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1.
The concentrations of lactogenic hormones (prolactin--PRL, growth hormone--GH, insulin-like growth factor I--IGF-I) and steroid hormones (progesterone--PG, estradiol--E2) were determined by RIA in the blood plasma of 8 lactating ewes (3 with twins) and compared with that of 3 non-lactating cycling ewes of the same age. All animals live in a flock of 30 Awassi sheep under identical conditions in Syria. The lactation period (192 +/- 25 days) is divided to a suckling period (until day 63) and a hand milking period (2 fold daily) with different levels of milk production (near 2 litres/day in the former, decreasing from 0.8 to 0.1 litre/day in the latter). During the suckling period the concentrations of steroid hormones in the blood plasma are lower, these of lactogenic hormones are higher of lactating than of non-lactating ewes. During the milking period only the concentrations of E2, PRL and IGF-I in the blood plasma of lactating animals are lower than in non-lactating ewes. But, during this time more and more seasonal influences (increasing day length and temperature) overwhelm the influence of lactation on the hormone secretion. Suckling of twins is accompanied with higher levels of E2, PRL and IGF-I in the blood plasma of their mothers than suckling of single lambs. During the lactation period a strong correlation exists between milk yield and the level of GH (r = 0.85) and IGF-I (r = 0.71), a smaller correlations to the level of E2 (r = 0.49) in the blood plasma of the lactating ewes. During the suckling period the milk yield is influenced positively by PRL (r = 0.77) and GH (r = 0.68), but negatively by PG (r = -0.76). During the milking period the milk yield is determined extensively by the level of IGF-I (r = 0.89) in the blood plasma. The concentrations of the analyzed hormones in the blood plasma correlate always positively together.  相似文献   

2.
Three-hour milk production measurements determined by machine milking at 3-d intervals throughout a 63-d lactation period were used to describe lactation curves for crossbred ewes lambing at 1 and 2 yr of age and rearing single and twin lambs. Age of ewe, type of rearing, and day of lactation affected (P < 0.05) milk production. Over the 63-d lactation, average daily milk production was 2.56 and 2.63 kg, respectively, for 1- and 2-yr-old ewes rearing single lambs and 2.73 and 3.47 kg, respectively, for 1- and 2-yr-old ewes rearing twins. Milk production of 2-yr-old ewes rearing twin lambs peaked at 21 d of lactation, and that of 1- and 2-yr-old ewes rearing singles peaked between 27 and 30 d of lactation. The largest differences in the lactation curves among age and rearing ewe classes were found in early lactation. These differences were reduced by midlactation, and by late lactation, milk production for all ewes was similar. Diurnal variation in milk production by ewes was evaluated in an 8 x 8 Latin square design. Diurnal variation in milk yield measurements of eight mature ewes, each bearing and rearing twin lambs, was similar between d 21 and 24 of lactation. Time of milk production measurements within a day did not affect yield determinations. Extrapolation from 3-h production estimates to daily milk production is valid in determining a ewe's milk contribution in support of lamb growth.  相似文献   

3.
The objective of this study was to examine the effect of long day photoperiod (LDPP) on milk production and reproduction in milk goats. A total of 79 goats were randomly assigned to three treatment groups blocked by day of kidding. Group 1 (Gr1, n = 26) was subjected to natural photoperiod from January 6 to December 5. Group 2 (Gr2, n = 24) was subjected to LDPP (20 h light, 4 h dark) from June 22 to December 5. Group 3 (Gr3, n = 29) was subjected to LDPP from January 6 to December 6. Weekly milk weights and samples were collected for fat, protein and somatic cell count (SCC) determinations. Blood serum was harvested for progesterone (P4) determination. Results indicated a significant effect (p < 0.001) between treatments for body weight changes, feed intake and milk yield. Both light treated groups had a significantly higher (p < 0.001) average daily milk output for the entire lactation period than the control group (G1, 2.193 kg/day; G2, 2.517 kg/day; G3, 2.305 kg/day). Milk fat for the overall lactation was significantly higher in Gr3 (+ 0.19 g/100 ml) than for Gr2 (+ 0.06 g/100 ml) when compared to the control group (x g/100 ml) under natural photoperiod. Somatic cell counts throughout lactation were significantly (p < 0.001) lower for Gr2 (1.70 million/ml) and higher for Gr3 (2.03 million/ml), with the control group (Gr1) having an intermediate level (1.96 million/ml). Progesterone levels between June 9 and August 30 indicated that 27%, 48% and 63% of the animals had P4 levels in excess of 1.0 ng/ml serum for Gr1, Gr2 and Gr3, respectively. Pregnancy diagnosis by ultrasound in December revealed that a high number of does in the light treated groups (10 of 37) were pseudo-pregnant when compared with the control group (1 of 21). Although light appeared to be effective in increasing milk production, further investigations are needed to evaluate the effect of LDPP on pseudo-pregnancy in dairy goats.  相似文献   

4.
In the Basque country lambing takes place during winter, followed by milking until late spring or summer, so it was considered that this would be the most profitable period for deworming, when there was an increased production pressure on ewes with depressed immune status owing to the peri-parturient relaxation of immunity. The drug employed was netobimin, and the trial was carried out in 22 commercial flocks, in each of which ewes were allocated to one of three similar groups. One group was left as a non-treated control (T0), the second was dosed 15 days before parturition (T1), and the remaining group dosed both at 15 days before and 15 days after lambing (T2). Mean total milk production in the T2 group increased by 8.8 and 6.3% in the second and third month post-partum, respectively, compared with that of the controls (T0), while over the standard lactation period of 120 days the T2 group showed a significant (8.9%) increase in production compared with the controls. The T1 group did not significantly differ from T0. The market value of the increase in milk production was calculated to be approximately 700% of the cost of treatment with netobimin.  相似文献   

5.
Two experiments were undertaken to examine the direct and residual responses of late lactation (mean of 232 days calved) autumn calving dairy cows (Experiment 1), and late lactation (mean of 240 days calved) spring calving dairy cows (Experiment 2), to once-daily milking. Experiments 1 and 2 involved 50 and 44 Holstein–Friesian dairy cows respectively. In each of the two experiments, cows were milked either once daily (ODM) or twice daily (TDM), during the late lactation period (mean of 79 and 66 days in Experiments 1 and 2 respectively). Cows in Experiment 1 were managed within a grazing system, and were offered 3.0 kg of concentrate/day, while cows in Experiment 2 were housed, and offered grass silage supplemented with 6.0 kg concentrate/day. Forty-one cows from Experiment 1, and 32 cows from Experiment 2, completed the first eight weeks of the subsequent lactation on a twice-daily milking regime. Food intakes were not measured in Experiment 1, while treatment had no significant effect on dry matter intake in Experiment 2 (P > 0.05). In each of Experiments 1 and 2, total milk output was increased with twice-daily milking (P ≤ 0.05), while milk fat (P ≤ 0.01) and protein (P < 0.001) concentrations increased with once-daily milking. Somatic cell counts were higher with animals milked once daily in Experiment 1 (P < 0.001), while not being significantly affected by milking frequency in Experiment 2 (P > 0.05). Milking frequency had no significant effect on cow live weight or on cow condition score at the point of drying off in either Experiment (P > 0.05). Milking time per cow during morning milking was unaffected by treatment in either experiment, while total daily milking time per cow (morning and evening combined) was significantly longer with the TDM treatment (P < 0.001). In Experiment 1, milk flow rates during the morning milking were higher with animals on the ODM treatment, compared to those on TDM treatment (P < 0.001), while being unaffected by treatment in Experiment 2 (P > 0.05). Neither daily milk yield, milk fat content, milk protein content, or somatic cell count during the subsequent lactation, were affected by previous lactation milking frequency in either of Experiments 1 or 2 (P > 0.05).  相似文献   

6.
Thirteen crossbred ewes were used to compare weigh-suckle-weigh (WSW) and machine milking (MM) methods for determining milk production of ewes that were rearing single or twin lambs. At parturition, ewes were 13 mo of age and produced six single lambs and seven pairs of twin lambs. Milk production estimates were initiated on d 6 of lactation and a 3-d rotation of the two techniques was implemented. On d 6, milk production was measured using WSW; on d 7, MM was used. No measurement was made on d 8. The 3-d rotation was repeated 20 times throughout a 63-d lactation, resulting in 20 point estimates of milk production for each method of measurement for each ewe. The WSW procedure consisted of a 3-h period in which lambs were withheld from suckling their dams. This was followed by a suckling period, a second 3-h withholding period, and a second suckling period. Differences in pre- and postsuckling lamb weights of the second suckling period were defined as milk consumption and, indirectly, 3-h milk production. The MM procedure included an administration of 10 IU of oxytocin (i.v.), followed by evacuation of the udder with a machine using commercially available sheep milking equipment, and the milk was discarded. Lambs were withheld from suckling the ewes for a 3-h period, followed by a repetition of the oxytocin and machine milking procedures. Milk from the second milking was weighed. Milk production estimates determined using the WSW and MM techniques were similar (P = .42). Average 3-h milk production was 340 and 351 g for WSW and MM, respectively. Machine milking provides a reliable tool in evaluating the milk-producing ability of ewes that are rearing single or twin lambs.  相似文献   

7.
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8.
Environmental influences on lactation efficiency are frequently associated with reductions in milk output. Heat stress, for example, leads to depressed feed intake and, subsequently, losses in production. Conversely, cold stress may limit nutrients available for milk synthesis. Fortunately, one environmental factor, photoperiod, can exert a positive effect on dairy performance when managed properly. Long days have consistently been shown to improve milk yield during established lactation. In addition, photoperiod management can be used to improve heifer growth and maximize accretion of lean tissue, including mammary parenchyma. There is, however, evidence of refractoriness to long day stimulation. Recent work has focused on the dry period as a time when photoperiod manipulation can influence subsequent milk production. In contrast to lactating cows, multiparous cows benefit from exposure to short days when the dry period is followed by long days or natural photoperiod after calving. Similarly, primiparous animals also respond positively to short days late in pregnancy when subsequently exposed to long days during lactation. Furthermore, emerging evidence suggests that short days positively influence immune function in cattle. Mechanistically, it appears that prolactin has a causal relationship with the observed dairy performance effects during the dry period and on immune function, via altered sensitivity to prolactin through differential expression of prolactin receptor in multiple tissues. The objectives of this paper include a review of fundamental aspects of photoperiod physiology, integration of applied and basic research findings, and development of management recommendations for the entire life cycle of the dairy cow to optimize performance.  相似文献   

9.
Infection by gastrointestinal nematodes (GIN) in grazing sheep can negatively influence the growth of lambs and milk yield. In the current study we evaluated the effect of high and low levels of infection with Teladorsagia circumcincta on production parameters of lactating ewes. Two groups of ewes were infected with 50,000 T. circumcincta third stage larvae (L3) 30 days before lambing. To obtain a high level of infection, Group HI was challenged with 30,000 L3 30 days post-partum (pp) and again 90 days pp with the same dose. The low infection group (LI) was treated with an intraruminal controlled-release albendazole bolus one-month pp. We determined the effect of the differing parasite loads on milk yield, milk composition, weight gain, and body condition (BC). Throughout the trial the milk yield was higher in the LI group and, consequently, at the end of the lactation, this group produced 11.1% more milk than the HI group. In the final third of lactation there was an overall increase in milk fat, protein, and lactose although the factor most affected by infection level was the protein percentage, with an increment of 11.9% in the HI group. The somatic cell counts remained low during the experiment indicating the absence of udder infection. Regarding weight and BC, significant differences were found only in BC although LI ewes weighed 2% more than the HI group. In conclusion, a low level of GIN infection in sheep leads to a better BC and a higher milk production with high protein percentage.  相似文献   

10.
The objective of this experiment was to develop a procedure for immunizing ewes against melatonin that would alter the effects of changing photoperiod on seasonal reproduction and prolactin secretion. Ewes were immunized against human serum albumin (HSA) as controls (n = 9) or a melatonin-human serum albumin conjugate (0.25 mg; n = 10) on December 14th (Day 0) and boosted 9 times. They were maintained on natural photoperiod and then transferred indoors and exposed to long days for 35 d, followed by short days for 146 d, long days for 93 d, and short days for a further 123 d. Antibody titers to melatonin (at a serum dilution of 1:1,250) were significantly higher in immunized ewes (27.3 ± 6.6%) than controls (0.7 ± 0.1%; P < 0.001). At the end of the experiment, antibody titers in immunized ewes (at dilution of 1:50) were higher in blood (43.7 ± 8.2%) than in cerebrospinal fluid (10.8 ± 3.9%; P < 0.05), and highly correlated (r2 = 0.746). Onset of the breeding season was advanced slightly after the second transfer from long to short days in immunized ewes (April 12 ± 3 d) compared with controls (April 25 ± 3 d; P < 0.05). Mean serum prolactin concentrations were lower (P < 0.05) in melatonin-immunized ewes compared with controls on natural photoperiod, after transfer from long to short days, during long days, and after the second transfer from long to short days. In conclusion, despite melatonin-immunization increasing antibody titers in blood and cerebrospinal fluid, and decreasing prolactin concentrations over much of the experiment, minimal effects on the timing of reproductive transitions in the ewes were evident. This discrepancy between the response of the prolactin and reproductive axes to melatonin immunization supports the hypothesis of a dual site of action of melatonin, with melatonin acting in the pituitary gland to mediate the effects of photoperiod on prolactin secretion and in the mediobasal hypothalamus to affect reproductive responses.  相似文献   

11.
Two experiments were conducted to determine whether exposure to a photoperiod of artificial long days in autumn increased milk yield in subtropical goats milked once (Exp. I) or twice daily (Exp. II). In Exp. I, starting at d 10 of lactation, 1 group of does was kept under naturally decreasing photoperiod (DD1X; n = 8), whereas the other group was submitted to an artificial photoperiod of long days (LD1X; n = 8; 16 h light:8 h darkness). The kids were weaned 28 d after parturition, and dams were manually milked once daily. Milk yield and milk components (fat, protein, and lactose) were assessed up to 140 d of lactation. From d 0 to 28 of lactation (suckling phase), mean daily milk yield did not differ between DD1X and LD1X goats (2.3 ± 0.2 kg vs. 2.4 ± 0.2 kg; P = 0.717). However, between d 29 and 84 (early milking phase), mean daily milk yield was greater in LD1X does than in DD1X does (2.6 ± 0.1 kg vs. 2.1 ± 0.1 kg; P = 0.001). Finally, between d 85 and 140 (late milking phase), mean daily milk yield was greater in LD1X goats than in DD1X goats (P ≤ 0.05) only during the first 2 wk. In Exp. II, one group of goats was exposed to a photoperiod of naturally decreasing days (DD2X; n = 8) and another group was submitted to an artificial photoperiod of long days (LD2X; n = 7). In both groups, kids were weaned on d 28 of lactation and the dams were manually milked twice daily. During the nursing phase, mean daily milk yield did not differ between the DD2X and LD2X groups (2.5 ± 0.3 kg vs. 2.6 ± 0.2 kg; P = 0.767). In the early milking phase, mean daily milk yield was greater in LD2X than in DD2X goats (3.3 ± 0.2 kg vs. 2.8 ± 0.2 kg; P = 0.022), whereas during the late milking phase, milk yield did not differ between the 2 groups (P = 0.946). In both experiments, milk composition was not significantly influenced by exposure to long-day photoperiod. We conclude that, in subtropical female goats that start lactation in late autumn, exposure to an artificial long-day photoperiod stimulates milk yield, even if goats are milked once daily. In addition, combining exposure to long days with twice-daily milking will increase further milk yield in such goats without affecting milk components.  相似文献   

12.
A time-to-event study for mastitis at first-lactation in Valle del Belice ewes was conducted, using survival analysis with an animal model. The goals were to evaluate the effect of lambing season and level of milk production on the time from lambing to the day when a ewe experienced a test-day with a recorded SCC greater than or equal to 750,000 cells/ml, and to estimate, for this trait, its heritability and the percentage of variation explained by the flock-year of lambing effect. A dataset with 2468 first-lactation records, collected from 1998 to 2003 in Valle del Belice ewes allocated in 17 flocks, was used. The Cox model used included lambing season and total milk yield adjusted for lactation length as fixed effects and flock-year of lambing effect and individual additive genetic effect as random effects. In total 40.5% of the records were censored. Results indicated that ewes lambing from April to July were at a higher risk of mastitis than those lambing from August to November (conventional season), and that ewes in the highest class of milk production were at a higher risk of mastitis than those in the lowest level. The heritability for the time interval between lambing and first test-day with mastitis was 3% on the logarithmic scale and 4% on the real scale. The proportion of variation, in the time interval between lambing and first test-day with mastitis, explained by the flock-year of lambing effect was 19% on the logarithmic scale and 27% on the real scale; this seems to stress the importance of flock management.  相似文献   

13.
繁殖母羊是羊场快速扩繁的基础,饲养繁殖母羊的最终目的是充分挖掘母羊的生产潜力,增加羊群数量,提高羊群质量。母羊每年都要经历1~2次配种、妊娠、哺乳这一复杂的繁殖生理过程,每一次繁殖经历,都是对繁殖母羊体质的一次重要考验。只有不断优化繁殖母羊空怀期、妊娠期和哺乳期各阶段、各环节的饲养管理,才能保证繁殖母羊的体质健康,提高产羔率和羔羊成活率,从而提高养羊效益。  相似文献   

14.
The purpose of this pilot study was to evaluate under field conditions the effect of a probiotic containing Bacillus licheniformis and Bacillus subtilis on young lamb mortality and sheep milk production when administered in the late pregnancy and lactation feed of ewes. In a sheep farm, two groups of milking ewes with identical genetic material, management, nutrition, health status and similar production characteristics were formed. One group (46 ewes) served as control, while the other one (48 ewes) served as a probiotic-treated group. Both groups of ewes received a similar feeding regiment, but the ewes of the second group were additionally offered a probiotic product containing B. licheniformis and B. subtilis (BioPlus 2B, Chr. Hansen, Denmark) at the approximate dose of 2.56 x 10(9) viable spores per ewe per day. Lamb mortality during the 1.5 months suckling period, and milk yield during the 2 months of milk collection for commercial purposes have been recorded. In the non-treated control group, 13.1% mortality was observed versus 7.8% in the probiotic-treated group (P = 0.33), with mortality being mainly due to diarrhoea. Microbiological examination of diarrhoeic faeces from some of the dead lambs in both groups revealed the presence of Escherichia coli. The average daily milk yield per ewe was significantly lower in the control group (0.80 l) than that in the probiotic-treated group (0.93 l) (P < 0.05). Fat and protein content of milk in ewes that received probiotics was significantly (P < 0.05) increased compared with untreated ewes. It was concluded that supplementing ewe's feed with probiotics may have beneficial effect on subsequent milk yields, fat and protein content.  相似文献   

15.
Ewes selected for fertility in autumn lambing were used to evaluate correlated responses in nocturnal hormone levels. Four jugular blood samples were obtained during nighttime in August from each of 113 selected and 69 control ewes. Melatonin levels were lower for selected ewes (143 +/- 14 pg/mL) than for control ewes (184 +/- 13 pg/mL), and melatonin levels decreased with increases in estimated breeding values (EBV) for fertility (-2.23 +/- 0.79 pg mL(-1) x %(-1)). Prolactin levels were higher for selected ewes (90 +/- 7 ng/mL) than for control ewes (52 +/- 7 ng/mL), but significant line x ewe age interaction was also observed, with smaller differences in prolactin levels in 2-yr-old and older ewes (74 +/- 7 vs. 56 +/- 9 ng/mL for select and control ewes, respectively; P < 0.20 before and P = 0.05 after logarithmic transformation). Prolactin levels increased with both fertility EBV (1.23 +/- 0.53 ng mL(-1) x %(-1)) and maternal birth weight EBV (9.0 +/- 4.0 ng x ml(-1) kg(-1)). Heritability estimates were 0.43 (P < 0.02) for melatonin levels and 0.11 (P > 0.25) for prolactin levels. Thus, we conclude that selection for fertility in autumn lambing has affected patterns of melatonin and prolactin secretion during the dark phase.  相似文献   

16.
Abstract

Factors influencing rate of barren ewes, number of lambs born per pregnant ewe, and autumn live weight of the lambs were studied in 627 Norwegian sheep flocks based on herd level data from the Norwegian Sheep Recording System and a mailed questionnaire to the sheep farmers. The following factors were significantly associated (P<0.05) with rate of barren ewes: breed, herd average lambing date, type of production/age of farmer, routines for treatments for parasites, and housing type. Number of lambs born per pregnant ewe was significantly associated with rate of barren ewes, herd average lambing date, breed, percentage grass silage of total roughage, and no separation of gimmers during the housing period. Corrected autumn live weight of the lambs was significantly associated with breed, flock size, lambs born per pregnant ewe, no separation of gimmers during the housing period, and type of summer pasture.  相似文献   

17.
Eight Holstein cows were utilized to examine the effect of prolactin on lactational performance prior to peak milk production (day 21–34 postpartum) and after peak milk production (day 60–73 postpartum). During each 14 day period, cows received daily intramuscular injections of pituitary-derived bovine prolactin (120 mg; 13.0 IU/ mg protein) or excipient. Cows were housed in a controlled environment at 18.1C, 47.8% relative humidity and a 15 hr light: 9 hr dark cycle. In cows administered exogenous prolactin, circulating prolaction concentrations increased within one-half hr post injection, peaked within 2 to 6 hours and declined through the remainder of the day. Average prolactin concentration in the plasma was increased 2 to 5 fold over the 24 hr period in response to prolactin treatment. Yields of milk and milk components (fat, lactose and protein) were not affected by prolactin treatment in either period but the concentration of -lactalbumin in milk was significantly increased (P<.10) in both periods. Circulating concentrations of somatotropin, triiodothyronine, thyroxine, glucagon, nonesterified fatty acids and glucose were not altered. In prolactin-treated cows, the milking-stimulated prolactin release was decreased at both the PM milking, when circulating concentrations of prolactin were high, and the AM milking, when prolactin concentrations had returned to baseline. Concentration of prolactin in milk tended to increase but was not significantly altered by administration of exogenous prolactin. However, prolactin concentrations in plasma were correlated (r=.56) with milk concentrations. It is clear that postpartum administration of exogenous prolactin during the period of lactation prior to peak milk yield or after peak milk yield does not alter lactational performance in high producing dairy cows.  相似文献   

18.
Forty mid-lactation, pasture-fed dairy cows were used to study the effects of milking interval on milk yield and quality and whether effects could be reversed during a short period of subsequent frequent milking. Following a 2-day pre-experimental period of normal twice-daily milking (TDM), cows were milked again after 6, 12, 18, 24 or 30 h, with each milking interval followed by 24 h of frequent milking (i.e., every 6 h). Milk yield increased linearly until 18 h and then started to plateau. Similarly, milk quality (serum albumin and proteolytic enzyme activity) became adversely affected after 18 h. These changes coincided with increased permeability of mammary tight junctions (TJ), starting after a milking interval of 18 h. A brief period of frequent milking helped restore milk yields to pre-experiment levels, even after the longest milking interval.  相似文献   

19.
The main objective of this research was to conduct an exploratory study of the lactation curve in order to characterize the productive potential of Pantaneiro ewes and lambs. Fifty ewes were bred using four rams in two different mating seasons. The ewes were kept with their lambs on pasture of Brachiaria brizantha. Ewe body score, ewe weight, and lamb weight were evaluated. Milk sampling was performed every week. In the morning for milk collections, the ewes were treated with 1 UI of oxytocin (intramuscular) for complete milking. Lambs were separated from the ewes for 4 h and milk collections were performed. The total milk production over 24 h was estimated by multiplying the production of this period (4 h) by 6. The data were analyzed using the MIXED procedure (P?<?0.05) in SAS. Milk production data were fitted to the curve using the incomplete gamma function of Wood, and lamb growth data were fitted using the Gompertiz equation. The average milk production of the ewes was 1.03 kg/day?1. Younger ewes had the lowest milk production (18?=?798?±?330, 24?=?1001?±?440, 36?=?1100?±?490, and 48?=?1106?±?490 g/day?1). Ewe body score at lambing affected initial milk production (1.0?=?816?±?660, 1.5?=?1089?±?105, and 2.0?=?1424?±?1600 g/day?1). Lambs were weaned with an average weight of 20.3 kg. Daily weight gain from birth to weaning was 181 g. Locally adapted Pantaneiro ewes showed a linear decreasing lactation curve, with reduced production from the second week of lactation. Overall, evaluation of the dairy production and lamb performance revealed great variation, denoting potential for selection.  相似文献   

20.
This study was conducted to investigate the effects of rumen-protected tryptophan (125 g tryptophan per day) in heifers and dairy cows. Blood samples from dairy cows and heifers were collected for 24h in 3-h intervals on the day before tryptophan supplementation, on day 2, 5 and 7 of tryptophan supplementation, and in heifers additionally on d 14 after tryptophan supplementation was ceased. Plasma tryptophan, melatonin, serotonin, and prolactin concentrations were determined. Tryptophan plasma concentrations on d 5 were augmented at day (11:00 h) and nighttime (02:00 h), (P<0.05) in response to tryptophan supplementation in heifers by 119% and in dairy cows by 47%, respectively, as compared with d 0. Melatonin increased (P<0.05) in response to tryptophan supplementation in heifers, but not in cows. The effect of tryptophan supplementation on plasma tryptophan and melatonin was reversible as demonstrated in heifers on d 14 after cessation of tryptophan supplementation. Serotonin and prolactin in plasma did not respond to tryptophan supplementation. However, milk yield during morning milking increased significantly in tryptophan supplemented cows on d 1, 3 and 4 as compared to the day before tryptophan supplementation. Additional blood samples were taken during afternoon milking in cows at 1-min intervals for the analyses of oxytocin and prolactin on the day before the start and on d 7 of tryptophan supplementation. Milk flow curves were recorded during milking. No effect of tryptophan supplementation on the milking related release of oxytocin and prolactin and on any characteristic of milk flow was observed. In conclusion, tryptophan supplementation caused increased plasma tryptophan in cows and heifers and plasma melatonin in heifers. However, plasma serotonin, prolactin and oxytocin release in cows remained unchanged by tryptophan supplementation. Milk yield at morning milking increased slightly and transiently in response to tryptophan supplementation.  相似文献   

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