Effect of zinc supplementation on the reproductive performance of grazing Merino ewes

Two experiments were carried out in Western Australia to investigate the effect of zinc supplementation, on the reproductive performance of grazing Merino ewes. We found that supplemental zinc, when provided prior to mating and throughout pregnancy, increased the number of lambs produced by 14% (P<0.05) in both experiments. An intermediate zinc treatment, when supplementation was begun later in pregnancy gave a 9% (P<0.01) increase in the number of lambs in one experiment and no increase in the second. Lamb birth weights were increased by zinc supplementation in Experiment 1 and in Experiment 2, 12–20-week-old lambs from zinc supplemented ewes were 2.1 kg heavier than those from nonsupplemented controls. Plasma zince levels decreased significantly during pregnancy and lactation, but were increased at some sampling dates by 20–25% by zinc supplementation.     

Fertilization and embryo loss in Booroola Merino x South Australian Merino ewes: Effect of the F gene

The effects of Booroola genotype (F+, ++); the number of ovulations per ewe (one, two or three); and the age of a ewe (2.5 yr vs 3.5 to 6.5 yr) on the percentage of ova fertilized, embryo loss and fetal loss were examined in Booroola x South Australian Merino ewes slaughtered on Days 4, 21 and 90 after insemination. Ewes slaughtered on Day 90 were examined by real-time ultrasound imaging (RUI) on Day 45. Fertilization failure was independent of ewe genotype, ovulation rate and age of ewe, and it was not an important source of wastage (F+, 9.4%; ++, 6.7%). Most embryo loss occurred during the first 21 d (F+, 54.7%; ++, 40.3%). Interpretation of the effects of genotype and ovulation rate on embryo wastage measured on Days 21, 45 and 90 was obscured by significant (P < 0.05) genotype and ovulation rate interactions with the day of slaughter/RUI. The effect of age on embryo loss was not significant (P > 0.05). Reasons for the high rate of wastage observed in this experiment require further study.     

Effect of litter size on blood haematocrit and liveweight in Booroola Merino and Merino ewes during pregnancy and the post-partum period

Blood haematocrit and liveweight were determined throughout pregnancy and the post-partum period in 217 Booroola Merino and Merino ewes in order to relate these parameters to litter size at birth. In pregnant ewes, haematocrit declined from three until five months gestation, rose immediately after parturition then declined until two months post-partum. During the third to fifth month of gestation, haematocrit decreased in proportion to litter size. Nonpregnant ewes, measured at similar intervals, did not show the same pattern. Haematocrit of nonpregnant animals was higher than that of triplet-bearing ewes at three, four and five months gestation, but was only significantly different to single- and twin-bearing ewes at five months. The liveweight of pregnant ewes increased up to parturition and then declined until two months post-partum. The liveweight of nonpregnant ewes increased over the experimental period. It was concluded that the number of foetuses a ewe carried had significant effects on the decline in haematocrit during pregnancy. Haematocrit was not a precise indicator of litter size in sheep. Haematocrit, ewe liveweight and ovulation rate together in a multiple regression only accounted for 37% of the variation in litter size.     

Effects of ewes grazing sulla or ryegrass pasture for different daily durations on forage intake,milk production and fatty acid composition of cheese

Sulla (Sulla coronarium L.) forage is valued for its positive impact on ruminant production, in part due to its moderate content of condensed tannin (CT). The duration of daily grazing is a factor affecting the feed intake and milk production of ewes. In this study, the effects of grazing sulla pasture compared with annual ryegrass, and the extension of grazing from 8 to 22 h/day, were evaluated with regard to ewe forage intake and milk production, as well as the physicochemical properties and fatty acid (FA) composition of cheese. During 42 days in the spring, 28 ewes of the Comisana breed were divided into four groups (S8, S22, R8 and R22) that grazed sulla (S) or ryegrass (R) for 8 (0800 to 1600 h) or 22 h/day, and received no feeding supplement. In six cheese-making sessions, cheeses were manufactured from the 48 h bulk milk of each group. Compared with ewes grazing ryegrass, those grazing sulla had higher dry matter (DM) intake, intake rate and milk yield, and produced milk that was lower in fat and higher in casein. Ewes grazing for 22 h spent more time eating, which reduced the intake rate, increased DM and nutrient intake and milk yield, and reduced milk fat. Due to the ability of CT to inhibit the complete ruminal biohydrogenation of polyunsaturated fatty acids (PUFA), the FA composition of sulla cheese was more beneficial for consumer health compared with ryegrass cheese, having lower levels of saturated fatty acids and higher levels of PUFA and n-3 FA. The FA profile of S8 cheese was better than that of S22 cheese, as it was higher in branched-chain FA, monounsaturated FA, PUFA, rumenic acid (c9,t11-C18:2), and had a greater health-promoting index. The effect of short grazing time on sulla was attributed to major inhibition of PUFA biohydrogenating ruminal bacteria, presumably stimulated by the higher accumulation of sulla CT in the rumen, which is related to a higher intake rate over a shorter eating time. Thus, grazing sulla improved the performance of ewes, thereby increasing, especially with short grazing time, the nutritional properties of cheese fat.     

Uterine presensitization and embryo survival and growth in Booroola Merino x South Australian Merino ewes

The fertility enhancing effects of semen were examined following the intra-uterine insemination of killed spermatozoa plus seminal plasma 17 d prior to insemination with viable spermatozoa. Three experiments were conducted: two on 1.5-yr old and 2.5 to 5.5 yr-old Booroola Merino x South Australian Merino ewes in 1986 and one on 1.5 yr-old ewes in 1987. Differences between treatment and control groups for the percentage of ewes exhibiting estrus by Days 21 and 35 following fertile insemination, the percentage of ewes with viable embryos at Day 35, the number and weight of viable embryos per ewe, the nubmer of caruncular implantation sites and the progesterone level were not statistically significant (P>0.05). There were no statistically significant treatment by experiment interactions for any of the variables examined. Inflammation and edema of the endometrial tissue was not observed following the presensitization treatment.     

Fertilization and early embryonic development in androstenedione-immunized Merino ewes

Ewes were immunized against androstenedione (Fecundin) and assigned to be mated 14 days (179 ewes Group C) or 25 days (174 ewes Group B) after a booster immunization with Fecundin. The anti-androstenedione titres at these times were 6790 and 3240 respectively (P less than 0.01). The remaining 169 ewes were untreated controls (Group A). Ewes were mated to entire rams (12 rams to 180 ewes) at their second oestrus after synchronization of oestrus. Immunization against androstenedione caused a shortening of the time from sponge removal to mating (Day 0) and a decrease in the percentage of ewes mated by the rams. Also, ovulation rate was increased after immunization (P less than 0.01), being 1.42, 2.16 and 1.93 for Groups A, C and B respectively. Egg recovery rates on Day 2 were lower in immunized ewes and there was some indication that fertilization rates were lowered. On Day 13 after mating a higher proportion of blastocysts was recovered from ewes in Group A than from those in Groups B and C. Immunization resulted in lower fertilization rates and smaller blastocysts with lower mitotic indexes (P less than 0.01). At Days 24-32 of pregnancy fetal weight was lower in the immunized ewes. At all sampling stages, the proportion of ewes pregnant (fertility) was lowered in immunized ewes. The results of the present study show that significant reproductive wastage occurs in androstenedione-immunized Merino ewes, with lower rates of embryo recovery and delayed embryonic development being found in comparison to controls.(ABSTRACT TRUNCATED AT 250 WORDS)     

Pasture intake and milk production of dairy cows rotationally grazing on multi-species swards

Increasing plant species diversity has been proposed as a means for enhancing annual pasture productivity and decreasing seasonal variability of pasture production facing more frequent drought scenarios due to climate change. Few studies have examined how botanical complexity of sown swards affects cow performance. A 2-year experiment was conducted to determine how sward botanical complexity, from a monoculture of ryegrass to multi-species swards (MSS) (grasses-legumes-forb), affect pasture chemical composition and nutritive value, pasture dry matter (DM) intake, milk production and milk solids production of grazing dairy cows. Five sward species: perennial ryegrass (L as Lolium), white clover and red clover (both referred to as T as Trifolium because they were always sown together), chicory (C as Cichorium) and tall fescue (F as Festuca) were assigned to four grazing treatments by combining one (L), three (LT), four (LTC) or five (LTCF) species. Hereafter, the LT swards are called mixed swards as a single combination of ryegrass and clovers, whereas LTC and LTCF swards are called MSS as a combination of at least four species from three botanical families. The experimental area (8.7 ha) was divided into four block replicates with a mineral nitrogen fertilisation of 75 kg N/ha per year for each treatment. In total, 13 grazing rotations were carried out by applying the same grazing calendar and the same pasture allowance of 19 kg DM/cow per day above 4 cm for all treatments. Clover represented 20% of DM for mixed and MSS swards; chicory represented 30% of DM for MSS and tall fescue represented 10% of DM for LTCF swards. Higher milk production (+1.1 kg/day) and milk solids production (+0.08 kg/day) were observed for mixed swards than for ryegrass swards. Pasture nutritive value and pasture DM intake were unaffected by the inclusion of clover. Pasture DM, organic matter and NDF concentrations were lower for MSS than for mixed swards. Higher milk production (+0.8 kg/day), milk solids production (+0.04 kg/day) and pasture DM intake (+1.5 kg DM/day) were observed for MSS than for mixed swards. These positive effects of MSS were observed for all seasons, but particularly during summer where chicory proportion was the highest. In conclusion, advantages of grazing MSS on cow performance were due to the cumulative effect of improved pasture nutritive value and increased pasture DM intake that raised milk production and milk solids production.     

Odour,and the recognition of lambs by Merino ewes

Ewes that had been separated from their lambs for several hours were each presented with a choice between three anaesthetized lambs, one of which was the ewe's own. Each lamb was in a separate cage adjacent to a passage-way in which the ewe was free to move. The ability of the ewe to select her own lamb was equally good whether the head or the tail region of the lamb was placed against the corridor for examination at close-quarters, but when the lamb was 0.25 m from the corridor, very few ewes appeared able to find their own lambs. Although the ewes displayed less interest in the lamb's head than in the tail region, the head, as well as the tail, appears to provide the ewe with close-quarter clues, presumably olfactory, to the identity of the lamb.     

Zinc supplements and reproduction in grazing ewes

Six experiments were carried out in Western Australia to further investigate the effect of zinc supplementation on the reproductive performance of grazing Merino ewes. There was a small increase (7%,P=0.1) in the number of lambs produced by zinc-supplemented ewes in only one of the six experiments. Plasma zinc levels just prior to lambing were increased by zinc supplementation in two experiments. These results are discussed and compared to the previously published reproductive responses to zinc supplementation by grazing Merino ewes.     

Reproductive capacity of Merino ewes fed a high-salt diet

An option to increase the productivity of saline land is to graze sheep on salt-tolerant plants, which, during the summer/autumn period, can contain 20% to 25% of their dry matter as salt. This study assessed the impact of coping with high dietary salt loads on the reproductive performance of grazing ewes. From the time of artificial insemination until parturition, 2-year-old maiden Merino ewes were fed either a high-salt diet (NaCl 13% of dry matter) or control diet (NaCl 0.5% of dry matter). Pregnancy rates, lamb birth weights, milk composition and the plasma concentrations of hormones related to salt and water balance, and energy metabolism were measured. Leptin and insulin concentrations were lower (1.4 ± 0.09 v. 1.5 ± 0.12 ng/ml; (P < 0.05) and 7.2 ± 0.55 v. 8.2 ± 0.83 ng/ml; P < 0.02) in response to high-salt ingestion as was aldosterone concentration (27 ± 2.7 v. 49 ± 5.4 pg/ml; P < 0.05), presumably to achieve salt and water homeostasis. Arginine vasopressin concentration was not significantly affected by the diets, but plasma concentration of T3 differed during gestation (P < 0.02), resulting in lower concentrations in the high-salt group in the first third of gestation (1.2 ± 0.18 v. 1.3 ± 0.14 pmol/ml) and higher concentrations in the final third of gestation (0.8 ± 0.16 v. 0.6 ± 0.06 pmol/ml). T4 concentration was lower in ewes ingesting high salt for the first two-thirds of pregnancy (162 ± 8.6 v. 212 ± 13 ng/ml; P < 0.001). No substantial effects of high salt ingestion on pregnancy rates, lamb birth weights or milk composition were detected.     

Calm Merino ewes have a higher ovulation rate and more multiple pregnancies than nervous ewes

In 1990, two selection lines of Merino sheep were established for low and high behavioural reactivity (calm and nervous temperament) at the University of Western Australia. Breeding records consistently showed that calm ewes weaned 10% to 19% more lambs than the nervous ewes. We hypothesise that calm ewes could have a higher ovulation rate than nervous ewes and/or calm ewes could have a lower rate of embryo mortality than nervous ewes. We tested these hypotheses by comparing the ovulation rate and the rate of embryo mortality between the calm and nervous lines before and after synchronisation and artificial insemination. Merino ewes from the temperament selection lines (calm, n=100; nervous, n=100) were synchronised (early breeding season) for artificial insemination (day 0) (intravaginal sponges containing fluogestone acetate and eCG immediately after sponge withdrawal). On day-17 and 11 ovarian cyclicity and corpora lutea, and on days 30 and 74 pregnancies and embryos/foetuses were determined by ultrasound. Progesterone, insulin and leptin concentrations were determined in blood plasma samples from days 5, 12 and 17. Ovarian cyclicity before and after oestrus synchronisation did not differ between the lines, but ovulation rate did (day-17: calm 1.63; nervous 1.26; P<0.01; day 11: calm 1.83; nervous 1.57; P<0.05). Ovulation rate on day 11 in nervous ewes was higher than on day-17. Loss of embryos by day 30 was high (calm: 71/150; nervous: 68/130); but nervous ewes had a lower proportion (15/47) of multiple pregnancies compared with calm ewes (30/46; P<0.01). Reproductive loss between days 30 and 74 represented 7.3% of the overall loss. Temperament did not affect concentrations of progesterone, but nervous ewes had higher insulin (32.0 pmol/l±1.17 SEM; P=0.013) and lower leptin (1.18 μg/l±0.04 SEM; P=0.002) concentrations than calm ewes (insulin: 27.8 pmol/l±1.17 SEM; leptin: 1.35 μg/l±0.04 SEM). The differences in reproductive outcomes between the calm and nervous ewes were mainly due to a higher ovulation rate in calm ewes. We suggest that reproduction in nervous ewes is compromised by factors leading up to ovulation and conception, or the uterine environment during early pregnancy, that reflect differences in energy utilisation.     

Comparison of four techniques to estimate milk production in singleton-rearing non-dairy ewes

Accurate estimates of milk production or milk intake are difficult, as all methods interfere to some degree with the natural behaviour of the dam and her young, and potentially alter milk yield itself. The present study compared milk yield obtained by the “oxytocin” method, udder dimensions (UD), the isotope dilution method, and live weight change of the lamb, in an attempt to select the most accurate and convenient way of measuring milk production in non-dairy sheep. In addition, the study investigated which of the three milk-estimation techniques was an accurate predictor of growth rates of lambs. Thirty-seven singleton-bearing and rearing ewes were milked once a week, for seven consecutive weeks, using the “oxytocin” method. Prior to each afternoon milking, the external dimensions of the ewe's udder were measured. Lambs were weighed weekly for the first seven weeks of life and live weight change was calculated. The deuterium oxide (D₂O) dilution technique was used to estimate milk intake of the lambs and performed at approximately 7 days post-partum and finishing on approximately day 14. Pearson's correlation coefficients and multiple regression coefficients among techniques were calculated. The UD-models at d7 (R² = 0.35), d35 (R² = 0.36) and d42 (R² = 0.34), were the best models explaining variation in milk yield (concordance correlation coefficient (CCC) = 0.49; 0.53; 0.51; for d7, d35 and d42, respectively). The lamb live weight-change model explained the variation in milk yield best at d28 (R² = 0.32; CCC = 0.49), at d35 (R² = 0.22; CCC = 0.36) and at d42 (R² = 0.28; CCC = 0.44). At d14, the intake of milk by lambs as measured by the D₂O technique, did not explain the variation in milk yield. In conclusion, udder dimensions, lamb live weight change and lamb milk intake are relatively poor estimators of the milk yield of singleton-rearing ewes obtained by the “oxytocin” method. Additionally, udder dimensions, milk yield and lamb milk intake do not give an accurate prediction of growth rates of singleton lambs. These results emphasize that there is a difference between ewe milk production potential and lamb milk intake, which need to be considered when estimating milk production in non-dairy animals.     

Transcervical artificial insemination of Australian Merino ewes with frozen-thawed semen

We compared conventional methods for laparoscopic and cervical artificial insemination (AI) to a transcervical AI procedure (Guelph System for Transcervical AI; GST-AI) for use with frozen semen in Merino ewes. The GST-AI procedure was performed by an experienced operator in Experiment 1 (771 ewes) and by 2 inexperienced operators in Experiment 2 (555 ewes). In Experiment 1, intrauterine insemination by GST-AI was achieved in 76% of the ewes. The pregnancy rate at Day 70 for ewes inseminated by laparoscopy (48%, 120 251 ) was higher (P<0.01) than for ewes inseminated by either intrauterine GST-AI (32%, 64 201 ) or cervical AI (9%, 24 256 ). The overall (intrauterine and intracervical) pregnancy rate for GST-AI was 26% (68 264 ) and was unaffected by depth of insemination within the cervix. Pregnancy rates were unaffected by ram or day of insemination. In Experiment 2, the operators achieved intrauterine inseminations by GST-AI in 43% (78 182 ) of the ewes, with a significant operator effect (P<0.01) on depth of cervical penetration. The pregnancy rate to intrauterine GST-AI (40%, 31 78 ) did not differ from that to laparoscopic insemination. The total pregnancy rate for GST-AI in Experiment 2 (19%, 34 182 ) was lower (P<0.05) than that for laparoscopic AI (39%, 72 187 ) but superior (P<0.05) to that for cervical AI (1%, 1 186 ). The GST-AI pregnancy rates were affected by depth of AI (P<0.01) and by operator (P<0.05). It is concluded that GST-AI is superior to cervical AI, and may have application in Merinos if cervical penetration rates can be improved.     

Model of lymphocyte migration in Merino ewes under physiological conditions

The paper presents an example of a new type of a structured model containing time delays in parallel branches. This model was selected as optimal to describe mathematically the lymphocyte migration between the venous blood and prescapular lymph in Merino ewes under physiological conditions. The model allowed to identify and quantify several lymphocyte fractions exhibiting different migration dynamics.     

Factors influencing the success of transcervical insemination in Merino ewes

The experiments described examined the effects of a number of factors on the level of uterine insemination achieved in Merino ewes by a transcervical insemination technique (Guelph system for transcervical artificial insemination; GST-AI). Cervical penetration rate is an important limitation to the use of such methods in Merinos. Simulated insemination was performed to estimate the proportion of ewes in which a pipette could be passed through the cervix to the uterus. In Experiment 1, cervical penetration rate (n = 14 to 30) was unaffected by an increase in postpartum interval at AI from 12 to 26 wk. The results of cervical penetration for individual ewes were found to be repeatable (P < 0.05). Experiment 2 (197 ewes) revealed a clear effect of ewe parity on penetration rates in hormonally synchronized ewes during the nonbreeding season (P < 0.05). In Experiment 3, estrus synchronization using progestagen (n = 51) or prostaglandin (n = 50) did not affect penetration rate. The penetration rate was slightly higher in the naturally cycling ewes, but the difference was not significant. Comparison of ewes from Experiments 2 and 3 suggests the possibility of a major effect of stage of the breeding season on the penetration rate (P < 0.05). It is concluded that ewe selection and management techniques may be used to increase the proportion of transcervical insemination attempts resulting in uterine insemination. However, fertility testing will be required to determine whether such improvements translate into correspondingly increased pregnancy rates.     

Effects of feeding sainfoin proanthocyanidins to lactating ewes on intake,milk production and plasma metabolites

There is increasing interest in using sainfoin (Onobrychis viciifolia) to feed sheep, but it contains proanthocyanidins (PACs), and the associated effects of PAC on sheep production are not well-known. The aim of the study was to assess the effect of the presence of PAC from sainfoin, through the inclusion of polyethylene glycol (PEG), on the intake and productive parameters of local ewes bearing one male lamb. For the experiment, 20 ewes and their newborn male lambs were placed in individual indoor cages. All ewes were fed ad libitum fresh sainfoin plus 200 g/d barley. Twice daily, half of the ewes were orally dosed with only water (Sainfoin Group; n = 10), and the other half were orally dosed with 100 g/d PEG 4000 per ewe (Sainfoin + PEG Group; n = 10). Sucking lambs were permanently housed with their dams until they reached 10–12 kg BW. The intake of sainfoin was recorded daily, and its chemical composition was analysed. Weekly, the BW, body condition score (BCS), milk yields and individual milk and blood samples were recorded. At the beginning and end of the experiment, faecal samples were collected from ewes and analysed for the anthelmintic role of PAC. The chemical composition, polyphenol content and antioxidant capacity of the diet and milk were analysed. The presence of PAC did not affect the intake, BW, BCS or milk yield of the dams (P > 0.05); however, all parameters were affected by the week of lactation (P < 0.05). Milk components were affected by the week of lactation (P < 0.001), but only the polyphenol and urea contents were reduced in the presence of PAC (P < 0.01). Similarly, the presence of PAC decreased the plasma urea concentration (P < 0.01) without effect on the rest of metabolites, polyphenols and antioxidant activity (P > 0.05). The presence of PAC had no effect on parasitism (P > 0.05). In conclusion, the presence of PAC had no relevant effects on milk production, although it affected protein metabolism, as indicated by the urea contents in milk and plasma.