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.     

Milk yield, residual milk, oxytocin and cortisol release during machine milking in Gir, Gir x Holstein and Holstein cows

This study evaluated the effect of exclusive machine milking on oxytocin (OT) and cortisol (CORT) release, and on milk yield and residual milk in Gir (group Gir), Holstein (group Hol) and crossbred animals (group GirHol). Six animals from each group were submitted to experimental milkings. As expected, milk yield was significantly higher in the Hol group than in the groups GirHol and Gir, and group GirHol produced more milk than the Gir group. In contrast, all groups exhibited significant but similar levels of OT, although OT increased more rapidly during milking for the groups Hol and GirHol than for the Gir group. In addition, CORT levels measured during and after milking were significantly influenced by the group. The Gir group showed higher levels of CORT than the groups GirHol and Hol. The lower performances of the Gir breed can not be explained by a less efficient milk ejection reflex because all cows studied released enough OT and had an effective milk ejection.     

Effect of calf suckling on oxytocin,prolactin, growth hormone and milk yield in crossbred Gir x Holstein cows during milking

This study evaluated the effect of different milking managements on oxytocin, prolactin and growth hormone release in Gir x Holstein cows. Six cows were suckled by their calves, before and after milking (SM group); another six cows were submitted to exclusive milking (M group). High OT levels were observed during suckling of the SM group, however both groups had similar levels of OT during milking. The SM group presented PRL levels significantly higher than the M group, however only during suckling. For GH levels, the SM group showed higher levels than the M group, however this difference was significant only during the first suckling, cleaning of the teats and at the beginning of machine milking. Despite these results, SM cows produced more milk (milking plus suckling) than M cows, however milk obtained by milking was similar for both groups.     

The effects of conditioning to suckling, milking and of calf presence on the release of oxytocin in dairy cows

The aim of the study was to record the oxytocin (OT) release during milking (M) without or with calf presence, suckling (S) and finally calf removal just before the next milking in cows during postpartum or early lactation periods. Furthermore, the release of OT was examined during S and M in unknown surroundings (parlour). A total of 20 Brown Swiss cows kept under loose housing environment were used in our experiment. In both periods, the cows were milked twice daily at 07.00 and 18.00h and suckled three times daily at 09.00, 14.00 and 20.00h in the stall (tie housing). In the postpartum period, 13 cows were suckled and milked in the presence of their calves in the stall for the first 5 days of postpartum. Five from seven primiparous cows were additionally suckled by their own calves in the parlour on day 5 at 20.00h. On day 6, calves were separated and moved from mothers to the calf barn 10min before morning M. After evening milking cows were relocated to the herd within the same stable and milked in the parlour for a period of 4 weeks without contact to their calf. For control, additional seven primiparous cows without calf presence (not suckled) were also milked in the tie housing. In the early lactation period, suckled cows were moved back to the tie housing 2 days before the start of two consecutive days of S by their own calves and milking. Afterwards, 10min before M calves were separated again. Before S, two consecutive M were considered as controls. Results: The S stimulus during postpartum resulted in a higher OT release as compared with M in the calf presence and M after calf separation but not during M of not suckled cows. S in parlour reduced OT release. However, when not suckled primiparous cows were first milked in parlour, OT release was more reduced and in some cows total inhibition was observed. In early lactation during the first S, release of OT was lower than during control M, but increased gradually with repeated S and reached a maximum already on the second day. After two S, during evening M, the M related OT release was reduced as compared with controls. Calf removal 10min before M reduced OT release as compared with control M or M in calf presence. In conclusion, the calf presence and its removal can negatively influence OT secretion during M. Conditioning to machine milking caused a short-term reduction of OT release during first suckling, which normalised within 1 day.     

Effect of haloperidol, suckling, oxytocin and hand milking on plasma relaxin and prolactin concentrations in cyclic and lactating pigs

Prolactin secretion was stimulated in 5 cyclic gilts during the luteal phase (Day 10-13) with 5 mg haloperidol given i.v. Stimulation of prolactin secretion was also attempted by inducing milk let-down by suckling (4 sows), or by the injection of 1 mg oxytocin i.v. followed by hand milking (3 sows). Plasma prolactin concentrations increased significantly 1-2 h after haloperidol injection, and in 3 of 4 sows during suckling (P = 0.001); plasma relaxin concentrations did not change significantly at these times. No change was observed in plasma prolactin or relaxin concentrations at 15 min or 1-2 h after oxytocin injection and hand milking. Plasma relaxin concentrations ranged from below the sensitivity of the assay (100 pg/ml) to 450 pg/ml in lactating sows and from 100 to 2000 pg/ml in cyclic gilts. The results suggest that in cyclic gilts treated in the luteal phase with a dopaminergic receptor blocker, and in lactating sows during suckling, elevations in plasma prolactin concentrations were not accompanied, during the same period, by detectable changes in relaxin concentrations.     

Resumption of gonadotrophin release during the post-partum period in suckling and non-suckling ewes

The post-partum secretion of LH, FSH and prolactin was monitored in 15 suckling and 6 non-suckling Préalpes du Sud ewes lambing during the breeding season by measuring plasma hormone concentrations daily at 6-h intervals and also weekly at 20-min intervals for 6 h from parturition to resumption of regular cyclic ovarian activity. There was a constant phenomenon in the resumption of normal patterns of FSH and LH secretion: there was a rise in FSH values culminating on average on Day 4 post partum and returning subsequently to values observed during the oestrous cycle, and concurrently an increase in the frequency and amplitude of LH pulses more progressive in suckling than in non-suckling ewes which led to an elevation of LH mean concentrations and occurrence of an LH surge. Since neither the FSH secretory pattern nor FSH mean values differed between suckling and non-suckling ewes, the results suggested that LH pulsatile pattern was a major limiting factor for the resumption of normal oestrous cycles. Before regular oestrous cycles resumed other changes in preovulatory LH surges also occurred: (i) they increased in duration and probably in amplitude; (ii) they were preceded by an acceleration in LH pulse frequency and a large decrease in FSH values as in normal cyclic ewes; and (iii) at least in non-suckling ewes they occurred concurrently with a prolactin surge.     

Prolactin release and milk removal induced by suckling and milking in lactating ewes is prevented by L-dopa treatment

The effect of L-DOPA on milk removal and on prolactin release during suckling or milking was studied in lactating ewes. Various doses of L-DOPA (25, 50, 100 and 200 mg per animal) were injected iv 30 min before the suckling or milking period. Control ewes were injected with 0.9% NaCl solution only. Milking induced a significant long-lasting release of prolactin. An inhibition of milk removal was obtained with the dose of 200 mg of L-DOPA. An inhibition of prolactin secretion was observed related to the dose of drug administered. The inhibitory effect of 200 mg of L-DOPA on the secretion of prolactin after milking lasted for about 120 min, and thereafter a significant increase in serum prolactin level occurred. This increase in serum prolactin was not due to a "rebound" effect of L-DOPA, since the milking stimulus had to be present to induce the delayed increase in prolactin. Doses of 25 or 50 mg of L-DOPA prevented the surge of prolactin observed immediately after milking, but a long-lasting release of prolactin was obtained thereafter. The inhibitory effect of L-DOPA on prolactin release could be overridden by the suckling or milking stimuli according to the dose administered. The suckling stimulus was more effective than milking in overriding the inhibitory effect of the low dose of L-DOPA. The results indicate that milk removal and prolactin release induced by milking or suckling in lactating ewes is inhibited by an increase in monoamines at the hypothalamic-hypophyseal level.     

Release of oxytocin and prolactin in response to suckling.

The oxytocin and prolactin responses to suckling were measured in 10 women in early (n = 5) and established lactation (n = 5). Oxytocin was released in a pulsatile manner during suckling in all women, but the response was not related to milk volume, prolactin response, or parity of the mother. In all 10 women plasma oxytocin concentrations increased three to 10 minutes before suckling began. In five women this occurred in response to the baby crying, in three it coincided with the baby becoming restless in expectation of the feed, while in two it corresponded with the mother preparing for the feed. There was no prolactin response to stimuli other than stimulation of the nipple associated with suckling. These results clearly indicate that the milk ejection reflex, with release of oxytocin, occurs in most women before the tactile stimulus of suckling. A second release of oxytocin follows in response to the suckling stimulus itself. Thus it is important that care is taken to protect breast feeding mothers from stress not only during suckling but also immediately before nursing, when conditioned releases of oxytocin will occur.     

Synergetic effect of pimozide and thyrotropin releasing hormone on prolactin and thyrotropin release during the drying off of ewes

The effect of pimozide and/or TRH was investigated on plasma prolactin, thyrotropin, T₄ and T₃ and udder distension in 38 ewes during drying off by feed restriction. The effect of daily injections of 2 mg pimozide (s.c.), combined or not with TRH stimulation (200 μg, i.v.) on three different days of the drying off period was examined. Blood samples were taken twice daily in each group for 9 days, while blood sampling on the days of TRH injection was also performed at 0, 15, 30 min, and 1, 2 and 4 h post-injection. Plasma was assayed for PRL, TSH, T₄ and T₃ levels. Udder distension and mastitis incidence were recorded at the end of the drying off period. TRH and pimozide both resulted in elevated plasma PRL levels and acted in a synergetic way. Udder distension and the incidence of mastitis was only influenced by pimozide. The TSH as well as the T₃ response to TRH was increased in ewes under a continuous influence of pimozide and T₃ peaks following TRH injection occurred earlier than T₄ peaks. The higher effect of pimozide upon TRH stimulated PRL and TSH release at day 8 compared to days 0 and 3 indicates a progressive involvement of dopamine on the inhibition of PRL and the sensitivity of the thyrotrophs to TRH during drying off.     

The effect of machine or hand milking on milk production,composition and SCC in mountainous Greek breed (Boutsiko) ewes

The aim of this work was to determine the effect of two different milking methods (machine versus hand milking) on milk yield, milk composition and somatic cell counts (SCC) in mountainous Greek Boutsiko ewes. Ninety-six ewes were divided in two groups of 48 ewes each. Milk yield, lactation number (parity) and type of lambing were taken into consideration for the separation of the ewes. One group was milked by machine and the other by hand. Milk production, milk composition (with Milkoscan 104) and SCC (with Fossomatic) were performed every 14 days, in the morning and evening milking; during the experimental period seven samplings were performed in total. The results of this study have shown that ewes milked by machine gave a greater daily milk yield as compared to those milked by hand (698 ml versus 652 ml; P < 0,05) and less log SCC (5.37 versus 5.62; P < 0,05). The composition of milk did not differ between the two treatments. Also, no phenotypic correlations were established between SCC and milk production or composition, apart from a negative correlation, which was noted between SCC and the percentage of lactose. The results of this experiment have shown that ewes of the Boutsiko breed can be milked by machine without any problems.     

Possible role of vasoactive intestinal polypeptide on prolactin release during suckling in lactating women

The effect of suckling on plasma vasoactive intestinal polypeptide (VIP) values was evaluated in 6 nursing women on the 3rd to 4th day postpartum. Plasma prolactin (PRL) concentrations were also measured. Plasma VIP values (20.6 +/- 3.2 pg/ml in baseline) significantly (p less than 0.05) increased, reaching a maximum (53.5 +/- 10.9 pg/ml) 20 min after the starting of suckling. A possible role of VIP in the suckling-induced PRL release in humans cannot be excluded.     

Naloxone cannot abolish the lack of oxytocin release during unexperienced suckling of dairy cows

To evaluate the role of opioids for the regulation of oxytocin release in response to teat stimulation, 10 brown-Swiss dairy cows were randomized to two experiments during mid of lactation. In the first experiment, four cows without previous suckling experience were suckled by an alien calf between two normal milkings. Before and during milking or suckling, frequent blood samples were collected via a jugular cannula for determination of oxytocin and beta-endorphin. In the second experiment, six cows were treated with naloxone or saline, 10min before the start of the first or second suckling, respectively. The collected blood samples were assayed for oxytocin.In the first experiment, the plasma levels of beta-endorphin were elevated during and after the unexperienced suckling in three cows, but not in the fourth cow, and the release of oxytocin during suckling was markedly reduced, suggesting no release of alveolar milk. In the second experiment, the release of oxytocin during suckling was again significantly reduced. Pretreatment with naloxone before suckling did not completely abolish the adverse effect of suckling and the oxytocin plasma level did not increase to levels comparable with control milking.In emotional stress situations, the release of oxytocin from the pituitary is inhibited with simultaneously elevated beta-endorphin plasma levels. Although there is some evidence for a regulatory role of opioids for the release of oxytocin, other mediators are suggested to be more potent in regulating oxytocin under stress conditions.     

Artificial induction of lactation in ewes: the relative importance of oxytocin and the milking stimulus.

Eight ovariectomized and four intact ewes were given oestrogen plus progesterone to develop the mammary glands. The intact ewes (group A) and four ovariectomized ewes (group B) then received four injections each day of 1 i.u. syntocinon for 5 days whereas the other four ovariectomized ewes (group C) received placebo injections of 0-9% saline. Milking commenced the day after the last of these injections. Yields of mammary secretion on the first day of milking--representing secretion accumulated during the injection of syntocinon or saline--for ewes in groups A and B were significantly higher than yields from group C (control) ewes. After 12 days of milking, yields of secretion from group A ewes were significantly higher than yields from group B ewes which in turn were significantly higher than yields from ewes in group C.     

Genistein-induced pituitary prolactin gene expression and prolactin release in ovariectomized ewes following a series of intracerebroventricular infusions

The aim of the study was to evaluate whether genistein, a phytoestrogen commonly present in feed plants, affects prolactin release and its gene expression in the pituitary gland. In the experimental model, genistein was infused into the third ventricle (IIIv) of the brain in ewes during the short-daylight period (November-December), when the physiological plasma level of prolactin is low. Animals were ovariectomized six weeks before the experiment, to remove the main source of endogenous estrogens, and three weeks later a stainless steel guide cannula was implanted into IIIv. Genistein (10 ng/100 microl/h, n=5) or vehicle (control, n=5) were infused in a series of four one-hour infusions at 30-min intervals (from 16:30 to 22:00). Plasma samples were collected at 15-min intervals from 14:00 to 22:00 through a catheter inserted into the jugular vein and after the experiment ewes were slaughtered. Northern blot analysis revealed that pituitary prolactin mRNA content increased significantly in response to genistein, compared to the vehicle-infused ewes (p<0.05). Prolactin concentration in plasma rose significantly during the periods of genistein infusion, as compared to the values found before infusion (p<0.05-p<0.01) as well as to the values of the concomitant periods in vehicle-infused ewes (p<0.001). Our results show an effective estrogenic action of genistein on prolactin synthesis and release in ovariectomized ewes that might in part be exerted at the central nervous system level.