Perinatal mortality is a major contributing factor to reproductive wastage in grazing sheep industries. Enhanced metabolic and endocrine maturity at birth may improve the behavioral competency and thermoregulatory ability of neonates, potentially improving lamb survival over the first 72 h of life. Maternal glucocorticoid treatment in late gestation was investigated as a mechanism for manipulating metabolic and endocrine maturity in the ovine neonate. Multiparous, fine-wool Merino ewes (n = 150) were divided into 3 groups to lamb on pasture. Within each group, 5 single-lamb and 5 twin-lamb bearing ewes were randomly allocated to 1 of 5 treatments. Treatments included a saline control (1 mL), or dexamethasone (2 mg/mL as the sodium phosphate) injected intramuscularly at 1 of 2 dose rates (1.5 or 3.0 mg) at d 130 or 141 of gestation. One-half of the control ewes were injected at d 130 and the remainder at d 141. Dexamethasone treatment had no effect on lamb survival to 72 h after birth, although there tended (P = 0.09) to be a smaller proportion of lambs dying due to dystocia than for control lambs. Heart girth at birth in singleton and twin lambs was reduced (P < 0.01) at the greater dose rate. Further, treatment also reduced birth weight (by about 5%) and presuckling rectal temperatures in twin lambs, but not in singleton lambs. These reductions were also dependent on the sex of the lamb. Dexamethasone treatment did not alter gestation length or lamb presuckling plasma glucose, NEFA, urea, or leptin concentrations, but treatment at d 141 increased (P < 0.05) ghrelin concentrations in singleton and male lambs. Behavioral interactions between ewes and neonatal lambs were generally unaffected, although treatment at d 130 produced lambs that took longer to bleat than lambs of untreated ewes (P < 0.05). Treatment did not affect the concentration of measured blood metabolites or hormones at weaning. Although there were interactions between litter size, lamb sex, and the dose rate and time of treatment on weaning weight, BW recorded 73 d after weaning was unaffected by treatment. Despite changes in birth weight, rectal temperature, lamb behavior, and presuckling plasma ghrelin concentrations, survival in the first 72 h of life, and lamb growth performance were unaffected by periparturient maternal glucocorticoid treatment.

This paper reports an investigation into metabolic and endocrine maturity in the neonate lamb and the relationships between litter size, birth weight, and maternal metabolic and endocrine variables on behavior at birth and survival over the first 72 h of life. Data were from multiparous, fine-wool Merino ewes (n = 150; equal numbers of single-lamb and twin-lamb bearing status) lambed on pasture after late gestational glucocorticoid treatments. Stepwise multiple regression analysis was used to investigate relationships between lamb survival, behavior, endocrinology, and physiology. Improved lamb viability at 72 h after birth was related to decreased chill indices at birth, singleton litter status, greater presuckling rectal temperature, increased ewe prelambing plasma ghrelin concentration, female sex, heavier birth weight, and decreased lamb presuckling plasma glucose concentration. Greater rectal temperatures were associated with heavier birth weight and gestation lengths shorter than 146 d, but no relationship with neonatal behavioral progression was evident. Presuckling glucose concentrations were greater in singletons and lambs born to ewes of greater BCS at d 95 of gestation, and lambs of heavier birth weight, but were also associated with decreased rectal temperatures. This might reflect a delay in glucose utilization during the adjustment from a fetal metabolic rate to a rate appropriate for cold external environments. Singleton lambs exhibited decreased presuckling plasma NEFA concentrations and were almost 8 times more likely to survive to 72 h than a twin-born lamb. Birth weight was lesser in lambs born to ewes with elevated plasma glucose and leptin concentrations before lambing and was positively related to ewe BW at d 95 of gestation and to length of gestation. Greater presuckling plasma ghrelin and leptin concentrations were measured for shorter gestation lengths. Neonate presuckling ghrelin concentrations above 650 pg/mL tended (P = 0.077) to be associated with improved lamb survival to 72 h. This was consistent with a curvilinear decline in neonate survival rates to 72 h after birth as time of latency to suckle increased. No relationship was observed between lamb plasma glucose concentrations and behavioral expression after lambing. Lambs exhibiting greater metabolic and endocrine maturity at birth had improved survival in a cold environment to 72 h after birth. The role of ghrelin in ovine fetal development warrants further investigation.

Summary. Male, fine wool Merino sheep which had been subjected to different methods of castration as lambs were assessed from 22 to 46 months of age for their suitability for wool production, their tolerance to posthitis and their carcass characteristics. Hemi-castrates produced significantly (P<0.001) more clean wool than induced cryptorchids of a similar fibre diameter. Induced cryptorchids and hemi-castrates were significantly (P<0.05) heavier than wethers. Partial hemi-castrates and induced cryptorchids had significantly (P<0.001) heavier and leaner carcasses (lower GR measurement) than wethers and testosterone-treated wethers. Induced cryptorchidism and hemi-castration proved to be effective means of reducing the prevalence of posthitis such that as the degree of castration decreased the proportion of animals with higher posthitis scores decreased (P<0.001). Testosterone levels in induced cryptorchids (1.01 ng/mL) and hemi-castrates with partial reduction of the parenchyma (0.83 ng/mL) were similar, whereas hemi-castrates with complete reduction of the parenchyma in the 1 remaining testicle had a significantly (P<0.001) lower level (0.32 ng/mL) and significantly (P<0.001) lighter testes. Development of horns and obvious scrotums by induced cryptorchids and hemi-castrates with partial reduction of the parenchyma in the 1 remaining testicle attracted penalty rates at shearing and slaughter. Some induced cryptorchids and hemi-castrates exhibited masculine behaviour, but they were unlikely to be fertile because although spermatozoa were present they were abnormal and/or non-motile. Hemi-castrates with full reduction of the parenchyma in the 1 remaining testicle offer significant advantages over the other groups for wool production. Severe posthitis was not observed, they were infertile, they did not attract penalty rates for shearing or slaughter and their clean fleece weight, wool quality, carcass weight and grade were comparable with or superior to wethers. To reduce dependence on synthetic hormones to control posthitis, traditional complete castration techniques could be replaced with this type of partial castration in wool-producing flocks.

Male lambs born to Merino, Polwarth and Merino x Polwarth ewes were used to study a technique for manipulating testicular size. Of these lambs, 82 were castrated at marking (wethers). For the remaining 100 the testicular parenchyma was removed at marking and then, at a subsequent date, the scrotal sac and any large testicles were removed (modified cryptorchids). Cryptorchids were significantly (P<0.05) heavier than wethers throughout the study and produced significantly (P<0.05) heavier fleeces (4.3 � 0.08 v. 4.0 � 0.06 kg). Bin class, as an indicator of wool quality, was not significantly different between the 2 groups. At all times of the year, cryptorchids had a significantly lower prevalence (P<0.001) and severity of posthitis. Posthitis increased in spring and decreased in summer. There was significantly (P<0.001) more horn development in the cryptorchids, and Merino-sired animals had more horn development than those sired by Polwarth rams. The basal level of testosterone in the wethers was 0.08 � 0.07 ng/mL averaged over 3 successive blood samples, compared to the cryptorchids at 0.95 � 0.16 ng/mL with an asymmetric distribution. The rank correlation between average testosterone levels and testicle score was significant (P<0.05) with a coefficient of 0.54. The rank correlations between testosterone levels and fleeceweight, liveweight or horn score were not significant (P>0.05).