Effects of recombinant bovine somatotropin
administration to lactating goats
S.E. Chadio
*, G. Zervas, K. Kiriakou, C. Goulas, J. Menegatos
Agricultural University of Athens, Laboratory of Anatomy and Physiology of Domestic Animals, Department of Animal Science, 75 Iera odos, 11855 Athens, Greece
Accepted 15 July 1999
Abstract
Eight multiparus lactating goats, matched for parity and days in milk were used to evaluate the effects of recombinant bovine somatotropin (rbST) administration on milk yield and composition, as well as on certain metabolic parameters. The experiment was a switch-back design, with three periods lasting 28 days each. Animals were divided into two groups (n4) and treatments consisted of subcutaneous injection of 160 mg rbST at 14-day intervals. Controls remained uninjected. Supplementation with rbST increased milk yield signi®cantly over the entire experimental period (150680.8 vs.
133781.8 ml/day,p< 0.05). Percentage of fat in milk was greater for goats treated with rbST than controls, (3.260.09% vs. 2.90.08%,p< 0.05), while protein percentage did not differ (p> 0.05) between treated and control animals. Lactose content also increased after rbST administration (3.880.06% vs. 3.550.06%, p< 0.01). Plasma NEFA and b -hydroxybutyrate levels were not affected by treatment. Short-chain fatty acids in milk were similar in both groups. In conclusion, rbST administration increased milk yield and the percentage of fat and lactose in milk, while no effect was recorded in milk protein content.#2000 Elsevier Science B.V. All rights reserved.
Keywords:Somatotropin; Goat; Milk; Metabolism
1. Introduction
The ability of growth hormone (GH) to increase milk yield in lactating ruminants has been well estab-lished. The extensive work concerning the galacto-poietic properties of pituitary derived or recombinant bovine somatotropin has detailed the effects in cows, where milk yield increases 20% or more (Bauman et al., 1985). Similar results have been reported for
ewes and goats, but a less consistent response in terms of milk yield has been noticed in these species (Mephan et al., 1984; Nielsen, 1988; Davis et al., 1989; Stelwagen et al., 1993; Fernandez et al., 1995). Recombinant bovine somatotropin (rbST) has been shown to be biologically active in sheep (Bauman, 1992). In goats, studies with rbST are limited and only few have examined the effects on milk composition and plasma metabolites (Knight et al., 1990; Prosser et al., 1991; Disenhaus et al., 1995).
In Greece, goat husbandry is a traditional enterprise of major agricultural economic importance in many parts of the country, as the 6 million dairy goats
*Corresponding author. Tel.: 301-5294428; fax: 301-5294388.
E-mail address: [email protected] (S.E. Chadio).
represent the 2.2% and 6% of the world goat meat and milk production, respectively. These ®gures show that in a great number of goat farms in Greece the income from milk is signi®cant, and thus emphasis is placed towards increasing milk yield through genetic, nutri-tional and biotechnological manipulation.
Therefore, the aim of the present study was to evaluate the effects of exogenous rbST in a sustained release formulation over a prolonged period of time, on milk yield and composition and on certain blood parameters in lactating goats.
2. Materials and methods
2.1. Animals and treatment
Eight multiparus crossbred Alpine goats, matched for parity and days in milk were used. The trial started at the 8th week of lactation, after a 2-week adjustment period. Animals were divided into two groups: treated (n4) and control (n4). Treatments were admi-nistered according to a switch-back experimental design with three 28-day periods. Treated goats were injected subcutaneously with 160 mg of a sustained-release formulation of rbST (Somidobove, Elli Lilly, Elanco), twice during a 28-day period at 14-day intervals, while controls remained uninjected. Goats were fed 1 kg alfalfa hay per day with concentrate and water available ad libitum. The composition of the concentrate diet (g kgÿ1
), which was given in a mass form, was the following: maize, 340; barley, 380; Soybean meal, 150; wheat middling, 110; calcium phosphate, 15; common salt, 3; trace minerals and vitamins premix, 2. Feed refusals were removed and weighed daily. Goats were individually fed and hand-milked twice a day.
2.2. Sampling and analysis
Feed intake was recorded daily. Feed samples were collected every 28 days and analyzed for DM, organic matter (OM), CP, EE, crude ®ber (CF), nitrogen free extracts (NFE) and ash, according to the Weende procedure. Goats were weighed at the beginning and end of each 28-day period. Milk yield was recorded weekly during three consecutive days
throughout the experimental period, and samples were taken for each morning and afternoon milking to form weekly composites (5%). They were analyzed for fat, protein and lactose by IR spectrometry (Milkoscan 133/; Foss Electric, Hillerod, Denmark), after appro-priate calibration of the instrument according to Ger-ber (British Standards Institution, 1955), Kjeldahl (International Dairy Federation, 1993) and Chlora-mine-T methods (International Dairy Federation, 1964). Somatic cell counts (SCC) were determined by Somacount 150 (Bentley). Milk fatty acids were determined following preparation of fatty acid methyl-esters according to the of®cial method of the E.E.C. (1977), and analyzed by chromatography. Brie¯y, the column used was 2 m long and 3.2 mm i.d., packed with W.H.P Chromosorb 10% EGSS-X. Oven tem-perature was raised from 908C to 1908C at a rate of 48C/min and carrier gas (nitrogen) ¯ow rate was 30 ml minÿ1
.
Blood samples were collected in heparinized tubes twice a week by jugular venepuncture. Samples were centrifuged at 2000 rpm and plasma was assayed for non-esteri®ed fatty acids (NEFA) according to the method described by Duncombe (1962), and for b -hydroxybutyrate by an enzymatic method, using a commercial kit (Sigma). One goat suffered an intra-mammary infection during the last part of the experi-ment and data from this animal were excluded from subsequent analysis.
Analysis of data was performed according to the statistical procedure described by Lucas (1956) for switch-back trials for more than two treatments.
Values represent meanSEM.
3. Results and discussion
3.1. Feed intake and milk yield
The pattern of milk yield is illustrated in Fig. 2. Milk yield increased immediately after rbST admin-istration and remained high, relative to the control group, throughout the trial. Milk yield during the second 28-day period was signi®cantly greater (40%;p< 0.01) compared to the control group. The average yield of milk during the ®rst (7.2% higher than the control group) and the third period (20.2% higher than the control group) was greater (p< 0.01) for rbST-treated goats. The administration of rbST increased milk yield by 12.6% for the entire experi-mental period (150680.8 vs. 133781.8 ml/day, meanSEM;p< 0.05).
The milk yield increase in the present study was within the range observed in previous studies with sheep and goats (Davis et al., 1989; Knight et al.,
1990). However, Fernandez et al. (1995) using the same dose of rbST in ewes, observed a more pro-nounced increase in milk yield, although in that study supplementation with rbST started at the 3rd week of lactation. A greater milk yield response (28.6%) than that observed in the present study was also reported for goats injected daily with 5 mg of rbST for 4 weeks (Disenhaus et al., 1995). It should be noticed, however, that during the second 28-day per-iod of the present study (12±15th week of lactation), the improvement in milk yield was 40%. Moreover, in another study, in which animals received the same formulation for the same time, but at a lower dose (90 mg at 4-week intervals) an increase of 13.9% in milk yield was recorded (Gallo et al., 1997). Finally, the results of the present study in terms of milk yield
Table 1
Chemical composition of diet components (% of DM)
Ingredient DM Ash CP EE CF NFE OM
Alfalfa hay 91.4 8.6 13.5 1.0 28.1 40.1 82.8
Concentrate 88.9 8.4 14.1 1.7 7.2 57.6 80.5
are in agreement with the ®ndings of Chiofalo et al. (1998), who also observed enhanced milk yield in sheep given the same release formulation of rbST.
3.2. Milk composition
Administration of rbST increased milk fat percen-tage throughout the experiment (3.260.09% vs. 2.90.08%,p< 0.05; Table 2).
Considering the entire treatment period, milk fat composition was not affected (p> 0.05) by treatment (Table 3). However, an increase in short chain fatty acids was evident, indicating probably an enhanced de novo synthesis in these animals.
An increase in milk fat content was also observed in rbST-treated ewes (Fernandez et al., 1995), but only after the ®rst rbST injection. In contrast, Knight et al. (1990) and Stelwagen et al. (1993) working with goats
Fig. 2. Milk yield (ml/day) of rbST-treated and control goats over the entire experimental period (12 weeks).
Table 2
Milk yield, fat corrected milk (FCM), milk composition and plasma metabolites (meanSEM) for treated and control goats over the entire experimental period (12 weeks)
Item Control Treated plevel
Milk yield (ml/day) 13378I.8 150680.8 p< 0.05
FCM (ml/day) 127478 142778 p<0.05
Milk fat (%) 2.90.08 3.260.09 p< 0.05
Milk protein (%) 3.430.08 3.570.08 p> 0.05
Milk lactose (%) 3.550.06 3.880.06 p< 0.01
Plasma NEFA (mequ mlÿ1) 0.0820.07 0.1020.07 p> 0.05
Plasma-HBA (mg/dl) 0.5540.04 0.6940.03 p> 0.05
and sheep, respectively, did not detect any change in milk fat percentage after treatment with rbST. An increase in milk fat content has been reported in rbST-treated cows (Bitman et al., 1984), which was attributed to an increase in long-chain fatty acids from body reserves, mobilized when cows were in negative energy balance. Disenhaus et al. (1995) observed an increase in short and medium chain fatty acids in the milk of lactating goats, particularly 2 weeks after rbST administration. In the present study feed intake was not affected, which suggests that an enhanced avail-ability of precursors of de novo synthesis of milk fat occurred, which may be related to the inhibition of insulin action on adipose tissue (Etherton et al., 1987) and to a decreased rate of lipogenesis in adipose tissue (Sechen et al., 1989).
It has been shown that GH increases cardiac output and mammary blood ¯ow, which results in more nutrients for milk synthesis (Davis et al., 1988). Increased mammary blood ¯ow has also been reported for goats after treatment with GH (Mephan et al., 1984). In the present study, the effect of rbST on milk fat content probably re¯ected an increased supply of FFA to the gland, consistent with increased mammary blood ¯ow.
Lactose content increased during the entire experi-mental period (3.880.06% vs. 3.550.06%,
p< 0.01; Table 2). This increase was most likely
due to increased glucose transport into mammary cells, related to the diabetogenic properties of GH (Hart, 1983). This ®nding is in agreement with pre-vious observations on cows (Davis et al., 1988). However, in other studies with ewes and goats, milk lactose content did not differ between GH-treated and control animals (Hart et al., 1985), but data of Stelwa-gen et al. (1993) indicate that total yield of this component increased in the treated animals. When lactose was expressed as gram per day, an increase of 15.7% was also noticed in the present study, which re¯ects the higher milk production of treated animals.
Percentage of protein in milk did not differ between treated and control goats (3.570.08% vs. 3.430.08%, p> 0.05; Table 2). The effects of GH on milk protein are quite con¯icting. Results range from no-change to decrease, or increase of protein content. It has been suggested (Peel et al., 1983; Bines et al., 1980) that GH-stimulated changes in milk composition may vary with animal's energy status, such that milk fat and protein percentage are increased and decreased respectively when animals are in negative energy and nitrogen balance, but remain relatively unchanged when they are in positive balance. The energy status of goats was not accurately determined during this experiment. However, plasma levels of NEFA as well as the body condition, recorded
Table 3
Milk fatty acid concentration (meanSEM; g/100g) in control and treated animalsa
Control SEM Treated SEM
according to Russel et al. (1969) remained unaffected, which suggests that goats were not in energy de®cit. SCC tended to be higher in treated than in control animals, although this difference failed to reach sig-ni®cance (1701176 vs. 1304166n103mlÿ1
,
p> 0.05; Table 2). These results are in agreement with studies both in cows and sheep, where the adminis-tration of GH has not altered the number of somatic cells in milk of treated animals (McGuffey et al., 1990; Chiofalo et al., 1998).
3.3. Blood parameters
Plasma concentration of b-hydroxybutyrate acid was not altered after rbST administration (Table 2), which was also observed in the study of Disenhaus et al. (1995). These authors suggested that this meta-bolite might be used preferentially for mammary lipogenesis, indicating a good adaptation to elevated demand. The same seems to be the case in the present study.
Plasma NEFA levels did not differ (p> 0.05) between treated and control animals (Table 2). These results are in agreement with previous data on cows (Bitman et al., 1984), where GH treatment did not change arterial and lipids in plasma, but increased mammary triglyceride uptake and the supply of FFA to the gland, which is consistent with increased mam-mary blood ¯ow.
In conclusion this study reaf®rm that rbST in a sustained release formulation increases milk yield of goats, accompanied by an increase in percentages of fat and lactose in milk.
Acknowledgements
The authors wish to thank Dr. M. Maliapis for his assistance with the statistical analysis of the results. Recombinant bST was kindly donated by Elli Lilly, Elanco, Wien.
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