Oxytocin release and milk ejection parameters during milking of dairy ewes in and out of natural season of lactation

Oxytocin and cortisol release during suckling, hand-milking and machine milking in camels

This research paper addresses the hypothesis that oxytocin (OT) could be released during suckling and during milking with and without the presence of a calf and that this release could be regulated by maternal behaviour. Plasma concentration patterns of OT and cortisol (CORT) were measured in six Tunisian dromedary camels during 2 suckling episodes, 2 manual milking episodes with calves beside the mother and 2 machine milking episodes without calves present. Various patterns of OT release were observed between each camel including specific two peak release patterns. Higher plasma OT concentrations were found during the suckling and hand-milking episodes with simultaneous suckling of calves, than during the machine milking episodes without calves. Exclusive mechanical milking episodes also evoked significant mean OT release, although greatly reduced compared to suckling and hand milking. The low basal levels and classical CORT release patterns suggested non-stressful management practices were used and there were very limited differences in udder stimulation between managements. The OT release induced by exclusive suckling and suckling together with hand-milking gives a reference point for what a good milk ejection stimulation is in camels. The important and specific reduction of OT release during machine milking without the calf present could be a physiological consequence of the maternal behaviour (selectivity for the own young) and to a lesser extent explained by a lower stimulation by machine milking.

Effect of somatic cell count on milkability and milk composition of ewes

The trial aimed to study the effect of somatic cell count, breed, milk flow type, and parity on the milkability and milk composition of ewes. The flock consists of purebred Lacaune ewes (LC; n = 29) and crossbreds ewes of Improved Valachian (IV x LC; n = 35) and Tsigai (TS x LC; n = 37) with LC (with a genetic portion of Lacaune 25 and 50%). Ewes were assigned according to somatic cell count (SCC) to one of the following three groups: SCC ≤300,000 cells per mL (SCC Group 300,000), SCC between 300,000 and 1000,000 cells per mL (SCC Group 300,000 – 1000,000), SCC ≥1000,000 cells per mL (SCC Group 1000,000). 56% of evaluated ewes had less than 300,000 cells per mL and 29% more than 1000,000 cells per mL in milk. No significant differences were observed between different groups of SCC in total, machine milk yield, and the proportion of milk yield in 30 s and 60 s. The significant differences were observed between SCC Group 300,000 and SCC Group 300,000 – 1000,000 in the proportion of machine stripping from total milk yield (41 ±2 vs. 57 ±4%). Milk flow type had a significant effect on all evaluated milkability parameters but not on milk composition. Ewes on fourth parity had the highest proportion of machine stripping from total milk yield then ewes on third, fifth, and sixth and higher (60% vs. 47, 45, 46%; resp.). Effect of SCC Group on milk composition manifested only in solids not fat. The significant differences were observed between SCC Group 1000,000 to SCC Group 300,000 and SCC Group 300,000 – 1000,000 (10.75 ±0.08% vs. 11.05 ±0.06 and 11.15 ±0.11%, p ≤0.0004).

Machine milkability of East Friesian and Lacaune dairy sheep

Udder morphology and milking characteristics are one of the factors determining milkability in dairy ewes. Udder morphology traits were measured and subjectively assessed by the use of linear scores in 150 ewes of Lacaune (LC) and East Friesian (EF) dairy breeds. Linear scores were assessed for udder depth, cistern depth, teat placement, teat length, udder attachment, udder cleft, and udder shape. Nine traits characterized by milk production and milkability were analyzed in machine milking conditions (150 measurements). Analysis of variance was done by the GLM procedure of SAS statistical package. Extraordinary great variability in all traits of linear udder evaluation was detected, as well as in traits connected with milk production and milkability. The obtained results suggest that LC breed has better milkability parameters than EF breed. The differences in milk production and analysed parameters of milkability were too large between the individual flocks.

Effect of weaning system and type of milk flow on milk production of crossbred ewes improved Valachian and Tsigai with Lacaune

Improved Valachian (IV x LC; n = 41) and Tsigai (TS x LC; n = 44) crossbred ewes with Lacaune were used to study the effects of three weaning systems on milk production. Prior to parturition, ewes were assigned to one of the following three treatments for the first 53 day of lactation: 1) ewes weaned from their lambs at 24 h postpartum and afterwards machine milked twice daily (MTD), 2) ewes, beginning 24 h postpartum, kept during the daytime with their lambs and allowed them to suckle for 12 h, nights separated from their lambs for 12 h and machine milked once daily in the morning (MIX), and 3) ewes exclusively suckled by their lambs (ES). After the treatment period, lambs were weaned from MIX and ES ewes, and all three groups were machine milked twice daily. Furthermore, ewes were evaluated according to number of live-born and weaned lambs (with one (n = 35) or with two lambs (n = 50)). The measurements of milk yield and milk flow were performed on 110 ±5 day of lactation by the equipment for graduated electronic recording of the milk level in a jar in one-second intervals. No significant differences were observed in the measured values (total milk yield, machine milk yield, latency time, milking time, machine stripping, milk flow rate, and machine milk yield in 30 and 60 s) among weaning treatments and between ewes with one or two lambs and evaluated breeds too. The highest occurrence of one peak milk flow (milk flow without milk ejection) was found out in MTD ewes (50%) compared to MIX (19%) and ES (17%). In conclusion, the different systems of weaning did not influence the milk yield and milk flow parameters in the mid-lactation.

UTILIZAÇÃO DA OCITOCINA EM GADO GIROLANDO: AVALIAÇÃO DA VIA VAGINAL COMO ALTERNATIVA À VIA ENDOVENOSA

Resumo O objetivo deste trabalho foi testar a viabilidade da utilização da via vaginal em fêmeas bovinas visando à aplicação de ocitocina a partir de formulações específicas. A ocitocina foi utilizada associada a facilitadores de absorção e na forma injetável (para comparação). Foram produzidas sete formulações, todas com concentração de 5 UI/mL de ocitocina. O delineamento experimental foi em quadrado latino 8x8 (oito dias, oito tratamentos e oito novilhas ciclando). As administrações de ocitocina foram pela via vaginal e a ocitocina injetável pela via endovenosa, contendo 10 UI cada. Amostras de sangue (n=7) foram coletadas de cada animal, no tempo 0, anterior à administração dos tratamentos, e de três em três minutos até 18 minutos. A ocitocina foi extraída do plasma utilizando coluna cromatográfica C-18 e dosada utilizando o kit comercial Oxytocin EIA. Os resultados obtidos foram avaliados por análise estatística não paramétrica utilizando o teste Kruskal Wallis para comparação das médias. A concentração de ocitocina diferiu entre o tempo 0 e o tempo 12 minutos (p<0,05) para a formulação ocitocina em glicerina. Concluiu-se que houve absorção através da via vaginal para essa formulação. Mais estudos serão necessários para seu emprego no manejo com as fêmeas bovinas de forma efetiva.

Comparison of the endocrinological and immunological results of different induction of parturition methods in ewes

OBJECTIVE

This study aimed to compare different induction of partu -rition (IP) methods in terms of endocrinological and immunological parameters in ewes and lambs.

MATERIALS AND METHODS

A total of 24 ewes and their respective 24 lambs were studied. Groups of six ewes were induced on the 138th day: groups I (control), II (dexamethasone), III (aglepristone) and IV (aglepristone + dexamethasone). Blood samples were taken from the ewes from IP to 2 days postpartum at 12-hour intervals for the prolactin and oxytocin analyses. Colostrum and blood samples were collected from the lambs at 0, 12, 24, 36 and 48 hours for the IgG analysis. The prolactin, oxytocin and IgG levels were measured by ELISA.

RESULTS

A significant difference was found in prolactin levels in all groups and in the colostral IgG level in group IV with respect to the sampling time. Additionally, a significant difference in prolactin level was found at 24 hours postpartum between group IV and groups I and III. A significant difference in the colostral IgG level was determined at 24 hours after parturition between group III and the other groups and at 48 hours after parturition between groups II and III. A positive and significant correlation between the colostral and serum IgG levels of the lambs was found at 24 hours in groups I and II.

CONCLUSION AND CLINICAL RELEVANCE

Although varying individual results were found within the groups, the endocrinological and immunological results did not suggest any superiority among the IP methods. Considering the presented study results, a single dose of aglepristone may be used alone or in combination with dexamethasone for I P.

Salsolinol Up-Regulates Oxytocin Expression and Release During Lactation in Sheep

Salsolinol (1-methyl-6,7-dihydroxy-1,2,3,4-tetrahydroisoquinoline) is a dopamine-derived compound present in the central nervous system and pituitary gland. Several previous studies on lactating sheep and rats have reported that salsolinol plays a crucial role in the regulation of prolactin secretion. The present study investigated the effects of salsolinol, which was infused into the third ventricle of the brain, on oxytocin expression and release in lactating sheep, 48 h after weaning of 8-week-old lambs. Serial 30-min infusions of salsolinol and vehicle were performed at 30-min intervals from 10.00 to 15.00 h. Blood samples were collected every 10 min. The supraoptic nucleus (SON), paraventricular nucleus (PVN) and posterior pituitary were collected immediately after the experiment. Expression levels of mRNAs for oxytocin and peptidylglycine α-amidating monooxygenase (PAM), the terminal enzyme in the oxytocin synthesis pathway, were measured using a real-time polymerase chain reaction. Oxytocin peptide content in the posterior pituitary was measured by an enzyme-linked immunosorbent assay, and plasma oxytocin concentration was measured by radioimmunoassay. Salsolinol treatment significantly up-regulated oxytocin and PAM gene expression in the SON (P < 0.01 and P < 0.05, respectively), PVN (P < 0.01 and P < 0.05, respectively) and posterior pituitary (P < 0.05 and P < 0.05, respectively). Oxytocin peptide content in the posterior pituitary and the area under the response curve of plasma oxytocin were significantly (P < 0.05 and P < 0.01, respectively) higher in salsolinol-treated sheep than in control animals. The present study shows for the first time that salsolinol stimulates oxytocin secretion during lactation in sheep.

The effect of ewes relocation on milk composition and milk flow kinetics

The investigation of an influence of ewes relocation and milking in other parlour (treatment) on milk flow kinetics, milkability and milk composition was the aim of this study. In total 34 ewes of two breeds and crosbreeds Tsigai (14 heads) and Improved Valachian (20 heads) with Lacaune were tested. Two weeks after lamb weaning the ewes were milked in parallel milking parlour (1x16 stalls) under shelter. On the last evening milking (first experimental milking, EB) before relocation of flock to another parlour, and during next three continuous evening milkings (E0 - second, E1 - third and E2 - fourth milking of exp.) after relocation the milk flow kinetics were measured using electronic collection jar. On day E0 after morning milking the flock was moved on a pasture and milked in other parlour (1x24-stalls). During E0 we recorded a significant decrease of total milk yield in comparison with EB (0.527 ±0.04 and 0.647 ±0.04 L). Significant differences were also recorded in machine milk yield, machine stripping, milking time and in maximum milk flow rate. During E0 there was a higher number of nonbimodal and lower numbers of bimodal flow types. The response of ewe to E0 depended on its response to EB. Ewes with bimodal flow at EB responded more negatively to E0 than ewes with nonbimodal or plateau flow. During E2 there were significantly increased protein content and solids not fat in milk. Thus the treatment significantly influenced the milkability of ewes in a negative way, but more clear response was found out in ewes with bimodal flow response to machine milking before treatment. We could assume that relocation to other milking conditions caused only short-term changes in milk flow kinetic and milk yield.

Dairy sheep production research at the University of Wisconsin-Madison, USA - a review

Commercial milking of sheep is a new agricultural industry in the United States starting approximately 30 yr ago. The industry is still small, but it is growing. The majority of the sheep milk is used in the production of specialty cheeses. The United States is the major importer of sheep milk cheeses with 50 to 60% of annual world exports coming to the United States during the past 20 yr. Therefore, there is considerable growth potential for the industry in the United States. The only dairy sheep research flock in North America is located at the Spooner Agricultural Research Station of the University of Wisconsin-Madison. The research program started in 1993 and has been multifaceted; dealing with several areas important to commercial dairy sheep farmers. The East Friesian and Lacaune dairy breeds were compared and introduced to the industry through the research program. Both dairy breeds produced significantly more milk than traditional meat-wool breeds found in the U.S., but the two breeds differed in their production traits. East Friesian-cross ewes produced more lambs and slightly more milk than Lacaune-cross ewes whereas Lacaune-cross ewes produced milk with a higher percentage of fat and protein than East Friesian-cross ewes. Lactation physiology studies have shown that ewes with active corpora lutea have increased milk yields, oxytocin release during milking is required to obtain normal fat percentages in the milk, large udder cisterns of dairy ewes can allow for increased milking intervals, and short daylengths during late pregnancy results in increased milk yield. In the nutrition area, legume-grass pastures and forages with a higher percentage of legume will result in increased milk production. Grazing ewes respond to additional supplementation with increased milk yield, but it is important to match the supplement to the quality of the grazing. Ewes on high quality legume-grass pastures that are high in rumen degradable protein respond with increased milk production to supplements high in energy and/or high in rumen undegraded protein.

The effect of combination treatment with trenbolone acetate and estradiol-17β on skeletal muscle expression and plasma concentrations of oxytocin in sheep

Implantation of trenbolone acetate (TBA) in conjunction with estradiol-17β (E(2)) increases growth, feed conversion efficiency, and carcass leanness in cattle. Our previous study in Brahman steers suggested that the neuropeptide hormone oxytocin (OXT) may be involved in increasing muscle growth after TBA-E(2) treatment. The present study aimed to determine whether OXT mRNA expression in the longissimus muscle (LM) is also up-regulated in TBA-E(2-)implanted wethers as has been found in steers. Real-time quantitative PCR was used to measure the expression of the gene encoding the OXT precursor, three genes with increased expression in the LM muscle of TBA-E(2)-treated steers, MYOD1 (muscle transcription factor), GREB1 (growth regulation by estrogen in breast cancer 1), and WISP2 (Wnt-1 inducible signaling pathway protein 2), and two genes encoding IGF pathway proteins, IGF1, IGFR, in the LM of both untreated and TBA-E(2)-treated wethers. The expression of OXT mRNA in wethers that received the TBA-E(2) treatment was increased ~4.4-fold (P = 0.01). TBA-E(2) treatment also induced a 2.3-fold increase in circulating OXT (P = 0.001). These data, together with the observation that untreated wethers had much higher baseline concentrations of circulating OXT than previously observed in steers, suggest that wethers and steers have quite different OXT hormone systems. TBA-E(2) treatment had no effect on the expression of IGF1, IGFR, and the muscle regulatory gene MYOD1 mRNA levels in wethers (P ≥ 0.15), but there was an increase in the expression of the two growth-related genes, GREB1 (P = 0.001) and WISP2 (P = 0.04). Both genes are common gene targets for both the estrogen and androgen signaling pathways. Consequently, their actions may contribute to the positive interaction between TBA and E(2) on additive improvements on muscle growth.

Milk yield and milk composition from grazing primiparous non-dairy crossbred ewes

Milk production and milk composition were studied in 520 primiparous Merino crossbred ewes that were the progeny of 30 sires from several maternal crossing breeds including Border Leicester, Coopworth, Finnsheep and East Friesian. The ewes were born in 3 years (1997, 1998, and 1999), with 3 sires used in every year to provide genetic links. The crossbred ewe lambs were randomly assigned to autumn or spring joining groups and mated to Poll Dorset rams to lamb at 12 or 19 months of age. Ewes were milked on 3 days during their first lactation at approximately 3, 4, and 12 weeks after lambing. On each milking day, each ewe was initially injected with oxytocin, milked out by machine, and then hand-stripped. This procedure was repeated approximately 4 h later, with the milk weight and time recorded to extrapolate to daily milk yield, and composition of the milk was determined. Daily milk yield was analysed using REML mixed models procedures and 3 measures of milk production were predicted: peak milk yield at 21 days of lactation, total milk yield from 21 to 90 days of lactation, and length of lactation (days for daily yield to decline to 600 g/day). Milk composition traits (%fat, %protein, %lactose) and proportion of machine milk yield were analysed with similar models. Sire breed, number of lambs born and suckled, season, and ewe weight gain from mid-pregnancy until lamb weaning were all significant (P < 0.01) for daily yield, which declined from 2.1 kg/day at 21 days to 0.7 kg/day at 90 days of lactation. The Finnsheep-cross ewes had lower peak milk yield (1.84 ± 0.08 v. 2.09–2.19 ± 0.1 kg/day) and lower total yield of lactation (21–90 days) than all the other breed-cross ewes (78 ± 3 v. 92–107 ± 5 kg). The East Friesian-cross ewes had significantly longer lactations (128.8 ± 10.9 days) than the Border Leicester (98.1 ± 4.4 days) and Coopworth (93.7 ± 4.2 days), with the Finnsheep-cross ewes the shortest (80.1 ± 3.1 days). The East Friesian-cross ewes had the greatest and the Finnsheep-cross ewes the least total yield of lactation (107 ± 5 and 78 ± 3 kg, respectively). There were significant differences in peak milk yield for ewes bearing and suckling single lambs, twin-born and single-raised lambs, and twin-born and raised lambs (1.86 ± 0.04, 2.03 ± 0.09, and 2.37 ± 0.07 kg/day, respectively). There was a significant decline in daily milk yield with increasing ewe weight gain from mid-pregnancy to lamb weaning (–18.1 ± 4.2 g/kg). All the components of milk composition changed from the peak of milk production at 3 weeks to the end of lactation. The East Friesian-cross ewes had significantly lower milk %fat (by approx. 1 percentage point) at both 21 days and 90 days of lactation than ewes by all other sire breeds. The 30 sire progeny mean deviations for daily milk yield ranged from –292 to +276 g/day, with considerable ranges between sires within the sire breeds. The implications for lamb production and breeding programs are discussed.

Produção de leite, leite residual e concentração hormonal de vacas Gir × Holandesa e Holandesa em ordenha mecanizada exclusiva

Avaliaram-se as concentrações de ocitocina e de cortisol e as produções de leite e de leite residual de três grupos genéticos de vacas: ½Gir×½Holandês (n=6, grupo genético F2), ¼Gir×¾Holandês (n=6, grupo genético F3) e Holandês (n=6, grupo genético H), ordenhadas mecanicamente e na ausência do bezerro. O grupo genético H produziu mais leite do que os grupos F2 e F3, e a concentração de ocitocina foi semelhante nos três grupos. O aumento de ocitocina durante a ordenha foi maior para os grupos H e F3 em relação ao grupo F2. O leite residual do grupo F2 foi maior do que o dos grupos genéticos F3 e H. O cortisol do grupo F2 foi maior do que o das vacas dos demais grupos genéticos. Vacas dos grupos F2 e F3 foram mais estressadas durante a ordenha do que vacas do grupo H, mas as dos dois grupos genéticos cruzados liberavam suficiente quantidade de ocitocina que permitiu a ejeção efetiva de leite.

Effect of weaning system on milk composition and distribution of milk fat within the udder of East Friesian dairy ewes

We investigated whether the inhibition of milk ejection during and/or between machine milkings is responsible for the low milk fat observed in commercial milk obtained from dairy ewes managed with a mixed system (MIX) of partial daily suckling (10 h) and once daily machine milking (after 14 h of udder filling). East Friesian crossbred dairy ewes were randomly allocated postpartum to the MIX system (n = 9) or to exclusive twice-daily machine milking (DY1, n = 8). Following wk 4, MIX ewes were permanently weaned from their lambs and milked twice daily. All ewes were injected with saline, oxytocin, or an oxytocin-receptor antagonist prior to three morning milkings during wk 2,4, and 6 of lactation to study cisternal and alveolar milk distribution. Overall milk yield (cisternal + alveolar) for MIX ewes was 42% greater than for DY1 ewes during wk 2 and 4, which demonstrates the beneficial effect of lamb suckling on milk production of dairy ewes. However, during normal machine milking, only the cisternal fraction was obtained from MIX ewes, confirming that milk ejection did not occur for as long as these ewes remained in partial daily contact with their lambs. Although the volume of milk stored within the cistern, and its concentration of milk protein was similar for the two weaning systems, milk of MIX ewes was significantly inferior in cisternal milk fat concentration and yield compared to DY1 ewes. This provides evidence that not only is there inhibition of milk ejection during machine milking of MIX ewes, there is additional inhibition of transfer of milk fat, but not milk protein, from the alveoli to the cistern during the evening when MIX ewes a reseparated from their lambs. Following weaning of MIX ewes, the majority of lactation traits studied were similar compared to DY1 ewes.

Maternal olfaction differentially modulates oxytocin and prolactin release during suckling in goats

In postparturient goats, olfactory recognition of the young allows the establishment of a selective bond between the mother and her kids. Once this bond is formed, the mother rejects alien young that attempt to suckle. We tested whether the development of the maternal selective bond in goats modulates prolactin (PRL) and oxytocin (OT) release in response to suckling. On day 37 of lactation, serial blood samples were taken during nursing of the mother's own or alien kid(s) in 10 intact/selective goats and in 10 goats rendered anosmic/nonselective through prepartum peripheral ZnSO(4) irrigation. Spontaneous nursing behavior was also studied weekly from day 7 to 30 of lactation, at which time milk production was measured. Maternal selectivity had no effect on PRL release, in contrast to OT release, which was significantly affected by this factor. Intact mothers released OT only when nursing their own kids, but not with aliens, while anosmic/nonselective dams showed an increase in OT levels regardless of the identity of the kids. In addition to these effects on maternal selectivity, the amplitude of the response of both hormones was lower in anosmic mothers than in intact mothers. Finally, nursing behavior and milk production were not significantly affected by anosmia. We conclude that maternal selective behavior in goats, which relies on the individual olfactory signature of the kid, modulates the OT, but not the PRL, response to suckling. In addition, perception of the smell of the young appears to have a general facilitatory effect, independent of the kid's identity, on the release of both hormones.

Effect of presence or absence of corpora lutea on milk production in East Friesian dairy ewes

The potential luteal effects on milk production were examined in dairy ewes that were not superovulated in contrast to studies using superovulated ewes. Lactating East Friesian crossbred ewes (n = 24) were synchronized using intravaginal progesterone (controlled intravaginal drug-releasing device), PGF2alpha, and gonadotropins. After ovulation, corpora lutea (CL) were counted via laparoscopy on d 4 and 11. On d 5, ewes received either saline (CLYES, n = 12) or PGF2alpha (CLNO, n = 12) to allow CL persistence (2.4 +/- 0.3 CL on d 11) or regression (0 CL on d 11), respectively. Each ewe received two CIDR d 5 to 18 to maintain high concentrations of plasma progesterone (P4) and to suppress estradiol (E2). Each ewe received PGF2alpha on d 18. Data were collected during three periods (pretreatment: d 0 to 5; treatment: d 6 to 18; posttreatment: d 19 to 25). Milk yield and milking time were recorded daily, milk samples were obtained for analyses of fat and protein, and blood samples were collected for P4 and E2 immunoassay. During treatment, CLYES ewes had higher milk yield (1.56 vs. 1.44 +/- 0.01 kg/d), milk fat (92.2 vs. 81.1 +/- 1.3 g/d), and milk protein (83.7 vs. 77.5 +/- 0.8 g/d) compared with CLNO ewes, respectively. Differences were maintained posttreatment, despite luteolysis in CLYES ewes. Estradiol concentrations did not differ between treatments and were low after d 5. Milk production was increased in East Friesian ewes in the presence of an average of 2.4 corpora lutea, an effect independent of estradiol.