixed diet were composited at the end of the pre-pubertal feeding period for analysis of ME, CP and in sacco degradability characteristics. ME was determined according to SCA (1990), while CP was calculated by multiplying the total nitrogen content by 6.25. Total nitrogen content was determined by a Kjedahl procedure (AOAC, 1980) using a Kjeltec Auto 1030 (Tecator AB, Sweden). In sacco degradability of protein was determined using three Hereford heifers (mean liveweight 444
10.99 179.90 40.60 68.30 6.60 8.10
a Diet A 5 high-energy, low-CP, high-REP; diet B 5 highenergy, high-CP, low-REP; Diet C high-energy, high-CP, highREP. REP 5 Undegradable protein; DM 5 dry matter; ME 5 metabolisable energy (estimated from SCA (1990)).
Table 2 Metabolisable energy, crude protein, undegradable protein and in sacco degradability characteristics for the three diets fed to pre-pubertal heifers Parameter
Metabolisable energy (ME MJ per kg DM) Crude protein (g CP per kg DM) REP (g REP per kg CP) a (g per kg CP) b (g per kg CP) c (g per h)
Diet a A
B
C
10.99 142.00 270.00 254.00 563.00 0.11
11.12 183.20 133.00 517.00 404.00 0.13
10.89 182.30 267.00 328.00 521.00 0.07
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. REP 5 Undegradable protein; a 5 the immediately soluble component; b 5 the slowly but potentially degradable component; c 5 rate of disappearance of b at an outflow rate of 0.02 per h.
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kg) fitted with rumen cannulae. Data on N residues were fitted to the equation of Ørskov and MacDonald (1979) to determine the in sacco degradability characteristics of each mixed diet. The amount of REP in each diet was calculated according to AFRC (1993). Table 2 shows the metabolisable energy (ME MJ per kg DM), CP (g per kg DM), REP (g per kg CP) and in sacco degradability characteristics of the three mixed diets.
2.4. Post-puberty to three months before calving At the end of the pre-pubertal feeding period, heifers were grouped as one herd. LW was recorded at weekly intervals. During the autumn and winter the heifers grazed pastures consisting of annual ryegrass (Lolium multiflorum, 10.760.06 MJ ME, 269616.1 g CP per kg DM) and dryland lucerne (Medicago sativa, 9.760.4 MJ ME, 202621.5 g CP per kg DM), while in spring and summer they grazed irrigated kikuyu (Pennisetum clandestinum, 9.460.3 MJ ME, 136613.7 g CP per kg DM) and dryland lucerne. In times of pasture shortage, the herd was offered pellets (diet B), sorghum silage (6.260.6 MJ ME, 109612.4 g CP per kg DM) and lucerne hay (9.360.4 MJ ME, 175611.9 g CP per kg DM). The target LWG in the post-pubertal period was set to be between 550 and 700 g per d. At 15 months of age, heifers were injected with 2 ml Estrumate (Mallinckrodt Vet Ltd., distributed by Jurox Pty. Ltd.) at day one of mating to synchronise oestrus. A heat mount detector (Unistar Pty Ltd) was applied to each heifer and heifers in oestrus were presented to an Angus bull. Pregnancy was diagnosed by rectal palpation 90 days after the last individual mating and if diagnosed as pregnant were removed from the mating group.
2.5. Three months before calving to end of first lactation Heifers were weighed at monthly intervals. During lactation, milk yield and a composite daily sample for analysis of milk fat and protein were obtained monthly. Before calving heifers grazed kikuyu pastures (9.060.3 MJ ME; 160612.1 g CP per kg DM) and they were supplemented with lucerne hay
(9.360.4 MJ ME; 175611.9 g CP per kg DM) to ensure a LWG of 700 g per d. During lactation, heifers grazed irrigated kikuyu (9.560.6 MJ ME; 128610.3 g CP per kg DM) in summer and annual rye-grass in winter (10.960.6 MJ ME; 269613.2 g CP per kg DM) and were supplemented with maize silage when the pasture did not meet requirements. Each heifer was offered pellets (5.0 kg per d as fed, 1260.2 MJ ME and 24168.2 g CP per kg DM) at both morning and afternoon milking. Using a tape measure, udders were measured for circumference, length and breadth on the same day 3 h after morning milking (mean6SE days in milk, 196.265.37).
2.6. Slaughter protocol Once heifers reached 16 months of age and were between 10 and 18 days after oestrus, six heifers per group were stunned and immediately exsanguinated at the abattoir. Udders were carefully removed within 5 min of death and placed in a bucket of ice for transportation to the laboratory. The udder was weighed before and after the removal of skin, teats, parts of median suspensory ligaments, supramammary lymph nodes and excess adipose tissue. Udders were then dissected into left and right halves down the median suspensory ligament and weighed. Both halves were frozen at 2 208C for later preparation of gland slices and biochemical analyses. At slaughter carcasses were weighed (hot) and 24 h later assessed for fat depth (12 / 13th rib) and weighed (cold).
2.7. Mammary gland analyses The right half of the udder was cut into slices of about 5 mm thickness using a meat slicer. Slices were made in the parasaggital plane, progressing from the medial aspect to the most lateral portion of the gland. Traces on acetate sheets were then made of each slice to determine the fat to secretory tissue ratio. Each trace was photocopied and tissue types separated by cutting. Photocopied traces were cut into fat and secretory tissue equivalents, weighed and the ratio of fat to secretory tissue determined. The left udder half was cut into small cubes (60–80 mm) and minced in a meat mincer. Aliquots were taken
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and freeze dried for the determination of moisture. Freeze dried aliquots also were used to determine lipid content (Folch et al., 1957) and amount of dry fat free tissue (DFFT). Duplicate samples of DFFT were used to determine the amount of DNA (Martin et al., 1972), hydroxyproline (Bergman and Loxley, 1963) and nitrogen in the udder. The hydroxyproline value was converted to collagen using a factor of 7.14, assuming 300 000 collagen g / mole.
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effects were each heifer within each month of lactation. The variance component estimation method was restricted maximum likelihood (REML) and the type of covariance matrix was compound symmetry.
3. Results
2.8. Statistical analyses
3.1. Pre-pubertal heifer growth, age and LW at slaughter
Liveweight gain during the pre-pubertal feeding period was determined from linear regression analysis of LW against age. Differences in mammary development between diets and dietary concentrations of CP and REP were compared by analysis of co-variance with initial LW and age and LW and age at slaughter as covariates. Covariates not contributing to the source of variation were removed. Differences in udder dimensions measured during lactation were compared by analysis of covariance with days in milk as a covariate. Monthly milk, protein and fat yields were analysed using a mixed model split-plot in time repeated measures analysis with calving date and LW at calving as covariates. The fixed effects were diet by month of lactation, while the random
Influence of dietary CP and REP concentration on pre-pubertal growth and age and LW at slaughter is summarised in Table 3. Pre-pubertal LWG was influenced (P 5 0.05) by dietary CP concentration, such that heifers consuming the high-CP diets grew at a faster rate (952 and 990 g per d) compared with those heifers that consumed the low-CP diet (918 g per d). However, pre-pubertal LWG was not influenced (P 5 0.23) by dietary REP concentration. At slaughter, LW averaged 364.6 kg across diets, with the least square mean LW of the heifers that had consumed diet A being 30 kg heavier compared to those heifers that consumed diets B and C (P 5 0.09). However, LW at slaughter was not influenced 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 Diet a A
Contrast B
C
SED
Diet
Low-CP vs. high-CP
Low-REP vs. high-REP
——————— P —————— All heifers N Initial LW (kg) Initial age (d) LWG (g per d)
21 114 160.3 918
21 115 160.5 952
21 122 156.1 990
5.7 10.1 50.6
0.31 0.89 0.09
0.38 0.82 0.05
0.82 0.66 0.23
Slaughter heifers N Initial LW (kg) Initial age (d) LW at slaughter (kg) Age at slaughter (d) LWG (g per d)
6 115 137.3 386 492.0 924
6 126 166.5 352 502.5 972
6 128 159.8 356 471.2 944
13.2 14.8 20.4 18.0 67.4
0.59 0.15 0.22 0.24 0.80
0.32 0.06 0.09 0.75 0.62
0.88 0.66 0.87 0.10 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.
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slaughter was not influenced by either dietary CP or REP concentration.
3.2. Pre-pubertal mammary gland development 3.2.1. Influence of dietary CP concentration (diet A vs. diets B and C) The influence of dietary CP concentration on prepubertal mammary gland development is shown in Table 4. At slaughter, heifers that consumed diet A during the pre-pubertal period had more (P , 0.001) area of fat tissue and a higher (P 5 0.002) ratio of fat to secretory tissue in their mammary glands compared to those that consumed diets B and C. Other mammary gland components were not different (P . 0.05, see Table 4). 3.2.2. Influence of dietary REP concentration (diet B vs. C) The influence of dietary REP concentration at the same dietary CP concentration on pre-pubertal mam-
mary gland development is shown in Table 4. At slaughter, heifers that consumed diet B during the pre-pubertal period had heavier dry udder weights (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 udder than those heifers that consumed diet C (820 vs. 519 g; 636 vs. 420 g; 64.2 vs. 39.9 m 2 ). Other mammary gland components were not different (P . 0.05, see Table 4).
3.3. Influence of dietary CP and REP concentration on first lactation production The influence of pre-pubertal dietary CP and REP concentration on age and LW at calving, first lactation production and udder dimensions is shown in Table 5. The average pre-calving age and LW across diets was 26.1 months and 524.6 kg, respectively. Heifers that consumed diet A were, on average, the lightest at calving (517.8 kg) compared to those 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 Diet a
Contrast
A
B
C
SED
6 2044 741
6 1903 820
6 1553 519
Diet
Low-CP vs. high-CP
Low-REP vs. high-REP
——————— P ——————— N Trimmed wet udder weight (g) Trimmed dry udder weight (g)
252.4 116.4
0.16 0.04
0.15 0.43
0.17 0.01
Composition of dry udder ( g) DFFT Protein Fat Ash
269 81 692 7.5
296 113 636 9.2
288 76 420 10.7
97.8 33.9 123.6 2.5
0.96 0.53 0.09 0.43
0.71 0.61 0.16 0.25
0.94 0.31 0.08 0.51
Composition of DFFT ( g) Protein DNA Protein / DNA
211 3.7 57.0
250 5.5 52.9
245 6.8 45.0
82.1 2.1 9.7
0.86 0.34 0.47
0.60 0.18 0.33
0.93 0.60 0.43
Collagen (% in DFFT) Fat tissue area (m 2 ) Secretory tissue area (m 2 ) Ratio fat / secretory tissue
34.3 74.9 53.4 1.6
1.7 11.8 12.4 0.29
0.21 0.002 0.18 0.007
0.45 , 0.001 0.90 0.002
0.16 0.14 0.07 0.77
34.5 42.7 64.2 0.69
32.0 24.1 39.9 0.61
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.
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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 Diet a
Contrast
A
B
C
15 518 26.3 18.8 0.61 0.70 129.8 64.6 73.5
13 531 26.0 17.8 0.57 0.73 125.3 65.0 72.0
11 525 26.1 19.4 0.65 0.78 127.3 66.5 73.7
SED
Diet
Low-CP vs. high-CP
Low-REP vs. high-REP
—————— P —————— N Calving LW (kg) Calving age (months) Milk (l per d) Protein (kg per d) Fat (kg per d) Udder circumference (cm) Udder length (cm) Udder breadth (cm)
12.8 0.50 0.63 0.05 0.07 5.3 2.9 3.0
0.29 0.56 0.55 0.11 0.86 0.66 0.81 0.80
0.36 0.61 0.66 0.40 0.58 0.40 0.68 0.73
0.59 0.77 0.37 0.08 0.99 0.65 0.67 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 not influenced (P . 0.05) by either pre-pubertal dietary CP or REP concentration. The average daily first lactation milk, protein and fat yields across diets was 18.6 l, 0.61 and 0.73 kg, respectively. Daily first lactation milk, protein and fat yields were not influenced by pre-pubertal dietary CP concentration. Pre-pubertal dietary REP concentration did not influence daily first lactation milk and fat yields but daily protein yield tended to be greater (P 5 0.08) in those heifers that had consumed diet C compared to those that consumed diet B during pre-puberty. Udder dimensions measured during first lactation were not influenced (P . 0.05) by either pre-pubertal dietary CP or REP concentration.
4. Discussion Pre-pubertal diets of high-CP consumed by heifers to achieve LWG in excess of 900 g per d did influence mammary gland development, such that the area of fat tissue and the ratio of fat to secretory tissue in these glands was decreased but did not affect first lactation daily milk, protein and fat yields. Further, pre-pubertal diets of high-energy, high-CP, high-REP decreased the weight of the dry gland and tended to decrease the amount of fat and the area of secretory tissue compared to glands from heifers that
consumed pre-pubertal diets of high-energy, high-CP, low-REP. Pre-pubertal dietary REP concentration did not influence first lactation production, although there was a tendency for more daily protein to be produced when pre-pubertal dietary REP concentration was increased. Our lactation results for pre-pubertal dietary CP concentration are in contrast to those of Pirlo et al. (1997), who found an increase in daily first lactation milk production of 1.6 kg when heifers were fed a high-CP diet (110% NRC, 1989) compared to a low-CP diet (90% NRC, 1989) at similar high prepubertal LWG. The comparison of pre-pubertal dietary REP concentration in our study indicated that 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 concentration, their increase in milk and protein may have been due to the higher REP concentration in the high-CP diet because of the higher intake of soybean meal. Capuco et al. (1995) found that pre-pubertal heifers grown in excess of 900 g per d and fed a high-CP diet (22% CP) had lighter mammary glands, less mammary fat and more total mammary DNA compared to those fed a low-CP diet (15% CP). Our study confirms this observation that high-CP diets consumed during pre-puberty tended to reduce the weight of mammary glands, as well as the area of fat
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tissue and ratio of fat to secretory tissue. Further reduction in mammary gland weight was observed in our study when pre-pubertal REP concentration at a high-CP concentration was increased. The comparison of dietary REP concentrations at the same dietary CP concentration, indicates that pre-pubertal heifers gaining in excess of 900 g per d had less developed mammary glands when REP was increased. However, these heifers were able to produce 1.6 l per d more milk than their herd-mates consuming a low-REP pre-pubertal diet. This could have been due to compensatory mammary growth after mating and differences in body composition at the start of calving. Capuco et al. (1995) have discussed the concept of compensatory mammary growth in terms of inhibition of either primary duct elongation or branching of ducts. Inhibition of 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 histological data were collected in our experiment to confirm this hypothesis. Capuco et al. (1995) also discuss the possible effects of body composition on the lack of differences between diet, LWG and diet within LWG in their experiment. In our study, heifers at slaughter did not differ in fat depth at the 12 / 13th rib between dietary REP concentrations but heifers consuming the low-CP pre-pubertal diet tended to have a greater fat depth than those consuming the high-CP prepubertal diet (Dobos et al., 1997).
5. Conclusion Pre-pubertal diets containing low-CP compared to high-CP increased the area of mammary gland fat tissue and the ratio of fat to secretory tissue area at 16 months of age. However, there was no effect on subsequent first lactation production. Pre-pubertal diets containing high-REP compared to low-REP at similar concentrations of CP reduced the weight of the dry gland and tended to reduce the amount of mammary fat and the area of secretory tissue. HighREP pre-pubertal diets tended to increase daily first lactation protein yield by 0.08 kg.
Acknowledgements The authors wish to acknowledge the contribution of funding from the Commonwealth Department of Employment, Education, Training and Youth Affairs, NSW Dairy Corporation, NSW Dairy Farmers Association, Elanco Animal Health (Australia), Dairy Farmers Ltd., Australian Dairy Research and Development Corporation, Semex Australia Pty. Ltd., Herd Improvers Australia Pty. Ltd., MillMaster Feeds Ltd., Wrightsons Seeds Pty. Ltd., University of Sydney and NSW Agriculture. Thanks to Mr B. Rhees, Ms Y. Leischke-Mercer and Ms S. Plowman for managing the heifers during the pre-calving stage of the experiment and to Dr J. Gooden and his dedicated staff at the University of Sydney MayFarm for heifer management during the lactation stage.
References AFRC, 1993. Energy and protein requirements of ruminants, CAB International, Wallingford, UK, An advisory manual prepared by the AFRC Technical Committee on Responses to Nutrients. Amir, S., Kali, J., 1974. Influence of plane of nutrition of the dairy heifer on growth and performance after calving. In: Dairy Science Handbook, Vol. 7. AgriServices Foundation, Davis, California, pp. 183–190. Association of Official Agricultural Chemists (AOAC), 1980. In: Official methods of analysis of the AOAC, 13th ed. AOAC, Washington, DC, pp. 126–127. Bergman, I., Loxley, R., 1963. Two improved and simplified methods for the spectrophotometric determination of hydroxyproline. Analytical Chemistry 35, 1961–1965. Capuco, A.V., Smith, J.J., Waldo, D.R., Rexroad, C.E., 1995. Influence of prepubertal dietary regimen on mammary growth of Holstein heifers. J. Dairy Sci. 78, 2709–2725. Capuco, A.V., Smith, J.J., Waldo, D.R., Elsasser, T.H., 1988. Effect of diet and pre-pubertal growth rate of Holstein heifers on mammary gland growth and milk production. J. Dairy Sci. 71 (suppl 1), 186. Dobos, R.C., Riley, K., Nandra, K.S., Kellaway, R.C., Fulkerson, W.J., Lean, I.J., 1997. The effect of rumen escape protein on carcass characteristics of rapidly growing pre-pubertal dairy heifers. In: Corbett, J.L., Choct, M., Nolan, J.V., Rowe, J.B. (Eds.), Recent Advances in Nutrition in Australia ’97. Department of Animal Science, University of New England, p. 255. Folch, J.M., Lees, M., Sloane-Stanley, G.H., 1957. A simple method for the isolation and purification of total lipids from animal tissues. J. Biol. Chem. 226, 497. Gardner, R.W., Schuh, J.D., Vargus, L.G., 1977. Accelerated
R.C. Dobos et al. / Livestock Production Science 63 (2000) 235 – 243 growth and early breeding of Holstein heifers. J. Dairy Sci. 60, 1941–1948. Kertz, A.F., Prewitt, L.R., Ballam, J.M., 1987. Increased weight gain and effects on growth parameters of Holstein heifer calves from 3 to 12 months of age. J. Dairy Sci. 70, 1612–1622. Little, W., Harrison, R.D., 1981. Effects of different rates of liveweight gain during rearing on the performance of Friesian heifers in their first lactation. Animal Production 32, 362, Abstract. ¨ Mantysaari, P., Ingvartsen, K.L., Toivonen, V., Sejrsen, K., 1995. The effects of feeding level and nitrogen source of the diet on mammary development and plasma hormone concentrations of pre-pubertal heifers. Acta Agric. Scand. Sect. A, Animal Sci. 45, 236–244. Martin, R.F., Donohue, D.C., Finch, L.R., 1972. New analytical procedure for the estimation of DNA with p-Nitrophenylhydrazine. Anal. Biochem. 47, 562–574. National Research Council (NRC), 1989. Nutrient Requirements of Dairy Cattle, 6th revised ed. National Academy of Science, Washington, DC. Ørskov, E.R., MacDonald, I., 1979. The estimation of protein degradability in the rumen from incubation measurements weighted according to rate of passage. J. Agric. Sci. Camb. 92, 499–503. Pirlo, G., Capelletti, M., Marchetto, G., 1997. Effects of energy and protein allowances in the diets of prepubertal heifers on growth and milk production. J. Dairy Sci. 80, 730–739.
243
Sejrsen, K., 1994. Relationships between nutrition, puberty and mammary development in cattle. Proceedings of the Nutrition Society 53, 103–111. Sejrsen, K., Foldager, J., 1992. Mammary growth and milk production capacity of replacement heifers in relation to diet energy concentration and plasma hormone levels. Acta Agric. Scand. Sect. A, Anim. Sci. 42, 99–105. Sejrsen, K., Huber, J.T., Tucker, H.A., Akers, R.M., 1982. Influence of plane of nutrition on mammary development in pre- and post-pubertal heifers. J. Dairy Sci. 65, 783–800. Standing Committee on Agriculture (SCA), 1990. Feeding Standards for Australian Livestock. Ruminants. CSIRO Publications, Melbourne, 266 pp. Valentine, S.C., Dobos, R.C., Lewis, P.A., Bartsch, B.D., Wickes, R.B., 1987. Effect of live weight gain before and during pregnancy on mammary gland development and subsequent milk production of Australian Holstein-Friesian heifers. Aust. J. Exp. Agric. 27, 195–204. van Amburgh, M.E., Galton, D.M., 1994. Accelerated growth of holstein heifers – effects on lactation. In: Cornell Nutrition Conference for Feed Manufacturers, Rochester, NY. Waldo, D.R., Capuco, A.V., Rexroad, Jr. C.E., 1989. Replacement heifer growth rates affects milk producing ability. Feedstuffs 27, 15–17.
The effect of dietary protein level during the pre-pubertal period of growth on mammary gland development and subsequent milk production in Friesian heifers a, b b c d e R.C. Dobos *, K.S. Nandra , K. Riley , W.J. Fulkerson , I.J. Lean , R.C. Kellaway b
a NSW Agriculture Beef Centre, Armidale, NSW 2351, Australia NSW Agriculture, Elizabeth Macarthur Agricultural Institute, Camden, NSW 2570, Australia c NSW Agriculture, Wollongbar Agricultural Institute, Wollongbar, NSW 2477, Australia d Bovine Research Australasia, Camden, NSW 2570, Australia e Department of Animal Science, University of Sydney, Camden, NSW 2570, Australia
Received 3 December 1998; received in revised form 14 June 1999; accepted 19 July 1999
Abstract Sixty-three Friesian heifers were assigned to three different diets (21 per group) of 11 MJ ME per kg DM containing low crude protein (CP, 142 g CP per kg DM) with high rumen protected protein (REP, 270 g REP per kg CP) (diet A), high-CP (183 g CP per kg DM) with low-REP (133 g REP per kg CP) (diet B) and high-CP (182 g CP per kg DM) with high-REP (267 g REP per kg CP) (diet C) to obtain liveweight gains (LWG) of greater than 900 g per day between five and ten months of age in order to study the influence of dietary CP and REP concentration on mammary gland development and subsequent milk production. Six heifers per group were slaughtered at 16 months of age for evaluation of mammary glands. Pre-pubertal LWG was influenced by dietary CP concentration, such that heifers consuming diets B and C gained more than those consuming diet A (918 vs. 952 vs. 990 g per d). Dietary REP concentration did not influence pre-pubertal LWG. At slaughter, heifers consuming pre-pubertal diets with high-CP concentrations had less mammary fat tissue area and a lower ratio of fat to secretory tissue compared with those on the low-CP diet (74.9 vs. 42.7 vs. 24.1 m 2 ; 1.6 vs. 0.69 vs. 0.61). Heifers that consumed diet B during the pre-pubertal period had heavier dry udder weights, and tended to have more mammary fat and more secretory tissue area in the dry udder at slaughter than those heifers that consumed diet C (820 vs. 519 g; 636 vs. 420 g; 64.2 vs. 39.9 m 2 ). Age and LW at calving were not influenced by either dietary CP or REP concentration. Daily first lactation milk, protein and fat yields were not influenced by pre-pubertal dietary CP concentration. The REP concentration in the pre-pubertal diets did not influence daily milk and fat yields but heifers that consumed diet C produced 0.08 kg more daily protein than did heifers that had consumed diet B. 2000 Elsevier Science B.V. All rights reserved. Keywords: Heifers; Mammary gland development; Dietary protein; Rumen escape protein; Milk production
*Corresponding author. Tel.: 1 61-2-6770-1824; fax: 1 61-2-6770-1830. E-mail address: [email protected] (R.C. Dobos) 0301-6226 / 00 / $ – see front matter 2000 Elsevier Science B.V. All rights reserved. PII: S0301-6226( 99 )00137-2
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1. Introduction Dairy heifers grown to achieve liveweight gains (LWG) greater than 800 g per d before puberty have significantly reduced milk yields in some studies (Amir and Kali, 1974; Gardner et al., 1977; Little and Harrison, 1981; Sejrsen et al., 1982; Valentine et al., 1987; Waldo et al., 1989, but not in others (Capuco et al., 1988; van Amburgh and Galton, 1994; Capuco et al., 1995; Pirlo et al., 1997). This lack of consistency has been attributed to the different feeding standards used (Sejrsen, 1994), and also to diet composition (Kertz et al., 1987). Kertz et al. (1987) suggested that the lower milk yield because of high pre-pubertal LWG could be prevented by increasing the dietary crude protein (CP) concentration within this period. However, investigations conducted by van Amburgh and Gal¨ ton (1994) and Mantysaari et al. (1995) indicated no effect of dietary CP concentration on milk production and mammary gland development, respectively. Pirlo et al. (1997) investigated the effects of various levels of dietary energy and CP fed to Italian Friesian heifers between 100 and 300 kg liveweight on milk production during first lactation. Heifers consuming the diets with 110% recommended CP (NRC, 1989) at either 110% or 90% recommended (NRC, 1989) energy concentration had significantly higher protein concentrations in their milk. Although there was no influence of either dietary energy or CP on milk and fat yield, heifers that consumed the high-energy (110% NRC, 1989), low-CP (90% NRC, 1989) diet, produced 1.6 kg per d less milk than heifers that consumed the high-energy, high-CP (110% NRC, 1989) diet. Milk and fat yields were not influenced by dietary CP concentrations within the low-energy (90% NRC, 1989) diets. Pirlo et al. (1997) concluded that Italian Friesian heifers can tolerate LWG in excess of 800 g per d between dietary energy and CP concentrations of 90–110% recommendations (NRC, 1989). Mammary gland growth is reduced during the pre-pubertal period when high-energy diets are consumed to achieve early breeding ages (Sejrsen et al., 1982). Capuco et al. (1995) found that pre-pubertal heifers grown in excess of 900 g per d on a corn based diet (15% CP) had reduced mammary DNA and increased weight of gland and mammary fat
compared to heifers grown on an alfalfa based diet (22% CP). Milk production was not affected by either diet, LWG or LWG within diet. However, heifers on the high-CP diet produced 1.0 kg per d less fat-corrected milk, independent of pre-pubertal LWG. There is continuing pressure for dairy managers to reduce costs of production. Reducing age at first breeding is an option but there is a need to determine if diet composition can alleviate the negative effects of high LWG during the pre-pubertal period. Sejrsen and Foldager (1992) suggested that type of diet may not be important at lower LWG. They found no effect on mammary parenchyma of diets based on straw in heifers at low feeding levels. The objective of this experiment was to determine the effect of dietary protein concentration and amount of protein protected from rumen degradation (REP) within iso-energetic diets on mammary gland development and subsequent production of dairy heifers grown at LWG in excess of 900 g per d before puberty.
2. Materials and methods
2.1. Study location This experiment was conducted at NSW Agriculture’s Elizabeth Macarthur Agricultural Institute (EMAI), Camden (during the period from birth to three months gestation) and at the Dairy Research Foundation, University of Sydney, Camden (from three months of pregnancy to the completion of the first lactation). The experiment was approved by NSW Agriculture’s Animal Care and Ethics Committee at EMAI (94 / 12).
2.2. Pre-pubertal feeding period Sixty-three Friesian heifers were blocked by age and liveweight (LW) and randomly assigned within blocks to one of three treatment diets from five to ten months of age. Because heifers entered the experiment at two distinct periods, two subgroups per treatment diet (N 5 10 and N 5 11) were formed to avoid the interactions of social influences on diet
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intake. Heifers were kept and fed in feedlot type pens, with two pens per treatment. The ingredient and chemical composition of the pelleted diets fed to heifers within the pre-pubertal period is given in Table 1.
To ensure adequate fibre intake, sorghum (Sorghum sudanense) hay (8.060.1 MJ ME per kg DM; 8066.2 g CP per kg DM) was added to the pellets at a maximum of 30% by wet weight at each feeding. Total mixed diets were formulated to be iso-energetic but differed in level of CP and REP (Table 2). Each mixed diet was offered ad libitum at 1400 h and the consumption was calculated on a group basis at the end of each week. Heifers were weighed weekly from entry until the end of the pre-pubertal feeding period. Total intake of each mixed diet during the prepubertal feeding period was similar (P . 0.05) for all groups (12.7 vs. 12.4 vs. 12.3 t DM), with no evident ill-effects from consuming the treatment diets. Four heifers consuming diet C did not calve, as one was an inter-sex freemartin, one had an uterine torsion and two were not in-calf for unknown reasons.
Table 1 Ingredient and chemical composition of the three pelleted prepubertal diets Ingredients (kg per 100 kg)
Diet a A
Sorghum Wheat Millrun Meat meal Cottonseed meal Tallow Limestone Salt Enfield dairy premix Dicalcium phosphate Sodium bicarbonate Urea
36.39 0.00 50.06 0.00 8.00 1.55 2.20 1.00 0.75 0.00 0.00 0.00
Chemical composition ( g per kg DM) ME (MJ per kg DM) 11.00 Crude protein 139.80 Fat 507.00 Fibre 60.20 Calcium 9.10 Phosphorous 4.60
B 12.05 20.00 60.00 0.00 0.00 1.75 0.00 0.00 0.75 2.20 0.50 2.25
10.86 182.00 511.00 59.80 6.00 8.10
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C 26.46 0.00 55.99 4.85 11.75 0.00 0.00 0.00 0.20 0.25 0.50 0.00
2.3. Pre-pubertal diet analyses Weekly samples of each mixed diet were composited at the end of the pre-pubertal feeding period for analysis of ME, CP and in sacco degradability characteristics. ME was determined according to SCA (1990), while CP was calculated by multiplying the total nitrogen content by 6.25. Total nitrogen content was determined by a Kjedahl procedure (AOAC, 1980) using a Kjeltec Auto 1030 (Tecator AB, Sweden). In sacco degradability of protein was determined using three Hereford heifers (mean liveweight 444
10.99 179.90 40.60 68.30 6.60 8.10
a Diet A 5 high-energy, low-CP, high-REP; diet B 5 highenergy, high-CP, low-REP; Diet C high-energy, high-CP, highREP. REP 5 Undegradable protein; DM 5 dry matter; ME 5 metabolisable energy (estimated from SCA (1990)).
Table 2 Metabolisable energy, crude protein, undegradable protein and in sacco degradability characteristics for the three diets fed to pre-pubertal heifers Parameter
Metabolisable energy (ME MJ per kg DM) Crude protein (g CP per kg DM) REP (g REP per kg CP) a (g per kg CP) b (g per kg CP) c (g per h)
Diet a A
B
C
10.99 142.00 270.00 254.00 563.00 0.11
11.12 183.20 133.00 517.00 404.00 0.13
10.89 182.30 267.00 328.00 521.00 0.07
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. REP 5 Undegradable protein; a 5 the immediately soluble component; b 5 the slowly but potentially degradable component; c 5 rate of disappearance of b at an outflow rate of 0.02 per h.
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kg) fitted with rumen cannulae. Data on N residues were fitted to the equation of Ørskov and MacDonald (1979) to determine the in sacco degradability characteristics of each mixed diet. The amount of REP in each diet was calculated according to AFRC (1993). Table 2 shows the metabolisable energy (ME MJ per kg DM), CP (g per kg DM), REP (g per kg CP) and in sacco degradability characteristics of the three mixed diets.
2.4. Post-puberty to three months before calving At the end of the pre-pubertal feeding period, heifers were grouped as one herd. LW was recorded at weekly intervals. During the autumn and winter the heifers grazed pastures consisting of annual ryegrass (Lolium multiflorum, 10.760.06 MJ ME, 269616.1 g CP per kg DM) and dryland lucerne (Medicago sativa, 9.760.4 MJ ME, 202621.5 g CP per kg DM), while in spring and summer they grazed irrigated kikuyu (Pennisetum clandestinum, 9.460.3 MJ ME, 136613.7 g CP per kg DM) and dryland lucerne. In times of pasture shortage, the herd was offered pellets (diet B), sorghum silage (6.260.6 MJ ME, 109612.4 g CP per kg DM) and lucerne hay (9.360.4 MJ ME, 175611.9 g CP per kg DM). The target LWG in the post-pubertal period was set to be between 550 and 700 g per d. At 15 months of age, heifers were injected with 2 ml Estrumate (Mallinckrodt Vet Ltd., distributed by Jurox Pty. Ltd.) at day one of mating to synchronise oestrus. A heat mount detector (Unistar Pty Ltd) was applied to each heifer and heifers in oestrus were presented to an Angus bull. Pregnancy was diagnosed by rectal palpation 90 days after the last individual mating and if diagnosed as pregnant were removed from the mating group.
2.5. Three months before calving to end of first lactation Heifers were weighed at monthly intervals. During lactation, milk yield and a composite daily sample for analysis of milk fat and protein were obtained monthly. Before calving heifers grazed kikuyu pastures (9.060.3 MJ ME; 160612.1 g CP per kg DM) and they were supplemented with lucerne hay
(9.360.4 MJ ME; 175611.9 g CP per kg DM) to ensure a LWG of 700 g per d. During lactation, heifers grazed irrigated kikuyu (9.560.6 MJ ME; 128610.3 g CP per kg DM) in summer and annual rye-grass in winter (10.960.6 MJ ME; 269613.2 g CP per kg DM) and were supplemented with maize silage when the pasture did not meet requirements. Each heifer was offered pellets (5.0 kg per d as fed, 1260.2 MJ ME and 24168.2 g CP per kg DM) at both morning and afternoon milking. Using a tape measure, udders were measured for circumference, length and breadth on the same day 3 h after morning milking (mean6SE days in milk, 196.265.37).
2.6. Slaughter protocol Once heifers reached 16 months of age and were between 10 and 18 days after oestrus, six heifers per group were stunned and immediately exsanguinated at the abattoir. Udders were carefully removed within 5 min of death and placed in a bucket of ice for transportation to the laboratory. The udder was weighed before and after the removal of skin, teats, parts of median suspensory ligaments, supramammary lymph nodes and excess adipose tissue. Udders were then dissected into left and right halves down the median suspensory ligament and weighed. Both halves were frozen at 2 208C for later preparation of gland slices and biochemical analyses. At slaughter carcasses were weighed (hot) and 24 h later assessed for fat depth (12 / 13th rib) and weighed (cold).
2.7. Mammary gland analyses The right half of the udder was cut into slices of about 5 mm thickness using a meat slicer. Slices were made in the parasaggital plane, progressing from the medial aspect to the most lateral portion of the gland. Traces on acetate sheets were then made of each slice to determine the fat to secretory tissue ratio. Each trace was photocopied and tissue types separated by cutting. Photocopied traces were cut into fat and secretory tissue equivalents, weighed and the ratio of fat to secretory tissue determined. The left udder half was cut into small cubes (60–80 mm) and minced in a meat mincer. Aliquots were taken
R.C. Dobos et al. / Livestock Production Science 63 (2000) 235 – 243
and freeze dried for the determination of moisture. Freeze dried aliquots also were used to determine lipid content (Folch et al., 1957) and amount of dry fat free tissue (DFFT). Duplicate samples of DFFT were used to determine the amount of DNA (Martin et al., 1972), hydroxyproline (Bergman and Loxley, 1963) and nitrogen in the udder. The hydroxyproline value was converted to collagen using a factor of 7.14, assuming 300 000 collagen g / mole.
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effects were each heifer within each month of lactation. The variance component estimation method was restricted maximum likelihood (REML) and the type of covariance matrix was compound symmetry.
3. Results
2.8. Statistical analyses
3.1. Pre-pubertal heifer growth, age and LW at slaughter
Liveweight gain during the pre-pubertal feeding period was determined from linear regression analysis of LW against age. Differences in mammary development between diets and dietary concentrations of CP and REP were compared by analysis of co-variance with initial LW and age and LW and age at slaughter as covariates. Covariates not contributing to the source of variation were removed. Differences in udder dimensions measured during lactation were compared by analysis of covariance with days in milk as a covariate. Monthly milk, protein and fat yields were analysed using a mixed model split-plot in time repeated measures analysis with calving date and LW at calving as covariates. The fixed effects were diet by month of lactation, while the random
Influence of dietary CP and REP concentration on pre-pubertal growth and age and LW at slaughter is summarised in Table 3. Pre-pubertal LWG was influenced (P 5 0.05) by dietary CP concentration, such that heifers consuming the high-CP diets grew at a faster rate (952 and 990 g per d) compared with those heifers that consumed the low-CP diet (918 g per d). However, pre-pubertal LWG was not influenced (P 5 0.23) by dietary REP concentration. At slaughter, LW averaged 364.6 kg across diets, with the least square mean LW of the heifers that had consumed diet A being 30 kg heavier compared to those heifers that consumed diets B and C (P 5 0.09). However, LW at slaughter was not influenced 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 Diet a A
Contrast B
C
SED
Diet
Low-CP vs. high-CP
Low-REP vs. high-REP
——————— P —————— All heifers N Initial LW (kg) Initial age (d) LWG (g per d)
21 114 160.3 918
21 115 160.5 952
21 122 156.1 990
5.7 10.1 50.6
0.31 0.89 0.09
0.38 0.82 0.05
0.82 0.66 0.23
Slaughter heifers N Initial LW (kg) Initial age (d) LW at slaughter (kg) Age at slaughter (d) LWG (g per d)
6 115 137.3 386 492.0 924
6 126 166.5 352 502.5 972
6 128 159.8 356 471.2 944
13.2 14.8 20.4 18.0 67.4
0.59 0.15 0.22 0.24 0.80
0.32 0.06 0.09 0.75 0.62
0.88 0.66 0.87 0.10 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.
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slaughter was not influenced by either dietary CP or REP concentration.
3.2. Pre-pubertal mammary gland development 3.2.1. Influence of dietary CP concentration (diet A vs. diets B and C) The influence of dietary CP concentration on prepubertal mammary gland development is shown in Table 4. At slaughter, heifers that consumed diet A during the pre-pubertal period had more (P , 0.001) area of fat tissue and a higher (P 5 0.002) ratio of fat to secretory tissue in their mammary glands compared to those that consumed diets B and C. Other mammary gland components were not different (P . 0.05, see Table 4). 3.2.2. Influence of dietary REP concentration (diet B vs. C) The influence of dietary REP concentration at the same dietary CP concentration on pre-pubertal mam-
mary gland development is shown in Table 4. At slaughter, heifers that consumed diet B during the pre-pubertal period had heavier dry udder weights (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 udder than those heifers that consumed diet C (820 vs. 519 g; 636 vs. 420 g; 64.2 vs. 39.9 m 2 ). Other mammary gland components were not different (P . 0.05, see Table 4).
3.3. Influence of dietary CP and REP concentration on first lactation production The influence of pre-pubertal dietary CP and REP concentration on age and LW at calving, first lactation production and udder dimensions is shown in Table 5. The average pre-calving age and LW across diets was 26.1 months and 524.6 kg, respectively. Heifers that consumed diet A were, on average, the lightest at calving (517.8 kg) compared to those 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 Diet a
Contrast
A
B
C
SED
6 2044 741
6 1903 820
6 1553 519
Diet
Low-CP vs. high-CP
Low-REP vs. high-REP
——————— P ——————— N Trimmed wet udder weight (g) Trimmed dry udder weight (g)
252.4 116.4
0.16 0.04
0.15 0.43
0.17 0.01
Composition of dry udder ( g) DFFT Protein Fat Ash
269 81 692 7.5
296 113 636 9.2
288 76 420 10.7
97.8 33.9 123.6 2.5
0.96 0.53 0.09 0.43
0.71 0.61 0.16 0.25
0.94 0.31 0.08 0.51
Composition of DFFT ( g) Protein DNA Protein / DNA
211 3.7 57.0
250 5.5 52.9
245 6.8 45.0
82.1 2.1 9.7
0.86 0.34 0.47
0.60 0.18 0.33
0.93 0.60 0.43
Collagen (% in DFFT) Fat tissue area (m 2 ) Secretory tissue area (m 2 ) Ratio fat / secretory tissue
34.3 74.9 53.4 1.6
1.7 11.8 12.4 0.29
0.21 0.002 0.18 0.007
0.45 , 0.001 0.90 0.002
0.16 0.14 0.07 0.77
34.5 42.7 64.2 0.69
32.0 24.1 39.9 0.61
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
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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 Diet a
Contrast
A
B
C
15 518 26.3 18.8 0.61 0.70 129.8 64.6 73.5
13 531 26.0 17.8 0.57 0.73 125.3 65.0 72.0
11 525 26.1 19.4 0.65 0.78 127.3 66.5 73.7
SED
Diet
Low-CP vs. high-CP
Low-REP vs. high-REP
—————— P —————— N Calving LW (kg) Calving age (months) Milk (l per d) Protein (kg per d) Fat (kg per d) Udder circumference (cm) Udder length (cm) Udder breadth (cm)
12.8 0.50 0.63 0.05 0.07 5.3 2.9 3.0
0.29 0.56 0.55 0.11 0.86 0.66 0.81 0.80
0.36 0.61 0.66 0.40 0.58 0.40 0.68 0.73
0.59 0.77 0.37 0.08 0.99 0.65 0.67 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 not influenced (P . 0.05) by either pre-pubertal dietary CP or REP concentration. The average daily first lactation milk, protein and fat yields across diets was 18.6 l, 0.61 and 0.73 kg, respectively. Daily first lactation milk, protein and fat yields were not influenced by pre-pubertal dietary CP concentration. Pre-pubertal dietary REP concentration did not influence daily first lactation milk and fat yields but daily protein yield tended to be greater (P 5 0.08) in those heifers that had consumed diet C compared to those that consumed diet B during pre-puberty. Udder dimensions measured during first lactation were not influenced (P . 0.05) by either pre-pubertal dietary CP or REP concentration.
4. Discussion Pre-pubertal diets of high-CP consumed by heifers to achieve LWG in excess of 900 g per d did influence mammary gland development, such that the area of fat tissue and the ratio of fat to secretory tissue in these glands was decreased but did not affect first lactation daily milk, protein and fat yields. Further, pre-pubertal diets of high-energy, high-CP, high-REP decreased the weight of the dry gland and tended to decrease the amount of fat and the area of secretory tissue compared to glands from heifers that
consumed pre-pubertal diets of high-energy, high-CP, low-REP. Pre-pubertal dietary REP concentration did not influence first lactation production, although there was a tendency for more daily protein to be produced when pre-pubertal dietary REP concentration was increased. Our lactation results for pre-pubertal dietary CP concentration are in contrast to those of Pirlo et al. (1997), who found an increase in daily first lactation milk production of 1.6 kg when heifers were fed a high-CP diet (110% NRC, 1989) compared to a low-CP diet (90% NRC, 1989) at similar high prepubertal LWG. The comparison of pre-pubertal dietary REP concentration in our study indicated that 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 concentration, their increase in milk and protein may have been due to the higher REP concentration in the high-CP diet because of the higher intake of soybean meal. Capuco et al. (1995) found that pre-pubertal heifers grown in excess of 900 g per d and fed a high-CP diet (22% CP) had lighter mammary glands, less mammary fat and more total mammary DNA compared to those fed a low-CP diet (15% CP). Our study confirms this observation that high-CP diets consumed during pre-puberty tended to reduce the weight of mammary glands, as well as the area of fat
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tissue and ratio of fat to secretory tissue. Further reduction in mammary gland weight was observed in our study when pre-pubertal REP concentration at a high-CP concentration was increased. The comparison of dietary REP concentrations at the same dietary CP concentration, indicates that pre-pubertal heifers gaining in excess of 900 g per d had less developed mammary glands when REP was increased. However, these heifers were able to produce 1.6 l per d more milk than their herd-mates consuming a low-REP pre-pubertal diet. This could have been due to compensatory mammary growth after mating and differences in body composition at the start of calving. Capuco et al. (1995) have discussed the concept of compensatory mammary growth in terms of inhibition of either primary duct elongation or branching of ducts. Inhibition of 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 histological data were collected in our experiment to confirm this hypothesis. Capuco et al. (1995) also discuss the possible effects of body composition on the lack of differences between diet, LWG and diet within LWG in their experiment. In our study, heifers at slaughter did not differ in fat depth at the 12 / 13th rib between dietary REP concentrations but heifers consuming the low-CP pre-pubertal diet tended to have a greater fat depth than those consuming the high-CP prepubertal diet (Dobos et al., 1997).
5. Conclusion Pre-pubertal diets containing low-CP compared to high-CP increased the area of mammary gland fat tissue and the ratio of fat to secretory tissue area at 16 months of age. However, there was no effect on subsequent first lactation production. Pre-pubertal diets containing high-REP compared to low-REP at similar concentrations of CP reduced the weight of the dry gland and tended to reduce the amount of mammary fat and the area of secretory tissue. HighREP pre-pubertal diets tended to increase daily first lactation protein yield by 0.08 kg.
Acknowledgements The authors wish to acknowledge the contribution of funding from the Commonwealth Department of Employment, Education, Training and Youth Affairs, NSW Dairy Corporation, NSW Dairy Farmers Association, Elanco Animal Health (Australia), Dairy Farmers Ltd., Australian Dairy Research and Development Corporation, Semex Australia Pty. Ltd., Herd Improvers Australia Pty. Ltd., MillMaster Feeds Ltd., Wrightsons Seeds Pty. Ltd., University of Sydney and NSW Agriculture. Thanks to Mr B. Rhees, Ms Y. Leischke-Mercer and Ms S. Plowman for managing the heifers during the pre-calving stage of the experiment and to Dr J. Gooden and his dedicated staff at the University of Sydney MayFarm for heifer management during the lactation stage.
References AFRC, 1993. Energy and protein requirements of ruminants, CAB International, Wallingford, UK, An advisory manual prepared by the AFRC Technical Committee on Responses to Nutrients. Amir, S., Kali, J., 1974. Influence of plane of nutrition of the dairy heifer on growth and performance after calving. In: Dairy Science Handbook, Vol. 7. AgriServices Foundation, Davis, California, pp. 183–190. Association of Official Agricultural Chemists (AOAC), 1980. In: Official methods of analysis of the AOAC, 13th ed. AOAC, Washington, DC, pp. 126–127. Bergman, I., Loxley, R., 1963. Two improved and simplified methods for the spectrophotometric determination of hydroxyproline. Analytical Chemistry 35, 1961–1965. Capuco, A.V., Smith, J.J., Waldo, D.R., Rexroad, C.E., 1995. Influence of prepubertal dietary regimen on mammary growth of Holstein heifers. J. Dairy Sci. 78, 2709–2725. Capuco, A.V., Smith, J.J., Waldo, D.R., Elsasser, T.H., 1988. Effect of diet and pre-pubertal growth rate of Holstein heifers on mammary gland growth and milk production. J. Dairy Sci. 71 (suppl 1), 186. Dobos, R.C., Riley, K., Nandra, K.S., Kellaway, R.C., Fulkerson, W.J., Lean, I.J., 1997. The effect of rumen escape protein on carcass characteristics of rapidly growing pre-pubertal dairy heifers. In: Corbett, J.L., Choct, M., Nolan, J.V., Rowe, J.B. (Eds.), Recent Advances in Nutrition in Australia ’97. Department of Animal Science, University of New England, p. 255. Folch, J.M., Lees, M., Sloane-Stanley, G.H., 1957. A simple method for the isolation and purification of total lipids from animal tissues. J. Biol. Chem. 226, 497. Gardner, R.W., Schuh, J.D., Vargus, L.G., 1977. Accelerated
R.C. Dobos et al. / Livestock Production Science 63 (2000) 235 – 243 growth and early breeding of Holstein heifers. J. Dairy Sci. 60, 1941–1948. Kertz, A.F., Prewitt, L.R., Ballam, J.M., 1987. Increased weight gain and effects on growth parameters of Holstein heifer calves from 3 to 12 months of age. J. Dairy Sci. 70, 1612–1622. Little, W., Harrison, R.D., 1981. Effects of different rates of liveweight gain during rearing on the performance of Friesian heifers in their first lactation. Animal Production 32, 362, Abstract. ¨ Mantysaari, P., Ingvartsen, K.L., Toivonen, V., Sejrsen, K., 1995. The effects of feeding level and nitrogen source of the diet on mammary development and plasma hormone concentrations of pre-pubertal heifers. Acta Agric. Scand. Sect. A, Animal Sci. 45, 236–244. Martin, R.F., Donohue, D.C., Finch, L.R., 1972. New analytical procedure for the estimation of DNA with p-Nitrophenylhydrazine. Anal. Biochem. 47, 562–574. National Research Council (NRC), 1989. Nutrient Requirements of Dairy Cattle, 6th revised ed. National Academy of Science, Washington, DC. Ørskov, E.R., MacDonald, I., 1979. The estimation of protein degradability in the rumen from incubation measurements weighted according to rate of passage. J. Agric. Sci. Camb. 92, 499–503. Pirlo, G., Capelletti, M., Marchetto, G., 1997. Effects of energy and protein allowances in the diets of prepubertal heifers on growth and milk production. J. Dairy Sci. 80, 730–739.
243
Sejrsen, K., 1994. Relationships between nutrition, puberty and mammary development in cattle. Proceedings of the Nutrition Society 53, 103–111. Sejrsen, K., Foldager, J., 1992. Mammary growth and milk production capacity of replacement heifers in relation to diet energy concentration and plasma hormone levels. Acta Agric. Scand. Sect. A, Anim. Sci. 42, 99–105. Sejrsen, K., Huber, J.T., Tucker, H.A., Akers, R.M., 1982. Influence of plane of nutrition on mammary development in pre- and post-pubertal heifers. J. Dairy Sci. 65, 783–800. Standing Committee on Agriculture (SCA), 1990. Feeding Standards for Australian Livestock. Ruminants. CSIRO Publications, Melbourne, 266 pp. Valentine, S.C., Dobos, R.C., Lewis, P.A., Bartsch, B.D., Wickes, R.B., 1987. Effect of live weight gain before and during pregnancy on mammary gland development and subsequent milk production of Australian Holstein-Friesian heifers. Aust. J. Exp. Agric. 27, 195–204. van Amburgh, M.E., Galton, D.M., 1994. Accelerated growth of holstein heifers – effects on lactation. In: Cornell Nutrition Conference for Feed Manufacturers, Rochester, NY. Waldo, D.R., Capuco, A.V., Rexroad, Jr. C.E., 1989. Replacement heifer growth rates affects milk producing ability. Feedstuffs 27, 15–17.