Roczniki Naukowe Polskiego Towarzystwa Zootechnicznego, t. 6 (2010), nr 1

Changes in melatonin, prolactinand growth hormone concentrationsin Olkuska sheep, Polish Mountain Sheepand their crosses during lactation

Edyta MolikI, Tomasz Misztal2,Katarzyna Romanowicz/, Maciej Murawski l

'University of Agriculture in Kraków, Department of Pig and Smali Ruminant Breeding,Laboratory of Biotechnology and Genomics,al. Mickiewicza 24/28,30-059 Kraków, Poland; email: rzmolik@cyf-kr.edu.pl2rhe Kielanowski Institute of AnimaI Physiology and Nutrition, Polish Academy of Sciences,lnstytucka 3,05-110 Jabłonna, Poland

An important element of improving sheep produetion profitability in mountain areas is toinerease efficieney by improving prolifieaey and milk yield of mountain sheep. These para-meters ean be improved using the indigenous breed of prolifie Olkuska sheep. The study wasearried out with 90 laetating sheep. Lambs we re reared with mothers until 56 days when theywere weaned and the mothers were assigned for milking. Sheep were milked twiee daily fromMay to the end of August using an Alfa Laval Agri milking maehine. Eaeh animai wasreeorded for milk yield at 10-day intervals. During the experiment blood was drawn from 6sheep of eaeh breed group. Blood was colleeted from sunset over a period of 6 hours at60-minute intervals. Colleeted blood was eentrifuged and the plasma obtained was sto red at-20°C until analysis. Melatonin, prolaetin and growth hormone eoneentrations were deter-mined by radioimmunoassay at the Institute of Animai Physiology and Nutrition of the PolishAeademy of Scienees in Jabłonna. The study revealed a 15% inerease in milk yield in FIcrosses. Analysis of changes in the hormone profile showed that as laetation progressed,prolaetin level deereased and growth hormone and melatonin eoneentrations inereased.

KEY WORDS: sheep / melatonin / prolaetin / growth hormone /Iaetation

Because harsh climatic and soi! conditions of the PoIish mountains make it impo-ssible to keep high-producing animals, the mountain landscape has for centuries beendominated by PoIish Mountain Sheep. Pastoralism in the Carpathian Mountains isevidence that the region's traditions and customs have been maintained, which enabledthe region to preserve its identity on a European scale [14]. The change of productive

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Materiał and methods

orientation from wool to dairy and the increased interest in sheeps milk products offera real chance to make the breeding of these ruminants more profitable. An importantelement of improving sheep production profitability in the mountain areas is to increaseefficiency by improving prolificacy and milk yield of mountain sheep. These twoparameters can be improved using the indigenous breed of Olkuska sheep [1, 3,16].

Until today, it was believed that the level of milk production in mammals isdetermined by genetic and environmental factors; however, Iight has recently be enshown to modulate prolactin levels (PRL). Molik et al. [15] demonstrated that in sheepenter ing lactation under different day Iengths, the concentration of hormones respon-sible for the initiation and maintenance of lactation depended on photoperiod, andsynthesis of the hormone melatonin was determined by day length. Like in othermarnmals, melatonin in sheep is synthesized at night. Because secretory activity of thepineal gland is lower during the day, the highest concentration of melatonin, known asthe darkness horrnone, is observed during the night [10, 19,20].

The endocrine mechanism controlling initiation and maintenance of lactation insheep is not fully understood, but it is known that it requires the action of manyhormones [7, 9, 18]. One of these horrnones, which determines both the initiation andmaintenance of lactation, is prolactin. According to Misztal et al. [12, 13], the highestprolactin concentration in sheep blood occurs during lon g days and is the lowest duringdecreasing photoperiod, when melatonin concentration is the highest. Seasonal changesin prolactin and growth hormone (GR) secretion during lactation have a definite effecton the amount of milk produced. Therefore, the aim of this study was to characterizethe profile of melatonin, prolactin and growth harmone in lactating Olkuska sheep,Polish Mountain Sheep and their crosses.

The study was carried out with 90 sheep, i.e. Olkuska sheep (n=30), Polish Moun-tai n Sheep (n=30) and their FI crosses (n=30). Ali sheep groups were mated between15 and 30 September and lambed in the second half of February. To deterrnine milkproduction parameters of the sheep based on weight gains of lambs, they were weighedat 2 and 28 days of age in the first period of lactation. Milk production of the ewes wasthen calculated using a conversion factor of 4.5 kg milk = 1 kg weight gain of the lamb.Lambs were reared with mothers until 56 days when they were weaned and the motherswere assigned for milking. Sheep were milked twice daily from May to the end ofAugust using an Alfa Laval Agri milking machine. Each animaI was recorded for milkyield at lO-day intervals using specially constructed containers, which enabled milkyield to be estimated for the whole milking period. During the study, the sheep werefed conventionally according to standards [17].

During the experiment, blood was drawn from 6 sheep of each group. Blood wascollected since sunset over a period of 6 hours at 60-minute intervals. The collectedblood was centrifuged and the plasma obtained was stored at -20°C until analysis.Melatonin, prolactin and growth hormone concentrations were determined by radio im-

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munoassay (RIA) at the Institute of Animai Physiology and Nutrition of the PolishAcademy of Sciences in Jabłonna. Melatonin concentration was determined in 500 ulof whole plasma using the method described by Fraser et al. [8] and modified by Misztalet al. [12]. Plasma prolactin was determined at the Department of Endocrinology of theInstitute of AnimaI Physiology and Nutrition of the Polish Academy of Sciences inJabłonna using the RIA method described by Kokot and Stupnicki [11]. Growth hor-mone was determined as described by Dvorak et a\. [5]. The results obtained as arith-metic means ± standard deviation were analysed statistically by SAS software usingone-way analysis of variance and Scheffes test.

Results and discussion

When analyzing lactation profile of the ewes based on test-day yields, it was foundthat mean daily milk yield in May was the highest in Olkuska sheep (0.63 ±0.02 l),followed by Polish Mountain Sheep (0.4 ±0.04 l) and FI crosses (0.38 ±0.01 l), withstatistically significant differences (P=:;0.0l) (Figure l). Also in June and July, thehighest milk yield was found in Olkuska sheep (0.57 ±0.03 I and 0.36 ±0.01 l, respec-tively) and significantly (P=:;O.Ol) the lowest in Polish Mountain Sheep (0.32 ± 0.02 I and0.23 ±0.06 l, respectively). As lactation progressed and day length shortened, the milk

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Fig, l. Changes in milk yield of Olkuska sheep, Polish Mountain Sheep and their crossesRys, l. Zmiany wydajności mlecznej u polskich owiec górskich, owiec olkuskich i ich mieszańców

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yield decreased in all the groups studied. The results obtained showed that during themil king period, Olkuska sheep were characterized by the highest milk yield (47.0 ± 8.7 l),which was significantly (P:S:O.Ol)higher than in FI crosses (31.2 ±7.6 l). The Iowestmilk production was found in Polish Mountain Sheep, which produced just 27.1 ± 5.9 lduring the whole milking period, with significant differences (P:S:O.O1). Such differentmilk production levels could be due to differences in the concentration of lactotropichormones, especially proIactin and growth hormone, whose profile is modulated bychan ges in day length.

The present study showed that during the long photoperiod (May), meIatonin eon-centration in all the groups was the lowest (Fig. 2). In the second month of milking(June), the highest melatonin leveI was found in FI crosses (114.6 ±9.4 pg ml) folIowedby Olkuska sheep (70.9 ±5.04 pg/ml) and Polish Mountain Sheep (54.3 ±4.1 pg/ml),with statistically significant differences (P:S:0.05). As lactation proceeded and dark phaseincreased with decreasing day length, melatonin concentration increased. In the lastmonth of milking (August), melatonin level was the highest in FI crosses (129.4 ±9.3pg/ml), Iower in Olkuska sheep (81.8 ±9.9 pg/ml) and the lowest in Polish MountainSheep (77.7 ± 6.6 pg/ml), with significant differences (P:S:0.05).

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Fig. 2. Changes in melatonin concentrations in Olkuska sheep, Polish Mountain Sheep and their crossesRys 2. Zmiany stężenia melatoniny u owiec olkuskich, polskich owiec górskich i ich mieszańców

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The results obtained for changes in PRL concentration in lactating sheep showedthat during the first collection in May, the highest prolactin level was found in PolishMountain Sheep (212.8 ±6.6 ng/ml), folIowed by Olkuska sheep (200.3 ±5.6 ng/ml)and FI crosses (199.2 ±6.9 ng/ml) (Figure 3). In the second month of milking (June),prolactin concentration increased in all sheep groups studied. The highest level wasfound in FI cross es (314.1 ±7.9 ng/ml) folIowed by Polish Mountain Sheep (306.8 ±3.2 ng/ml) and Olkuska sheep (274.1 ±9.04 ng/ml). In July, the highest PRL level wascharacteristic of Polish Mountain Sheep (258.4 ±5.7 ng/ml), folIowed by FI cross es(252.6 ±7.3 ng/ml) and Olkuska sheep (235.2 ±9.3 ng/ml). In August, with advancinglactation, prolactin level was the highest in Polish Mountain Sheep (128.4 ±3.7 ng/ml),significantly lower in FI crosses (94.4 ±6.2 ng/ml), and the lowest in Olkuska sheep(65.7 ±3.7 ng/ml), with significant differences (P::;O.Ol).

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Fig. 3. Changes in prolactin concentrations in Olkuska sheep, Polish Mountain Sheep and their crossesRys 3. Zmiany stężenia prolaktyny u owiec olkuskich, polskich owiec górskich i ich mieszańców

At the first sampling in May, the highest growth hormone (GH) concentration wascharacteristic of FI crosses (7.54 ±3.2 ng/ml) and the lowest of Olkuska sheep (4.3 ±1.5 ng/ml); the differences were statistically significant at P::;O.OI (Figure 4). In PolishMountain Sheep, GH concentration in May was 6.9 ±2.3 ng/ml with significant(P::;O.Ol) differences in relation to GH concentration in Olkuska sheep. In June, GHconcentration was the lowest in Olkuska sheep (4.95 ± 1.2 ng/ml) and significantly

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higher in FI crosses (6.38 ± 1.7 ng/ml) and in Polish Mountain Sheep (5.85 ± 1.3 ng/ml),with significant differences (P~O.Ol). In July, GH levels in the sheep groups studieddecreased considerably; the highest GH concentration was found in Polish MountainSheep (5.5 ±2.4 ng/ml) and the lowest in Olkuska sheep (3.5 ± 1.3 ng/ml). In FI crosses,GH concentration was 4.69 ± 1.9 ng/ml with significant differences (P~O.Ol). Duringthe last month of milking, the highest GH concentration was found in Polish MountainSheep (7.54 ±2.4 ng/ml), lower in FI erosses (6.61 ±2.9 ng/ml) and the lowest inOlkuska sheep (5.0 ±2.4 ng/ml), with signifieant differenees (P~O.Ol).

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Fig. 4. Changes in growth hormone concentrations in Olkuska sheep, Polish Mountain Sheep and theircrossesRys 4. Zmiany stężenia hormonu wzrostu u owiec olkuskich, polskich owiec górskich i ich mieszańców

The present study demonstrated that Olkuska sheep were charaeterized by thehighest milk produetion and FI erosses had higher milk yield than Polish MountainSheep. The use of Olkuska ram s in the eommereial erossing with Polish Mountain Sheepwas found to improve the milk produetion parameters of FI ewes and enabled them tobe used in mountain and submontane regions. Likewise, Ciuruś [2] and Drożdż [4]showed that the use of prolifie breeds (East Friesian rams) in single-stage erossingimproves the produetive parameters of mountain sheep. Recent researeh has shown thatmilk produetion in sheep is determined also by photoperiod length [15]. The melatoninseeretion profile observed in our study had the eharacteristies of the annual rhythmdeseribed by Misztal et al. [12]. During the long photoperiod, melatonin eoneentrationdeereased while prolaetin seeretion and milk yield inereased. During deereasing photo-

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period, the increase in melatonin concentration reduced the level of prolactin, whichcontributed to a decrease in the milk yield of the sheep gro up investigated.

One of the main hormones responsible for the initiation and maintenance of lacta-tion is prolactin, but an equally important role in this process is played by the growthhormone (GR). Until now, research on the role of GR in regulating prolactin secretionand, indirectly, milk yield has been focused on cattle. According to Etherton et al. [6],the growth hormone has an effect on milk yield and chemical composition in ruminants.In seasonal sheep, the role of growth hormone in regulating lactation is not entirelyunderstood. However, the present study showed that growth hormone concentrationdepended on day length. When comparing changes in the concentration of growthhormone and prolactin in different months, it was found that during the long photope-riod, when sheep had a high milk yield, the level of prolactin increased while the growthhormone concentration decreased. During decreasing photoperiod, when milk yield ofsheep decreased, prolactin concentration also decreased while growth hormone concen-tration increased. Due to their low reproductive parameters and level of milk production,Polish Mountain Sheep have been the subject of discussion and research aimed atimproving their productive traits. However, when analyzing the present findings, theaccount must be taken of the profile of lactotropic hormon es in this breed. During theperiod between May and July, there were no significant differences in prolactin eon-centration in the analysed groups of sheep and milk yield was significantly lower inPolish Mountain Sheep. Our findings lead us to conclude that responsible and conscien-tious breeding mayaIso improve productive traits because the profile of lactotropichormones (PRL, GR) suggests that Polish Mountain Sheep have a potential to increasemilk production.

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