Effects of TRH on circulating growth hormone, prolactin and triiodothyronine levels in the bovine.

The effects of administration of synthetic thyrotropin-releasing hormone (TRH) on circulating growth hormone (GH), PROLACTIN (PRL) and triiodothyronine (T3) levels of lactating dairy cows, non-lactating dairy heifers, and beef cows were studied. Intravenous administration of 0.1, 1, and 5 microgram of TRH per kg of body weight (bw) elevated plasma GH and PRL levels of lactating cows within 5 min. The plasma GH and PRL levels increased in proportion to the dose of TRH and reached a peak 10 to 30 min after TRH injection. Intravenous administration of 1 microgram of TRH per kg of bw to 7 non-lactating heifers, 14 lactating dairy cows, and 5 non-lactating beef cows elevated plasma GH level to peak values after 15 min, the increase rates being 6.9, 5.6, and 3.8 times as high as those in the pretreatment levels. The mean maximum vale was also in that order. Plasma T3 levels of non lactating dairy heifers at pre- and post-injection of TRH were significantly higher than those of lactating cows. The peak values of plasma PRL were obtained between 5 to 30 min after TRH administration. The increase rates of lactating dairy cows, heifers, and beef cows were 19.2, 13.9, and 20.9 times as high as those in the pretreatment. In contrast to GH and T3, plasma PRL levels of both pre- and post-injection with TRH in lactating cows and heifers were significantly higher in May than in October, though the increase rates were similar. Plasma PRL levels of lactating dairy cows at pre- and post-injection with TRH were significantly higher than those of non-lactating heifers. Subcutaneous administration of TRH was also effective to increase plasma TH, rl, and T3 levels in lactating cows. No significant change of GH or PRL response to TRH was observed after a short-term pretreatment of thyroid hormones.     

Studies of pituitary function in lactating ewes.

The release of LH from the pituitary of lactating ewes was studied. In Exp. 1, ewes were injected with 50 microng oestradiol benzoate (OB), 2-0 mg testosterone propionate (TP) or oil only (control) on days 5, 10, or 20 after lambing. LH was measured in peripheral plasma samples obtained 20-38 h after treatment, and the ovulations were recorded. The number of ewes in which an LH release was detected, and the amount released, declined between Day 5 and 20 after OB treatment but increased after TP treatment. The releases of LH were not always accompanied by ovulation and the incidence of ovulation was higher in ewes treated with TP. In Exp. 2, lactating ewes were injected with 1 or 5 (at 2-h intervals) doses of 50 microng Gn-RH, on Days 12 or 25 after lambing. LH was measured in peripheral plasma samples collected every 2 h for 10 h and every 3 h for a further 70 h. Release of LH occurred in all ewes, the amount being greater in ewes receiving multiple injections and in ewes treated on Day 25. The incidence of ovulation was higher after treatment on Day 25. Multiple injections of Gn-RH appeared to reduce the incidence of abnormal corpora lutea.     

Plasma GH, IGF-I, and conception rate in cattle treated with low doses of recombinant bovine GH

Blood and uterine concentrations of GH and insulin-like growth factor (IGF)-I are correlated with improved fertility in cattle. We tested incremental doses of a 14-d sustained release recombinant bovine GH (rbGH) to increase blood GH and IGF-I (Experiments 1 and 2). Conception rate after administration of an optimized rbGH dose was also tested (Experiment 3). In Experiment 1, lactating Holstein cows (n = 18) were randomly assigned to receive 0 (n = 5), 100 (n = 5), 200 (n = 5), or 500 (n = 3) mg sc rbGH. Increasing the doses of rbGH was associated with increased serum concentrations of GH and IGF-I. The 100- and 200-mg doses caused an IGF-I release that was below and above, respectively, the perceived optimum response. Therefore, Experiment 2 was designed to test a rbGH dose (167 mg), which was intermediate to the doses tested in Experiment 1. Lactating and nonlactating postpartum beef cows were treated with 0 (n = 9) or 167 (n = 9) mg rbGH at insemination. Plasma concentrations of GH and IGF-I were greater in rbGH-treated cows than in controls. Lactating cows had initial IGF-I concentrations that were lower than nonlactating cows. The 167-mg dose of rbGH increased plasma IGF-I concentrations in lactating cows to the levels of those of nonlactating cows. In Experiment 3, cows and heifers were administered either 0 or 167 mg rbGH at insemination. The conception rate for rbGH-treated and control cows was 54.4 and 49.5% (n = 617), and 46.0 and 46.3% for heifers (n = 1123), respectively. Herd (P<0.01) and parity (P<0.01) affected conception rate, but conception rates for rbGH and control cattle were similar. In summary, low doses of rbGH increased blood GH and restored blood IGF-I concentrations in lactating cows to those of nonlactating cows, but the conception rate in cows and heifers was not affected by administration of 14-d sustained-release rbGH at insemination.     

Endocrine regulation of phosphorus and calcium metabolism during pregnancy in domestic ruminants

In pregnant domestic ruminants (cows, ewes, goats) foetal plasma calcium and inorganic phosphorus concentrations are higher than those measured in the dam. The foetus regulates its own calcaemia and phosphataemia. Changes in maternal plasma calcium levels have no significant effect on foetal calcaemia. Calcium and phosphorus are transported from the dam to the foetus according to a one-way process, the transport from the foetus to the dam being negligible. An important part of the calcium transferred to the foetus comes from the maternal skeleton. The true molecular mechanisms involved in placental transport of calcium are still unknown. This is an active transport, stimulated by vitamin D metabolites (of maternal, foetal or placental origin) and maternal prolactin. Maternal calcitonin protects the skeleton of the pregnant (and lactating) female ruminant against excessive demineralization, partly by modulating placental transport of calcium during periods of intense mineralization of foetal skeleton.     

Strategic use of gonadotrophin-releasing hormone (GnRH) to increase pregnancy rate and reduce pregnancy loss in lactating dairy cows subjected to synchronization of ovulation and timed insemination

The objective of this study was to determine the effect of GnRH (100 microg i.m.) treatment 5 and 15 days after timed insemination (TAI) on pregnancy rate and pregnancy loss in lactating dairy cows subjected to synchronization of ovulation. The study included 831 lactating dairy cows subjected to a Presynch-Ovsynch protocol for first service. On the day of TAI (Day 0), cows were randomly assigned to one of four experimental groups. Cows in Group 1 (n = 214) were treated with GnRH on Day 5; cows in Group 2 (n = 209) were treated with GnRH on Day 15; cows in Group 3 (n = 212) were treated with GnRH on both Day 5 and Day 15; cows in Group 4 (n = 196) were not treated. Pregnancy rate was evaluated at Day 27 and Day 45 after TAI. The interestrus interval and the proportion of cows diagnosed not pregnant based on expression of estrus and insemination before pregnancy diagnosis on Day 27 were determined. The results of this study are: (1) GnRH treatment on Day 5 or Day 15 did not increase pregnancy rate, or reduce pregnancy loss between Day 27 and Day 55 after TAI; (2) cows treated with GnRH on both Day 5 and Day 15 had a lower (P < 0.01) proportion of cows diagnosed not pregnant based on expression of estrus before ultrasonography on Day 27 (26.5%) compared to control cows (52.9%), and these cows had an extended (P = 0.05) interestrus interval (23.4 days vs. 21.5 days); and (3) GnRH treatment on both Day 5 and Day 15 after TAI reduced pregnancy rate on Day 27 (36.8% vs. 44.4% for control cows; P < 0.03) and Day 55 (28.3% vs. 36.2% for control cows; P < 0.01). Therefore, strategies to stimulate CL function using multiple doses of GnRH during the luteal phase need to consider potential negative effects.     

Does inadequate luteal function limit the establishment of pregnancy in the early post-partum ewe?

In Exp. 1 the effect of lactation versus early weaning on luteal function was examined in seasonally anoestrous Finn Dorset ewes that were induced to ovulate at 21 (N = 14) or 35 (N = 14) days post partum by using a CIDR device and PMSG. Prolactin concentrations were significantly higher (P less than 0.001) in lactating compared with early weaned ewes throughout the study. The proportion of lactating ewes with inadequate luteal function (as assessed by daily progesterone concentrations) in the 21-day group was 0.43 (3 or 7) compared with 0.67 (4 of 6) for those weaned within 2 days after parturition. Corresponding values for the 35-day group were 0 (0 of 4) and 0.14 (1 of 7) respectively. There was no evidence of abnormal luteal function in standard ewes (N = 8) for which the interval from parturition was greater than 150 days. In Exp. 2 we examined whether pregnancy can be successfully established during the breeding season following transfer of embryos into lactating or early weaned ewes in the early post-partum period. Embryos were donated from Border Leicester x Scottish Blackface ewes for which the interval from previous parturition was greater than 150 days. These embryos were transferred synchronously on Day 5 after behavioural oestrus to recipient ewes with the same breeding history as the donors (standard ewes, N = 15) or to lactating or early weaned recipients that had been induced to ovulate on Day 21 (N = 16) or 35 (N = 24) post partum. In the 21-day group inadequate luteal function was observed in 2 of 7 (0.28) lactating and 4 of 9 (0.44) early weaned ewes compared with corresponding values of 1 of 13 (0.08) and 2 of 11 (0.18) in the 35-day post-partum group. Luteal function was normal in all standard ewes. The proportion of successful pregnancies in the standard ewes was 0.80 (12 of 15) compared with 0 in lactating and early weaned ewes in the 21-day group and 0.08 (1 of 13) and 0.36 (4 of 11) respectively in the 35-day group. The incidence of inadequate luteal function is therefore independent of the suckling stimulus and is higher in ewes induced to ovulate on Day 21 than Day 35 post partum during breeding and non-breeding seasons.(ABSTRACT TRUNCATED AT 250 WORDS)     

Synchronization of ovulation in dairy cows using PGF2alpha and GnRH

This paper reports a new method for synchronizing the time of ovulation in cattle using GnRH and PGF(2alpha). In Experiments 1 and 2, lactating dairy cows (n=20) ranging from 36 to 280 d postpartum and dairy heifers (n=24) 14 to 16 mo old were treated with an intramuscular injection of 100 mug GnRH at a random stage of the estrous cycle. Seven d later the cattle received PGF(2alpha) to regress corpora lutea (CL). Lactating cows and heifers received a second injection of 100 mug GnRH 48 and 24 h later, respectively. Lactating cows were artificially inseminated 24 h after the second GnRH injection. Ovarian morphology was monitored daily by trans-rectal ultrasonography from 5 d prior to treatment until ovulation. In Experiment 3, the flexibility in the timing of hormonal injections with this synchronization protocol was evaluated by randomly assigning 66 lactating dairy cows to 3 different treatment groups. Lactating cows received the injection of PGF(2alpha) 48 (Group 1), 24 (Group 2), and 0 h (Group 3) prior to the second injection of GnRH, which was administered at the same time in each group to ensure the second injection of GnRH was given when follicles were at a similar stage of growth. In Experiments 1 and 2, the first injection of GnRH caused ovulation and formation of a new or accessory CL in 18 20 cows and 13 24 heifers. In addition, this injection of GnRH initiated or was coincident with initiation of a new follicular wave in 20 20 lactating cows and 18 24 heifers. Corpora lutea regressed after PGF(2alpha) in 20 20 cows and in 18 24 heifers. All cows and 18 24 heifers ovulated a newly formed dominant follicle between 24 and 32 h after the second injection of GnRH. Ten of 20 cows conceived to the timed artificial insemination. In Experiment 3, the conception rate in Groups 1 and 2 were greater than in Group 3, (55 and 46 % vs 11%, respectively). In summary, this protocol could have a major impact on managing reproduction in lactating dairy cows, because it allows for AI to occur at a known time of ovulation and eliminates the need for detection of estrus.     

Changes in some blood constituents of Barki ewes during pregnancy and lactation under semi arid conditions

A study based on 12 pregnant and six dry Barki ewes was carried out to examine the changes in blood constituents during pregnancy and lactation periods. The blood parameters were blood hemoglobin, packed cell volume percent (PCV%), mean corpuscular hemoglobin concentration (MCHC), glucose, aspartate aminotransaminase (AST or GOT), alanine aminotransaminase (ALT or GPT), total plasma protein, albumin, globulin, albumin to globulin ratio (A/G), urea and creatinine. During pregnancy all these parameters started to increase significantly, but in different stages, reaching maximum values at parturition. In contrast, dry ewes showed almost stable values during the experimental period. From 10th week to parturition, PCV% and MCHC increased (P<0.01) in pregnant ewes, which resulted in increased (P<0.01) blood hemoglobin. Blood glucose increased from the 4th week of pregnancy to reach its maximum at parturition (60.15–90.08 mg/dl). The two transaminases increased significantly from the 2nd week (52.23–65.02 IU for AST and 8.02–15.12 IU for ALT). Plasma protein with its two components, albumin and globulin, increased significantly at the 6th week, but dropped throughout the 16–18th week of pregnancy. Urea and creatinine began to increase significantly after 10–12 weeks of pregnancy (from 54.73 to 72.11 mg/dl for urea and from 0.882 to 2.475 mg/dl for creatinine). During the first month of lactation, PCV decreased sharply in lactating ewes and was significantly lower than in dry ewes at the 3rd week of lactation (24.25 versus 27.17%), which resulted in a drop in blood hemoglobin at the 4th week (68.42 versus 74.00 g/l). However, lactating ewes maintained significantly higher values of MCHC (30.01–31.19% for lactating versus 29.87–27.48% for dry). In lactating ewes, levels of glucose, ALT, urea and creatinine returned to levels comparable to those in dry ewes. The same occurred with total plasma proteins, mainly due to a sharp decrease in globulin, while albumin remained higher than in dry ewes with a slow decline, which resulted in higher values of A/G ratio during lactation. Aspartate aminotransferase remained higher than in dry ewes.     

Effect of supplemental dietary biotin on performance of lactating ewes

Seventy-two lactating Chios ewes were used in two experiments to determine effects of supplemental dietary biotin on productivity and milk composition. The first experiment started after weaning on day 42 postpartum, and lasted 20 weeks, while the second started on week 24 postpartum and lasted 12 weeks. In both experiments, ewes were allocated, after equal distribution relative to milk yield, body weight, time of lambing, and lactation number (i.e., two or three), into three groups of 24 ewes each, and were accommodated in three floor pens/groups of eight ewes/treatment. Ewes were fed one of three diets varying in supplemental biotin (BIOTIN0, no supplemental biotin; BIOTIN3, 3 mg supplemental biotin/ewe/day; BIOTIN5, 5 mg supplemental biotin/ewe/day) in each experiment. Milk, fat, protein, lactose and ash yield, and milk fat content increased linearly (P<0.012) with increased dietary biotin in both studies. Dietary biotin supplementation improved the productive performance of these lactating ewes at both an early and late stage of lactation.     

Inter-breed variation in the postpartum ewe response to continuous low dose infusion of GnRH

During the nonbreeding season the pituitary and ovarian responses to a subcutaneous GnRH infusion were investigated in acyclic, lactating Mule ewes which exhibit a deep seasonal anestrus and in Finn x Dorset ewes in which seasonal anestrus is ill-defined. Each breed received 10 d of progestagen priming before being subdivided into 3 groups. In Group L + G, 5 lactating ewes received GnRH (250 ng/h sc) for 96 h; in Group D + G, 5 dry ewes received GnRH (250 ng/h sc) for 96 h; in Group L, 5 lactating ewes received saline vehicle for 96 h. The infusions began when lactating and dry ewes were approximately 28 d and 120 d post partum, respectively. Blood samples were collected for LH, progesterone and estradiol analysis. Estrous behavior was monitored between Day -4 and Day +7. On Day +7 the reproductive tract was also examined. In the Mule ewes the mean plasma LH concentration increased (P < 0.05) following minipump insertion in each treatment group, although mean LH levels were greater (P < 0.05) in Group D + G, than in either Group L + G or Group L. Following the GnRH infusion, mean plasma estradiol levels increased (P < 0.05) in Group D + G but not in Group L + G. A preovulatory LH surge and subsequent ovulation occurred in 5 5 , 2 5 and 0 5 ewes from Group D + G, L + G and L, respectively, and estrus was recorded in 5 5 , 1 5 and 0 5 of these ewes, respectively. The LH surges began earlier (P < 0.05) (43.2 +/- 6.8 h vs 77.0 +/- 1.0 h) and the ovulation rate was greater (2.2 +/- 0.37 vs 1.00 +/- 0.00) in Group D + G than Group L + G. In the Finn x Dorset ewes mean LH concentrations increased (P < 0.05), to a similar level following minipump insertion in Groups D + G and L + G, but not Group L. The elevated LH levels were accompanied by increased (P < 0.05) plasma estradiol levels in Group D + G, but not in Group L + G. The GnRH infusion culminated in an LH surge and estrous behavior in 5 5 , 1 5 and 0 5 ewes from Groups D + G, L + D and L, respectively. The interval to the LH surge was similar between Group D + G (48.4 +/- 6.6 h) and Group L + G (46.0 h). Ovulation was evident in those ewes which exhibited an LH surge plus one additional ewe from Group L + G. The mean ovulation rate was greater in Group D + G (4.00 +/- 1.05) than in Group L + G (1.5 +/- 0.50). These data show that continuous GnRH infusion can consistently induce out of season breeding in the nonlactating Mule and Finn x Dorset ewe but can not break combined seasonal and lactational anestrous in these breeds. Further, between-breed differences are evident in the site along the hypothalamic-pituitary-ovarian axis at which reproduction is compromised in ewes at the same chronological stage post partum.     

The effect of the intramammary infusion of Escherichia coli endotoxin on ovulation in lactating dairy cows

The purpose of this experiment was to determine if intramammary inflammation during the periovulatory period affects the occurrence of ovulation in lactating dairy cows. Ten lactating, cyclic, Holstein dairy cows received 2 injections of prostaglandin F2alpha at eleven-day intervals, to synchronize luteolysis. The day of the second injection was designated as day 0. Ovulation was anticipated to occur 3-5 days later (on days 3-5). Beginning at the morning milking on day 1, cows received intramammary infusions of either Escherichia coli endotoxin (10 microg; n=5) or infusion vehicle (pyrogen free Hank's balanced salt solution; n=5) into 2 quarters immediately after milking. The same quarters were infused after each milking through day 4. Venous blood samples were collected daily from day -1 through 13 for determination of progesterone to monitor luteolysis and formation of a new corpus luteum. Blood samples were also collected at 4-h intervals (days -1 to 2), then at 2-h intervals (days 2 to 5) to measure concentrations of luteinizing hormone. Ovaries were examined ultrasonographically on days -1 through 5 and on day 12 to monitor follicular growth and formation of the corpus luteum. Collectively, these observations were used to determine if and when ovulation occurred. Intramammary infusion of E. coli endotoxin induced an immediate increase in the concentration of somatic cells in milk from treated quarters. However, this treatment had no effect on the occurrence or timing of ovulation. Based on ultrasonography and concentrations of progesterone, four of five cows in each treatment group appeared to have ovulated. Preovulatory surges of LH were detected within the intensive bleeding periods for three cows in each treatment group. The magnitude of the LH surge was reduced in cows receiving endotoxin.     

Plasma growth hormone, insulin-like growth factor-I, and milk production responses to exogenous human growth hormone-releasing factor analogs in dairy cows

Responses of plasma growth hormone (GH) and insulin-like growth factor-I (IGF-I), and milk production to subcutaneous (sc) injection(s) of two synthetic human growth hormone-releasing factor (hGRF) analogs were studied in dairy cows. Two mg of each hGRF analog dissolved in 5 ml saline per cow were injected into the shoulder area of each experimental animal, and jugular venous blood samples were collected via an indwelling catheter or by venipuncture. Plasma GH and IGF-I concentrations were measured by radioimmunoassay methods. In dry cows, the mean concentration of plasma GH after a single sc injection of hGRF analogs rose to 22.0-28.3 ng/ml at about 5 h from 1.4-1.7 ng/ml at 0 h (just before injection), and returned to the level before injection after 10-12 h. On the other hand, the plasma IGF-I began to increase after a lag of 4-6 h following a single injection of hGRF analogs, and reached maximum values of 71.1-89.4 ng/ml at 20 h from 43.7-46.4 ng/ml at 0 h. The IGF-I concentration at 24 h after a single injection of hGRF analogs was still higher than the value for the dry cows given saline. In lactating cows, the plasma concentration of GH at 2 h after daily sc injections of hGRF analogs during 14 consecutive days (an injection period) was higher than those for the lactating cows which received saline. Also, during the injection period, the concentration of IGF-I was higher in the lactating cows which received hGRF analog injections than in the cows which received saline injections. During the last 7 days of the injection period, the administration of hGRF analogs increased the mean milk yield by 11-19% in comparison with those for the saline injected cows. A positive correlation was observed between the mean plasma IGF-I concentration and the mean milk yield in the lactating cows treated with hGRF analogs throughout the injection and a postinjection (11 consecutive days after cessation of hGRF analog injection) periods. The results demonstrate that a single sc injection of hGRF analogs stimulates both GH release and the circulating level of IGF-I in dry cows, and that daily sc injections of hGRF analogs over 14 days enhance milk production, and plasma GH and IGF-I levels in lactating cows.     

The effects of nutrition on the reproductive performance of Finn x Dorset ewes. II. Post-partum ovarian activity, conception and the plasma concentration of progesterone and LH.

After lambing forty-five ewes were allocated to three groups, two of sixteen and one of thirteen ewes. The lambs of the two groups of sixteen ewes were weaned on Day 1 after lambing and the ewes were fed a diet of 100% (Group H) or 50% (Group R) of maintenance energy requirements. The thirteen ewes in the third group (Group L) suckled twin lambs and were fed freely. During the first 3 weeks after lambing, oestrus was observed for 11/16 (Group H) and 8/16 (Group R) ewes; of the ewes which had shown oestrus in the two groups, ovulation occurred in 5/8 and 5/7 respectively. Only 1/13 Group-L ewes showed oestrus and ovulated during the same period. The mean plasma concentrations of progesterone and LH were unaffected by the treatments and were around 0-4 and 1-5 ng/ml, respectively. Restricted feeding had no effect on oestrus, ovulation or the hormone levels during the oestrus cycle following synchronization. The onset of oestrus and the start of the preovulatory discharge of LH were 3 and 6 hr later, respectively, in the lactating ewes (Group L) than in those in Groups H and R. Ewes in Group L also had a higher ovulation rate, 2-8 +/- 0-2 versus 2-1 +/- 0-2 (P less than 0-05). Restricted feeding reduced the number of ewes lambing; only 1/11 ewes in Group R, considered to have conceived because of the presence of high progesterone levels 17 days after mating, subsequently lambed compared with 6/12 in Group H and 5/9 in Group L.     

Daily rumination time of lactating dairy cows under heat stress conditions

The dairy industry in regions with moderate climates, such as Central Europe, will be increasingly challenged in the future by climate change. The problem of heat stress will especially affect dairy husbandry in naturally ventilated barns (NVB). The approach of the study was to determine a heat stress threshold of the average daily temperature-humidity index (THI) that results in changes in the daily rumination time (RT) of lactating, high-yielding cows. The data set was composed of a high sample size of 183 cows and long-duration measurements of 21240 daily observations over two years from June 2015 to May 2017, which were collected in an NVB in Groβ Kreutz, Germany. The THI was calculated in 5-min intervals by data from several sensors in different positions inside the barn. Additionally, every cow from the herd of an average of 53 cows in the experimental procedure was wearing a neck collar with a Lely Qwes HR system that provided the RT 24 h a day (12 2-h recordings were summarized). The study showed that heat stress also negatively influenced RT in moderate climates. The heat stress threshold of 52 THI was determined by broken-stick regression and indicated changes of RT of lactating dairy cows in Germany. During the experimental period, the heat stress threshold for RT was reached from April to September for up to 720 h per month. The changes in RT to the heat stress threshold will be affected by cows' characteristics. Therefore, we considered several cow-related factors, such as milk yield (MY), lactation number (LN), lactation stage (days in milk, or DIM) and pregnancy stage (P) to better understand cows’ individual reactions to heat stress. Multiparous, high-yielding cows in later lactation stages are potentially more strongly affected than other cows.     

The effect of physiological state (lactating or dry) and sward surface height on grazing behaviour and intake by dairy cows

The effect of physiological state lactating vs. non-lactating (dry) on grazing behaviour and herbage intake by Holstein-Friesian cows was examined on grass pastures maintained at 5, 7 or 9 cm sward surface height (SSH), typical of those provided under continuous variable stocking management. Intake rates were estimated over periods of 1 h by weighing the animals before and after grazing, retaining the faeces and urine excreted, and applying a correction for insensible weight loss. Grazing behaviour during these periods and over 24 h was recorded automatically using sensors to measure jaw movements. Bite mass (BM) did not differ significantly between lactating and dry cows but decreased (P<0.001) from 0.42 to 0.30 g organic matter (OM) bite⁻¹ as overall mean SSH decreased from 9 to 5 cm. An increase (P=0.040) in grazing jaw movement (GJM) rate, from 75.3 to 80.3 GJM min⁻¹, as SSH decreased, did not compensate for reductions in bite mass, and intake rate declined linearly (P=0.006) from 24.6 to 18.9 g OM min⁻¹. Lactating and dry cows compensated for the reduction in intake rate, by increasing total grazing time and total number of bites per day. As SSH decreased from 9 to 5 cm, lactating and dry cows increased total eating time (528 to 607 and 419 to 510 min), total GJM (40 400 to 49 300 and 31 300 to 40 600 GJM) and total bites (31 100 to 37 900 and 24 600 to 31 200 bites, respectively). As a result, there was no significant effect of SSH on daily intake of OM, although lactating cows had greater intakes than dry cows; 12.9 vs. 9.3 kg day⁻¹, (P<0.001). The increased time spent grazing as SSH decreased was associated with a reduction in the time spent ruminating (P<0.001), despite similar levels of daily intake being achieved across SSH treatments. Although dry cows had much lower daily intakes, they spent only about 30 min less each day ruminating than the lactating cows (P=0.060), allowing them 120 to 160 min more idling (i.e., non-grazing, non-ruminating) behaviour (P=0.001).     

Successful pregnancies after transfer of embryos recovered from ewes induced to ovulate 24-29 days post partum

After lambing in late November, oestrus and ovulation were induced by using a CIDR device and PMSG in early weaned (N = 13) or lactating (N = 14) Border Leicester x Scottish Blackface ewes between 23 and 29 days after parturition. Ewes were intrauterine inseminated under laparoscopic visualization 54-55 h after CIDR-device withdrawal and eggs recovered on Day 3 of the cycle. Ovum recovery and fertilization rates were higher in lactating than in early weaned ewes, with fertilization being achieved as early as 24 days post partum in both groups. Of the 7 early weaned and 11 lactating ewes yielding eggs, fertilization occurred in 4 and 7 ewes respectively. A total of 20 embryos were transferred to the normal uterine environment of 15 recipient ewes in which the interval from parturition was greater than 150 days. Pregnancies were successfully established in 9 recipient ewes, resulting in the birth of 10 viable lambs. Prolactin concentrations were significantly higher (P less than 0.001) in lactating than in early weaned ewes throughout the study. Nevertheless, normal luteal function (as assessed by daily progesterone concentrations) was exhibited by 12 of 14 lactating and 8 of 13 early weaned ewes. Two post-partum donors in which the corpora lutea completely failed to secrete progesterone yielded fertilized eggs which developed to term when transferred to a normal uterine environment. The results show that sheep oocytes can be fertilized using laparoscopic intrauterine insemination as early as 24 days after parturition and that the resulting embryos are viable when recovered on Day 3 after oestrus and transferred to a normal uterine environment.     

Ovine trophoblast protein-1 and bovine trophoblast protein-1 are present as specific components of uterine flushings of pregnant ewes and cows

A rabbit antiserum raised against ovine trophoblast protein-1 (oTP-1) was used to stain Western blots of the protein components from the uterine flushings of pregnant ewes (n = 61), non-bred cyclic ewes (n = 22), bred-but-nonpregnant ewes (n = 36), pregnant cows (n = 34), and bred-but-nonpregnant cows (n = 15). Nonpregnant animals were defined as ones from which no embryo was recovered. Uterine flushings of pregnant ewes contained oTP-1 between Days 14 and 24 of pregnancy, but not at Day 12. All of the cyclic ewes and 34 of 36 bred ewes, judged as nonpregnant, tested negatively for the presence of oTP-1. With one exception, oTP-1 was not detected in the nongravid uterine horns of pregnant ewes in which the conceptus had been confined to one uterine horn. Bovine trophoblast protein-1 (bTP-1), which cross-reacts immunologically with oTP-1, was also detectable specifically in the uterine flushings of pregnant cows when anti-oTP-1 antiserum was used. The urine (n = 14) and certival mucus (n = 20) samples of all the pregnant ewes tested were free of any detectable oTP-1. Thus, a useful pregnancy test for ewes based on oTP-1 release into these fluids seems unlikely. Results of this study show that oTP-1 and bTP-1 are pregnancy-specific proteins that are secreted into the uterine lumen where they possibly exert a local response.     

Effect of farm and simulated laboratory cold environmental conditions on the performance and physiological responses of lactating dairy cows supplemented with bovine somatotropin (BST)

A study was conducted to evaluate the effect of bovine somatotropin (BST) supplementation in twelve lactating dairy cows maintained in cold environmental conditions. Six cows were injected daily with 25 mg of BST; the other six were injected with a control vehicle. Cows were maintained under standard dairy management during mid-winter for 30 days. Milk production was recorded twice daily, and blood samples were taken weekly. Animals were then transferred to environmentally controlled chambers and exposed to cycling thermoneutral (15° to 20° C) and cycling cold (–5° to +5° C) temperatures for 10 days in a split-reversal design. Milk production, feed and water intake, body weights and rectal temperatures were monitored. Blood samples were taken on days 1, 3, 5, 8 and 10 of each period and analyzed for plasma triiodothyronine (T³), thyroxine (T⁴), cortisol, insulin and prolactin. Under farm conditions, BST-treated cows produced 11% more milk than control-treated cows and in environmentally controlled chambers produced 17.4% more milk. No differences due to BST in feed or water intake, body weights or rectal temperatures were found under laboratory conditions. Plasma T³ and insulin increased due to BST treatment while no effect was found on cortisol, prolactin or T⁴. The results showed that the benefits of BST supplementation in lactating dairy cows were achieved under cold environmental conditions.     

Partitioning of nutrients in merino ewes. II. Glucose utilization by skeletal muscle, the pregnant uterus and the lactating mammary gland in relation to whole body glucose utilization

The net uptake and oxidation of glucose by leg muscle, pregnant uterus, and lactating mammary gland, together with the rate of irreversible loss and oxidation of glucose in the whole body of Merino ewes are reported. The ewes were fed on either chaffed oaten hay (OH), chaffed lucerne hay (L), or a mixture of chaffed oaten and lucerne hays (OHL). Measurements were made during five different physiological states: dry (nonpregnant), at 94 and 125 days of pregnancy, and at 20 and 50 days after lambing. Whole body glucose irreversible loss was related significantly to intake of metabolizable energy and fleece-free maternal body weight and this relation was the same in dry, pregnant and lactating ewes. The proportion of glucose oxidized in the whole body was unaffected by diet, but was lower in pregnant than in dry or lactating ewes. Some 6% of whole body carbon dioxide (CO2) production was derived from oxidation of glucose, and in ewes eating the OH diet this proportion was lower than for ewes fed on other diets. The proportion of CO2 derived from glucose was lower in pregnant ewes than in dry and lactating ewes. Leg (muscle) glucose uptake was lower in ewes fed on the OH diet than in ewes given the other diets. This arose partly because of decreased blood flow to the leg in ewes fed OH. Muscle glucose uptake, corrected for lactate output, accounted for 20, 44 and 34% of glucose irreversible loss in ewes fed OH, OHL and L respectively. There was no significant effect of physiological state on glucose uptake by leg muscle. The maximum contribution glucose uptake, corrected for output of lactate, could make to leg muscle oxygen consumption was 31% and there were no differences due to diet or physiological state. Uterine glucose uptake was 10.5 mg min-1 kg-1, and was unaffected by diet and stage of pregnancy. Glucose uptake was maintained, despite a decline in blood flow per kilogram of uterus from 399 to 237 ml min-1 kg-1, between 94 and 125 days of pregnancy by an increase in arteriovenous difference of glucose over the same period from 2.8 to 4.4 mg 100 ml-1. Total uptake of glucose by the uterus increased from 26 to 47 mg min-1 between 94 and 125 days of pregnancy. The proportion of glucose irreversible loss accounted for by uterine uptake increased from 46 to 65% between 94 and 125 days, and was greater for ewes fed OH (84%) than L (46%) at 125 days of pregnancy. A maximum of 71% of milk lactose could have been derived directly from glucose; 17% of glucose taken up by the mammary gland was oxidized, contributing to 20% of mammary CO2 output. Mammary glucose uptake was lower in ewes fed OH than in ewes fed the other diets.(ABSTRACT TRUNCATED AT 400 WORDS)     

Development of a radioimmunoassay for plasma C-peptide in sheep: kinetics of C-peptide and effects of exogenous growth hormone and glucose on insulin and C-peptide

An antiserum to purified bovine C-peptide was used to develop a sensitive radioimmunoassay for C-peptide in sheep. The assay was used to measure kinetics of C-peptide and insulin in non-pregnant and non-lactating sheep. Injected, purified C-peptide was distributed in pools comprising c. 11.4% of liveweight, the half time of C-peptide was estimated as 13.7 min and its clearance rate was c. 5 ml kg-1 min-1. In lactating ewes exogenous recombinant bovine growth hormone (rebGH) increased both plasma insulin and C-peptide as did glucose challenge given before and during administration of rebGH. Estimates of insulin secretion rate in lactating ewes were c. 7 x 10(-3) and 8.5 x 10(-3) nmol kg-1 min-1 before and after glucose challenge prior to injections of rebGH. After 4 days of injection of rebGH, corresponding values were c. 8 x 10(-3) and 10 x 10(-3) nmol min-1 kg-1.