Ewes In Lactation Research Articles

Parathyroid hormone-related protein and calcium concentrations in milk and blood of ewes

Parathyroid hormone-related protein (PTHrP) and calcium (Ca) concentrations were measured 2 to 3 months postpartum in milk and plasma or serum of 22 ewes by the use of commercial radioimmunoassay kits for PTHrP concentration, colorimetry for serum total Ca concentration (Ca tot), and atomic absorption spectrophotometry for milk total Ca concentration. Scatter plots did not reveal dependency between milk Ca and Ca tot, Ca tot and plasma PTHrP, milk Ca and milk PTHrP, and milk PTHrP and plasma PTHrP. Thus, the systemic and mammary effects of PTHrP are not major determinants of the endocrine, paracrine, and autocrine regulation of Ca homeostasis during lactation in ewes.

Effects of underfeeding Awassi ewes in late pregnancy and early lactation on body weight changes and milk production

Effects of underfeeding Awassi ewes in late pregnancy and early lactation on body weight changes and milk production

Effects of underfeeding Awassi ewes in late pregnancy and early lactation on body weight changes and milk production

Effects of underfeeding Awassi ewes in late pregnancy and early lactation on body weight changes and milk production

Induction of breeding in anoestrous crossbred ewes with progestagen and PMSG with or without prior immunisation against an androstenedione-protein conjugate

Results are presented of an investigation into the potential value of immunisation of anoestrous ewes with androstenedione-7-HSA, using a commercial preparation (Fecundin; PitmandashMoore, Australia) prior to treatment with intravaginal sponges impregnated with fluorogestone acetate (Cronolone; Searle) and Pregnant Mare Serum Gonadotrophin (PMSG) for out-of-season breeding. Five experiments, involving treatment of 1292 ewes in various physiological states, were conducted during one anoestrous period of 4 months. Factors introduced were: whether or not immunised; interval from booster dose to mating; and dose of PMSG. The ewes were in three stages of anoestrus, namely early, middle or late. Other associated factors were whether or not they were suckling lambs (lactating) and stage of lactation. In early anoestrus, ewes in early lactation were difficult to impregnate compared with maiden ewes (30.6% vs. 51.9% ewes lambed). In mid-anoestrus, ewes in mid-lactation were comparable with maiden ewes (60.6% lambed). In late anoestrus, by which time most lambs had been weaned, 64.3% lambed. The response to immunisation varied with the time from the booster injection to that of the induced oestrus. A 13–14-day interval was too short and had deleterious effects. At 48 days, there were no deleterious effects and a slight residual beneficial effect on lambing performance. An interval of 21 days was much more effective. It had little effect on the time of onset of oestrus, markedly increased the ovulation rate, did not reduce the percentage ewes that lambed, and resulted in a 47% increase in lambs born to ewes in late lactation or from which lambs had recently been weaned. Immunised ewes consistently shed more ova than did nondashimmunised ewes, and this difference increased with increasing doses of PMSG, raising the question of the potential value of immunised animals as donors in embryo transplant programmes. The use of immunisation in a controlled breeding programme requires evaluation of each particular circumstance. There are potential advantages in terms of increased lambs born but the programme needs to be carefully timed.

The effect of concentrate level on the intakes of silages or hays by ewes in the 1st month of lactation

AbstractIn three experiments, four grass silages and four grass hays were offeredad libitum to a total of 164 Finn Dorset ewes rearing twins in the 1st month of lactation. In addition, one of three constant daily levels (300, 650 or 1000 g fresh weight per ewe) of a barley-based concentrate was offered. In the first experiment, replacement rate of silage with in vitro organic matter digestibility (OMD) of 0·65 was less than for hay (OMD 0·59), at –0·09 v. –0·62 g forage OM per g concentrates OM. Consequently, lamb growth rate was greater and ewe weight loss was less with increased concentrate level for the silage than for the hay. In the second experiment, the replacement rates of three silages (OMD 0·56, 0·60 and 0·67) were not significantly different (mean –0·29) and, once again, increased concentrate level gave significantly better ewe and lamb performance. Finally, the replacement rates for three hays (OMD 0·51, 0·59 and 0·72) were also not significantly different (mean –0·30). Equations are presented to predict the intakes of hays and silages by ewes in early lactation.

Prime lamb production in relation to time of mating

Over 3 years, we examined the possible benefits of moving the joining date from mid March to early February for the productivity of a prime lamb system based on Border Leicester x Merino ewes on the southern tablelands of New South Wales. The proportion of ewes with >1 lamb (fertility) was affected more by year and by age of ewe than by joining date. The mean proportion of fertile ewes with >1 lamb (fecundity) was reduced from 0.28 to 0.15 at the earlier date, while immunisation against androstenedione increased fecundity at both mating times to 0.42 but significantly reduced fertility in the earlier group. Over the 3 years, the earlier joining produced 12 fewer lambs per 100 ewes mated and immunisation increased lamb number by 17, but flushing (for 3 weeks with sunflower meal) had no significant effect. Immunisation did not have a consistently greater effect at the earlier joining. Groups of these ewes, balanced for fetus number, grazed at 6.5, 10, or 13 per ha on pastures based on phalaris and subterranean clover. Ewe liveweight after lambing, lamb birth weight, and perinatal mortality were not affected by joining date, but mean daily weight gain by later born lambs over the first 90 days of life was 44 g greater than for earlier born lambs. However, earlier joining enabled 17 more lambs per 100 ewes to reach a marketable weight of 31 kg within the pasture season. Twins grew more slowly and relatively few reached sale weight. With a mean 1.4 lambs per ewe, the optimum stocking rate on these pastures appeared to be 6.5-10 ewes/ha. Superphosphate application to half of the experimental area, after 17 years without treatment, increased pasture weight, lamb growth rate, and numbers sold. The increase was such that a treated pasture could have carried an extra 3 ewes/ha without depression in individual productivity, relative to an untreated pasture. Supplementation of ewes in late pregnancy and early lactation benefited only twin lambs at the higher stocking rates. The results suggest that a prime lamb system in this environment is more likely to succeed with the earlier joining date. The lower lambing percentage, resulting from a decrease in fecundity, is likely to be of benefit, rather than detriment, to the efficiency of a system in which single- and twin-bearing ewes and their lambs are given equivalent treatment.

Successful fostering of orphan lambs by nonpregnant ewes induced to lactate using exogenous hormone treatment

Six nonpregnant ewes were induced to lactate by an exogenous hormone treatment lasting 6 weeks. At the end of the treatment one alien lamb was adopted by each ewe. Each ewe was initially indifferent to the alien lamb and required only mild restraint to allow the lambs to suck successfully. Maternal interest subsequently increased and strong ewe-lamb bonding was evident by 80 minutes (n=1), 10 hours (n=4) or 24 hours (n=1) in different cases. The lambs required supplementary milk for 4-6 days while milk production by the ewes increased to adequate levels. Thereafter they were reared entirely by the ewes. Another four nonpregnant ewes were induced to lactate by a similar hormone treatment and were then hand-milked thrice daily for 23 weeks. One alien lamb was then removed after 10-30 minutes. The ewes were then injected subcutaneously with 5 mg of oestradiol-17beta and were placed in fostering stocks. After a further 3-5 hours the lambs were re-introduced. Strong ewe-lamb bonding occurred during the subsequent 10 hours in all cases. All 10 lambs were reared successfully by these ewes until at least 3 months of age, when observations stopped. It was concluded firstly that nonpregnant ewes induced to lactate artificially will adopt and rear orphan lambs successfully, provided that additional milk is given to meet shortfalls during the first 4-6 days; and secondly that a 5 mg injection of oestradiol-17beta may facilitate fostering of lambs by ewes in established lactation whether the lactation is induced artificially or not.

Acute or chronic administration of prolactin alters ovine infections of Haemonchus contortus

Prolactin has been implicated as a modulator in the phenomenon of periparturient egg rise during ovine nematodiasis. In the first experiment, lambs (4 months of age) with patent infections (10 000 infective larvae) of Haemonchus contortus were injected daily (Days 28–39 post-inoculation (PI)) with prolactin (20 or 200 IU) or saline. Fecal egg concentrations and total daily egg production were monitored for each lamb. After 12 days, lambs injected with the lower dose of prolactin had the highest daily egg production. Fewer adult worms were collected from prolactin-treated lambs, and the female worms were larger than those from the saline-injected controls. Worm size and number were not correlated. In the second experiment, lambs were injected daily with ovine prolactin (25 IU) or saline. Five days after initiation of treatments, each lamb was inoculated with 3000 infective larvae of H. contortus. After 42 days of injections (Day 37 PI), prolactin-treated lambs had larger and fewer worms, with higher fecundity, than saline-treated controls. Increases in endogenous circulating prolactin during late pregnancy and lactation in ewes, therefore, might contribute to periparturient egg rise irrespective of the developmental stage of the parasite when the hormone exposure occurs.

Effect of supplementary feeding on grazing behaviour of Comisana ewes in a Mediterranean semi-extensive production system

A trial was conducted with two groups of ten Comisana lactating ewes to study the effect of concentrate supplementation level (Group L, 300 g mixed concentrate and 500 g hay; Group H, 600 g mixed concentrate and 500 g hay) on herbage intake, grazing behaviour, milk production and live weight changes. The additional 300 g of concentrate given to Group H had only a partial substitution effect (30% in terms of net energy). No differences were found in selectivity at pasture between groups. The data did not allow us to find any single criterion for selectivity. Ewes of Group L showed a lower biting rate than Group H (mean values: 26.3 vs. 29.5). Total milk production from Day 45 to Day 158 of lactation was 57.6 kg for Group L and 73.3 kg for Group H. Group H showed a better feed conversion index than group L (mean values: 2.02 UFL l −1 vs. 2.14 UFL l −1 (unité fourragère lait)). It was concluded that supplementary feeding, even at high levels, induced a beneficial effect on ewe lactation.

An evaluation of pure-bred and cross-bred dairy ewes in a commercial sheep milking operation

Sheep milk and its products are regaining popularity with approximately 15,000 sheep currently being milked in the UK. Extreme dairy type ewes such as the Friesland are expensive compared to commercial genotypes and the crossing of dairy type sires with commercial ewes to produce cross-bred daughters for milking offers an alternative route of entry into milking sheep. An investigation was carried out on a commercial unit in Aberdeenshire milking around 150 ewes to assess the relative suitability and performance of pure-bred and cross-bred dairy ewes under commercial conditions.The study involved first lactation ewes, 5 Friesland x Scotch Halfbreds being compared with 5 pure-bred Frieslands. The ewes lambed at 15 months of age between 20 and 27 May and the ewes were grazed on ryegrass/white clover swards. Ewes nursed their lambs for four weeks after lambing and machine milking started on day 29 of lactation. Milk yield was recorded weekly while milk fat and protein were measured at two weekly intervals.

Strategies to minimize helminth challenge to summer born lambs grazing clover rich swards on an organic management system

Clean grazing systems for sheep have been developed to minimize helminth challenge to susceptible lambs. Provision of clean grazing relies upon effective control of overwintering helminth infection on pasture and particularly in the post parturient ewe. During early lactation ewes immuno-competence is reduced resulting in the excretion of helminth eggs for approximately six weeks post lambing (Thomas, 1973). Control of this source of infection may be achieved by strategic anthelmintic administration while overwintering pasture infection may be avoided by use of pasture which has not carried sheep in the previous year.Prophylactic anthelmintic administration is unacceptable under an organic management system and consequently alternative strategies must be sought to eliminate the ewe as a source of infection. The objective of the present study was to evaluate strategic transfer of ewes and lambs to a silage aftermath as a means of minimizing helminth challenge to susceptible lambs.

Suckling behavior of ewes in early lactation

Previous studies have described the basic suckling behavior of ewe/lamb pairs during daylight hours, but no information is available for the hours of darkness. In this study, the natural pattern of suckling was recorded over a 24-h period once a week for the first 7 weeks of lactation in 7 free-ranging Merino ewes with single lambs. Both the mean suckling frequency per 24 hours and the mean duration of individual suckling bouts declined with increasing age of the lamb. Suckling frequencies fell from 36±5.5 sucks/24 h at 1–2 weeks of age to 14.3±2.78 sucks/24 h at 6–7 weeks of age. Individual suckling bout duration fell from 41.1±9.9 s at 1–2 weeks of age to 11.9±1.2 s by 6–7 weeks. Suckling frequencies per hour were significantly greater during daylight as compared to darkness ( p<0.05). We suggest that the declining frequency and duration of suckling bouts with age probably accounts for the waning influence of lactation on the reproductive state of the ewe, and that the maintenance of a critical interbout interval may first break down at night.

Regulation of adipose tissue metabolism during pregnancy and lactation in the ewe: the role of insulin1

This study was conducted to examine the effect of insulin on lipid metabolism of adipocytes during pregnancy and lactation in ewes. During the first 3 mo of pregnancy, metabolism of adipocytes from omental adipose tissue was characterized by a high rate of de novo lipogenesis (90 to 125 nmol of acetate incorporated into lipids.2 h-1.10(6) cells-1) and a 38% reduction in response to beta-lipolytic stimulus (isoproterenol 10(-6) M). Simultaneously, there was a rise in the number of high-affinity insulin receptors (Kd = .2 nM), and insulin binding characteristics showed a decrease in the negative cooperativity phenomenon. Moreover, lipogenesis stimulated by insulin (1 mU/ml) increased in comparison with observations in nonpregnant ewes. The last third of pregnancy and early lactation were characterized by a marked fall in lipogenesis and a simultaneous increase in isoproterenol-stimulated lipolysis. During lactation, the number of total insulin receptors was decreased by 62% and insulin stimulation of lipogenesis became inefficient. Results suggest that insulin plays a direct role in adipose tissue metabolism during pregnancy.

Effect of forage type on the digestion of whole barley grain by breeding ewes

ABSTRACTThe proportion of whole grain consumed that was voided intact in the faeces of ewes in late pregnancy and early lactation was measured for diets based on a range of forages in two experiments. The proportions of grain voided intact varied widely between ewes and was to some extent a characteristic of the individual ewe. During late pregnancy on hay-based diets the mean proportion of grain recovered was 0·053 with a range from 0·042 to 0·063 while on silage-based diets 0·135 (range 0·082 to 0·209) was recovered. On silage-based diets after lambing 0·196 and 0·235 of grain was voided intact in the faeces. The proportion of intact grain voided was affected by forage intake. The estimated increase in the proportion of grain voided intact was 0·012 measured over a range of forages before lambing and 0·021 on silage after lambing per 100 g increase in dry matter intake. However, when the total digestibility was measured, there were no differences between feeding of whole and processed grain where proportionately 0·06 of whole grain consumed was voided intact.

Teladorsagia circumcincta egg output at the onset of natural and induced lactation in ewes

Nineteen ewes maintained under ‘worm-free’ conditions received anthelmintic and 1 week later were dosed on 5 days each week with 500 Teladorsagia circumcincta larvae for between 10 and 12.5 weeks. Faecal egg counts were determined twice weekly. There were three groups: pregnant (P) ewes ( n = 6) which each reared twin lambs, hormone-treated (H) ewes ( n = 7) which were not pregnant and were given exogenous hormones (dexamethasone, oestradiol-17β, progesterone) for 37 days to induce udder development and milk production, and untreated barren (B) ewes ( n = 6). The plasma concentrations of oestradiol-17β, prolactin and progesterone were measured. Starting 10–15 days before birth in Group P, there was a biphasic periparturient rise in egg count and the onset of the first peak in egg count preceded the parturient peak in plasma prolactin concentration by several days. Most Group H ( 5 7 ) and all Group B ewes remained highly resistant to Teladorsagia infection throughout, despite an induced rise in prolactin concentrations in Group H ewes. It was concluded that factors other than prolactin initiate the periparturient rise but that prolactin is one factor which maintains the response once lactation commences.

The clearance of bromosulphthalein from plasma as a measure of the changes in hepatic function during pregnancy and lactation in ewes

Single intravenous injections of bromosulphthalein (BSP) were given to sheep and the change in plasma BSP concentration with time was analysed by computer to obtain the proportionality transfer constants ‘ a’, ‘ h’ and ‘ b’ and plasma volume. The BSP half-time, fractional clearance and retention values were also calculated. Alterations in BSP clearance were compared with changes in bilirubin and liver specific enzyme activities in ewes in late pregnancy and early lactation. The measurement of BSP clearance, particularly the proportionality transfer constants, yielded more information about the alterations in hepatocellular function during pregnancy and lactation than the changes in clinical chemistry. It is suggested that these alterations in liver function are physiological rather than pathological at these times.

Attempts to improve the function of GnRH-induced corpora lutea in early post-partum ewes through oestradiol and/or PMSG priming or exogenous luteotrophin

In order to investigate whether subnormal luteal function following induction of ovulation with gonadotrophin releasing hormone (GnRH) could be counteracted by appropriate stimulation before or after ovulation, S.A. Mutton Merino ewes ( n=65) in early lactation were induced to ovulate using GnRH at a time when subnormal luteal function was likely to result. In two experiments the ewes were infused with physiological saline (SRFS), pregnant mare serum gonadotrophin (PMSG) prior to (PRFS), PMSG after (SRFP), PMSG prior to and after (PRFP) or with PMSG plus oestradiol (E 2) prior to (EPRFS) a single injection of GnRH. A group of spontaneously cycling ewes (CYC) was used to characterize normal luteal function. At laparotomy on day 15 (experiment 1) or day 11 (experiment 2) a higher incidence (83.9%) of macroscopically active corpora lutea occurred in the ewes treated with PMSG prior to GnRH (PRFS+PRFP) than where saline was infused (65.5%) at this time (SRFP+SRFS). Of the 56 ewes which completed the experiments only five showed a short cycle of approximately 6 days, while in a further 14 ewes the cycle length approached 12 days. Of the progesterone profiles 37.2% were judged to be inadequate. In both experiments, ewes which did not receive gonadotrophin, SRFS, exhibited a progesterone profile which differed ( P<0.01) from the pooled response of those infused with PMSG. The provision of luteotrophin after GnRH was superior to PMSG priming ( P<0.01) in augmenting progesterone secretion. In experiment 2 PMSG priming improved luteal function so that it equalled that of spontaneously cycling ewes while infusion of oestradiol in addition to PMSG priming further improved luteal function ( P<0.05). The pre-ovulatory LH release was reduced ( P<0.01) by PMSG infusion before and after GnRH (not significant in experiment 1). Tonic LH levels showed that PMSG infusion raised the endogenous release of assayable LH ( P<0.05).

Radial and tibial nerve pathology of two lactating ewes with “kangaroo gait”

Radial and tibial nerves of two ewes with clinical signs of chronic “kangaroo gait” were examined by qualitative and quantitative techniques and compared to the same nerves of a clinically normal ewe in late lactation. In affected ewes, there was extensive axonal degeneration of myelinated fibres in the radial nerve. Large and small myelinated fibres were affected equally and unmyelinated fibres were normal. Nerve fibre regeneration was present. In contrast, tibial nerve changes in the “kangaroo giat” ewes were minimal. The chronic nature of the radial nerve pathology was consistent with the clinical time course of “kangaroo gait”. Regeneration may account for gradual improvement with eventual recovery in most chronically affected ewes. An episode of bilateral severe compression of a proximal radial nerve site is proposed as an explanation for the neuropathy, although the specific mechanism of this trauma is not known.

Estimation of the intake of milk by lambs, from the turnover of deuterium- or tritium-labelled water

1. The total water turnovers of grazing ewes and their lambs were estimated on days 9, 23, 44, 69 and 86 of lactation from the dilution of tritiated water injected into the dam and deuterium oxide injected into the offspring. The contribution of milk to the total water turnover of the lambs was estimated at the same times from the accumulation of tritium in their body water. 2. Mean total water turnover in the ewes was 6.5 titres/d over the entire period. In lambs, total turnover rose from 1459 ml/d at 9 d to 2791 ml/d at 86 d, and was closely related to live weight (r2 0.760, P less than 0.001). The corrections to total water turnover, which were required because of the increasing body water pool size of the lambs during each measurement period, fell from + 10.6% at 9 d to + 3.7% at 86 d. All corrections were significant (P less than 0.001). 3. The intake of water as milk fell throughout the study, from 1501 ml/d at 9 d to 471 ml/d at 86 d. Pool-size corrections were significant (P less than 0.001). Milk intakes calculated from these results were 1816, 1054, 862, 742 and 588 ml/d at 9, 23, 44, 69 and 86 d of lactation. The rapid decline in milk intake reflected undernutrition of the ewes in early lactation. 4. The level of live-weight gain in early lactation was closely related to, and at a level expected from, the estimated milk intakes. From comparisons of estimated milk intakes with published estimates, it is concluded that the combined use of deuterium oxide and tritiated water results in accurate estimates of milk intake by the lamb throughout the ewe's lactation.

EFFECTS OF DIETARY MOLYBDENUM ON PRODUCTIVITY AND METABOLIC PARAMETERS OF LACTATING EWES AND THEIR OFFSPRING

A trial was undertaken to determine ewe lactation, lamb growth and metabolic responses to varying concentrations of molybdenum (Mo) in the diet of ewes. Twelve lactating ewes with twin lambs were assigned to one of three dietary treatments for the first 6 wk of lactation. Ewes were individually fed a corn silage-barley diet supplemented to contain 0.9 (0 Mo), 18.4 (20 Mo) or 40.7 (40 Mo) mg Mo kg−1 dry matter (DM) using ammonium molybdate [(NH4)6Mo7O24∙4H2O]. No feed was offered to lambs. Ewe milk yield and composition, ewe and lamb body weight and blood samples were obtained weekly. Two ewes assigned to 40 Mo and one ewe assigned to 20 Mo developed a condition that was corrected by thiamin administration during their fourth to fifth week on test. Diet did not influence (P &gt; 0.05) milk yield or composition with the exception of milk Mo which increased (P &lt; 0.05) for ewes fed Mo-supplemented rations. Dietary Mo concentration did not influence (P &gt; 0.05) ewe plasma copper (Cu), trichloroacetic acid soluble plasma Cu or ceruloplasmin activity in ewes. Ewe plasma Mo concentrations increased (P &lt; 0.05) 11- and 16-fold, respectively, for ewes fed 20 Mo and 40 Mo relative to those fed 0 Mo. Ewe liver Cu and Mo concentrations at the end of the trial tended (P &lt; 0.10) to be greater for the Mo-supplemented diets. Lamb plasma and liver Cu concentration were not influenced by ewe diet. Milk Mo concentration did not influence (P &gt; 0.05) lamb weight gain but did influence (P &lt; 0.05) plasma Mo. Lamb age influenced (P &lt; 0.05) plasma Mo levels which peaked when lambs were 2–3 wk old and declined thereafter. Key words: Ewe, lamb, lactation, growth, molybdenum, copper