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Feeding intensity of pregnant heifers
Livestock Production Science 62 (1999) 29–41 www.elsevier.com / locate / livprodsci
Feeding intensity of pregnant heifers Effect of feeding intensity during gestation on performance and plasma parameters of primiparous Ayrshire cows a, *, K.L. Ingvartsen b , V. Toivonen a ¨ P. Mantysaari b
a Agricultural Research Centre, Animal Production Research, FIN-31600 Jokioinen, Finland Danish Institute of Agricultural Sciences, Department of Animal Health and Welfare, Research Centre Foulum, P.O. Box 50, DK-8830 Tjele, Denmark
Received 3 September 1998; received in revised form 22 February 1999; accepted 15 March 1999
Abstract The effect of different feeding intensity at two stages of gestation on performance of primiparous cows was studied in 40 pregnant Ayrshire cows. The feeding intensity was either medium (M) or high (H) in period 1 (2–6 months of pregnancy) or period 2 (7–9 months of pregnancy) resulting in treatments MM, MH, HM and HH. Before pregnancy all heifers were reared to gain 650 g / day. In period 1, heifers on H feeding intensity, grew significantly faster than heifers on M (844 vs. 638 g / day; SEM 5 18.9). Daily gains in period 2 were affected by feeding intensity in period 1 and were 710, 1042, 636 and 874 g on MM, MH, HM, and HH diets, respectively. The body weights at calving were 462, 498, 480 and 499 kg on MM, MH, HM and HH diet, respectively. Feeding intensity in period 1 had no effect on milk production, but H plane of nutrition in period 2 increased milk yield by approximately 11% (22.6 vs. 20.3 kg / day, P , 0.004). Medium feeding intensity in period 1 increased postpartum DMI, and decreased postpartum mobilization of body reserves. Mobilization was positively correlated with BCS at calving (r 5 0.48; P , 0.003) and with plasma free fatty acid (r 5 0.73; P , 0.0001) and b-hydroxybutyrate concentrations (r 5 0.69; P , 0.0001). Prepartum treatments had no effect on postpartum plasma growth hormone (GH) or prolactin concentration, but high feeding intensity in period 2 decreased insulin (INS) concentration postpartum. No relationships were found across treatments between milk yield and prepartum plasma hormone concentrations, but a positive correlation was found between milk yield and postpartum GH and GH / INS. The results show that high compared with medium feeding intensity during the first two trimesters of gestation does not improve milk production of primiparous cows. Instead, during the last trimester a high feeding intensity is required for maximum milk yield. 1999 Elsevier Science B.V. All rights reserved. Keywords: Feeding during gestation; Feeding intensity; Milk yield; Plasma parameters; Primiparous cows
1. Introduction *Corresponding author. Tel.: 1358-3-41881; fax.: 1358-34188-3661. ¨ E-mail address: [email protected] (P. Mantysaari)
Feeding intensity during gestation can influence milk producing ability of primiparous cows by affecting calving body weight (BW), mobilizable
0301-6226 / 99 / $ – see front matter 1999 Elsevier Science B.V. All rights reserved. PII: S0301-6226( 99 )00055-X
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body reserves (MBR), and mammary growth and development. Many studies have shown that the first lactation milk yield correlates positively with BW at calving (Clark and Touchberry, 1962; Ingvartsen et al., 1988; Foldager and Sejrsen, 1991). However, a high plane of nutrition during gestation has often failed to increase milk production of primiparous cows (Ducker et al., 1985; Valentine et al., 1987; Lacasse et al., 1993; Grummer et al., 1995; Ingvartsen et al., 1995a). The degree and duration of high feeding level and also the plane of nutrition before gestation are likely to be important for these results. Foldager and Sejrsen (1991) reported an increase in mammary development and milk production when prepartum (325 kg BW to calving) daily gain increased from 400 to 600 g. A further increase in daily gain (800 g / day) did not improve milk production further. In other studies, a high feeding intensity during the last 6, 12 or 24 weeks before calving had no effect on milk yield (Foldager and Ingvartsen, 1995). A high feeding intensity for 24 weeks was, however, associated with decreased postpartum feed intake which is in accordance with Grummer et al. (1995) who also found negative effect of high prepartum feeding intensity on dry matter intake (DMI) with no change in milk production. Stair-step feeding (high feeding intensity following lower) of pregnant heifers has been reported to increase milk yield postpartum (Park et al., 1987, 1989; Choi et al., 1997). Furthermore, stair-step feeding increased the differentiation and functional activity of the mammary glands (Park et al., 1989; Choi et al., 1997) which, at least in part, may explain differences in milk yield. A possible explanation for enhanced mammary differentiation and milk production measured in the compensatory growth pattern associated with stair-step rearing are the changes in hormone secretion and enzymatic activities (Park et al., 1988, 1989). Furthermore, Stelwagen et al. (1992) showed that bGH injection during the last trimester increases the milk production. This is supposed to be due to an increase in mammary parenchymal cell number (Stelwagen et al., 1992). However, the effect of changing feeding intensity during gestation in heifers on plasma hormone concentrations and subsequent milk yield of primiparous cows has not been thoroughly investigated.
The purpose of the present experiment was to study the effect of high prepartum feeding intensity at different stages of pregnancy on milk production, feed intake and plasma hormone concentrations and metabolites of primiparous Ayrshire cows.
2. Material and methods
2.1. Animals and diets Forty pregnant Finnish Ayrshire heifers were blocked by due date (three blocks) and assigned randomly to one of four treatments on their fourth week of gestation. The gestation was divided into two periods: months 2–6 (period 1) and months 7–9 of pregnancy (period 2; the last trimester). During period 1, one half of the heifers had the medium (M) and the other half high (H) plane of nutrition. In period 2, half of the heifers on both planes of nutrition were changed to the other plane of nutrition. Thus, the treatments were MM, MH, HM and HH. Before breeding all heifers were treated the same and reared to gain 650 g / day. During gestation the heifers were fed grass silage, barley, and mineral and vitamin supplements to meet the requirements for 650 and 850 g daily gain on M and H plane of nutrition, respectively. The amount of barley varied according to weight from 0.5–1.00 kg / day on M and from 1.75 to 2.25 kg / day on H plane of nutrition. All heifers received the same concentrate mix for the last 2 weeks before due date. The concentrate mix which included 318 g / kg barley, 318 g / kg oats, 180 g / kg rapeseed meal, 150 g / kg molassed sugar beet pulp, and 34 g / kg minerals and vitamins was given in an increasing amount and reached 5 kg / day at parturition. After parturition the amount of concentrate mix was increased to 7.5 kg / day over a period of 1 week and was kept constant until 160 days of lactation. From 2 weeks before parturition and for the rest of the experimental period postpartum heifers were offered grass silage ad libitum.
2.2. Measurements and sampling During periods 1 and 2 live weight, heart girth, wither height, body length (from the point of the shoulder to the pinbone), hip width, and body
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condition score (BCS; from 1 5 skinny to 5 5 very fat; Lowman et al., 1976) of the heifers were recorded every fourth week. The calving BW was measured on calving day or the day after. BW of calves were measured on the day of birth. During lactation cows were weighed once a week and BCS were recorded at the end of the experiment (day 160 of lactation). Individual feed intakes were recorded daily through out gestation and lactation periods. Daily samples of each feed were composited to give a 4-week sample for proximate and NDF analysis. The chemical composition of feeds is given in Table 1. Milk yields were recorded daily and milk protein, fat, and lactose were analyzed once a week. Blood samples were taken from each animal from the coccygeal vein at 35, 28, 21, 16, 12, 8 and 4 days before due date and 0, 1, 3, 7, 14, 21, 28, 35, 42, 56, 84 and 112 days postpartum. Blood was collected in heparinized tubes and stored on ice until centrifuged at 2 48C for 15 min at 2000 3 g. Blood for bhydroxybutyrate (BHBA) analysis was precipitated with HClO 4 and centrifuged. Plasma and HClO 4 precipitated blood samples were frozen and stored at 2 208C for later analysis of glucose, free fatty acids (FFA), growth hormone (GH), prolactin (PRL), and insulin (INS). Glucose was analysed using Peridochrom GOD-PAP/ glucose kit (Boehringer Mannheim, Germany) and FFA using an analytical kit (Waco Pure Chemical Industries) which was optimised to conditions for an Opera TM autoanalyser. BHBA was
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analysed with KONE Specific autoanalyser according to Hansen and Freier (1978). Hormones were analysed with double antibody radioimmunoassays. For the assays of GH and PRL bovine GH antigen (AFP11182B) and bovine PRL antigen (AFP4835B) were separately iodinated with the iodogen method (Salacinsku et al., 1981). First antibodies used were NIDDK-anti-oGH-2 (AFPC0123080) and NIDDK-anti-bPRL-2 (AFP753180). Second antibody in both assays was anti-rabbit IgG (Sigma R-0881). As standards USDA-bGH-B-1 (AFP-5200) and bPRL, BIO (AFP7170E) were used. INS was measured with Phaseseph Insulin RIA (Pharmacia Diagnostics, Uppsala, Sweden). The recommended procedures accompanying the above mentioned hormones, antibodies and the insulin kit were followed. Inter-assay variation for hormone measurements was included in the block effect and, therefore, does not influence the comparisons. Intra-assay variation for GH, PRL, and INS were 4.4, 5.6 and 5.8%, respectively. Intra- and inter-assay variation were 6.0 and 9.1% for free fatty acids (FFA), 2.3 and 3.8% for BHBA and 2.0 and 3.9% for glucose, respectively.
2.3. Calculations and statistical analyses Metabolizable energy (ME) values of the feeds were calculated according to MAFF (MAFF, 1975). The digestibility coefficients of the feeds were from the feed tables by Tuori et al. (1996). Every 4-week
Table 1 Chemical composition of the feeds fed during gestation and lactation Gestation
Lactation
Grass silage
Barley
Grass silage
Concentrate a
18 228.5620.1
12 886.060.3
22 239.9631.3
10 886.963.2
In DM (g / kg) Ash Crude protein Crude fibre Ether extract NDF
6.760.5 14.061.5 33.061.3 4.360.3 61.061.7
2.660.2 13.260.9 5.360.4 2.360.1 22.561.7
7.760.9 13.961.2 29.364.2 4.560.3 55.865.6
7.760.2 16.560.5 10.160.4 3.560.2 28.161.4
ME b (MJ)
10.760.4
13.260.1
10.760.5
12.060.04
n DM (g / kg)
a
A mix of barley (318 g / kg, oats (318 g / kg), rapeseed meal (180 g / kg), molassed sugar beet pulp (150 g / kg) and minerals and vitamins (34 g / kg). b ME is calculated according to MAFF (1975).
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weights before parturition and 1-week weights after parturition were used to compute growth curves using a cubic function on time for each animal. From the individual growth curves, initial and final weights in periods 1, 2, and lactation were predicted and used in the statistical analyses. Energy value of weight gain during pregnancy (EVg , MJ / kg) was calculated from the ME above maintenance and activity using the efficiency of utilization of ME for growth (k f 5 0.78q 1 0.006). Requirement of ME for maintenance and activity was calculated using equations proposed by AFRC (1993). One heifer on HM and one on HH treatment gave birth to a stillborn about 2.5 months before due date. Data from these two heifers were excluded. Feed intake, growth, and body measurement data of the heifers during gestation were analyzed using the GLM procedure (SAS , 1987). The full model was:
y ijklmn 5 m 1 P1 i 1 P2 j 1 (P1 3 P2 ) ij 1 Bk 1 Anrl
y ijk 5 m 1 P1 i 1 P2 j 1 (P1 3 P2) ij 1 Bk 1 e ijk ,
where P1 i and P2 j are as described in the previous model, b BWI is the linear effect of the pedigree index for BW (BWI k ). The BWI k was included only in the analysis of BW data. The relationship between production measurements and circulating mean plasma metabolite concentrations were described by Pearsons correlations calculated across individuals across treatments.
where P1 i is the fixed effect of plane of nutrition in period 1; P2 j the fixed effect of plane of nutrition in period 2; Bk is the fixed effect of block; terms P2 j and (P1 i 3P2 j ) were not included in the analyses of data from period 1. In period 2 data no interaction between periods 1 and 2 was found, therefore, only the main effects (P1 i and P2 j ) were considered. Production and feed intake data during lactation and also plasma parameters were analyzed as repeated measurements using the MIXED procedure (SAS , 1992). The variance component estimation method was REML and the type of covariance matrix was first-order autoregressive [AR(1)]. The model used for production and feed intake data was: y ijklmn 5 m 1 P1 i 1 P2 j 1 (P1 3 P2 ) ij 1 b I Ik 1 bA A l 1 Sijklm 1 T n 1 (T 3 P1 ) ni 1 (T 3 P2 ) nj 1 (T 3 P1 3 P2 ) nij 1 e ijklmn , where P1 i and P2 j are as described in the previous model, b I is the linear effect of pedigree index (Ik ) of the heifers appropriate for milk, fat%, protein%, or protein yield, bA is the linear effect of the age (A l ) at parturition, Sijklm is the random effect of the heifer, and T n the week of lactation. Prior to analyses, GH, PRL, and INS were transformed into natural logarithms to improve normality. The model used for plasma parameters was:
1 Sijklm 1 T n 1 (T 3 P1 ) ni 1 (T 3 P2 ) nj 1 (T 3 P1 3 P2 ) nij 1 e ijklmn , where P1 i , P2 j , Sijklm and T n are as described in the previous models, Anrl is the fixed effect of assay number. Anrl was included in the analyses of hormones. For plasma data no interactions were found. Therefore, only the main effects (P1 i , P2 j and T n ) were tested. The body weight change during lactation as well as energy and protein efficiency were analyzed from the combined data of each cow. The following model was used: y ijk 5 m 1 P1 i 1 P2 j 1 (P1 3 P2) ij 1 b BWI BWI k 1 e ijk ,
3. Results and discussion
3.1. Growth during pregnancy The effect of plane of nutrition on growth and feed intake of heifers during pregnancy is presented in Table 2. Average initial body weight of heifers was 356 kg. In period 1, the daily gain were 638 and 844 g for M and H, respectively. The M plane of nutrition in period 1 led to significantly higher growth of the heifers in period 2. Thus, in period 2 the daily gains of heifers were 710, 1042, 636 and 874 g on MM, MH, HM and HH treatments, respectively. Heifers on MH and HH treatments had almost equal BW at calving due to higher growth of the heifers in period 2 on treatment MH compared with heifers on treatment HH. The plane of nutrition in period 1 had no effect on final BW. Because of the compensatory growth in period 2, feed conversion (ME MJ / kg gain) was better (P,0.02) for heifers
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Table 2 Body weight, growth and feed intake of heifers during gestation (LS-means) Plane of nutrition a Period 1: Period 2:
M
503
Daily gain (g / day) Period 1 Period 2
710
ME (MJ / day) Period 1 Period 2 CP (kg / day) Period 1 Period 2
H
MM
Body weight (kg) Initial After 1st period After 2nd period
Feed intake DM (kg / day) Period 1 Period 2
SEM MH
HM
361 450 522
1042
636
638
5.87
60.8
89.3
Energy value of gain EVg c (MJ / kg) Period 1 Period 2
18.3
874
18.9 45.9
0.001 0.01
– 0.0001
0.058 0.024
0.0001 0.08
– 0.0001
0.67 1.04
0.0001 0.06
– 0.0001
0.008 0.013
0.0001 0.09
– 0.0001
99.4
2.58 7.32
0.02
26.2
0.66 1.87
0.0003 0.02
6.99
65.2
0.75
Feed conversion ME (MJ) / gain (kg) Period 1 Period 2
– – 0.0005
76.0 79.1
0.76
0.02
544
4.4 5.5 8.2
6.64 6.92
62.1
Period 2
844
5.48 5.60
Period 1 HH
351 470 545
80.0 0.91
0.93
0.80
96.8
0.94
90.9 79.0
107.7
20.9
22.4
22.0
Effect (P)b
25.7
–
– 0.10
a Plane of nutrition during gestation. M, medium feeding intensity; H, high feeding intensity; period 1, the first and second trimesters; period 2, the last trimester; n in period 1 is 20 animals / treatment while it is 10 animals / treatment in period 2. b P,0.1 is shown. c EVg 5[(ME intake2ME maintenance2ME activity)3k f ] / live weight gain. ME maintenance and activity calculated according to the AFRC (1993). k f 50.78q10.006.
fed M diet in period 1. The compensatory growth of pregnant heifers is reported also by Lacasse et al. (1993) when high feeding level followed moderate feeding level. In their study the experimental period was divided into two parts, from 12 months of age to 3 months of gestation and from 3 months of gestation to 2 weeks prepartum. The plane of nutrition prepartum had no effect on wither height or body length of the heifers at parturition (Table 3). In agreement, Lacasse et al. (1993) found no difference in wither height of the heifers reared by different planes of nutrition pre-
partum. The H feeding intensity in period 1 increased heart girth, hip width and BCS of the heifers at the end of period 1, but only the effect for BCS was significant. The final heart girth, hip width and BCS of the heifers were affected by the plane of nutrition in period 1 and 2 being the highest on HH and the lowest on MM treatment (Table 3). These results indicate that a high compared to moderate plane of nutrition during pregnancy had no effect on body size (wither height, body length) of primiparous cows. However, the high plane of nutrition especially during the first two trimester of pregnancy increased
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Table 3 Body measurements of heifers during gestation (LS-means) Plane of nutrition a Period 1: Period 2: Heart girth (cm) Initial After 1st period After 2nd period Wither height (cm) Initial After 1st period After 2nd period Body length (cm) Initial After 1st period After 2nd period Hip width (cm) Initial After 1st period After 2nd period Body condition score c Initial After 1st period After 2nd period
SEM
M
H
MM
MH
HM
166 178 177
183
121 124 125
126
121 135 142
141
43.0 46.9 49.0
50.7
3.03 3.11 3.11
3.23
0.37 0.43 0.52
0.009
0.08
0.066 0.034 0.047
0.001 0.001
0.0002
125
141
0.9 1.1 1.0
51.4
3.09 3.28 3.27
0.05
0.8 0.6 0.9
43.4 47.7 50.2
0.04
185
120 134 143
Period 2
1.0 1.2 1.5
120 123 127
Period 1 HH
165 181 183
Effect (P)b
3.47
a
Plane of nutrition during gestation. M, medium feeding intensity; H, high feeding intensity; period 1, the first and second trimesters; period 2, the last trimester; n in period 1 is 20 animals / treatment while it is 10 animals / treatment in period 2. b P,0.1 is shown. c Body condition score measured from a scale 1–5 with interval 0.25 as described by Lowman et al. (1976).
the amount of body fat reserves as indicated by the calculated energy value of the weight gain (Table 2).
3.2. Milk production and composition A high plane of nutrition during the first two trimesters of pregnancy did not affect milk production. During the last trimester a high feeding intensity increased (P,0.004) milk yield and ECM yield by approximately 11% (Table 4, Fig. 1). Therefore, the results indicate that a high feeding intensity at late pregnancy is required to ensure the maximum milk production of primiparous cows. Foldager and Sejrsen (1991) reported an enhanced mammary development and increased milk production when prepartum daily gain increased from 400 to 600 g, but they found no benefits from increasing
daily gain to 800 g. In agreement with Foldager and Sejrsen (1991), Ducker et al. (1985), Lacasse et al. (1993), and Foldager and Ingvartsen (1995) found no improvement in milk production when heifers gained more than 600–700 g a day prepartum. Valentine et al. (1987) observed no difference in milk production in primiparous cows gaining 220, 590, or 1090 g / day during the last 4.5 months of gestation. Harrison et al. (1983), on the other hand, recorded an increased mammary development when the daily gain of heifers during pregnancy increased from 680 to 840 g. A comparison of the above studies is difficult, however, since the breed of the heifers and the duration of treatment periods vary. Furthermore, rearing during the prepubertal period varies among studies and sometimes also between animals within a study. This can disturb results
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Table 4 Production and feed intake of heifers during the 160-days lactation period (LS-means) Variable
Plane of nutrition a MM
Production Milk (kg / day) ECM d (kg / day) Milk fat (g / kg) Milk protein (g / kg) Milk lactose (g / kg) Feed intake DM (kg / day) ME (MJ / day) CP (kg / day) Feed conversion ECM / ME (MJ) Milk protein / CPI e
MH
SEM HM
HH
P1
20.4 22.4 4.64 3.47 4.99
22.8 25.3 4.69 3.45 5.13
20.2 22.4 4.64 3.54 5.06
22.3 24.5 4.77 3.35 5.10
0.71 0.63 0.064 0.065 0.044
15.6 176 2.29
16.2 183 2.37
15.1 171 2.23
14.9 168 2.20
0.22 2.5 0.031
0.127 0.31
0.139 0.33
0.132 0.32
0.145 0.33
Effect (P)b
0.0041 0.007
P2 0.004 0.0005
T 3P13P2 c
0.04 0.004 0.0001
0.05
0.0004 0.0005 0.0006
0.005 0.007
– –
a Plane of nutrition during gestation. M, medium feeding intensity; H, high feeding intensity; P1 (period 1), the first and second trimesters; P2 (period 2), the last trimester. b P,0.1 is shown c T, week of lactation. d ECM, energy corrected milk. e CPI, crude protein intake.
Fig. 1. Daily milk yield of primiparous cows fed a different feeding intensity during pregnancy (medium plane of nutrition during gestation (1), high plane of nutrition during gestation (j), medium plane of nutrition in period 1 (first two trimesters of gestation) and high plane of nutrition in period 2 (last trimester of gestation) (m), or high plane of nutrition in period 1 and medium plane of nutrition in period 2 (*)).
because prepubertal plane of nutrition can affect milk yield (Little and Kay, 1979; Ingvartsen et al., 1988; Foldager and Sejrsen, 1991). In the present study, the heifers were reared equally from birth to the beginning of the experiment to diminish the effect of prepubertal management. The prepartum plane of nutrition had no effect on mean milk fat or protein content during the experiment as such (Table 4). However, there was a significant interaction of treatment3time of lactation for milk fat and protein content. During the first weeks of lactation, the milk fat content on HH treatment was higher than on other treatments. This was assumed to be due to a larger body fat mobilization and, therefore, higher plasma FFA concentration of cows on HH treatment than on other treatments prepartum. In agreement with our results, Grummer et al. (1995) and Foot et al. (1963) reported a significantly higher milk fat percentage during the first weeks of lactation for primiparous cows fed a high plane of nutrition compared with a standard plane of nutrition prepartum. The prepartum plane of feeding does not usually affect milk protein content of primiparous cows
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(Lacasse et al., 1993; Foldager and Ingvartsen, 1995; Grummer et al., 1995). However, in the present study, ignoring the first week of lactation, we observed a higher (P,0.04) protein content for heifers fed M plane of nutrition in period 2. The reason for this is unclear, but might be related to the negative correlation between milk production and milk protein content.
3.3. Calving body weight, mobilization of body fat and feed intake Feeding intensity in period 1 had no significant effect on BW at calving whereas a high plane of nutrition in period 2 increased it (Table 5). Milk yield was positively correlated with BW at calving (r50.33; P,0.05) as has also been seen in many previous studies (Ingvartsen et al., 1988; Foldager and Sejrsen, 1991; Hoffman and Funk, 1992). The cows on MH and HH feeding intensity prepartum had the same (498 and 499 kg) calving BW. However, the heifers on MH treatment were probably closer to their mature body size at calving than the heifers on HH treatment even if no significant differences in wither height or body length were measured. The background for this assumption was the expected difference in body content of the cows as indicated by the differences in energy value of weight gain (Table 2), BCS at calving (Table 3) and mobilized body reserves (MBR) during lactation (Table 5, Fig. 2). On day 160 of lactation cows on
Fig. 2. Postpartum body weight change of primiparous cows fed at different feeding intensity during pregnancy (medium plane of nutrition during gestation (1), high plane of nutrition during gestation (j), medium plane of nutrition in period 1 (first two trimesters of gestation) and high plane of nutrition in period 2 (last trimester of gestation) (m), or high plane of nutrition in period 1 and medium plane of nutrition in period 2 (*)).
MH treatment were 28 kg heavier than cows on HH treatment with no difference in BCS. The MBR was positively correlated with BCS at calving (r50.48; P,0.003). The cows on HH treatment prepartum mobilized more body weight during lactation than others and cows on MM treatment during pregnancy did not lose any body weight. Instead, their demand for energy for growth was high already from the beginning of lactation
Table 5 Body weight change of the cows during lactation period and body weight of their calves at birth (LS-means) Variable
BW at calving (kg) BW on day 160 of lactation Aver. gain (days 0–160) (kg / day) Total mobilization of BW in lactation (kg) Final BCS c a
Plane of nutrition a
SEM
MM
MH
HM
HH
462 513
498 520
480 505
499 492
Effect (P)b P1
8.1 12.1
P2 0.003
0.31
0.12
0.15
20.04
0.050
0.003
0.0008
0.0 3.20
11.6 2.92
10.1 3.03
28.4 2.83
3.54 0.124
0.0006
0.0002 0.06
Plane of nutrition during gestation. M, medium feeding intensity; H, high feeding intensity. P1 (period 1), the first and second trimesters; P2 (period 2), the last trimester. b P,0.1 is shown. c BCS, body condition score on day 160 of lactation.
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for total DMI was measured (Table 4) and no correlation between BCS at calving and DMI postpartum was measured (r5 20.005; P,0.97). However, the HH cows had lower concentrate intake during the first 5 weeks of lactation (5.39 vs. 6.11 kg DM / day; P,0.03) than the cows on other treatments.
3.4. Plasma concentration of hormones and metabolites
Fig. 3. Postpartum daily dry matter intake of primiparous cows fed at different feeding intensity during pregnancy (medium plane of nutrition during gestation (1), high plane of nutrition during gestation (j), medium plane of nutrition in period 1 (first two trimesters of gestation) and high plane of nutrition in period 2 (last trimester of gestation) (m), or high plane of nutrition in period 1 and medium plane of nutrition in period 2 (*)).
(Figs. 2 and 3). Thus, the low milk yields of MM cows are, at least in part, explained by the lack of body energy reserves to support the production in early lactation. The heifers on medium feeding intensity during period 1 had a higher postpartum DMI. On both treatments MM and MH the initial DMI was equal. After week 8 of lactation the increase in DMI of the cows fed MM diet prepartum decrease compared to cows on MH diet (Fig. 3). This is mostly explained by two cases of ketosis on MM treatment. The feeding intensity in period 2 had no significant effect on postpartum DMI (Table 4). This is in agreement with Foldager and Ingvartsen (1995) who measured no change in postpartum DMI due to increase in feeding intensity in weeks 6 or 12 prepartum. But when the feeding intensity was high throughout the last 24 weeks before calving, DMI decreased dramatically. The heifers with high feeding intensity throughout the last 24 weeks prepartum were fat at calving. Based on their review, Ingvartsen et al. (1995a) suggested that the high prepartum feeding and high BCS at calving will cause lower initial and delayed maximum feed intake. In our study no significant interaction of treatment3time of lactation
Plasma glucose and BHBA concentrations during lactation and plasma FFA and hormone concentrations pre- and postpartum are given in Figs. 4 and 5. The feeding intensity prepartum had no significant effect on plasma FFA concentrations from day 35 prepartum to calving. A high feeding intensity in periods 1 and 2 increased the plasma concentration of BHBA (period 1, P,0.003; period 2, P,0.01) and FFA (period 1, P,0.0001; period 2, P,0.02) during early lactation. The effect of period 1 was higher than the effect of period 2. Thus, the concentrations of BHBA and FFA were directly correlated with the duration of high feeding intensity during gestation. The correlations of BHBA and FFA with BCS (r50.41 and r50.62; P,0.02) and MBR (r50.69 and r50.73; P,0.0001) were positive. Thus, especially FFA, but also BHBA plasma concentrations were indicating the degree of utilization of body fat reserves. The prepartum treatments had no significant effects on postpartum plasma glucose which is in accordance with Ingvartsen et al. (1995b). The feeding intensity during gestation had no effect on the prepartum plasma PRL concentration or periparturient surge of PRL (P,0.09). Lacasse et al. (1994) measured an increased prepartum PRL concentration with the H plane of nutrition. They speculated that the increase in PRL was associated with an increased lipogenesis in heifers. In the present study prepartum PRL was not correlated with BCS at calving (r50.02, P,0.90) or MBR during lactation (r50.13, P,0.44). A high feeding intensity during the last trimester of gestation increased significantly (P,0.0001) the prepartum plasma INS concentration, but decreased (P,0.006) it during lactation. The postpartum INS was highly correlated with the plasma concentration of FFA (r5 20.54,
38
¨ et al. / Livestock Production Science 62 (1999) 29 – 41 P. Mantysaari
Fig. 4. Plasma FFA (a), BHBA (b) and glucose (c) concentration of primiparous cows fed at different feeding intensity during pregnancy (medium plane of nutrition during gestation (1), high plane of nutrition during gestation (j), medium plane of nutrition in period 1 (first two trimesters of gestation) and high plane of nutrition in period 2 (last trimester of gestation) (m), or high plane of nutrition in period 1 and medium plane of nutrition in period 2 (*)).
Fig. 5. Plasma growth hormone (a), prolactin (b) and insulin (c) concentrations of primiparous cows fed at different intensity during pregnancy (medium plane of nutrition during gestation (1), high plane of nutrition during gestation (j), medium plane of nutrition in period 1 (first two trimesters of gestation) and high plane of nutrition in period 2 (last trimester of gestation) (m), or high plane of nutrition in period 1 and medium plane of nutrition in period 2 (*)).
¨ et al. / Livestock Production Science 62 (1999) 29 – 41 P. Mantysaari
P,0.0006), BHBA (r5 20.44, P,0.007) and glucose (r50.56, P,0.0004). In agreement with Lacasse et al. (1994) the prepartum plasma concentration of GH was decreased by H plane of nutrition (P, 0.0001). In contrast to our findings, Ingvartsen et al. (1995b) measured no difference in the plasma GH concentration between heifers fed a high or a medium plane of nutrition during late pregnancy. In our study, the prepartum treatments had no effect on postpartum plasma GH concentrations which is in agreement with findings by Lacasse et al. (1994) and Ingvartsen et al. (1995b). The GH, INS and PRL have a mammogenic effect during gestation (Forsyth, 1971; Akers et al., 1981; Stelwagen et al., 1993). Stelwagen et al. (1992) measured an increased milk production with an injection of bGH during the last trimester of gestation. Based on their study with ewes, they proposed that improved milk yields with prepartum bGH injections are due to an increased number of mammary cells (Stelwagen et al., 1993). In the present study, the prepartum GH concentration was not related to milk yield (Table 6). Furthermore, neither the prepartum INS nor PRL concentration was correlated with milk production (Table 6). Therefore, it seems unlikely that the increased milk with high feeding intensity in period 2 should be related to changes in prepartum mammary development due to endocrine (GH, INS, PRL) factors. More likely, the higher production was due to differences in physiological status (calving BW, body reserves) of the heifers at calving. The correlations between postpartum hormone concentrations and milk production calculated across treatments are listed in Table 6. The postpartum PRL concentration was not related to milk production as was shown by Lacasse et al. (1994). The correlations
39
between milk yield and postpartum plasma concentration of GH, INS and GH / INS were 0.35 (P, 0.04), 20.51 (P,0.002), and 0.51 (P,0.002), respectively. This indicates the galactopoietic effect of GH and the lipogenic effect of INS. The postpartum ratio of GH to INS was significantly increased (P,0.05) by a high feeding intensity in period 2, which partly explains the increased partitioning of nutrients towards the mammary gland in treatments MH and HH.
4. Conclusions The feeding intensity from 2 to 6 months of gestation (period 1) had no effect on milk production ability of primiparous cows, but a high feeding intensity during the last trimester (period 2) increased milk yields. The BW change during lactation differed markedly between treatments. The mobilization of body reserves correlated with BCS at calving, and was the highest on the HH treatment. A high feeding intensity in period 2 increased the INS and decreased the GH prepartum plasma concentration. The postpartum plasma GH concentration was not affected by the prepartum feeding intensity, but a high feeding intensity in period 2 decreased the postpartum INS concentration and, consequently, increased the GH / INS level. No significant correlations between prepartum hormone concentrations and milk yield were found. The increased milk yields of the cows fed a high feeding intensity during the last trimester of gestation are believed primarily to be due to the differences in physiological status (calving BW, body fat reserves) of the heifers at calving. The postpartum plasma levels of the GH and the GH / INS were positively correlated with the milk yield. It can
Table 6 Correlations between plasma growth hormone (GH), insulin (INS) and prolactin (PRL) concentrations pre- and postpartum and milk production Hormone
GH INS PRL GH / INS
Prepartum hormone concentration3 Milk yield
Postpartum hormone concentration3 Milk yield
r
P
r
P
0.10 20.07 20.07 0.01
0.56 0.69 0.69 0.95
0.35 20.51 20.05 0.51
0.04 0.002 0.79 0.002
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be concluded that a high feeding intensity during the first 6 months of gestation does not improve the performance of primiparous Ayrshire cows reared to gain 650 g / day prior to breeding. Instead, during the last trimester of gestation a high plane of nutrition is required for optimum performance.
Acknowledgements GH and PRL antigens, standards and antibodies were kindly donated by USDA Animal Hormone Program, the National Hormone and Pituitary Program, the National Institute of Diabetes and Digestive and Kidney Diseases, the National Institute of Child Health and Human Development, US Department of Agriculture and Dr A.F. Parlow from the Harbor-UCLA Medical Center. Dr J. Proudman (USDA) and Dr A.F. Parlow are acknowledged for instructions concerning GH and PRL radioimmunoassays. This study is financially supported by Academy of Finland.
References AFRC, 1993. In: Energy and Protein Requirements of Ruminants, CAB International, Wallingford, UK, An advisory manual prepared by the AFRC Technical Committee on Responses to Nutrients. Akers, R.M., Bauman, D.E., Goodman, G.T., Capuco, A.V., Tucer, H.A., 1981. Prolactin Regulation of cytological differentiation of mammary epithelial cells in periparturient cows. Endocrinology 109, 31–40. Choi, Y.J., Han, I.K., Woo, J.H., Lee, H.J., Jang, K., Myung, K.H., Kim, Y.S., 1997. Compensatory growth in dairy heifers: The effect of a compensatory growth pattern on growth rate and lactation performance. J. Dairy Sci. 80, 519–524. Clark, D., Touchberry, R.W., 1962. Effect of body weight and age at calving on milk production in Holstein cattle. J. Dairy Sci. 45, 1500–1509. Ducker, M.J., Haggett, R.A., Fisher, W.J., Morant, S.V., Bloomfield, G.A., 1985. Nutrition and reproductive performance of dairy cattle. 1. The effect of level of feeding in late pregnancy and around the time of insemination on the reproductive performance of first lactation dairy heifers. Anim. Prod. 41, 1–12. Foldager, J., Ingvartsen, K.L., 1995. In: The 46 th Eur. Assoc. Anim. Prod. Annual Meeting, Prague, 1995, Production and Health in First Lactation in Dairy Cows in Relation to Prepartum Ration Energy Concentration and Daily Energy Level.
Foldager, J., Sejrsen, K., 1991. In: Rearing Intensity in Dairy Heifers and the Effect On Subsequent Milk Production, National Institute of Animal Science, Foulum, Denmark, Report 693. Foot, A.S., Line, C., Rowland, S.J., 1963. The effect of prepartum feeding of heifers on milk composition. J. Dairy Res. 30, 403–409. Forsyth, I.A., 1971. Reviews of the progress of dairy science. Section A. Physiology. Organ culture techniques and the study of hormone effects on the mammary gland. J. Dairy Res. 3, 419–445. Grummer, R.R., Hoffman, P.C., Luck, M.L., Bertics, S.J., 1995. Effect of prepartum and postpartum dietary energy on growth and lactation of primiparous cows. J. Dairy Sci. 78, 172–180. Hansen, J.L., Freier, E.F., 1978. Direct assays of lactate, pyruvate, b-hydroxybutyrate, and acetoacetate with a centrifugal analyzer. Clin. Chem. 24 (3), 475–479. Harrison, R.D., Reynolds, I.P., Little, W., 1983. A quantitative analysis of mammary glands of dairy heifers reared at different rates of live weight gain. J. Dairy Res. 50, 405–412. Hoffman, P.C., Funk, D.A., 1992. Applied dynamics of dairy replacement growth and management. J. Dairy Sci. 75, 2504– 2516. Ingvartsen, K.L., Danfaer, A., Andersen, P.H., Foldager, J., 1995a. In: The 46 th Eur. Assoc. Anim. Prod. Annual Meeting, Prague, Prepartum Feeding of Dairy Cattle: A Review of the Effect On Peripartum Metabolism, Feed Intake, Production, and Health. Ingvartsen, K.L., Sejrsen, K., Foldager, J., 1995b. In: Virkning af immunisering mod somatostatin i draegtighedsperioden og foderniveauet 12 uger for kaelving pa˚ foderoptagelse og productio hos kvier, National Institute of Animal Science, Denmark, pp. 49–59, Internal Report no. 47. Ingvartsen, K.L., Foldager, J., Larsen, J.B., Ostergaard, V., 1988. In: Growth and Milk Yield By Jersey Reared at Different Planes of Nutrition, National Institute of Animal Science, Foulum, Denmark, Report 645. Lacasse, P., Block, E., Guilbault, L.A., Petitclerc, D., 1993. Effect of plane of nutrition of dairy heifers before and during gestation on milk production, reproduction, and health. J. Dairy Sci. 76, 3420–3427. Lacasse, P., Block, E., Petitclerc, D., 1994. Effect of plane of nutrition before and during gestation on the concentration of hormones in dairy heifers. J. Dairy Sci. 77, 439–445. Little, W., Kay, R.M., 1979. The effects of rapid rearing and early calving on the subsequent performance of dairy heifers. Anim. Prod. 29, 131–142. Lowman, B.G., Scott, N.A., Somerville, S.H., 1976. Condition scoring of cattle. The East of Scotland Coll. Agric. Bull. No.6. MAFF, 1975. Energy allowances and feeding systems for ruminants. Tech. Bull 33. Her Majesty’s Stationary Office, London. Park, C.S., Erickson, G.M., Choi, Y.J., Marx, G.D., 1987. Effect of compensatory growth on regulation of growth and lactation: response of dairy heifers to a stair-step growth pattern. J. Anim. Sci. 64, 1751–1758. Park, C.S., Choi, Y.J., Keller, L.K., Harrold, R.L., 1988. Effect of compensatory growth on milk protein gene expression and mammary differentiation. FASEB J. 2, 2619–2624. Park, C.S., Baik, M.G., Keller, W.L., Berg, I.E., Erickson, G.M., 1989. Role of compencatory growth in lactation: A stair-step
¨ et al. / Livestock Production Science 62 (1999) 29 – 41 P. Mantysaari nutrient regimen modulates differentiation and lactation of bovine mammary gland. Growth Dev. Aging 53, 159–166. Salacinsku, P.R., McLean, C., Sykes, J.C., Clement-Jones, V.V., Lowry, P.J., 1981. Iodination of proteins, glycoproteins, and peptides using a solid-phase oxidizing agent, 1,3,4,6-tetrachloro-3a,6a-diphenyl glycolouril (Iodogen). Anal. Biochem. 117, 136–146. SAS , 1987. In: SAS / STATE Guide for Personal Computers, version 6 ed, SAS Institute, Cary, NC. SAS , 1992. In: SAS / STAT Software: Changes and Enhancements, SAS Institute, Cary, NC, SAS * Technical Report, P-229. Stelwagen, K., Grieve, D.G., McBride, W.B., Rehman, J.D., 1992. Growth and subsequent lactation in primigravid Holstein heifers after prepartum bovine somatotropin treatment. J. Dairy Sci. 75, 463–471.
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Stelwagen, K., Grieve, D.G., Walton, J.S., Ball, J.L., McBride, B.W., 1993. Effect of prepartum bovine somatotropin in primigravid ewes on mammogenesis, milk production, and hormone concentrations. J. Dairy Sci. 76, 992–1001. Tuori, M., Kaustell, K., Valaja, J., Aimonen, E., Saarisalo, E., Huhtanen, P., 1996. In: Rehutaulukot ja ruokintasuositukset ¨ ¨ – siat – siipikarja – turkiselaimet ¨ marehtijat – hevoset, Yliopistopaino, Helsinki, Finland. Valentine, S.C., Dobos, R.C., Lewis, P.A., Bartsch, B.D., Wickes, R.B., 1987. Effect of liveweight gain before or during pregnancy on mammary gland development and subsequent milk production of Australian Holstein–Friesian heifers. Aust. J. Exp. Agric. 27, 195–204.
Feeding intensity of pregnant heifers Effect of feeding intensity during gestation on performance and plasma parameters of primiparous Ayrshire cows a, *, K.L. Ingvartsen b , V. Toivonen a ¨ P. Mantysaari b
a Agricultural Research Centre, Animal Production Research, FIN-31600 Jokioinen, Finland Danish Institute of Agricultural Sciences, Department of Animal Health and Welfare, Research Centre Foulum, P.O. Box 50, DK-8830 Tjele, Denmark
Received 3 September 1998; received in revised form 22 February 1999; accepted 15 March 1999
Abstract The effect of different feeding intensity at two stages of gestation on performance of primiparous cows was studied in 40 pregnant Ayrshire cows. The feeding intensity was either medium (M) or high (H) in period 1 (2–6 months of pregnancy) or period 2 (7–9 months of pregnancy) resulting in treatments MM, MH, HM and HH. Before pregnancy all heifers were reared to gain 650 g / day. In period 1, heifers on H feeding intensity, grew significantly faster than heifers on M (844 vs. 638 g / day; SEM 5 18.9). Daily gains in period 2 were affected by feeding intensity in period 1 and were 710, 1042, 636 and 874 g on MM, MH, HM, and HH diets, respectively. The body weights at calving were 462, 498, 480 and 499 kg on MM, MH, HM and HH diet, respectively. Feeding intensity in period 1 had no effect on milk production, but H plane of nutrition in period 2 increased milk yield by approximately 11% (22.6 vs. 20.3 kg / day, P , 0.004). Medium feeding intensity in period 1 increased postpartum DMI, and decreased postpartum mobilization of body reserves. Mobilization was positively correlated with BCS at calving (r 5 0.48; P , 0.003) and with plasma free fatty acid (r 5 0.73; P , 0.0001) and b-hydroxybutyrate concentrations (r 5 0.69; P , 0.0001). Prepartum treatments had no effect on postpartum plasma growth hormone (GH) or prolactin concentration, but high feeding intensity in period 2 decreased insulin (INS) concentration postpartum. No relationships were found across treatments between milk yield and prepartum plasma hormone concentrations, but a positive correlation was found between milk yield and postpartum GH and GH / INS. The results show that high compared with medium feeding intensity during the first two trimesters of gestation does not improve milk production of primiparous cows. Instead, during the last trimester a high feeding intensity is required for maximum milk yield. 1999 Elsevier Science B.V. All rights reserved. Keywords: Feeding during gestation; Feeding intensity; Milk yield; Plasma parameters; Primiparous cows
1. Introduction *Corresponding author. Tel.: 1358-3-41881; fax.: 1358-34188-3661. ¨ E-mail address: [email protected] (P. Mantysaari)
Feeding intensity during gestation can influence milk producing ability of primiparous cows by affecting calving body weight (BW), mobilizable
0301-6226 / 99 / $ – see front matter 1999 Elsevier Science B.V. All rights reserved. PII: S0301-6226( 99 )00055-X
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body reserves (MBR), and mammary growth and development. Many studies have shown that the first lactation milk yield correlates positively with BW at calving (Clark and Touchberry, 1962; Ingvartsen et al., 1988; Foldager and Sejrsen, 1991). However, a high plane of nutrition during gestation has often failed to increase milk production of primiparous cows (Ducker et al., 1985; Valentine et al., 1987; Lacasse et al., 1993; Grummer et al., 1995; Ingvartsen et al., 1995a). The degree and duration of high feeding level and also the plane of nutrition before gestation are likely to be important for these results. Foldager and Sejrsen (1991) reported an increase in mammary development and milk production when prepartum (325 kg BW to calving) daily gain increased from 400 to 600 g. A further increase in daily gain (800 g / day) did not improve milk production further. In other studies, a high feeding intensity during the last 6, 12 or 24 weeks before calving had no effect on milk yield (Foldager and Ingvartsen, 1995). A high feeding intensity for 24 weeks was, however, associated with decreased postpartum feed intake which is in accordance with Grummer et al. (1995) who also found negative effect of high prepartum feeding intensity on dry matter intake (DMI) with no change in milk production. Stair-step feeding (high feeding intensity following lower) of pregnant heifers has been reported to increase milk yield postpartum (Park et al., 1987, 1989; Choi et al., 1997). Furthermore, stair-step feeding increased the differentiation and functional activity of the mammary glands (Park et al., 1989; Choi et al., 1997) which, at least in part, may explain differences in milk yield. A possible explanation for enhanced mammary differentiation and milk production measured in the compensatory growth pattern associated with stair-step rearing are the changes in hormone secretion and enzymatic activities (Park et al., 1988, 1989). Furthermore, Stelwagen et al. (1992) showed that bGH injection during the last trimester increases the milk production. This is supposed to be due to an increase in mammary parenchymal cell number (Stelwagen et al., 1992). However, the effect of changing feeding intensity during gestation in heifers on plasma hormone concentrations and subsequent milk yield of primiparous cows has not been thoroughly investigated.
The purpose of the present experiment was to study the effect of high prepartum feeding intensity at different stages of pregnancy on milk production, feed intake and plasma hormone concentrations and metabolites of primiparous Ayrshire cows.
2. Material and methods
2.1. Animals and diets Forty pregnant Finnish Ayrshire heifers were blocked by due date (three blocks) and assigned randomly to one of four treatments on their fourth week of gestation. The gestation was divided into two periods: months 2–6 (period 1) and months 7–9 of pregnancy (period 2; the last trimester). During period 1, one half of the heifers had the medium (M) and the other half high (H) plane of nutrition. In period 2, half of the heifers on both planes of nutrition were changed to the other plane of nutrition. Thus, the treatments were MM, MH, HM and HH. Before breeding all heifers were treated the same and reared to gain 650 g / day. During gestation the heifers were fed grass silage, barley, and mineral and vitamin supplements to meet the requirements for 650 and 850 g daily gain on M and H plane of nutrition, respectively. The amount of barley varied according to weight from 0.5–1.00 kg / day on M and from 1.75 to 2.25 kg / day on H plane of nutrition. All heifers received the same concentrate mix for the last 2 weeks before due date. The concentrate mix which included 318 g / kg barley, 318 g / kg oats, 180 g / kg rapeseed meal, 150 g / kg molassed sugar beet pulp, and 34 g / kg minerals and vitamins was given in an increasing amount and reached 5 kg / day at parturition. After parturition the amount of concentrate mix was increased to 7.5 kg / day over a period of 1 week and was kept constant until 160 days of lactation. From 2 weeks before parturition and for the rest of the experimental period postpartum heifers were offered grass silage ad libitum.
2.2. Measurements and sampling During periods 1 and 2 live weight, heart girth, wither height, body length (from the point of the shoulder to the pinbone), hip width, and body
¨ et al. / Livestock Production Science 62 (1999) 29 – 41 P. Mantysaari
condition score (BCS; from 1 5 skinny to 5 5 very fat; Lowman et al., 1976) of the heifers were recorded every fourth week. The calving BW was measured on calving day or the day after. BW of calves were measured on the day of birth. During lactation cows were weighed once a week and BCS were recorded at the end of the experiment (day 160 of lactation). Individual feed intakes were recorded daily through out gestation and lactation periods. Daily samples of each feed were composited to give a 4-week sample for proximate and NDF analysis. The chemical composition of feeds is given in Table 1. Milk yields were recorded daily and milk protein, fat, and lactose were analyzed once a week. Blood samples were taken from each animal from the coccygeal vein at 35, 28, 21, 16, 12, 8 and 4 days before due date and 0, 1, 3, 7, 14, 21, 28, 35, 42, 56, 84 and 112 days postpartum. Blood was collected in heparinized tubes and stored on ice until centrifuged at 2 48C for 15 min at 2000 3 g. Blood for bhydroxybutyrate (BHBA) analysis was precipitated with HClO 4 and centrifuged. Plasma and HClO 4 precipitated blood samples were frozen and stored at 2 208C for later analysis of glucose, free fatty acids (FFA), growth hormone (GH), prolactin (PRL), and insulin (INS). Glucose was analysed using Peridochrom GOD-PAP/ glucose kit (Boehringer Mannheim, Germany) and FFA using an analytical kit (Waco Pure Chemical Industries) which was optimised to conditions for an Opera TM autoanalyser. BHBA was
31
analysed with KONE Specific autoanalyser according to Hansen and Freier (1978). Hormones were analysed with double antibody radioimmunoassays. For the assays of GH and PRL bovine GH antigen (AFP11182B) and bovine PRL antigen (AFP4835B) were separately iodinated with the iodogen method (Salacinsku et al., 1981). First antibodies used were NIDDK-anti-oGH-2 (AFPC0123080) and NIDDK-anti-bPRL-2 (AFP753180). Second antibody in both assays was anti-rabbit IgG (Sigma R-0881). As standards USDA-bGH-B-1 (AFP-5200) and bPRL, BIO (AFP7170E) were used. INS was measured with Phaseseph Insulin RIA (Pharmacia Diagnostics, Uppsala, Sweden). The recommended procedures accompanying the above mentioned hormones, antibodies and the insulin kit were followed. Inter-assay variation for hormone measurements was included in the block effect and, therefore, does not influence the comparisons. Intra-assay variation for GH, PRL, and INS were 4.4, 5.6 and 5.8%, respectively. Intra- and inter-assay variation were 6.0 and 9.1% for free fatty acids (FFA), 2.3 and 3.8% for BHBA and 2.0 and 3.9% for glucose, respectively.
2.3. Calculations and statistical analyses Metabolizable energy (ME) values of the feeds were calculated according to MAFF (MAFF, 1975). The digestibility coefficients of the feeds were from the feed tables by Tuori et al. (1996). Every 4-week
Table 1 Chemical composition of the feeds fed during gestation and lactation Gestation
Lactation
Grass silage
Barley
Grass silage
Concentrate a
18 228.5620.1
12 886.060.3
22 239.9631.3
10 886.963.2
In DM (g / kg) Ash Crude protein Crude fibre Ether extract NDF
6.760.5 14.061.5 33.061.3 4.360.3 61.061.7
2.660.2 13.260.9 5.360.4 2.360.1 22.561.7
7.760.9 13.961.2 29.364.2 4.560.3 55.865.6
7.760.2 16.560.5 10.160.4 3.560.2 28.161.4
ME b (MJ)
10.760.4
13.260.1
10.760.5
12.060.04
n DM (g / kg)
a
A mix of barley (318 g / kg, oats (318 g / kg), rapeseed meal (180 g / kg), molassed sugar beet pulp (150 g / kg) and minerals and vitamins (34 g / kg). b ME is calculated according to MAFF (1975).
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weights before parturition and 1-week weights after parturition were used to compute growth curves using a cubic function on time for each animal. From the individual growth curves, initial and final weights in periods 1, 2, and lactation were predicted and used in the statistical analyses. Energy value of weight gain during pregnancy (EVg , MJ / kg) was calculated from the ME above maintenance and activity using the efficiency of utilization of ME for growth (k f 5 0.78q 1 0.006). Requirement of ME for maintenance and activity was calculated using equations proposed by AFRC (1993). One heifer on HM and one on HH treatment gave birth to a stillborn about 2.5 months before due date. Data from these two heifers were excluded. Feed intake, growth, and body measurement data of the heifers during gestation were analyzed using the GLM procedure (SAS , 1987). The full model was:
y ijklmn 5 m 1 P1 i 1 P2 j 1 (P1 3 P2 ) ij 1 Bk 1 Anrl
y ijk 5 m 1 P1 i 1 P2 j 1 (P1 3 P2) ij 1 Bk 1 e ijk ,
where P1 i and P2 j are as described in the previous model, b BWI is the linear effect of the pedigree index for BW (BWI k ). The BWI k was included only in the analysis of BW data. The relationship between production measurements and circulating mean plasma metabolite concentrations were described by Pearsons correlations calculated across individuals across treatments.
where P1 i is the fixed effect of plane of nutrition in period 1; P2 j the fixed effect of plane of nutrition in period 2; Bk is the fixed effect of block; terms P2 j and (P1 i 3P2 j ) were not included in the analyses of data from period 1. In period 2 data no interaction between periods 1 and 2 was found, therefore, only the main effects (P1 i and P2 j ) were considered. Production and feed intake data during lactation and also plasma parameters were analyzed as repeated measurements using the MIXED procedure (SAS , 1992). The variance component estimation method was REML and the type of covariance matrix was first-order autoregressive [AR(1)]. The model used for production and feed intake data was: y ijklmn 5 m 1 P1 i 1 P2 j 1 (P1 3 P2 ) ij 1 b I Ik 1 bA A l 1 Sijklm 1 T n 1 (T 3 P1 ) ni 1 (T 3 P2 ) nj 1 (T 3 P1 3 P2 ) nij 1 e ijklmn , where P1 i and P2 j are as described in the previous model, b I is the linear effect of pedigree index (Ik ) of the heifers appropriate for milk, fat%, protein%, or protein yield, bA is the linear effect of the age (A l ) at parturition, Sijklm is the random effect of the heifer, and T n the week of lactation. Prior to analyses, GH, PRL, and INS were transformed into natural logarithms to improve normality. The model used for plasma parameters was:
1 Sijklm 1 T n 1 (T 3 P1 ) ni 1 (T 3 P2 ) nj 1 (T 3 P1 3 P2 ) nij 1 e ijklmn , where P1 i , P2 j , Sijklm and T n are as described in the previous models, Anrl is the fixed effect of assay number. Anrl was included in the analyses of hormones. For plasma data no interactions were found. Therefore, only the main effects (P1 i , P2 j and T n ) were tested. The body weight change during lactation as well as energy and protein efficiency were analyzed from the combined data of each cow. The following model was used: y ijk 5 m 1 P1 i 1 P2 j 1 (P1 3 P2) ij 1 b BWI BWI k 1 e ijk ,
3. Results and discussion
3.1. Growth during pregnancy The effect of plane of nutrition on growth and feed intake of heifers during pregnancy is presented in Table 2. Average initial body weight of heifers was 356 kg. In period 1, the daily gain were 638 and 844 g for M and H, respectively. The M plane of nutrition in period 1 led to significantly higher growth of the heifers in period 2. Thus, in period 2 the daily gains of heifers were 710, 1042, 636 and 874 g on MM, MH, HM and HH treatments, respectively. Heifers on MH and HH treatments had almost equal BW at calving due to higher growth of the heifers in period 2 on treatment MH compared with heifers on treatment HH. The plane of nutrition in period 1 had no effect on final BW. Because of the compensatory growth in period 2, feed conversion (ME MJ / kg gain) was better (P,0.02) for heifers
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Table 2 Body weight, growth and feed intake of heifers during gestation (LS-means) Plane of nutrition a Period 1: Period 2:
M
503
Daily gain (g / day) Period 1 Period 2
710
ME (MJ / day) Period 1 Period 2 CP (kg / day) Period 1 Period 2
H
MM
Body weight (kg) Initial After 1st period After 2nd period
Feed intake DM (kg / day) Period 1 Period 2
SEM MH
HM
361 450 522
1042
636
638
5.87
60.8
89.3
Energy value of gain EVg c (MJ / kg) Period 1 Period 2
18.3
874
18.9 45.9
0.001 0.01
– 0.0001
0.058 0.024
0.0001 0.08
– 0.0001
0.67 1.04
0.0001 0.06
– 0.0001
0.008 0.013
0.0001 0.09
– 0.0001
99.4
2.58 7.32
0.02
26.2
0.66 1.87
0.0003 0.02
6.99
65.2
0.75
Feed conversion ME (MJ) / gain (kg) Period 1 Period 2
– – 0.0005
76.0 79.1
0.76
0.02
544
4.4 5.5 8.2
6.64 6.92
62.1
Period 2
844
5.48 5.60
Period 1 HH
351 470 545
80.0 0.91
0.93
0.80
96.8
0.94
90.9 79.0
107.7
20.9
22.4
22.0
Effect (P)b
25.7
–
– 0.10
a Plane of nutrition during gestation. M, medium feeding intensity; H, high feeding intensity; period 1, the first and second trimesters; period 2, the last trimester; n in period 1 is 20 animals / treatment while it is 10 animals / treatment in period 2. b P,0.1 is shown. c EVg 5[(ME intake2ME maintenance2ME activity)3k f ] / live weight gain. ME maintenance and activity calculated according to the AFRC (1993). k f 50.78q10.006.
fed M diet in period 1. The compensatory growth of pregnant heifers is reported also by Lacasse et al. (1993) when high feeding level followed moderate feeding level. In their study the experimental period was divided into two parts, from 12 months of age to 3 months of gestation and from 3 months of gestation to 2 weeks prepartum. The plane of nutrition prepartum had no effect on wither height or body length of the heifers at parturition (Table 3). In agreement, Lacasse et al. (1993) found no difference in wither height of the heifers reared by different planes of nutrition pre-
partum. The H feeding intensity in period 1 increased heart girth, hip width and BCS of the heifers at the end of period 1, but only the effect for BCS was significant. The final heart girth, hip width and BCS of the heifers were affected by the plane of nutrition in period 1 and 2 being the highest on HH and the lowest on MM treatment (Table 3). These results indicate that a high compared to moderate plane of nutrition during pregnancy had no effect on body size (wither height, body length) of primiparous cows. However, the high plane of nutrition especially during the first two trimester of pregnancy increased
¨ et al. / Livestock Production Science 62 (1999) 29 – 41 P. Mantysaari
34
Table 3 Body measurements of heifers during gestation (LS-means) Plane of nutrition a Period 1: Period 2: Heart girth (cm) Initial After 1st period After 2nd period Wither height (cm) Initial After 1st period After 2nd period Body length (cm) Initial After 1st period After 2nd period Hip width (cm) Initial After 1st period After 2nd period Body condition score c Initial After 1st period After 2nd period
SEM
M
H
MM
MH
HM
166 178 177
183
121 124 125
126
121 135 142
141
43.0 46.9 49.0
50.7
3.03 3.11 3.11
3.23
0.37 0.43 0.52
0.009
0.08
0.066 0.034 0.047
0.001 0.001
0.0002
125
141
0.9 1.1 1.0
51.4
3.09 3.28 3.27
0.05
0.8 0.6 0.9
43.4 47.7 50.2
0.04
185
120 134 143
Period 2
1.0 1.2 1.5
120 123 127
Period 1 HH
165 181 183
Effect (P)b
3.47
a
Plane of nutrition during gestation. M, medium feeding intensity; H, high feeding intensity; period 1, the first and second trimesters; period 2, the last trimester; n in period 1 is 20 animals / treatment while it is 10 animals / treatment in period 2. b P,0.1 is shown. c Body condition score measured from a scale 1–5 with interval 0.25 as described by Lowman et al. (1976).
the amount of body fat reserves as indicated by the calculated energy value of the weight gain (Table 2).
3.2. Milk production and composition A high plane of nutrition during the first two trimesters of pregnancy did not affect milk production. During the last trimester a high feeding intensity increased (P,0.004) milk yield and ECM yield by approximately 11% (Table 4, Fig. 1). Therefore, the results indicate that a high feeding intensity at late pregnancy is required to ensure the maximum milk production of primiparous cows. Foldager and Sejrsen (1991) reported an enhanced mammary development and increased milk production when prepartum daily gain increased from 400 to 600 g, but they found no benefits from increasing
daily gain to 800 g. In agreement with Foldager and Sejrsen (1991), Ducker et al. (1985), Lacasse et al. (1993), and Foldager and Ingvartsen (1995) found no improvement in milk production when heifers gained more than 600–700 g a day prepartum. Valentine et al. (1987) observed no difference in milk production in primiparous cows gaining 220, 590, or 1090 g / day during the last 4.5 months of gestation. Harrison et al. (1983), on the other hand, recorded an increased mammary development when the daily gain of heifers during pregnancy increased from 680 to 840 g. A comparison of the above studies is difficult, however, since the breed of the heifers and the duration of treatment periods vary. Furthermore, rearing during the prepubertal period varies among studies and sometimes also between animals within a study. This can disturb results
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35
Table 4 Production and feed intake of heifers during the 160-days lactation period (LS-means) Variable
Plane of nutrition a MM
Production Milk (kg / day) ECM d (kg / day) Milk fat (g / kg) Milk protein (g / kg) Milk lactose (g / kg) Feed intake DM (kg / day) ME (MJ / day) CP (kg / day) Feed conversion ECM / ME (MJ) Milk protein / CPI e
MH
SEM HM
HH
P1
20.4 22.4 4.64 3.47 4.99
22.8 25.3 4.69 3.45 5.13
20.2 22.4 4.64 3.54 5.06
22.3 24.5 4.77 3.35 5.10
0.71 0.63 0.064 0.065 0.044
15.6 176 2.29
16.2 183 2.37
15.1 171 2.23
14.9 168 2.20
0.22 2.5 0.031
0.127 0.31
0.139 0.33
0.132 0.32
0.145 0.33
Effect (P)b
0.0041 0.007
P2 0.004 0.0005
T 3P13P2 c
0.04 0.004 0.0001
0.05
0.0004 0.0005 0.0006
0.005 0.007
– –
a Plane of nutrition during gestation. M, medium feeding intensity; H, high feeding intensity; P1 (period 1), the first and second trimesters; P2 (period 2), the last trimester. b P,0.1 is shown c T, week of lactation. d ECM, energy corrected milk. e CPI, crude protein intake.
Fig. 1. Daily milk yield of primiparous cows fed a different feeding intensity during pregnancy (medium plane of nutrition during gestation (1), high plane of nutrition during gestation (j), medium plane of nutrition in period 1 (first two trimesters of gestation) and high plane of nutrition in period 2 (last trimester of gestation) (m), or high plane of nutrition in period 1 and medium plane of nutrition in period 2 (*)).
because prepubertal plane of nutrition can affect milk yield (Little and Kay, 1979; Ingvartsen et al., 1988; Foldager and Sejrsen, 1991). In the present study, the heifers were reared equally from birth to the beginning of the experiment to diminish the effect of prepubertal management. The prepartum plane of nutrition had no effect on mean milk fat or protein content during the experiment as such (Table 4). However, there was a significant interaction of treatment3time of lactation for milk fat and protein content. During the first weeks of lactation, the milk fat content on HH treatment was higher than on other treatments. This was assumed to be due to a larger body fat mobilization and, therefore, higher plasma FFA concentration of cows on HH treatment than on other treatments prepartum. In agreement with our results, Grummer et al. (1995) and Foot et al. (1963) reported a significantly higher milk fat percentage during the first weeks of lactation for primiparous cows fed a high plane of nutrition compared with a standard plane of nutrition prepartum. The prepartum plane of feeding does not usually affect milk protein content of primiparous cows
¨ et al. / Livestock Production Science 62 (1999) 29 – 41 P. Mantysaari
36
(Lacasse et al., 1993; Foldager and Ingvartsen, 1995; Grummer et al., 1995). However, in the present study, ignoring the first week of lactation, we observed a higher (P,0.04) protein content for heifers fed M plane of nutrition in period 2. The reason for this is unclear, but might be related to the negative correlation between milk production and milk protein content.
3.3. Calving body weight, mobilization of body fat and feed intake Feeding intensity in period 1 had no significant effect on BW at calving whereas a high plane of nutrition in period 2 increased it (Table 5). Milk yield was positively correlated with BW at calving (r50.33; P,0.05) as has also been seen in many previous studies (Ingvartsen et al., 1988; Foldager and Sejrsen, 1991; Hoffman and Funk, 1992). The cows on MH and HH feeding intensity prepartum had the same (498 and 499 kg) calving BW. However, the heifers on MH treatment were probably closer to their mature body size at calving than the heifers on HH treatment even if no significant differences in wither height or body length were measured. The background for this assumption was the expected difference in body content of the cows as indicated by the differences in energy value of weight gain (Table 2), BCS at calving (Table 3) and mobilized body reserves (MBR) during lactation (Table 5, Fig. 2). On day 160 of lactation cows on
Fig. 2. Postpartum body weight change of primiparous cows fed at different feeding intensity during pregnancy (medium plane of nutrition during gestation (1), high plane of nutrition during gestation (j), medium plane of nutrition in period 1 (first two trimesters of gestation) and high plane of nutrition in period 2 (last trimester of gestation) (m), or high plane of nutrition in period 1 and medium plane of nutrition in period 2 (*)).
MH treatment were 28 kg heavier than cows on HH treatment with no difference in BCS. The MBR was positively correlated with BCS at calving (r50.48; P,0.003). The cows on HH treatment prepartum mobilized more body weight during lactation than others and cows on MM treatment during pregnancy did not lose any body weight. Instead, their demand for energy for growth was high already from the beginning of lactation
Table 5 Body weight change of the cows during lactation period and body weight of their calves at birth (LS-means) Variable
BW at calving (kg) BW on day 160 of lactation Aver. gain (days 0–160) (kg / day) Total mobilization of BW in lactation (kg) Final BCS c a
Plane of nutrition a
SEM
MM
MH
HM
HH
462 513
498 520
480 505
499 492
Effect (P)b P1
8.1 12.1
P2 0.003
0.31
0.12
0.15
20.04
0.050
0.003
0.0008
0.0 3.20
11.6 2.92
10.1 3.03
28.4 2.83
3.54 0.124
0.0006
0.0002 0.06
Plane of nutrition during gestation. M, medium feeding intensity; H, high feeding intensity. P1 (period 1), the first and second trimesters; P2 (period 2), the last trimester. b P,0.1 is shown. c BCS, body condition score on day 160 of lactation.
¨ et al. / Livestock Production Science 62 (1999) 29 – 41 P. Mantysaari
37
for total DMI was measured (Table 4) and no correlation between BCS at calving and DMI postpartum was measured (r5 20.005; P,0.97). However, the HH cows had lower concentrate intake during the first 5 weeks of lactation (5.39 vs. 6.11 kg DM / day; P,0.03) than the cows on other treatments.
3.4. Plasma concentration of hormones and metabolites
Fig. 3. Postpartum daily dry matter intake of primiparous cows fed at different feeding intensity during pregnancy (medium plane of nutrition during gestation (1), high plane of nutrition during gestation (j), medium plane of nutrition in period 1 (first two trimesters of gestation) and high plane of nutrition in period 2 (last trimester of gestation) (m), or high plane of nutrition in period 1 and medium plane of nutrition in period 2 (*)).
(Figs. 2 and 3). Thus, the low milk yields of MM cows are, at least in part, explained by the lack of body energy reserves to support the production in early lactation. The heifers on medium feeding intensity during period 1 had a higher postpartum DMI. On both treatments MM and MH the initial DMI was equal. After week 8 of lactation the increase in DMI of the cows fed MM diet prepartum decrease compared to cows on MH diet (Fig. 3). This is mostly explained by two cases of ketosis on MM treatment. The feeding intensity in period 2 had no significant effect on postpartum DMI (Table 4). This is in agreement with Foldager and Ingvartsen (1995) who measured no change in postpartum DMI due to increase in feeding intensity in weeks 6 or 12 prepartum. But when the feeding intensity was high throughout the last 24 weeks before calving, DMI decreased dramatically. The heifers with high feeding intensity throughout the last 24 weeks prepartum were fat at calving. Based on their review, Ingvartsen et al. (1995a) suggested that the high prepartum feeding and high BCS at calving will cause lower initial and delayed maximum feed intake. In our study no significant interaction of treatment3time of lactation
Plasma glucose and BHBA concentrations during lactation and plasma FFA and hormone concentrations pre- and postpartum are given in Figs. 4 and 5. The feeding intensity prepartum had no significant effect on plasma FFA concentrations from day 35 prepartum to calving. A high feeding intensity in periods 1 and 2 increased the plasma concentration of BHBA (period 1, P,0.003; period 2, P,0.01) and FFA (period 1, P,0.0001; period 2, P,0.02) during early lactation. The effect of period 1 was higher than the effect of period 2. Thus, the concentrations of BHBA and FFA were directly correlated with the duration of high feeding intensity during gestation. The correlations of BHBA and FFA with BCS (r50.41 and r50.62; P,0.02) and MBR (r50.69 and r50.73; P,0.0001) were positive. Thus, especially FFA, but also BHBA plasma concentrations were indicating the degree of utilization of body fat reserves. The prepartum treatments had no significant effects on postpartum plasma glucose which is in accordance with Ingvartsen et al. (1995b). The feeding intensity during gestation had no effect on the prepartum plasma PRL concentration or periparturient surge of PRL (P,0.09). Lacasse et al. (1994) measured an increased prepartum PRL concentration with the H plane of nutrition. They speculated that the increase in PRL was associated with an increased lipogenesis in heifers. In the present study prepartum PRL was not correlated with BCS at calving (r50.02, P,0.90) or MBR during lactation (r50.13, P,0.44). A high feeding intensity during the last trimester of gestation increased significantly (P,0.0001) the prepartum plasma INS concentration, but decreased (P,0.006) it during lactation. The postpartum INS was highly correlated with the plasma concentration of FFA (r5 20.54,
38
¨ et al. / Livestock Production Science 62 (1999) 29 – 41 P. Mantysaari
Fig. 4. Plasma FFA (a), BHBA (b) and glucose (c) concentration of primiparous cows fed at different feeding intensity during pregnancy (medium plane of nutrition during gestation (1), high plane of nutrition during gestation (j), medium plane of nutrition in period 1 (first two trimesters of gestation) and high plane of nutrition in period 2 (last trimester of gestation) (m), or high plane of nutrition in period 1 and medium plane of nutrition in period 2 (*)).
Fig. 5. Plasma growth hormone (a), prolactin (b) and insulin (c) concentrations of primiparous cows fed at different intensity during pregnancy (medium plane of nutrition during gestation (1), high plane of nutrition during gestation (j), medium plane of nutrition in period 1 (first two trimesters of gestation) and high plane of nutrition in period 2 (last trimester of gestation) (m), or high plane of nutrition in period 1 and medium plane of nutrition in period 2 (*)).
¨ et al. / Livestock Production Science 62 (1999) 29 – 41 P. Mantysaari
P,0.0006), BHBA (r5 20.44, P,0.007) and glucose (r50.56, P,0.0004). In agreement with Lacasse et al. (1994) the prepartum plasma concentration of GH was decreased by H plane of nutrition (P, 0.0001). In contrast to our findings, Ingvartsen et al. (1995b) measured no difference in the plasma GH concentration between heifers fed a high or a medium plane of nutrition during late pregnancy. In our study, the prepartum treatments had no effect on postpartum plasma GH concentrations which is in agreement with findings by Lacasse et al. (1994) and Ingvartsen et al. (1995b). The GH, INS and PRL have a mammogenic effect during gestation (Forsyth, 1971; Akers et al., 1981; Stelwagen et al., 1993). Stelwagen et al. (1992) measured an increased milk production with an injection of bGH during the last trimester of gestation. Based on their study with ewes, they proposed that improved milk yields with prepartum bGH injections are due to an increased number of mammary cells (Stelwagen et al., 1993). In the present study, the prepartum GH concentration was not related to milk yield (Table 6). Furthermore, neither the prepartum INS nor PRL concentration was correlated with milk production (Table 6). Therefore, it seems unlikely that the increased milk with high feeding intensity in period 2 should be related to changes in prepartum mammary development due to endocrine (GH, INS, PRL) factors. More likely, the higher production was due to differences in physiological status (calving BW, body reserves) of the heifers at calving. The correlations between postpartum hormone concentrations and milk production calculated across treatments are listed in Table 6. The postpartum PRL concentration was not related to milk production as was shown by Lacasse et al. (1994). The correlations
39
between milk yield and postpartum plasma concentration of GH, INS and GH / INS were 0.35 (P, 0.04), 20.51 (P,0.002), and 0.51 (P,0.002), respectively. This indicates the galactopoietic effect of GH and the lipogenic effect of INS. The postpartum ratio of GH to INS was significantly increased (P,0.05) by a high feeding intensity in period 2, which partly explains the increased partitioning of nutrients towards the mammary gland in treatments MH and HH.
4. Conclusions The feeding intensity from 2 to 6 months of gestation (period 1) had no effect on milk production ability of primiparous cows, but a high feeding intensity during the last trimester (period 2) increased milk yields. The BW change during lactation differed markedly between treatments. The mobilization of body reserves correlated with BCS at calving, and was the highest on the HH treatment. A high feeding intensity in period 2 increased the INS and decreased the GH prepartum plasma concentration. The postpartum plasma GH concentration was not affected by the prepartum feeding intensity, but a high feeding intensity in period 2 decreased the postpartum INS concentration and, consequently, increased the GH / INS level. No significant correlations between prepartum hormone concentrations and milk yield were found. The increased milk yields of the cows fed a high feeding intensity during the last trimester of gestation are believed primarily to be due to the differences in physiological status (calving BW, body fat reserves) of the heifers at calving. The postpartum plasma levels of the GH and the GH / INS were positively correlated with the milk yield. It can
Table 6 Correlations between plasma growth hormone (GH), insulin (INS) and prolactin (PRL) concentrations pre- and postpartum and milk production Hormone
GH INS PRL GH / INS
Prepartum hormone concentration3 Milk yield
Postpartum hormone concentration3 Milk yield
r
P
r
P
0.10 20.07 20.07 0.01
0.56 0.69 0.69 0.95
0.35 20.51 20.05 0.51
0.04 0.002 0.79 0.002
40
¨ et al. / Livestock Production Science 62 (1999) 29 – 41 P. Mantysaari
be concluded that a high feeding intensity during the first 6 months of gestation does not improve the performance of primiparous Ayrshire cows reared to gain 650 g / day prior to breeding. Instead, during the last trimester of gestation a high plane of nutrition is required for optimum performance.
Acknowledgements GH and PRL antigens, standards and antibodies were kindly donated by USDA Animal Hormone Program, the National Hormone and Pituitary Program, the National Institute of Diabetes and Digestive and Kidney Diseases, the National Institute of Child Health and Human Development, US Department of Agriculture and Dr A.F. Parlow from the Harbor-UCLA Medical Center. Dr J. Proudman (USDA) and Dr A.F. Parlow are acknowledged for instructions concerning GH and PRL radioimmunoassays. This study is financially supported by Academy of Finland.
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